- About these Docs
- Synopsis
- Assertion Testing
- Buffer
- C/C++ Addons
- Child Processes
- Cluster
- Command Line Options
- Console
- Crypto
- Debugger
- DNS
- Domain
- Errors
- Events
- File System
- Globals
- HTTP
- HTTPS
- Modules
- Net
- OS
- Path
- Process
- Punycode
- Query Strings
- Readline
- REPL
- Stream
- String Decoder
- Timers
- TLS/SSL
- TTY
- UDP/Datagram
- URL
- Utilities
- V8
- VM
- ZLIB
Node.js v6.0.0-rc.3 Documentation
Table of Contents
- About this Documentation
- Synopsis
- Addons
- Assert
- assert(value[, message])
- assert.deepEqual(actual, expected[, message])
- assert.deepStrictEqual(actual, expected[, message])
- assert.doesNotThrow(block[, error][, message])
- assert.equal(actual, expected[, message])
- assert.fail(actual, expected, message, operator)
- assert.ifError(value)
- assert.notDeepEqual(actual, expected[, message])
- assert.notDeepStrictEqual(actual, expected[, message])
- assert.notEqual(actual, expected[, message])
- assert.notStrictEqual(actual, expected[, message])
- assert.ok(value[, message])
- assert.strictEqual(actual, expected[, message])
- assert.throws(block[, error][, message])
- Buffer
Buffer.from()
,Buffer.alloc()
, andBuffer.allocUnsafe()
- Buffers and Character Encodings
- Buffers and TypedArray
- Buffers and ES6 iteration
- Class: Buffer
- new Buffer(array)
- new Buffer(buffer)
- new Buffer(arrayBuffer[, byteOffset [, length]])
- new Buffer(size)
- new Buffer(str[, encoding])
- Class Method: Buffer.alloc(size[, fill[, encoding]])
- Class Method: Buffer.allocUnsafe(size)
- Class Method: Buffer.allocUnsafeSlow(size)
- Class Method: Buffer.byteLength(string[, encoding])
- Class Method: Buffer.compare(buf1, buf2)
- Class Method: Buffer.concat(list[, totalLength])
- Class Method: Buffer.from(array)
- Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])
- Class Method: Buffer.from(buffer)
- Class Method: Buffer.from(str[, encoding])
- Class Method: Buffer.isBuffer(obj)
- Class Method: Buffer.isEncoding(encoding)
- buf[index]
- buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
- buf.copy(targetBuffer[, targetStart[, sourceStart[, sourceEnd]]])
- buf.entries()
- buf.equals(otherBuffer)
- buf.fill(value[, offset[, end]][, encoding])
- buf.indexOf(value[, byteOffset][, encoding])
- buf.includes(value[, byteOffset][, encoding])
- buf.keys()
- buf.length
- buf.readDoubleBE(offset[, noAssert])
- buf.readDoubleLE(offset[, noAssert])
- buf.readFloatBE(offset[, noAssert])
- buf.readFloatLE(offset[, noAssert])
- buf.readInt8(offset[, noAssert])
- buf.readInt16BE(offset[, noAssert])
- buf.readInt16LE(offset[, noAssert])
- buf.readInt32BE(offset[, noAssert])
- buf.readInt32LE(offset[, noAssert])
- buf.readIntBE(offset, byteLength[, noAssert])
- buf.readIntLE(offset, byteLength[, noAssert])
- buf.readUInt8(offset[, noAssert])
- buf.readUInt16BE(offset[, noAssert])
- buf.readUInt16LE(offset[, noAssert])
- buf.readUInt32BE(offset[, noAssert])
- buf.readUInt32LE(offset[, noAssert])
- buf.readUIntBE(offset, byteLength[, noAssert])
- buf.readUIntLE(offset, byteLength[, noAssert])
- buf.slice([start[, end]])
- buf.swap16()
- buf.swap32()
- buf.toString([encoding[, start[, end]]])
- buf.toJSON()
- buf.values()
- buf.write(string[, offset[, length]][, encoding])
- buf.writeDoubleBE(value, offset[, noAssert])
- buf.writeDoubleLE(value, offset[, noAssert])
- buf.writeFloatBE(value, offset[, noAssert])
- buf.writeFloatLE(value, offset[, noAssert])
- buf.writeInt8(value, offset[, noAssert])
- buf.writeInt16BE(value, offset[, noAssert])
- buf.writeInt16LE(value, offset[, noAssert])
- buf.writeInt32BE(value, offset[, noAssert])
- buf.writeInt32LE(value, offset[, noAssert])
- buf.writeIntBE(value, offset, byteLength[, noAssert])
- buf.writeIntLE(value, offset, byteLength[, noAssert])
- buf.writeUInt8(value, offset[, noAssert])
- buf.writeUInt16BE(value, offset[, noAssert])
- buf.writeUInt16LE(value, offset[, noAssert])
- buf.writeUInt32BE(value, offset[, noAssert])
- buf.writeUInt32LE(value, offset[, noAssert])
- buf.writeUIntBE(value, offset, byteLength[, noAssert])
- buf.writeUIntLE(value, offset, byteLength[, noAssert])
- buffer.INSPECT_MAX_BYTES
- Class: SlowBuffer
- Child Process
- Asynchronous Process Creation
- Synchronous Process Creation
- Class: ChildProcess
maxBuffer
and Unicode
- Cluster
- How It Works
- Class: Worker
- Event: 'disconnect'
- Event: 'exit'
- Event: 'fork'
- Event: 'listening'
- Event: 'message'
- Event: 'online'
- Event: 'setup'
- cluster.disconnect([callback])
- cluster.fork([env])
- cluster.isMaster
- cluster.isWorker
- cluster.schedulingPolicy
- cluster.settings
- cluster.setupMaster([settings])
- cluster.worker
- cluster.workers
- Command Line Options
- Synopsis
- Options
-v
,--version
-h
,--help
-e
,--eval "script"
-p
,--print "script"
-c
,--check
-i
,--interactive
-r
,--require module
--no-deprecation
--trace-deprecation
--throw-deprecation
--no-warnings
--trace-warnings
--trace-sync-io
--zero-fill-buffers
--track-heap-objects
--prof-process
--v8-options
--tls-cipher-list=list
--enable-fips
--force-fips
--icu-data-dir=file
- Environment Variables
- Console
- Crypto
- Determining if crypto support is unavailable
- Class: Certificate
- Class: Cipher
- Class: Decipher
- Class: DiffieHellman
- diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])
- diffieHellman.generateKeys([encoding])
- diffieHellman.getGenerator([encoding])
- diffieHellman.getPrime([encoding])
- diffieHellman.getPrivateKey([encoding])
- diffieHellman.getPublicKey([encoding])
- diffieHellman.setPrivateKey(private_key[, encoding])
- diffieHellman.setPublicKey(public_key[, encoding])
- diffieHellman.verifyError
- Class: ECDH
- Class: Hash
- Class: Hmac
- Class: Sign
- Class: Verify
crypto
module methods and properties- crypto.DEFAULT_ENCODING
- crypto.fips
- crypto.createCipher(algorithm, password)
- crypto.createCipheriv(algorithm, key, iv)
- crypto.createCredentials(details)
- crypto.createDecipher(algorithm, password)
- crypto.createDecipheriv(algorithm, key, iv)
- crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])
- crypto.createDiffieHellman(prime_length[, generator])
- crypto.createECDH(curve_name)
- crypto.createHash(algorithm)
- crypto.createHmac(algorithm, key)
- crypto.createSign(algorithm)
- crypto.createVerify(algorithm)
- crypto.getCiphers()
- crypto.getCurves()
- crypto.getDiffieHellman(group_name)
- crypto.getHashes()
- crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)
- crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)
- crypto.privateDecrypt(private_key, buffer)
- crypto.privateEncrypt(private_key, buffer)
- crypto.publicDecrypt(public_key, buffer)
- crypto.publicEncrypt(public_key, buffer)
- crypto.randomBytes(size[, callback])
- crypto.setEngine(engine[, flags])
- Notes
- Debugger
- UDP / Datagram Sockets
- Class: dgram.Socket
- Event: 'close'
- Event: 'error'
- Event: 'listening'
- Event: 'message'
- socket.addMembership(multicastAddress[, multicastInterface])
- socket.address()
- socket.bind([port][, address][, callback])
- socket.bind(options[, callback])
- socket.close([callback])
- socket.dropMembership(multicastAddress[, multicastInterface])
- socket.send(msg, [offset, length,] port, address[, callback])
- socket.setBroadcast(flag)
- socket.setMulticastLoopback(flag)
- socket.setMulticastTTL(ttl)
- socket.setTTL(ttl)
- socket.ref()
- socket.unref()
- Change to asynchronous
socket.bind()
behavior
dgram
module functions
- Class: dgram.Socket
- DNS
- dns.getServers()
- dns.lookup(hostname[, options], callback)
- dns.lookupService(address, port, callback)
- dns.resolve(hostname[, rrtype], callback)
- dns.resolve4(hostname, callback)
- dns.resolve6(hostname, callback)
- dns.resolveCname(hostname, callback)
- dns.resolveMx(hostname, callback)
- dns.resolveNs(hostname, callback)
- dns.resolveSoa(hostname, callback)
- dns.resolveSrv(hostname, callback)
- dns.resolvePtr(hostname, callback)
- dns.resolveTxt(hostname, callback)
- dns.reverse(ip, callback)
- dns.setServers(servers)
- Error codes
- Implementation considerations
- Domain
- Errors
- Events
- Passing arguments and
this
to listeners - Asynchronous vs. Synchronous
- Handling events only once
- Error events
- Class: EventEmitter
- Event: 'newListener'
- Event: 'removeListener'
- EventEmitter.listenerCount(emitter, eventName)
- EventEmitter.defaultMaxListeners
- emitter.addListener(eventName, listener)
- emitter.emit(eventName[, arg1][, arg2][, ...])
- emitter.eventNames()
- emitter.getMaxListeners()
- emitter.listenerCount(eventName)
- emitter.listeners(eventName)
- emitter.on(eventName, listener)
- emitter.once(eventName, listener)
- emitter.removeAllListeners([eventName])
- emitter.removeListener(eventName, listener)
- emitter.setMaxListeners(n)
- Passing arguments and
- File System
- Buffer API
- Class: fs.FSWatcher
- Class: fs.ReadStream
- Class: fs.Stats
- Class: fs.WriteStream
- fs.access(path[, mode], callback)
- fs.accessSync(path[, mode])
- fs.appendFile(file, data[, options], callback)
- fs.appendFileSync(file, data[, options])
- fs.chmod(path, mode, callback)
- fs.chmodSync(path, mode)
- fs.chown(path, uid, gid, callback)
- fs.chownSync(path, uid, gid)
- fs.close(fd, callback)
- fs.closeSync(fd)
- fs.createReadStream(path[, options])
- fs.createWriteStream(path[, options])
- fs.exists(path, callback)
- fs.existsSync(path)
- fs.fchmod(fd, mode, callback)
- fs.fchmodSync(fd, mode)
- fs.fchown(fd, uid, gid, callback)
- fs.fchownSync(fd, uid, gid)
- fs.fdatasync(fd, callback)
- fs.fdatasyncSync(fd)
- fs.fstat(fd, callback)
- fs.fstatSync(fd)
- fs.fsync(fd, callback)
- fs.fsyncSync(fd)
- fs.ftruncate(fd, len, callback)
- fs.ftruncateSync(fd, len)
- fs.futimes(fd, atime, mtime, callback)
- fs.futimesSync(fd, atime, mtime)
- fs.lchmod(path, mode, callback)
- fs.lchmodSync(path, mode)
- fs.lchown(path, uid, gid, callback)
- fs.lchownSync(path, uid, gid)
- fs.link(srcpath, dstpath, callback)
- fs.linkSync(srcpath, dstpath)
- fs.lstat(path, callback)
- fs.lstatSync(path)
- fs.mkdir(path[, mode], callback)
- fs.mkdirSync(path[, mode])
- fs.mkdtemp(prefix, callback)
- fs.mkdtempSync(template)
- fs.open(path, flags[, mode], callback)
- fs.openSync(path, flags[, mode])
- fs.read(fd, buffer, offset, length, position, callback)
- fs.readdir(path[, options], callback)
- fs.readdirSync(path[, options])
- fs.readFile(file[, options], callback)
- fs.readFileSync(file[, options])
- fs.readlink(path[, options], callback)
- fs.readlinkSync(path[, options])
- fs.realpath(path[, options], callback)
- fs.readSync(fd, buffer, offset, length, position)
- fs.realpathSync(path[, options])
- fs.rename(oldPath, newPath, callback)
- fs.renameSync(oldPath, newPath)
- fs.rmdir(path, callback)
- fs.rmdirSync(path)
- fs.stat(path, callback)
- fs.statSync(path)
- fs.symlink(target, path[, type], callback)
- fs.symlinkSync(target, path[, type])
- fs.truncate(path, len, callback)
- fs.truncateSync(path, len)
- fs.unlink(path, callback)
- fs.unlinkSync(path)
- fs.unwatchFile(filename[, listener])
- fs.utimes(path, atime, mtime, callback)
- fs.utimesSync(path, atime, mtime)
- fs.watch(filename[, options][, listener])
- fs.watchFile(filename[, options], listener)
- fs.write(fd, buffer, offset, length[, position], callback)
- fs.write(fd, data[, position[, encoding]], callback)
- fs.writeFile(file, data[, options], callback)
- fs.writeFileSync(file, data[, options])
- fs.writeSync(fd, buffer, offset, length[, position])
- fs.writeSync(fd, data[, position[, encoding]])
- Global Objects
- HTTP
- Class: http.Agent
- Class: http.ClientRequest
- Event: 'abort'
- Event: 'checkExpectation'
- Event: 'connect'
- Event: 'continue'
- Event: 'response'
- Event: 'socket'
- Event: 'upgrade'
- request.abort()
- request.end([data][, encoding][, callback])
- request.flushHeaders()
- request.setNoDelay([noDelay])
- request.setSocketKeepAlive([enable][, initialDelay])
- request.setTimeout(timeout[, callback])
- request.write(chunk[, encoding][, callback])
- Class: http.Server
- Event: 'checkContinue'
- Event: 'clientError'
- Event: 'close'
- Event: 'connect'
- Event: 'connection'
- Event: 'request'
- Event: 'upgrade'
- server.close([callback])
- server.listen(handle[, callback])
- server.listen(path[, callback])
- server.listen(port[, hostname][, backlog][, callback])
- server.listening
- server.maxHeadersCount
- server.setTimeout(msecs, callback)
- server.timeout
- Class: http.ServerResponse
- Event: 'close'
- Event: 'finish'
- response.addTrailers(headers)
- response.end([data][, encoding][, callback])
- response.finished
- response.getHeader(name)
- response.headersSent
- response.removeHeader(name)
- response.sendDate
- response.setHeader(name, value)
- response.setTimeout(msecs, callback)
- response.statusCode
- response.statusMessage
- response.write(chunk[, encoding][, callback])
- response.writeContinue()
- response.writeHead(statusCode[, statusMessage][, headers])
- Class: http.IncomingMessage
- http.METHODS
- http.STATUS_CODES
- http.createClient([port][, host])
- http.createServer([requestListener])
- http.get(options[, callback])
- http.globalAgent
- http.request(options[, callback])
- HTTPS
- Modules
- net
- Class: net.Server
- Event: 'close'
- Event: 'connection'
- Event: 'error'
- Event: 'listening'
- server.address()
- server.close([callback])
- server.connections
- server.getConnections(callback)
- server.listen(handle[, backlog][, callback])
- server.listen(options[, callback])
- server.listen(path[, backlog][, callback])
- server.listen(port[, hostname][, backlog][, callback])
- server.listening
- server.maxConnections
- server.ref()
- server.unref()
- Class: net.Socket
- new net.Socket([options])
- Event: 'close'
- Event: 'connect'
- Event: 'data'
- Event: 'drain'
- Event: 'end'
- Event: 'error'
- Event: 'lookup'
- Event: 'timeout'
- socket.address()
- socket.bufferSize
- socket.bytesRead
- socket.bytesWritten
- socket.connect(options[, connectListener])
- socket.connect(path[, connectListener])
- socket.connect(port[, host][, connectListener])
- socket.destroy()
- socket.end([data][, encoding])
- socket.localAddress
- socket.localPort
- socket.pause()
- socket.ref()
- socket.remoteAddress
- socket.remoteFamily
- socket.remotePort
- socket.resume()
- socket.setEncoding([encoding])
- socket.setKeepAlive([enable][, initialDelay])
- socket.setNoDelay([noDelay])
- socket.setTimeout(timeout[, callback])
- socket.unref()
- socket.write(data[, encoding][, callback])
- net.connect(options[, connectListener])
- net.connect(path[, connectListener])
- net.connect(port[, host][, connectListener])
- net.createConnection(options[, connectListener])
- net.createConnection(path[, connectListener])
- net.createConnection(port[, host][, connectListener])
- net.createServer([options][, connectionListener])
- net.isIP(input)
- net.isIPv4(input)
- net.isIPv6(input)
- Class: net.Server
- OS
- Path
- process
- Event: 'beforeExit'
- Event: 'exit'
- Event: 'message'
- Event: 'rejectionHandled'
- Event: 'uncaughtException'
- Event: 'unhandledRejection'
- Event: 'warning'
- Exit Codes
- Signal Events
- process.abort()
- process.arch
- process.argv
- process.chdir(directory)
- process.config
- process.connected
- process.cwd()
- process.disconnect()
- process.env
- process.emitWarning(warning[, name][, ctor])
- process.execArgv
- process.execPath
- process.exit([code])
- process.exitCode
- process.getegid()
- process.geteuid()
- process.getgid()
- process.getgroups()
- process.getuid()
- process.hrtime()
- process.initgroups(user, extra_group)
- process.kill(pid[, signal])
- process.mainModule
- process.memoryUsage()
- process.nextTick(callback[, arg][, ...])
- process.pid
- process.platform
- process.release
- process.send(message[, sendHandle[, options]][, callback])
- process.setegid(id)
- process.seteuid(id)
- process.setgid(id)
- process.setgroups(groups)
- process.setuid(id)
- process.stderr
- process.stdin
- process.stdout
- process.title
- process.umask([mask])
- process.uptime()
- process.version
- process.versions
- punycode
- Query String
- Readline
- REPL
- Stream
- API for Stream Consumers
- API for Stream Implementors
- Simplified Constructor API
- Streams: Under the Hood
- StringDecoder
- Timers
- TLS (SSL)
- ALPN, NPN and SNI
- Client-initiated renegotiation attack mitigation
- Modifying the Default TLS Cipher suite
- Perfect Forward Secrecy
- Class: CryptoStream
- Class: SecurePair
- Class: tls.Server
- Event: 'tlsClientError'
- Event: 'newSession'
- Event: 'OCSPRequest'
- Event: 'resumeSession'
- Event: 'secureConnection'
- server.addContext(hostname, context)
- server.address()
- server.close([callback])
- server.connections
- server.getTicketKeys()
- server.listen(port[, hostname][, callback])
- server.setTicketKeys(keys)
- server.maxConnections
- Class: tls.TLSSocket
- new tls.TLSSocket(socket[, options])
- Event: 'OCSPResponse'
- Event: 'secureConnect'
- tlsSocket.address()
- tlsSocket.authorized
- tlsSocket.authorizationError
- tlsSocket.encrypted
- tlsSocket.getCipher()
- tlsSocket.getEphemeralKeyInfo()
- tlsSocket.getPeerCertificate([ detailed ])
- tlsSocket.getProtocol()
- tlsSocket.getSession()
- tlsSocket.getTLSTicket()
- tlsSocket.localAddress
- tlsSocket.localPort
- tlsSocket.remoteAddress
- tlsSocket.remoteFamily
- tlsSocket.remotePort
- tlsSocket.renegotiate(options, callback)
- tlsSocket.setMaxSendFragment(size)
- tls.connect(options[, callback])
- tls.connect(port[, host][, options][, callback])
- tls.createSecureContext(options)
- tls.createSecurePair([context][, isServer][, requestCert][, rejectUnauthorized][, options])
- tls.createServer(options[, secureConnectionListener])
- tls.getCiphers()
- TTY
- URL
- util
- util.debug(string)
- util.debuglog(section)
- util.deprecate(function, string)
- util.error([...])
- util.format(format[, ...])
- util.inherits(constructor, superConstructor)
- util.inspect(object[, options])
- util.isArray(object)
- util.isBoolean(object)
- util.isBuffer(object)
- util.isDate(object)
- util.isError(object)
- util.isFunction(object)
- util.isNull(object)
- util.isNullOrUndefined(object)
- util.isNumber(object)
- util.isObject(object)
- util.isPrimitive(object)
- util.isRegExp(object)
- util.isString(object)
- util.isSymbol(object)
- util.isUndefined(object)
- util.log(string)
- util.print([...])
- util.puts([...])
- util._extend(obj)
- V8
- Executing JavaScript
- Zlib
- Examples
- Memory Usage Tuning
- Constants
- Class Options
- Class: zlib.Deflate
- Class: zlib.DeflateRaw
- Class: zlib.Gunzip
- Class: zlib.Gzip
- Class: zlib.Inflate
- Class: zlib.InflateRaw
- Class: zlib.Unzip
- Class: zlib.Zlib
- zlib.createDeflate([options])
- zlib.createDeflateRaw([options])
- zlib.createGunzip([options])
- zlib.createGzip([options])
- zlib.createInflate([options])
- zlib.createInflateRaw([options])
- zlib.createUnzip([options])
- Convenience Methods
- zlib.deflate(buf[, options], callback)
- zlib.deflateSync(buf[, options])
- zlib.deflateRaw(buf[, options], callback)
- zlib.deflateRawSync(buf[, options])
- zlib.gunzip(buf[, options], callback)
- zlib.gunzipSync(buf[, options])
- zlib.gzip(buf[, options], callback)
- zlib.gzipSync(buf[, options])
- zlib.inflate(buf[, options], callback)
- zlib.inflateSync(buf[, options])
- zlib.inflateRaw(buf[, options], callback)
- zlib.inflateRawSync(buf[, options])
- zlib.unzip(buf[, options], callback)
- zlib.unzipSync(buf[, options])
About this Documentation#
The goal of this documentation is to comprehensively explain the Node.js API, both from a reference as well as a conceptual point of view. Each section describes a built-in module or high-level concept.
Where appropriate, property types, method arguments, and the arguments provided to event handlers are detailed in a list underneath the topic heading.
Every .html
document has a corresponding .json
document presenting
the same information in a structured manner. This feature is
experimental, and added for the benefit of IDEs and other utilities that
wish to do programmatic things with the documentation.
Every .html
and .json
file is generated based on the corresponding
.markdown
file in the doc/api/
folder in Node.js's source tree. The
documentation is generated using the tools/doc/generate.js
program.
The HTML template is located at doc/template.html
.
If you find a error in this documentation, please submit an issue or see the contributing guide for directions on how to submit a patch.
Stability Index#
Throughout the documentation, you will see indications of a section's stability. The Node.js API is still somewhat changing, and as it matures, certain parts are more reliable than others. Some are so proven, and so relied upon, that they are unlikely to ever change at all. Others are brand new and experimental, or known to be hazardous and in the process of being redesigned.
The stability indices are as follows:
Stability: 0 - Deprecated This feature is known to be problematic, and changes are planned. Do not rely on it. Use of the feature may cause warnings. Backwards compatibility should not be expected.
Stability: 1 - Experimental This feature is subject to change, and is gated by a command line flag. It may change or be removed in future versions.
Stability: 2 - Stable The API has proven satisfactory. Compatibility with the npm ecosystem is a high priority, and will not be broken unless absolutely necessary.
Stability: 3 - Locked Only fixes related to security, performance, or bug fixes will be accepted. Please do not suggest API changes in this area; they will be refused.
JSON Output#
Stability: 1 - Experimental
Every HTML file in the markdown has a corresponding JSON file with the same data.
This feature was added in Node.js v0.6.12. It is experimental.
Syscalls and man pages#
System calls like open(2) and read(2) define the interface between user programs
and the underlying operating system. Node functions which simply wrap a syscall,
like fs.open()
, will document that. The docs link to the corresponding man
pages (short for manual pages) which describe how the syscalls work.
Caveat: some syscalls, like lchown(2), are BSD-specific. That means, for
example, that fs.lchown()
only works on Mac OS X and other BSD-derived systems,
and is not available on Linux.
Most Unix syscalls have Windows equivalents, but behavior may differ on Windows relative to Linux and OS X. For an example of the subtle ways in which it's sometimes impossible to replace Unix syscall semantics on Windows, see Node issue 4760.
Synopsis#
An example of a web server written with Node.js which responds with
'Hello World'
:
const http = require('http');
http.createServer( (request, response) => {
response.writeHead(200, {'Content-Type': 'text/plain'});
response.end('Hello World\n');
}).listen(8124);
console.log('Server running at http://127.0.0.1:8124/');
To run the server, put the code into a file called example.js
and execute
it with the node program
$ node example.js
Server running at http://127.0.0.1:8124/
All of the examples in the documentation can be run similarly.
Addons#
Node.js Addons are dynamically-linked shared objects, written in C or C++, that
can be loaded into Node.js using the require()
function, and used
just as if they were an ordinary Node.js module. They are used primarily to
provide an interface between JavaScript running in Node.js and C/C++ libraries.
At the moment, the method for implementing Addons is rather complicated, involving knowledge of several components and APIs :
V8: the C++ library Node.js currently uses to provide the JavaScript implementation. V8 provides the mechanisms for creating objects, calling functions, etc. V8's API is documented mostly in the
v8.h
header file (deps/v8/include/v8.h
in the Node.js source tree), which is also available online.libuv: The C library that implements the Node.js event loop, its worker threads and all of the asynchronous behaviors of the platform. It also serves as a cross-platform abstraction library, giving easy, POSIX-like access across all major operating systems to many common system tasks, such as interacting with the filesystem, sockets, timers and system events. libuv also provides a pthreads-like threading abstraction that may be used to power more sophisticated asynchronous Addons that need to move beyond the standard event loop. Addon authors are encouraged to think about how to avoid blocking the event loop with I/O or other time-intensive tasks by off-loading work via libuv to non-blocking system operations, worker threads or a custom use of libuv's threads.
Internal Node.js libraries. Node.js itself exports a number of C/C++ APIs that Addons can use — the most important of which is the
node::ObjectWrap
class.Node.js includes a number of other statically linked libraries including OpenSSL. These other libraries are located in the
deps/
directory in the Node.js source tree. Only the V8 and OpenSSL symbols are purposefully re-exported by Node.js and may be used to various extents by Addons. See Linking to Node.js' own dependencies for additional information.
All of the following examples are available for download and may be used as a starting-point for your own Addon.
Hello world#
This "Hello world" example is a simple Addon, written in C++, that is the equivalent of the following JavaScript code:
module.exports.hello = () => 'world';
First, create the file hello.cc
:
// hello.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}
void init(Local<Object> exports) {
NODE_SET_METHOD(exports, "hello", Method);
}
NODE_MODULE(addon, init)
} // namespace demo
Note that all Node.js Addons must export an initialization function following the pattern:
void Initialize(Local<Object> exports);
NODE_MODULE(module_name, Initialize)
There is no semi-colon after NODE_MODULE
as it's not a function (see
node.h
).
The module_name
must match the filename of the final binary (excluding
the .node suffix).
In the hello.cc
example, then, the initialization function is init
and the
Addon module name is addon
.
Building#
Once the source code has been written, it must be compiled into the binary
addon.node
file. To do so, create a file called binding.gyp
in the
top-level of the project describing the build configuration of your module
using a JSON-like format. This file is used by node-gyp -- a tool written
specifically to compile Node.js Addons.
{
"targets": [
{
"target_name": "addon",
"sources": [ "hello.cc" ]
}
]
}
Note: A version of the node-gyp
utility is bundled and distributed with
Node.js as part of npm
. This version is not made directly available for
developers to use and is intended only to support the ability to use the
npm install
command to compile and install Addons. Developers who wish to
use node-gyp
directly can install it using the command
npm install -g node-gyp
. See the node-gyp
installation instructions for
more information, including platform-specific requirements.
Once the binding.gyp
file has been created, use node-gyp configure
to
generate the appropriate project build files for the current platform. This
will generate either a Makefile
(on Unix platforms) or a vcxproj
file
(on Windows) in the build/
directory.
Next, invoke the node-gyp build
command to generate the compiled addon.node
file. This will be put into the build/Release/
directory.
When using npm install
to install a Node.js Addon, npm uses its own bundled
version of node-gyp
to perform this same set of actions, generating a
compiled version of the Addon for the user's platform on demand.
Once built, the binary Addon can be used from within Node.js by pointing
require()
to the built addon.node
module:
// hello.js
const addon = require('./build/Release/addon');
console.log(addon.hello()); // 'world'
Please see the examples below for further information or
https://github.com/arturadib/node-qt for an example in production.
Because the exact path to the compiled Addon binary can vary depending on how
it is compiled (i.e. sometimes it may be in ./build/Debug/
), Addons can use
the bindings package to load the compiled module.
Note that while the bindings
package implementation is more sophisticated
in how it locates Addon modules, it is essentially using a try-catch pattern
similar to:
try {
return require('./build/Release/addon.node');
} catch (err) {
return require('./build/Debug/addon.node');
}
Linking to Node.js' own dependencies#
Node.js uses a number of statically linked libraries such as V8, libuv and
OpenSSL. All Addons are required to link to V8 and may link to any of the
other dependencies as well. Typically, this is as simple as including
the appropriate #include <...>
statements (e.g. #include <v8.h>
) and
node-gyp
will locate the appropriate headers automatically. However, there
are a few caveats to be aware of:
When
node-gyp
runs, it will detect the specific release version of Node.js and download either the full source tarball or just the headers. If the full source is downloaded, Addons will have complete access to the full set of Node.js dependencies. However, if only the Node.js headers are downloaded, then only the symbols exported by Node.js will be available.node-gyp
can be run using the--nodedir
flag pointing at a local Node.js source image. Using this option, the Addon will have access to the full set of dependencies.
Loading Addons using require()#
The filename extension of the compiled Addon binary is .node
(as opposed
to .dll
or .so
). The require()
function is written to look for
files with the .node
file extension and initialize those as dynamically-linked
libraries.
When calling require()
, the .node
extension can usually be
omitted and Node.js will still find and initialize the Addon. One caveat,
however, is that Node.js will first attempt to locate and load modules or
JavaScript files that happen to share the same base name. For instance, if
there is a file addon.js
in the same directory as the binary addon.node
,
then require('addon')
will give precedence to the addon.js
file
and load it instead.
Native Abstractions for Node.js#
Each of the examples illustrated in this document make direct use of the Node.js and V8 APIs for implementing Addons. It is important to understand that the V8 API can, and has, changed dramatically from one V8 release to the next (and one major Node.js release to the next). With each change, Addons may need to be updated and recompiled in order to continue functioning. The Node.js release schedule is designed to minimize the frequency and impact of such changes but there is little that Node.js can do currently to ensure stability of the V8 APIs.
The Native Abstractions for Node.js (or nan
) provide a set of tools that
Addon developers are recommended to use to keep compatibility between past and
future releases of V8 and Node.js. See the nan
examples for an
illustration of how it can be used.
Addon examples#
Following are some example Addons intended to help developers get started. The examples make use of the V8 APIs. Refer to the online V8 reference for help with the various V8 calls, and V8's Embedder's Guide for an explanation of several concepts used such as handles, scopes, function templates, etc.
Each of these examples using the following binding.gyp
file:
{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}
In cases where there is more than one .cc
file, simply add the additional
filename to the sources
array. For example:
"sources": ["addon.cc", "myexample.cc"]
Once the binding.gyp
file is ready, the example Addons can be configured and
built using node-gyp
:
$ node-gyp configure build
Function arguments#
Addons will typically expose objects and functions that can be accessed from JavaScript running within Node.js. When functions are invoked from JavaScript, the input arguments and return value must be mapped to and from the C/C++ code.
The following example illustrates how to read function arguments passed from JavaScript and how to return a result:
// addon.cc
#include <node.h>
namespace demo {
using v8::Exception;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
// This is the implementation of the "add" method
// Input arguments are passed using the
// const FunctionCallbackInfo<Value>& args struct
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
// Check the number of arguments passed.
if (args.Length() < 2) {
// Throw an Error that is passed back to JavaScript
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong number of arguments")));
return;
}
// Check the argument types
if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong arguments")));
return;
}
// Perform the operation
double value = args[0]->NumberValue() + args[1]->NumberValue();
Local<Number> num = Number::New(isolate, value);
// Set the return value (using the passed in
// FunctionCallbackInfo<Value>&)
args.GetReturnValue().Set(num);
}
void Init(Local<Object> exports) {
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, Init)
} // namespace demo
Once compiled, the example Addon can be required and used from within Node.js:
// test.js
const addon = require('./build/Release/addon');
console.log('This should be eight:', addon.add(3, 5));
Callbacks#
It is common practice within Addons to pass JavaScript functions to a C++ function and execute them from there. The following example illustrates how to invoke such callbacks:
// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };
cb->Call(Null(isolate), argc, argv);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(addon, Init)
} // namespace demo
Note that this example uses a two-argument form of Init()
that receives
the full module
object as the second argument. This allows the Addon
to completely overwrite exports
with a single function instead of
adding the function as a property of exports
.
To test it, run the following JavaScript:
// test.js
const addon = require('./build/Release/addon');
addon((msg) => {
console.log(msg); // 'hello world'
});
Note that, in this example, the callback function is invoked synchronously.
Object factory#
Addons can create and return new objects from within a C++ function as
illustrated in the following example. An object is created and returned with a
property msg
that echoes the string passed to createObject()
:
// addon.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Object> obj = Object::New(isolate);
obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());
args.GetReturnValue().Set(obj);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, Init)
} // namespace demo
To test it in JavaScript:
// test.js
const addon = require('./build/Release/addon');
var obj1 = addon('hello');
var obj2 = addon('world');
console.log(obj1.msg + ' ' + obj2.msg); // 'hello world'
Function factory#
Another common scenario is creating JavaScript functions that wrap C++ functions and returning those back to JavaScript:
// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void MyFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));
}
void CreateFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);
Local<Function> fn = tpl->GetFunction();
// omit this to make it anonymous
fn->SetName(String::NewFromUtf8(isolate, "theFunction"));
args.GetReturnValue().Set(fn);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateFunction);
}
NODE_MODULE(addon, Init)
} // namespace demo
To test:
// test.js
const addon = require('./build/Release/addon');
var fn = addon();
console.log(fn()); // 'hello world'
Wrapping C++ objects#
It is also possible to wrap C++ objects/classes in a way that allows new
instances to be created using the JavaScript new
operator:
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Local;
using v8::Object;
void InitAll(Local<Object> exports) {
MyObject::Init(exports);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
Then, in myobject.h
, the wrapper class inherits from node::ObjectWrap
:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Local<v8::Object> exports);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
In myobject.cc
, implement the various methods that are to be exposed.
Below, the method plusOne()
is exposed by adding it to the constructor's
prototype:
// myobject.cc
#include "myobject.h"
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Local<Object> exports) {
Isolate* isolate = exports->GetIsolate();
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
exports->Set(String::NewFromUtf8(isolate, "MyObject"),
tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
args.GetReturnValue().Set(cons->NewInstance(argc, argv));
}
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
To build this example, the myobject.cc
file must be added to the
binding.gyp
:
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
Test it with:
// test.js
const addon = require('./build/Release/addon');
var obj = new addon.MyObject(10);
console.log(obj.plusOne()); // 11
console.log(obj.plusOne()); // 12
console.log(obj.plusOne()); // 13
Factory of wrapped objects#
Alternatively, it is possible to use a factory pattern to avoid explicitly
creating object instances using the JavaScript new
operator:
var obj = addon.createObject();
// instead of:
// var obj = new addon.Object();
First, the createObject()
method is implemented in addon.cc
:
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void InitAll(Local<Object> exports, Local<Object> module) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
In myobject.h
, the static method NewInstance()
is added to handle
instantiating the object. This method takes the place of using new
in
JavaScript:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
The implementation in myobject.cc
is similar to the previous example:
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
args.GetReturnValue().Set(cons->NewInstance(argc, argv));
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance = cons->NewInstance(argc, argv);
args.GetReturnValue().Set(instance);
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
Once again, to build this example, the myobject.cc
file must be added to the
binding.gyp
:
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
Test it with:
// test.js
const createObject = require('./build/Release/addon');
var obj = createObject(10);
console.log(obj.plusOne()); // 11
console.log(obj.plusOne()); // 12
console.log(obj.plusOne()); // 13
var obj2 = createObject(20);
console.log(obj2.plusOne()); // 21
console.log(obj2.plusOne()); // 22
console.log(obj2.plusOne()); // 23
Passing wrapped objects around#
In addition to wrapping and returning C++ objects, it is possible to pass
wrapped objects around by unwrapping them with the Node.js helper function
node::ObjectWrap::Unwrap
. The following examples shows a function add()
that can take two MyObject
objects as input arguments:
// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
args[0]->ToObject());
MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
args[1]->ToObject());
double sum = obj1->value() + obj2->value();
args.GetReturnValue().Set(Number::New(isolate, sum));
}
void InitAll(Local<Object> exports) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(exports, "createObject", CreateObject);
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
In myobject.h
, a new public method is added to allow access to private values
after unwrapping the object.
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
inline double value() const { return value_; }
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
The implementation of myobject.cc
is similar to before:
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
args.GetReturnValue().Set(cons->NewInstance(argc, argv));
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance = cons->NewInstance(argc, argv);
args.GetReturnValue().Set(instance);
}
} // namespace demo
Test it with:
// test.js
const addon = require('./build/Release/addon');
var obj1 = addon.createObject(10);
var obj2 = addon.createObject(20);
var result = addon.add(obj1, obj2);
console.log(result); // 30
AtExit hooks#
An "AtExit" hook is a function that is invoked after the Node.js event loop
has ended by before the JavaScript VM is terminated and Node.js shuts down.
"AtExit" hooks are registered using the node::AtExit
API.
void AtExit(callback, args)#
callback
:void (*)(void*)
- A pointer to the function to call at exit.args
:void*
- A pointer to pass to the callback at exit.
Registers exit hooks that run after the event loop has ended but before the VM is killed.
AtExit takes two parameters: a pointer to a callback function to run at exit, and a pointer to untyped context data to be passed to that callback.
Callbacks are run in last-in first-out order.
The following addon.cc
implements AtExit:
// addon.cc
#undef NDEBUG
#include <assert.h>
#include <stdlib.h>
#include <node.h>
namespace demo {
using node::AtExit;
using v8::HandleScope;
using v8::Isolate;
using v8::Local;
using v8::Object;
static char cookie[] = "yum yum";
static int at_exit_cb1_called = 0;
static int at_exit_cb2_called = 0;
static void at_exit_cb1(void* arg) {
Isolate* isolate = static_cast<Isolate*>(arg);
HandleScope scope(isolate);
Local<Object> obj = Object::New(isolate);
assert(!obj.IsEmpty()); // assert VM is still alive
assert(obj->IsObject());
at_exit_cb1_called++;
}
static void at_exit_cb2(void* arg) {
assert(arg == static_cast<void*>(cookie));
at_exit_cb2_called++;
}
static void sanity_check(void*) {
assert(at_exit_cb1_called == 1);
assert(at_exit_cb2_called == 2);
}
void init(Local<Object> exports) {
AtExit(sanity_check);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb1, exports->GetIsolate());
}
NODE_MODULE(addon, init);
} // namespace demo
Test in JavaScript by running:
// test.js
const addon = require('./build/Release/addon');
Assert#
Stability: 3 - Locked
The assert
module provides a simple set of assertion tests that can be used to
test invariants. The module is intended for internal use by Node.js, but can be
used in application code via require('assert')
. However, assert
is not a
testing framework, and is not intended to be used as a general purpose assertion
library.
The API for the assert
module is Locked. This means that there will be no
additions or changes to any of the methods implemented and exposed by
the module.
assert(value[, message])#
An alias of assert.ok()
.
const assert = require('assert');
assert(true); // OK
assert(1); // OK
assert(false);
// throws "AssertionError: false == true"
assert(0);
// throws "AssertionError: 0 == true"
assert(false, 'it\'s false');
// throws "AssertionError: it's false"
assert.deepEqual(actual, expected[, message])#
Tests for deep equality between the actual
and expected
parameters.
Primitive values are compared with the equal comparison operator ( ==
).
Only enumerable "own" properties are considered. The deepEqual()
implementation does not test object prototypes, attached symbols, or
non-enumerable properties. This can lead to some potentially surprising
results. For example, the following example does not throw an AssertionError
because the properties on the Error
object are non-enumerable:
// WARNING: This does not throw an AssertionError!
assert.deepEqual(Error('a'), Error('b'));
"Deep" equality means that the enumerable "own" properties of child objects are evaluated also:
const assert = require('assert');
const obj1 = {
a : {
b : 1
}
};
const obj2 = {
a : {
b : 2
}
};
const obj3 = {
a : {
b : 1
}
}
const obj4 = Object.create(obj1);
assert.deepEqual(obj1, obj1);
// OK, object is equal to itself
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
// values of b are different
assert.deepEqual(obj1, obj3);
// OK, objects are equal
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
// Prototypes are ignored
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.deepStrictEqual(actual, expected[, message])#
Generally identical to assert.deepEqual()
with two exceptions. First,
primitive values are compared using the strict equality operator ( ===
).
Second, object comparisons include a strict equality check of their prototypes.
const assert = require('assert');
assert.deepEqual({a:1}, {a:'1'});
// OK, because 1 == '1'
assert.deepStrictEqual({a:1}, {a:'1'});
// AssertionError: { a: 1 } deepStrictEqual { a: '1' }
// because 1 !== '1' using strict equality
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.doesNotThrow(block[, error][, message])#
Asserts that the function block
does not throw an error. See
assert.throws()
for more details.
When assert.doesNotThrow()
is called, it will immediately call the block
function.
If an error is thrown and it is the same type as that specified by the error
parameter, then an AssertionError
is thrown. If the error is of a different
type, or if the error
parameter is undefined, the error is propagated back
to the caller.
The following, for instance, will throw the TypeError
because there is no
matching error type in the assertion:
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError
);
However, the following will result in an AssertionError
with the message
'Got unwanted exception (TypeError)..':
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError
);
If an AssertionError
is thrown and a value is provided for the message
parameter, the value of message
will be appended to the AssertionError
message:
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError,
'Whoops'
);
// Throws: AssertionError: Got unwanted exception (TypeError). Whoops
assert.equal(actual, expected[, message])#
Tests shallow, coercive equality between the actual
and expected
parameters
using the equal comparison operator ( ==
).
const assert = require('assert');
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({a: {b: 1}}, {a: {b: 1}});
//AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.fail(actual, expected, message, operator)#
Throws an AssertionError
. If message
is falsy, the error message is set as
the values of actual
and expected
separated by the provided operator
.
Otherwise, the error message is the value of message
.
const assert = require('assert');
assert.fail(1, 2, undefined, '>');
// AssertionError: 1 > 2
assert.fail(1, 2, 'whoops', '>');
// AssertionError: whoops
assert.ifError(value)#
Throws value
if value
is truthy. This is useful when testing the error
argument in callbacks.
const assert = require('assert');
assert.ifError(0); // OK
assert.ifError(1); // Throws 1
assert.ifError('error') // Throws 'error'
assert.ifError(new Error()); // Throws Error
assert.notDeepEqual(actual, expected[, message])#
Tests for any deep inequality. Opposite of assert.deepEqual()
.
const assert = require('assert');
const obj1 = {
a : {
b : 1
}
};
const obj2 = {
a : {
b : 2
}
};
const obj3 = {
a : {
b : 1
}
}
const obj4 = Object.create(obj1);
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK, obj1 and obj2 are not deeply equal
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK, obj1 and obj2 are not deeply equal
If the values are deeply equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.notDeepStrictEqual(actual, expected[, message])#
Tests for deep strict inequality. Opposite of assert.deepStrictEqual()
.
const assert = require('assert');
assert.notDeepEqual({a:1}, {a:'1'});
// AssertionError: { a: 1 } notDeepEqual { a: '1' }
assert.notDeepStrictEqual({a:1}, {a:'1'});
// OK
If the values are deeply and strictly equal, an AssertionError
is thrown
with a message
property set equal to the value of the message
parameter. If
the message
parameter is undefined, a default error message is assigned.
assert.notEqual(actual, expected[, message])#
Tests shallow, coercive inequality with the not equal comparison operator
( !=
).
const assert = require('assert');
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
If the values are equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.notStrictEqual(actual, expected[, message])#
Tests strict inequality as determined by the strict not equal operator
( !==
).
const assert = require('assert');
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError: 1 != 1
assert.notStrictEqual(1, '1');
// OK
If the values are strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned.
assert.ok(value[, message])#
Tests if value
is truthy. It is equivalent to
assert.equal(!!value, true, message)
.
If value
is not truthy, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined
, a default error message is assigned.
const assert = require('assert');
assert.ok(true); // OK
assert.ok(1); // OK
assert.ok(false);
// throws "AssertionError: false == true"
assert.ok(0);
// throws "AssertionError: 0 == true"
assert.ok(false, 'it\'s false');
// throws "AssertionError: it's false"
assert.strictEqual(actual, expected[, message])#
Tests strict equality as determined by the strict equality operator ( ===
).
const assert = require('assert');
assert.strictEqual(1, 2);
// AssertionError: 1 === 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual(1, '1');
// AssertionError: 1 === '1'
If the values are not strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned.
assert.throws(block[, error][, message])#
Expects the function block
to throw an error.
If specified, error
can be a constructor, RegExp
, or validation
function.
If specified, message
will be the message provided by the AssertionError
if
the block fails to throw.
Validate instanceof using constructor:
assert.throws(
() => {
throw new Error('Wrong value');
},
Error
);
Validate error message using RegExp
:
assert.throws(
() => {
throw new Error('Wrong value');
},
/value/
);
Custom error validation:
assert.throws(
() => {
throw new Error('Wrong value');
},
function(err) {
if ( (err instanceof Error) && /value/.test(err) ) {
return true;
}
},
'unexpected error'
);
Note that error
can not be a string. If a string is provided as the second
argument, then error
is assumed to be omitted and the string will be used for
message
instead. This can lead to easy-to-miss mistakes:
// THIS IS A MISTAKE! DO NOT DO THIS!
assert.throws(myFunction, 'missing foo', 'did not throw with expected message');
// Do this instead.
assert.throws(myFunction, /missing foo/, 'did not throw with expected message');
Buffer#
Stability: 2 - Stable
Prior to the introduction of TypedArray
in ECMAScript 2015 (ES6), the
JavaScript language had no mechanism for reading or manipulating streams
of binary data. The Buffer
class was introduced as part of the Node.js
API to make it possible to interact with octet streams in the context of things
like TCP streams and file system operations.
Now that TypedArray
has been added in ES6, the Buffer
class implements the
Uint8Array
API in a manner that is more optimized and suitable for Node.js'
use cases.
Instances of the Buffer
class are similar to arrays of integers but
correspond to fixed-sized, raw memory allocations outside the V8 heap.
The size of the Buffer
is established when it is created and cannot be
resized.
The Buffer
class is a global within Node.js, making it unlikely that one
would need to ever use require('buffer')
.
const buf1 = Buffer.alloc(10);
// Creates a zero-filled Buffer of length 10.
const buf2 = Buffer.alloc(10, 1);
// Creates a Buffer of length 10, filled with 0x01.
const buf3 = Buffer.allocUnsafe(10);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using either fill() or write().
const buf4 = Buffer.from([1,2,3]);
// Creates a Buffer containing [01, 02, 03].
const buf5 = Buffer.from('test');
// Creates a Buffer containing ASCII bytes [74, 65, 73, 74].
const buf6 = Buffer.from('tést', 'utf8');
// Creates a Buffer containing UTF8 bytes [74, c3, a9, 73, 74].
Buffer.from()
, Buffer.alloc()
, and Buffer.allocUnsafe()
#
In versions of Node.js prior to v6, Buffer
instances were created using the
Buffer
constructor function, which allocates the returned Buffer
differently based on what arguments are provided:
- Passing a number as the first argument to
Buffer()
(e.g.new Buffer(10)
), allocates a newBuffer
object of the specified size. The memory allocated for suchBuffer
instances is not initialized and can contain sensitive data. SuchBuffer
objects must be initialized manually by using eitherbuf.fill(0)
or by writing to theBuffer
completely. While this behavior is intentional to improve performance, development experience has demonstrated that a more explicit distinction is required between creating a fast-but-uninitializedBuffer
versus creating a slower-but-saferBuffer
. - Passing a string, array, or
Buffer
as the first argument copies the passed object's data into theBuffer
. - Passing an
ArrayBuffer
returns aBuffer
that shares allocated memory with the givenArrayBuffer
.
Because the behavior of new Buffer()
changes significantly based on the type
of value passed as the first argument, applications that do not properly
validate the input arguments passed to new Buffer()
, or that fail to
appropriately initialize newly allocated Buffer
content, can inadvertently
introduce security and reliability issues into their code.
To make the creation of Buffer
objects more reliable and less error prone,
the various forms of the new Buffer()
constructor have been deprecated
and replaced by separate Buffer.from()
, Buffer.alloc()
, and
Buffer.allocUnsafe()
methods.
Developers should migrate all existing uses of the new Buffer()
constructors
to one of these new APIs.
Buffer.from(array)
returns a newBuffer
containing a copy of the provided octets.Buffer.from(arrayBuffer[, byteOffset [, length]])
returns a newBuffer
that shares the same allocated memory as the givenArrayBuffer
.Buffer.from(buffer)
returns a newBuffer
containing a copy of the contents of the givenBuffer
.Buffer.from(str[, encoding])
returns a newBuffer
containing a copy of the provided string.Buffer.alloc(size[, fill[, encoding]])
returns a "filled"Buffer
instance of the specified size. This method can be significantly slower thanBuffer.allocUnsafe(size)
but ensures that newly createdBuffer
instances never contain old and potentially sensitive data.Buffer.allocUnsafe(size)
andBuffer.allocUnsafeSlow(size)
each return a newBuffer
of the specifiedsize
whose content must be initialized using eitherbuf.fill(0)
or written to completely.
Buffer
instances returned by Buffer.allocUnsafe(size)
may be allocated
off a shared internal memory pool if size
is less than or equal to half
Buffer.poolSize
. Instances returned by Buffer.allocUnsafeSlow(size)
never
use the shared internal memory pool.
The --zero-fill-buffers
command line option#
Node.js can be started using the --zero-fill-buffers
command line option to
force all newly allocated Buffer
instances created using either
new Buffer(size)
, Buffer.allocUnsafe(size)
, Buffer.allocUnsafeSlow(size)
or new SlowBuffer(size)
to be automatically zero-filled upon creation. Use
of this flag changes the default behavior of these methods and can have a
significant impact on performance. Use of the --zero-fill-buffers
option is
recommended only when absolutely necessary to enforce that newly allocated
Buffer
instances cannot contain potentially sensitive data.
$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
What makes Buffer.allocUnsafe(size)
and Buffer.allocUnsafeSlow(size)
"unsafe"?#
When calling Buffer.allocUnsafe()
(and Buffer.allocUnsafeSlow()
), the
segment of allocated memory is uninitialized (it is not zeroed-out). While
this design makes the allocation of memory quite fast, the allocated segment of
memory might contain old data that is potentially sensitive. Using a Buffer
created by Buffer.allocUnsafe()
without completely overwriting the memory
can allow this old data to be leaked when the Buffer
memory is read.
While there are clear performance advantages to using Buffer.allocUnsafe()
,
extra care must be taken in order to avoid introducing security
vulnerabilities into an application.
Buffers and Character Encodings#
Buffers are commonly used to represent sequences of encoded characters such as UTF8, UCS2, Base64 or even Hex-encoded data. It is possible to convert back and forth between Buffers and ordinary JavaScript string objects by using an explicit encoding method.
const buf = Buffer.from('hello world', 'ascii');
console.log(buf.toString('hex'));
// prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// prints: aGVsbG8gd29ybGQ=
The character encodings currently supported by Node.js include:
'ascii'
- for 7-bit ASCII data only. This encoding method is very fast and will strip the high bit if set.'utf8'
- Multibyte encoded Unicode characters. Many web pages and other document formats use UTF-8.'utf16le'
- 2 or 4 bytes, little-endian encoded Unicode characters. Surrogate pairs (U+10000 to U+10FFFF) are supported.'ucs2'
- Alias of'utf16le'
.'base64'
- Base64 string encoding. When creating a buffer from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC 4648, Section 5.'binary'
- A way of encoding the buffer into a one-byte (latin-1
) encoded string. The string'latin-1'
is not supported. Instead, pass'binary'
to use'latin-1'
encoding.'hex'
- Encode each byte as two hexadecimal characters.
Buffers and TypedArray#
Buffers are also Uint8Array
TypedArray instances. However, there are subtle
incompatibilities with the TypedArray specification in ECMAScript 2015. For
instance, while ArrayBuffer#slice()
creates a copy of the slice,
the implementation of Buffer#slice()
creates a view over the
existing Buffer without copying, making Buffer#slice()
far more efficient.
It is also possible to create new TypedArray instances from a Buffer
with the
following caveats:
The
Buffer
object's memory is copied to the TypedArray, not shared.The
Buffer
object's memory is interpreted as an array of distinct elements, and not as a byte array of the target type. That is,new Uint32Array(Buffer.from([1,2,3,4]))
creates a 4-elementUint32Array
with elements[1,2,3,4]
, not aUint32Array
with a single element[0x1020304]
or[0x4030201]
.
It is possible to create a new Buffer
that shares the same allocated memory as
a TypedArray instance by using the TypeArray object's .buffer
property:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf1 = Buffer.from(arr); // copies the buffer
const buf2 = Buffer.from(arr.buffer); // shares the memory with arr;
console.log(buf1);
// Prints: <Buffer 88 a0>, copied buffer has only two elements
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
Note that when creating a Buffer
using the TypedArray's .buffer
, it is
possible to use only a portion of the underlying ArrayBuffer
by passing in
byteOffset
and length
parameters:
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
// Prints: 16
The Buffer.from()
and TypedArray.from()
(e.g.Uint8Array.from()
) have
different signatures and implementations. Specifically, the TypedArray variants
accept a second argument that is a mapping function that is invoked on every
element of the typed array:
TypedArray.from(source[, mapFn[, thisArg]])
The Buffer.from()
method, however, does not support the use of a mapping
function:
Buffer.from(array)
Buffer.from(buffer)
Buffer.from(arrayBuffer[, byteOffset [, length]])
Buffer.from(str[, encoding])
Buffers and ES6 iteration#
Buffers can be iterated over using the ECMAScript 2015 (ES6) for..of
syntax:
const buf = Buffer.from([1, 2, 3]);
for (var b of buf)
console.log(b)
// Prints:
// 1
// 2
// 3
Additionally, the buf.values()
, buf.keys()
, and
buf.entries()
methods can be used to create iterators.
Class: Buffer#
The Buffer class is a global type for dealing with binary data directly. It can be constructed in a variety of ways.
new Buffer(array)#
Stability: 0 - Deprecated: Use Buffer.from(array)
instead.
array
<Array>
Allocates a new Buffer using an array
of octets.
const buf = new Buffer([0x62,0x75,0x66,0x66,0x65,0x72]);
// creates a new Buffer containing ASCII bytes
// ['b','u','f','f','e','r']
new Buffer(buffer)#
Stability: 0 - Deprecated: Use Buffer.from(buffer)
instead.
buffer
<Buffer>
Copies the passed buffer
data onto a new Buffer
instance.
const buf1 = new Buffer('buffer');
const buf2 = new Buffer(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// 'auffer'
console.log(buf2.toString());
// 'buffer' (copy is not changed)
new Buffer(arrayBuffer[, byteOffset [, length]])#
Stability: 0 - Deprecated: Use
Buffer.from(arrayBuffer[, byteOffset [, length]])
instead.
arrayBuffer
<ArrayBuffer> The.buffer
property of aTypedArray
or anew ArrayBuffer()
byteOffset
<Number> Default:0
length
<Number> Default:arrayBuffer.length - byteOffset
When passed a reference to the .buffer
property of a TypedArray
instance,
the newly created Buffer will share the same allocated memory as the
TypedArray.
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf = new Buffer(arr.buffer); // shares the memory with arr;
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// changing the TypdArray changes the Buffer also
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
new Buffer(size)#
Stability: 0 - Deprecated: UseBuffer.alloc(size[, fill[, encoding]])
instead (also seeBuffer.allocUnsafe(size)
).
size
<Number>
Allocates a new Buffer
of size
bytes. The size
must be less than
or equal to the value of require('buffer').kMaxLength
(on 64-bit
architectures, kMaxLength
is (2^31)-1
). Otherwise, a RangeError
is
thrown. A zero-length Buffer will be created if a size
less than or equal to
0 is specified.
Unlike ArrayBuffers
, the underlying memory for Buffer
instances created in
this way is not initialized. The contents of a newly created Buffer
are
unknown and could contain sensitive data. Use buf.fill(0)
to initialize
a Buffer
to zeroes.
const buf = new Buffer(5);
console.log(buf);
// <Buffer 78 e0 82 02 01>
// (octets will be different, every time)
buf.fill(0);
console.log(buf);
// <Buffer 00 00 00 00 00>
new Buffer(str[, encoding])#
Stability: 0 - Deprecated:
Use Buffer.from(str[, encoding])
instead.
Creates a new Buffer containing the given JavaScript string str
. If
provided, the encoding
parameter identifies the strings character encoding.
const buf1 = new Buffer('this is a tést');
console.log(buf1.toString());
// prints: this is a tést
console.log(buf1.toString('ascii'));
// prints: this is a tC)st
const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');
console.log(buf2.toString());
// prints: this is a tést
Class Method: Buffer.alloc(size[, fill[, encoding]])#
Allocates a new Buffer
of size
bytes. If fill
is undefined
, the
Buffer
will be zero-filled.
const buf = Buffer.alloc(5);
console.log(buf);
// <Buffer 00 00 00 00 00>
The size
must be less than or equal to the value of
require('buffer').kMaxLength
(on 64-bit architectures, kMaxLength
is
(2^31)-1
). Otherwise, a RangeError
is thrown. A zero-length Buffer will
be created if a size
less than or equal to 0 is specified.
If fill
is specified, the allocated Buffer
will be initialized by calling
buf.fill(fill)
. See [buf.fill()
][] for more information.
const buf = Buffer.alloc(5, 'a');
console.log(buf);
// <Buffer 61 61 61 61 61>
If both fill
and encoding
are specified, the allocated Buffer
will be
initialized by calling buf.fill(fill, encoding)
. For example:
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
// <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
Calling Buffer.alloc(size)
can be significantly slower than the alternative
Buffer.allocUnsafe(size)
but ensures that the newly created Buffer
instance
contents will never contain sensitive data.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.allocUnsafe(size)#
size
<Number>
Allocates a new non-zero-filled Buffer
of size
bytes. The size
must
be less than or equal to the value of require('buffer').kMaxLength
(on 64-bit
architectures, kMaxLength
is (2^31)-1
). Otherwise, a RangeError
is
thrown. A zero-length Buffer will be created if a size
less than or equal to
0 is specified.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use buf.fill(0)
to initialize such
Buffer
instances to zeroes.
const buf = Buffer.allocUnsafe(5);
console.log(buf);
// <Buffer 78 e0 82 02 01>
// (octets will be different, every time)
buf.fill(0);
console.log(buf);
// <Buffer 00 00 00 00 00>
A TypeError
will be thrown if size
is not a number.
Note that the Buffer
module pre-allocates an internal Buffer
instance of
size Buffer.poolSize
that is used as a pool for the fast allocation of new
Buffer
instances created using Buffer.allocUnsafe(size)
(and the deprecated
new Buffer(size)
constructor) only when size
is less than or equal to
Buffer.poolSize >> 1
(floor of Buffer.poolSize
divided by two). The default
value of Buffer.poolSize
is 8192
but can be modified.
Use of this pre-allocated internal memory pool is a key difference between
calling Buffer.alloc(size, fill)
vs. Buffer.allocUnsafe(size).fill(fill)
.
Specifically, Buffer.alloc(size, fill)
will never use the internal Buffer
pool, while Buffer.allocUnsafe(size).fill(fill)
will use the internal
Buffer pool if size
is less than or equal to half Buffer.poolSize
. The
difference is subtle but can be important when an application requires the
additional performance that Buffer.allocUnsafe(size)
provides.
Class Method: Buffer.allocUnsafeSlow(size)#
size
<Number>
Allocates a new non-zero-filled and non-pooled Buffer
of size
bytes. The
size
must be less than or equal to the value of
require('buffer').kMaxLength
(on 64-bit architectures, kMaxLength
is
(2^31)-1
). Otherwise, a RangeError
is thrown. A zero-length Buffer will
be created if a size
less than or equal to 0 is specified.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use buf.fill(0)
to initialize such
Buffer
instances to zeroes.
When using Buffer.allocUnsafe()
to allocate new Buffer
instances,
allocations under 4KB are, by default, sliced from a single pre-allocated
Buffer
. This allows applications to avoid the garbage collection overhead of
creating many individually allocated Buffers. This approach improves both
performance and memory usage by eliminating the need to track and cleanup as
many Persistent
objects.
However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer instance using Buffer.allocUnsafeSlow()
then
copy out the relevant bits.
// need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// allocate for retained data
const sb = Buffer.allocUnsafeSlow(10);
// copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of Buffer.allocUnsafeSlow()
should be used only as a last resort after
a developer has observed undue memory retention in their applications.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.byteLength(string[, encoding])#
string
<String> | <Buffer> | <TypedArray> | <DataView> | <ArrayBuffer>encoding
<String> Default:'utf8'
- Return: <Number>
Returns the actual byte length of a string. This is not the same as
String.prototype.length
since that returns the number of characters in
a string.
Example:
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
// ½ + ¼ = ¾: 9 characters, 12 bytes
When string
is a Buffer
/DataView
/TypedArray
/ArrayBuffer
,
returns the actual byte length.
Otherwise, converts to String
and returns the byte length of string.
Class Method: Buffer.compare(buf1, buf2)#
Compares buf1
to buf2
typically for the purpose of sorting arrays of
Buffers. This is equivalent is calling buf1.compare(buf2)
.
const arr = [Buffer.from('1234'), Buffer.from('0123')];
arr.sort(Buffer.compare);
Class Method: Buffer.concat(list[, totalLength])#
Returns a new Buffer which is the result of concatenating all the Buffers in
the list
together.
If the list has no items, or if the totalLength
is 0, then a new zero-length
Buffer is returned.
If totalLength
is not provided, it is calculated from the Buffers in the
list
. This, however, adds an additional loop to the function, so it is faster
to provide the length explicitly.
Example: build a single Buffer from a list of three Buffers:
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
console.log(totalLength);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
console.log(bufA.length);
// 42
// <Buffer 00 00 00 00 ...>
// 42
Class Method: Buffer.from(array)#
array
<Array>
Allocates a new Buffer
using an array
of octets.
const buf = Buffer.from([0x62,0x75,0x66,0x66,0x65,0x72]);
// creates a new Buffer containing ASCII bytes
// ['b','u','f','f','e','r']
A TypeError
will be thrown if array
is not an Array
.
Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])#
arrayBuffer
<ArrayBuffer> The.buffer
property of aTypedArray
or anew ArrayBuffer()
byteOffset
<Number> Default:0
length
<Number> Default:arrayBuffer.length - byteOffset
When passed a reference to the .buffer
property of a TypedArray
instance,
the newly created Buffer
will share the same allocated memory as the
TypedArray.
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
const buf = Buffer.from(arr.buffer); // shares the memory with arr;
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// changing the TypedArray changes the Buffer also
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
// Prints: 2
A TypeError
will be thrown if arrayBuffer
is not an ArrayBuffer
.
Class Method: Buffer.from(buffer)#
buffer
<Buffer>
Copies the passed buffer
data onto a new Buffer
instance.
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// 'auffer'
console.log(buf2.toString());
// 'buffer' (copy is not changed)
A TypeError
will be thrown if buffer
is not a Buffer
.
Class Method: Buffer.from(str[, encoding])#
Creates a new Buffer
containing the given JavaScript string str
. If
provided, the encoding
parameter identifies the character encoding.
If not provided, encoding
defaults to 'utf8'
.
const buf1 = Buffer.from('this is a tést');
console.log(buf1.toString());
// prints: this is a tést
console.log(buf1.toString('ascii'));
// prints: this is a tC)st
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf2.toString());
// prints: this is a tést
A TypeError
will be thrown if str
is not a string.
Class Method: Buffer.isBuffer(obj)#
Returns 'true' if obj
is a Buffer.
Class Method: Buffer.isEncoding(encoding)#
Returns true if the encoding
is a valid encoding argument, or false
otherwise.
buf[index]#
The index operator [index]
can be used to get and set the octet at position
index
in the Buffer. The values refer to individual bytes, so the legal value
range is between 0x00
and 0xFF
(hex) or 0
and 255
(decimal).
Example: copy an ASCII string into a Buffer, one byte at a time:
const str = "Node.js";
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length ; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf.toString('ascii'));
// Prints: Node.js
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])#
target
<Buffer>targetStart
<Integer> The offset withintarget
at which to begin comparison. default =0
.targetEnd
<Integer> The offset withtarget
at which to end comparison. Ignored whentargetStart
isundefined
. default =target.byteLength
.sourceStart
<Integer> The offset withinbuf
at which to begin comparison. Ignored whentargetStart
isundefined
. default =0
sourceEnd
<Integer> The offset withinbuf
at which to end comparison. Ignored whentargetStart
isundefined
. default =buf.byteLength
.- Return: <Number>
Compares two Buffer instances and returns a number indicating whether buf
comes before, after, or is the same as the target
in sort order.
Comparison is based on the actual sequence of bytes in each Buffer.
0
is returned iftarget
is the same asbuf
1
is returned iftarget
should come beforebuf
when sorted.-1
is returned iftarget
should come afterbuf
when sorted.
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: 1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
[buf1, buf2, buf3].sort(Buffer.compare);
// produces sort order [buf1, buf3, buf2]
The optional targetStart
, targetEnd
, sourceStart
, and sourceEnd
arguments can be used to limit the comparison to specific ranges within the two
Buffer
objects.
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1
A RangeError
will be thrown if: targetStart < 0
, sourceStart < 0
,
targetEnd > target.byteLength
or sourceEnd > source.byteLength
.
buf.copy(targetBuffer[, targetStart[, sourceStart[, sourceEnd]]])#
Copies data from a region of this Buffer to a region in the target Buffer even if the target memory region overlaps with the source.
Example: build two Buffers, then copy buf1
from byte 16 through byte 19
into buf2
, starting at the 8th byte in buf2
.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0 ; i < 26 ; i++) {
buf1[i] = i + 97; // 97 is ASCII a
}
buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
Example: Build a single Buffer, then copy data from one region to an overlapping region in the same Buffer
const buf = Buffer.allocUnsafe(26);
for (var i = 0 ; i < 26 ; i++) {
buf[i] = i + 97; // 97 is ASCII a
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
// efghijghijklmnopqrstuvwxyz
buf.entries()#
- Return: <Iterator>
Creates and returns an iterator of [index, byte]
pairs from the Buffer
contents.
const buf = Buffer.from('buffer');
for (var pair of buf.entries()) {
console.log(pair);
}
// prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
buf.equals(otherBuffer)#
Returns a boolean indicating whether this
and otherBuffer
have exactly the
same bytes.
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
buf.fill(value[, offset[, end]][, encoding])#
Fills the Buffer with the specified value. If the offset
(defaults to 0
)
and end
(defaults to buf.length
) are not given the entire buffer will be
filled. The method returns a reference to the Buffer, so calls can be chained.
This is meant as a small simplification to creating a Buffer. Allowing the
creation and fill of the Buffer to be done on a single line:
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
encoding
is only relevant if value
is a string. Otherwise it is ignored.
value
is coerced to a uint32
value if it is not a String or Number.
The fill()
operation writes bytes into the Buffer dumbly. If the final write
falls in between a multi-byte character then whatever bytes fit into the buffer
are written.
Buffer(3).fill('\u0222');
// Prints: <Buffer c8 a2 c8>
buf.indexOf(value[, byteOffset][, encoding])#
Operates similar to Array#indexOf()
in that it returns either the
starting index position of value
in Buffer or -1
if the Buffer does not
contain value
. The value
can be a String, Buffer or Number. Strings are by
default interpreted as UTF8. Buffers will use the entire Buffer (to compare a
partial Buffer use buf.slice()
). Numbers can range from 0 to 255.
const buf = Buffer.from('this is a buffer');
buf.indexOf('this');
// returns 0
buf.indexOf('is');
// returns 2
buf.indexOf(Buffer.from('a buffer'));
// returns 8
buf.indexOf(97); // ascii for 'a'
// returns 8
buf.indexOf(Buffer.from('a buffer example'));
// returns -1
buf.indexOf(Buffer.from('a buffer example').slice(0,8));
// returns 8
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
utf16Buffer.indexOf('\u03a3', 0, 'ucs2');
// returns 4
utf16Buffer.indexOf('\u03a3', -4, 'ucs2');
// returns 6
buf.includes(value[, byteOffset][, encoding])#
Operates similar to Array#includes()
. The value
can be a String, Buffer
or Number. Strings are interpreted as UTF8 unless overridden with the
encoding
argument. Buffers will use the entire Buffer (to compare a partial
Buffer use buf.slice()
). Numbers can range from 0 to 255.
The byteOffset
indicates the index in buf
where searching begins.
const buf = Buffer.from('this is a buffer');
buf.includes('this');
// returns true
buf.includes('is');
// returns true
buf.includes(Buffer.from('a buffer'));
// returns true
buf.includes(97); // ascii for 'a'
// returns true
buf.includes(Buffer.from('a buffer example'));
// returns false
buf.includes(Buffer.from('a buffer example').slice(0,8));
// returns true
buf.includes('this', 4);
// returns false
buf.keys()#
- Return: <Iterator>
Creates and returns an iterator of Buffer keys (indices).
const buf = Buffer.from('buffer');
for (var key of buf.keys()) {
console.log(key);
}
// prints:
// 0
// 1
// 2
// 3
// 4
// 5
buf.length#
Returns the amount of memory allocated for the Buffer in number of bytes. Note that this does not necessarily reflect the amount of usable data within the Buffer. For instance, in the example below, a Buffer with 1234 bytes is allocated, but only 11 ASCII bytes are written.
const buf = Buffer.alloc(1234);
console.log(buf.length);
// Prints: 1234
buf.write('some string', 0, 'ascii');
console.log(buf.length);
// Prints: 1234
While the length
property is not immutable, changing the value of length
can result in undefined and inconsistent behavior. Applications that wish to
modify the length of a Buffer should therefore treat length
as read-only and
use buf.slice()
to create a new Buffer.
var buf = Buffer.allocUnsafe(10);
buf.write('abcdefghj', 0, 'ascii');
console.log(buf.length);
// Prints: 10
buf = buf.slice(0,5);
console.log(buf.length);
// Prints: 5
buf.readDoubleBE(offset[, noAssert])#
buf.readDoubleLE(offset[, noAssert])#
Reads a 64-bit double from the Buffer at the specified offset
with specified
endian format (readDoubleBE()
returns big endian, readDoubleLE()
returns
little endian).
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
const buf = Buffer.from([1,2,3,4,5,6,7,8]);
buf.readDoubleBE();
// Returns: 8.20788039913184e-304
buf.readDoubleLE();
// Returns: 5.447603722011605e-270
buf.readDoubleLE(1);
// throws RangeError: Index out of range
buf.readDoubleLE(1, true); // Warning: reads passed end of buffer!
// Segmentation fault! don't do this!
buf.readFloatBE(offset[, noAssert])#
buf.readFloatLE(offset[, noAssert])#
Reads a 32-bit float from the Buffer at the specified offset
with specified
endian format (readFloatBE()
returns big endian, readFloatLE()
returns
little endian).
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
const buf = Buffer.from([1,2,3,4]);
buf.readFloatBE();
// Returns: 2.387939260590663e-38
buf.readFloatLE();
// Returns: 1.539989614439558e-36
buf.readFloatLE(1);
// throws RangeError: Index out of range
buf.readFloatLE(1, true); // Warning: reads passed end of buffer!
// Segmentation fault! don't do this!
buf.readInt8(offset[, noAssert])#
Reads a signed 8-bit integer from the Buffer at the specified offset
.
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
Integers read from the Buffer are interpreted as two's complement signed values.
const buf = Buffer.from([1,-2,3,4]);
buf.readInt8(0);
// returns 1
buf.readInt8(1);
// returns -2
buf.readInt16BE(offset[, noAssert])#
buf.readInt16LE(offset[, noAssert])#
Reads a signed 16-bit integer from the Buffer at the specified offset
with
the specified endian format (readInt16BE()
returns big endian,
readInt16LE()
returns little endian).
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
Integers read from the Buffer are interpreted as two's complement signed values.
const buf = Buffer.from([1,-2,3,4]);
buf.readInt16BE();
// returns 510
buf.readInt16LE(1);
// returns 1022
buf.readInt32BE(offset[, noAssert])#
buf.readInt32LE(offset[, noAssert])#
Reads a signed 32-bit integer from the Buffer at the specified offset
with
the specified endian format (readInt32BE()
returns big endian,
readInt32LE()
returns little endian).
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
Integers read from the Buffer are interpreted as two's complement signed values.
const buf = Buffer.from([1,-2,3,4]);
buf.readInt32BE();
// returns 33424132
buf.readInt32LE();
// returns 67370497
buf.readInt32LE(1);
// throws RangeError: Index out of range
buf.readIntBE(offset, byteLength[, noAssert])#
buf.readIntLE(offset, byteLength[, noAssert])#
Reads byteLength
number of bytes from the Buffer at the specified offset
and interprets the result as a two's complement signed value. Supports up to 48
bits of accuracy. For example:
const buf = Buffer.allocUnsafe(6);
buf.writeUInt16LE(0x90ab, 0);
buf.writeUInt32LE(0x12345678, 2);
buf.readIntLE(0, 6).toString(16); // Specify 6 bytes (48 bits)
// Returns: '1234567890ab'
buf.readIntBE(0, 6).toString(16);
// Returns: -546f87a9cbee
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
buf.readUInt8(offset[, noAssert])#
Reads an unsigned 8-bit integer from the Buffer at the specified offset
.
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
const buf = Buffer.from([1,-2,3,4]);
buf.readUInt8(0);
// returns 1
buf.readUInt8(1);
// returns 254
buf.readUInt16BE(offset[, noAssert])#
buf.readUInt16LE(offset[, noAssert])#
Reads an unsigned 16-bit integer from the Buffer at the specified offset
with
specified endian format (readUInt16BE()
returns big endian,
readUInt16LE()
returns little endian).
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
Example:
const buf = Buffer.from([0x3, 0x4, 0x23, 0x42]);
buf.readUInt16BE(0);
// Returns: 0x0304
buf.readUInt16LE(0);
// Returns: 0x0403
buf.readUInt16BE(1);
// Returns: 0x0423
buf.readUInt16LE(1);
// Returns: 0x2304
buf.readUInt16BE(2);
// Returns: 0x2342
buf.readUInt16LE(2);
// Returns: 0x4223
buf.readUInt32BE(offset[, noAssert])#
buf.readUInt32LE(offset[, noAssert])#
Reads an unsigned 32-bit integer from the Buffer at the specified offset
with
specified endian format (readUInt32BE()
returns big endian,
readUInt32LE()
returns little endian).
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
Example:
const buf = Buffer.from([0x3, 0x4, 0x23, 0x42]);
buf.readUInt32BE(0);
// Returns: 0x03042342
console.log(buf.readUInt32LE(0));
// Returns: 0x42230403
buf.readUIntBE(offset, byteLength[, noAssert])#
buf.readUIntLE(offset, byteLength[, noAssert])#
Reads byteLength
number of bytes from the Buffer at the specified offset
and interprets the result as an unsigned integer. Supports up to 48
bits of accuracy. For example:
const buf = Buffer.allocUnsafe(6);
buf.writeUInt16LE(0x90ab, 0);
buf.writeUInt32LE(0x12345678, 2);
buf.readUIntLE(0, 6).toString(16); // Specify 6 bytes (48 bits)
// Returns: '1234567890ab'
buf.readUIntBE(0, 6).toString(16);
// Returns: ab9078563412
Setting noAssert
to true
skips validation of the offset
. This allows the
offset
to be beyond the end of the Buffer.
buf.slice([start[, end]])#
Returns a new Buffer that references the same memory as the original, but
offset and cropped by the start
and end
indices.
Note that modifying the new Buffer slice will modify the memory in the original Buffer because the allocated memory of the two objects overlap.
Example: build a Buffer with the ASCII alphabet, take a slice, then modify one byte from the original Buffer.
const buf1 = Buffer.allocUnsafe(26);
for (var i = 0 ; i < 26 ; i++) {
buf1[i] = i + 97; // 97 is ASCII a
}
const buf2 = buf1.slice(0, 3);
buf2.toString('ascii', 0, buf2.length);
// Returns: 'abc'
buf1[0] = 33;
buf2.toString('ascii', 0, buf2.length);
// Returns : '!bc'
Specifying negative indexes causes the slice to be generated relative to the end of the Buffer rather than the beginning.
const buf = Buffer.from('buffer');
buf.slice(-6, -1).toString();
// Returns 'buffe', equivalent to buf.slice(0, 5)
buf.slice(-6, -2).toString();
// Returns 'buff', equivalent to buf.slice(0, 4)
buf.slice(-5, -2).toString();
// Returns 'uff', equivalent to buf.slice(1, 4)
buf.swap16()#
- Return: <Buffer>
Interprets the Buffer
as an array of unsigned 16-bit integers and swaps
the byte-order in-place. Throws a RangeError
if the Buffer
length is
not a multiple of 16 bits. The method returns a reference to the Buffer, so
calls can be chained.
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf);
// Prints Buffer(0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8)
buf.swap16();
console.log(buf);
// Prints Buffer(0x2, 0x1, 0x4, 0x3, 0x6, 0x5, 0x8, 0x7)
buf.swap32()#
- Return: <Buffer>
Interprets the Buffer
as an array of unsigned 32-bit integers and swaps
the byte-order in-place. Throws a RangeError
if the Buffer
length is
not a multiple of 32 bits. The method returns a reference to the Buffer, so
calls can be chained.
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
console.log(buf);
// Prints Buffer(0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8)
buf.swap32();
console.log(buf);
// Prints Buffer(0x4, 0x3, 0x2, 0x1, 0x8, 0x7, 0x6, 0x5)
buf.toString([encoding[, start[, end]]])#
Decodes and returns a string from the Buffer data using the specified
character set encoding
.
const buf = Buffer.allocUnsafe(26);
for (var i = 0 ; i < 26 ; i++) {
buf[i] = i + 97; // 97 is ASCII a
}
buf.toString('ascii');
// Returns: 'abcdefghijklmnopqrstuvwxyz'
buf.toString('ascii',0,5);
// Returns: 'abcde'
buf.toString('utf8',0,5);
// Returns: 'abcde'
buf.toString(undefined,0,5);
// Returns: 'abcde', encoding defaults to 'utf8'
buf.toJSON()#
- Return: <Object>
Returns a JSON representation of the Buffer instance. JSON.stringify()
implicitly calls this function when stringifying a Buffer instance.
Example:
const buf = Buffer.from('test');
const json = JSON.stringify(buf);
console.log(json);
// Prints: '{"type":"Buffer","data":[116,101,115,116]}'
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer'
? Buffer.from(value.data)
: value;
});
console.log(copy.toString());
// Prints: 'test'
buf.values()#
- Return: <Iterator>
Creates and returns an iterator for Buffer values (bytes). This function is
called automatically when the Buffer is used in a for..of
statement.
const buf = Buffer.from('buffer');
for (var value of buf.values()) {
console.log(value);
}
// prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (var value of buf) {
console.log(value);
}
// prints:
// 98
// 117
// 102
// 102
// 101
// 114
buf.write(string[, offset[, length]][, encoding])#
Writes string
to the Buffer at offset
using the given encoding
.
The length
parameter is the number of bytes to write. If the Buffer did not
contain enough space to fit the entire string, only a partial amount of the
string will be written however, it will not write only partially encoded
characters.
const buf = Buffer.allocUnsafe(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
// Prints: 12 bytes: ½ + ¼ = ¾
buf.writeDoubleBE(value, offset[, noAssert])#
buf.writeDoubleLE(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
with specified endian
format (writeDoubleBE()
writes big endian, writeDoubleLE()
writes little
endian). The value
argument should be a valid 64-bit double. Behavior is
not defined when value
is anything other than a 64-bit double.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
Example:
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);
console.log(buf);
// Prints: <Buffer 43 eb d5 b7 dd f9 5f d7>
buf.writeDoubleLE(0xdeadbeefcafebabe, 0);
console.log(buf);
// Prints: <Buffer d7 5f f9 dd b7 d5 eb 43>
buf.writeFloatBE(value, offset[, noAssert])#
buf.writeFloatLE(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
with specified endian
format (writeFloatBE()
writes big endian, writeFloatLE()
writes little
endian). Behavior is not defined when value
is anything other than a 32-bit
float.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
Example:
const buf = Buffer.allocUnsafe(4);
buf.writeFloatBE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer 4f 4a fe bb>
buf.writeFloatLE(0xcafebabe, 0);
console.log(buf);
// Prints: <Buffer bb fe 4a 4f>
buf.writeInt8(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
. The value
should be a
valid signed 8-bit integer. Behavior is not defined when value
is anything
other than a signed 8-bit integer.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
The value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
console.log(buf);
// Prints: <Buffer 02 fe>
buf.writeInt16BE(value, offset[, noAssert])#
buf.writeInt16LE(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
with specified endian
format (writeInt16BE()
writes big endian, writeInt16LE()
writes little
endian). The value
should be a valid signed 16-bit integer. Behavior is
not defined when value
is anything other than a signed 16-bit integer.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
The value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(4);
buf.writeInt16BE(0x0102,0);
buf.writeInt16LE(0x0304,2);
console.log(buf);
// Prints: <Buffer 01 02 04 03>
buf.writeInt32BE(value, offset[, noAssert])#
buf.writeInt32LE(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
with specified endian
format (writeInt32BE()
writes big endian, writeInt32LE()
writes little
endian). The value
should be a valid signed 32-bit integer. Behavior is
not defined when value
is anything other than a signed 32-bit integer.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
The value
is interpreted and written as a two's complement signed integer.
const buf = Buffer.allocUnsafe(8);
buf.writeInt32BE(0x01020304,0);
buf.writeInt32LE(0x05060708,4);
console.log(buf);
// Prints: <Buffer 01 02 03 04 08 07 06 05>
buf.writeIntBE(value, offset, byteLength[, noAssert])#
buf.writeIntLE(value, offset, byteLength[, noAssert])#
Writes value
to the Buffer at the specified offset
and byteLength
.
Supports up to 48 bits of accuracy. For example:
const buf1 = Buffer.allocUnsafe(6);
buf1.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf1);
// Prints: <Buffer 12 34 56 78 90 ab>
const buf2 = Buffer.allocUnsafe(6);
buf2.writeUIntLE(0x1234567890ab, 0, 6);
console.log(buf2);
// Prints: <Buffer ab 90 78 56 34 12>
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
Behavior is not defined when value
is anything other than an integer.
buf.writeUInt8(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
. The value
should be a
valid unsigned 8-bit integer. Behavior is not defined when value
is anything
other than an unsigned 8-bit integer.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
Example:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
console.log(buf);
// Prints: <Buffer 03 04 23 42>
buf.writeUInt16BE(value, offset[, noAssert])#
buf.writeUInt16LE(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
with specified endian
format (writeUInt16BE()
writes big endian, writeUInt16LE()
writes little
endian). The value
should be a valid unsigned 16-bit integer. Behavior is
not defined when value
is anything other than an unsigned 16-bit integer.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
Example:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer de ad be ef>
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
console.log(buf);
// Prints: <Buffer ad de ef be>
buf.writeUInt32BE(value, offset[, noAssert])#
buf.writeUInt32LE(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
with specified endian
format (writeUInt32BE()
writes big endian, writeUInt32LE()
writes little
endian). The value
should be a valid unsigned 32-bit integer. Behavior is
not defined when value
is anything other than an unsigned 32-bit integer.
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
Example:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32BE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer fe ed fa ce>
buf.writeUInt32LE(0xfeedface, 0);
console.log(buf);
// Prints: <Buffer ce fa ed fe>
buf.writeUIntBE(value, offset, byteLength[, noAssert])#
buf.writeUIntLE(value, offset, byteLength[, noAssert])#
Writes value
to the Buffer at the specified offset
and byteLength
.
Supports up to 48 bits of accuracy. For example:
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf);
// Prints: <Buffer 12 34 56 78 90 ab>
Set noAssert
to true to skip validation of value
and offset
. This means
that value
may be too large for the specific function and offset
may be
beyond the end of the Buffer leading to the values being silently dropped. This
should not be used unless you are certain of correctness.
Behavior is not defined when value
is anything other than an unsigned integer.
buffer.INSPECT_MAX_BYTES#
- <Number> Default: 50
Returns the maximum number of bytes that will be returned when
buffer.inspect()
is called. This can be overridden by user modules. See
util.inspect()
for more details on buffer.inspect()
behavior.
Note that this is a property on the buffer
module as returned by
require('buffer')
, not on the Buffer global or a Buffer instance.
Class: SlowBuffer#
Stability: 0 - Deprecated: Use
Buffer.allocUnsafeSlow(size)
instead.
Returns an un-pooled Buffer
.
In order to avoid the garbage collection overhead of creating many individually
allocated Buffers, by default allocations under 4KB are sliced from a single
larger allocated object. This approach improves both performance and memory
usage since v8 does not need to track and cleanup as many Persistent
objects.
In the case where a developer may need to retain a small chunk of memory from a
pool for an indeterminate amount of time, it may be appropriate to create an
un-pooled Buffer instance using SlowBuffer
then copy out the relevant bits.
// need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
var data = socket.read();
// allocate for retained data
var sb = SlowBuffer(10);
// copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of SlowBuffer
should be used only as a last resort after a developer
has observed undue memory retention in their applications.
new SlowBuffer(size)#
Stability: 0 - Deprecated: Use
Buffer.allocUnsafeSlow(size)
instead.
size
Number
Allocates a new SlowBuffer
of size
bytes. The size
must be less than
or equal to the value of require('buffer').kMaxLength
(on 64-bit
architectures, kMaxLength
is (2^31)-1
). Otherwise, a RangeError
is
thrown. A zero-length Buffer will be created if a size
less than or equal to
0 is specified.
The underlying memory for SlowBuffer
instances is not initialized. The
contents of a newly created SlowBuffer
are unknown and could contain
sensitive data. Use buf.fill(0)
to initialize a SlowBuffer
to zeroes.
const SlowBuffer = require('buffer').SlowBuffer;
const buf = new SlowBuffer(5);
console.log(buf);
// <Buffer 78 e0 82 02 01>
// (octets will be different, every time)
buf.fill(0);
console.log(buf);
// <Buffer 00 00 00 00 00>
Child Process#
Stability: 2 - Stable
The child_process
module provides the ability to spawn child processes in
a manner that is similar, but not identical, to popen(3)
. This capability
is primarily provided by the child_process.spawn()
function:
const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
By default, pipes for stdin
, stdout
and stderr
are established between
the parent Node.js process and the spawned child. It is possible to stream data
through these pipes in a non-blocking way. Note, however, that some programs
use line-buffered I/O internally. While that does not affect Node.js, it can
mean that data sent to the child process may not be immediately consumed.
The child_process.spawn()
method spawns the child process asynchronously,
without blocking the Node.js event loop. The child_process.spawnSync()
function provides equivalent functionality in a synchronous manner that blocks
the event loop until the spawned process either exits or is terminated.
For convenience, the child_process
module provides a handful of synchronous
and asynchronous alternatives to child_process.spawn()
and
child_process.spawnSync()
. Note that each of these alternatives are
implemented on top of child_process.spawn()
or child_process.spawnSync()
.
child_process.exec()
: spawns a shell and runs a command within that shell, passing thestdout
andstderr
to a callback function when complete.child_process.execFile()
: similar tochild_process.exec()
except that it spawns the command directly without first spawning a shell.child_process.fork()
: spawns a new Node.js process and invokes a specified module with an IPC communication channel established that allows sending messages between parent and child.child_process.execSync()
: a synchronous version ofchild_process.exec()
that will block the Node.js event loop.child_process.execFileSync()
: a synchronous version ofchild_process.execFile()
that will block the Node.js event loop.
For certain use cases, such as automating shell scripts, the synchronous counterparts may be more convenient. In many cases, however, the synchronous methods can have significant impact on performance due to stalling the event loop while spawned processes complete.
Asynchronous Process Creation#
The child_process.spawn()
, child_process.fork()
, child_process.exec()
,
and child_process.execFile()
methods all follow the idiomatic asynchronous
programming pattern typical of other Node.js APIs.
Each of the methods returns a ChildProcess
instance. These objects
implement the Node.js EventEmitter
API, allowing the parent process to
register listener functions that are called when certain events occur during
the life cycle of the child process.
The child_process.exec()
and child_process.execFile()
methods additionally
allow for an optional callback
function to be specified that is invoked
when the child process terminates.
Spawning .bat
and .cmd
files on Windows#
The importance of the distinction between child_process.exec()
and
child_process.execFile()
can vary based on platform. On Unix-type operating
systems (Unix, Linux, OSX) child_process.execFile()
can be more efficient
because it does not spawn a shell. On Windows, however, .bat
and .cmd
files are not executable on their own without a terminal, and therefore cannot
be launched using child_process.execFile()
. When running on Windows, .bat
and .cmd
files can be invoked using child_process.spawn()
with the shell
option set, with child_process.exec()
, or by spawning cmd.exe
and passing
the .bat
or .cmd
file as an argument (which is what the shell
option and
child_process.exec()
do).
// On Windows Only ...
const spawn = require('child_process').spawn;
const bat = spawn('cmd.exe', ['/c', 'my.bat']);
bat.stdout.on('data', (data) => {
console.log(data);
});
bat.stderr.on('data', (data) => {
console.log(data);
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
// OR...
const exec = require('child_process').exec;
exec('my.bat', (err, stdout, stderr) => {
if (err) {
console.error(err);
return;
}
console.log(stdout);
});
child_process.exec(command[, options][, callback])#
command
<String> The command to run, with space-separated argumentsoptions
<Object>cwd
<String> Current working directory of the child processenv
<Object> Environment key-value pairsencoding
<String> (Default: 'utf8')shell
<String> Shell to execute the command with (Default: '/bin/sh' on UNIX, 'cmd.exe' on Windows, The shell should understand the-c
switch on UNIX or/s /c
on Windows. On Windows, command line parsing should be compatible withcmd.exe
.)timeout
<Number> (Default: 0)maxBuffer
<Number> largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed (Default:200*1024
)killSignal
<String> (Default: 'SIGTERM')uid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)
callback
<Function> called with the output when process terminates- Return: <ChildProcess>
Spawns a shell then executes the command
within that shell, buffering any
generated output.
const exec = require('child_process').exec;
const child = exec('cat *.js bad_file | wc -l',
(error, stdout, stderr) => {
console.log(`stdout: ${stdout}`);
console.log(`stderr: ${stderr}`);
if (error !== null) {
console.log(`exec error: ${error}`);
}
});
If a callback
function is provided, it is called with the arguments
(error, stdout, stderr)
. On success, error
will be null
. On error,
error
will be an instance of Error
. The error.code
property will be
the exit code of the child process while error.signal
will be set to the
signal that terminated the process. Any exit code other than 0
is considered
to be an error.
The stdout
and stderr
arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The encoding
option
can be used to specify the character encoding used to decode the stdout and
stderr output. If encoding
is 'buffer'
, Buffer
objects will be passed to
the callback instead.
The options
argument may be passed as the second argument to customize how
the process is spawned. The default options are:
{
encoding: 'utf8',
timeout: 0,
maxBuffer: 200*1024,
killSignal: 'SIGTERM',
cwd: null,
env: null
}
If timeout
is greater than 0
, the parent will send the the signal
identified by the killSignal
property (the default is 'SIGTERM'
) if the
child runs longer than timeout
milliseconds.
Note: Unlike the exec()
POSIX system call, child_process.exec()
does not
replace the existing process and uses a shell to execute the command.
child_process.execFile(file[, args][, options][, callback])#
file
<String> The name or path of the executable file to runargs
<Array> List of string argumentsoptions
<Object>cwd
<String> Current working directory of the child processenv
<Object> Environment key-value pairsencoding
<String> (Default: 'utf8')timeout
<Number> (Default: 0)maxBuffer
<Number> largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed (Default: 200*1024)killSignal
<String> (Default: 'SIGTERM')uid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)
callback
<Function> called with the output when process terminates- Return: <ChildProcess>
The child_process.execFile()
function is similar to child_process.exec()
except that it does not spawn a shell. Rather, the specified executable file
is spawned directly as a new process making it slightly more efficient than
child_process.exec()
.
The same options as child_process.exec()
are supported. Since a shell is not
spawned, behaviors such as I/O redirection and file globbing are not supported.
const execFile = require('child_process').execFile;
const child = execFile('node', ['--version'], (error, stdout, stderr) => {
if (error) {
throw error;
}
console.log(stdout);
});
The stdout
and stderr
arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The encoding
option
can be used to specify the character encoding used to decode the stdout and
stderr output. If encoding
is 'buffer'
, Buffer
objects will be passed to
the callback instead.
child_process.fork(modulePath[, args][, options])#
modulePath
<String> The module to run in the childargs
<Array> List of string argumentsoptions
<Object>cwd
<String> Current working directory of the child processenv
<Object> Environment key-value pairsexecPath
<String> Executable used to create the child processexecArgv
<Array> List of string arguments passed to the executable (Default:process.execArgv
)silent
<Boolean> If true, stdin, stdout, and stderr of the child will be piped to the parent, otherwise they will be inherited from the parent, see the'pipe'
and'inherit'
options forchild_process.spawn()
'sstdio
for more details (default is false)uid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)
- Return: <ChildProcess>
The child_process.fork()
method is a special case of
child_process.spawn()
used specifically to spawn new Node.js processes.
Like child_process.spawn()
, a ChildProcess
object is returned. The returned
ChildProcess
will have an additional communication channel built-in that
allows messages to be passed back and forth between the parent and child. See
ChildProcess#send()
for details.
It is important to keep in mind that spawned Node.js child processes are independent of the parent with exception of the IPC communication channel that is established between the two. Each process has it's own memory, with their own V8 instances. Because of the additional resource allocations required, spawning a large number of child Node.js processes is not recommended.
By default, child_process.fork()
will spawn new Node.js instances using the
process.execPath
of the parent process. The execPath
property in the
options
object allows for an alternative execution path to be used.
Node.js processes launched with a custom execPath
will communicate with the
parent process using the file descriptor (fd) identified using the
environment variable NODE_CHANNEL_FD
on the child process. The input and
output on this fd is expected to be line delimited JSON objects.
Note: Unlike the fork()
POSIX system call, child_process.fork()
does
not clone the current process.
child_process.spawn(command[, args][, options])#
command
<String> The command to runargs
<Array> List of string argumentsoptions
<Object>cwd
<String> Current working directory of the child processenv
<Object> Environment key-value pairsstdio
<Array> | <String> Child's stdio configuration. (Seeoptions.stdio
)detached
<Boolean> Prepare child to run independently of its parent process. Specific behavior depends on the platform, seeoptions.detached
)uid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)shell
<Boolean> | <String> Iftrue
, runscommand
inside of a shell. Uses '/bin/sh' on UNIX, and 'cmd.exe' on Windows. A different shell can be specified as a string. The shell should understand the-c
switch on UNIX, or/s /c
on Windows. Defaults tofalse
(no shell).
- return: <ChildProcess>
The child_process.spawn()
method spawns a new process using the given
command
, with command line arguments in args
. If omitted, args
defaults
to an empty array.
A third argument may be used to specify additional options, with these defaults:
{
cwd: undefined,
env: process.env
}
Use cwd
to specify the working directory from which the process is spawned.
If not given, the default is to inherit the current working directory.
Use env
to specify environment variables that will be visible to the new
process, the default is process.env
.
Example of running ls -lh /usr
, capturing stdout
, stderr
, and the
exit code:
const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
Example: A very elaborate way to run 'ps ax | grep ssh'
const spawn = require('child_process').spawn;
const ps = spawn('ps', ['ax']);
const grep = spawn('grep', ['ssh']);
ps.stdout.on('data', (data) => {
grep.stdin.write(data);
});
ps.stderr.on('data', (data) => {
console.log(`ps stderr: ${data}`);
});
ps.on('close', (code) => {
if (code !== 0) {
console.log(`ps process exited with code ${code}`);
}
grep.stdin.end();
});
grep.stdout.on('data', (data) => {
console.log(`${data}`);
});
grep.stderr.on('data', (data) => {
console.log(`grep stderr: ${data}`);
});
grep.on('close', (code) => {
if (code !== 0) {
console.log(`grep process exited with code ${code}`);
}
});
Example of checking for failed exec:
const spawn = require('child_process').spawn;
const child = spawn('bad_command');
child.on('error', (err) => {
console.log('Failed to start child process.');
});
options.detached#
On Windows, setting options.detached
to true
makes it possible for the
child process to continue running after the parent exits. The child will have
its own console window. Once enabled for a child process, it cannot be
disabled.
On non-Windows platforms, if options.detached
is set to true
, the child
process will be made the leader of a new process group and session. Note that
child processes may continue running after the parent exits regardless of
whether they are detached or not. See setsid(2)
for more information.
By default, the parent will wait for the detached child to exit. To prevent
the parent from waiting for a given child
, use the child.unref()
method.
Doing so will cause the parent's event loop to not include the child in its
reference count, allowing the parent to exit independently of the child, unless
there is an established IPC channel between the child and parent.
When using the detached
option to start a long-running process, the process
will not stay running in the background after the parent exits unless it is
provided with a stdio
configuration that is not connected to the parent.
If the parent's stdio
is inherited, the child will remain attached to the
controlling terminal.
Example of a long-running process, by detaching and also ignoring its parent
stdio
file descriptors, in order to ignore the parent's termination:
const spawn = require('child_process').spawn;
const child = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: ['ignore']
});
child.unref();
Alternatively one can redirect the child process' output into files:
const fs = require('fs');
const spawn = require('child_process').spawn;
const out = fs.openSync('./out.log', 'a');
const err = fs.openSync('./out.log', 'a');
const child = spawn('prg', [], {
detached: true,
stdio: [ 'ignore', out, err ]
});
child.unref();
options.stdio#
The options.stdio
option is used to configure the pipes that are established
between the parent and child process. By default, the child's stdin, stdout,
and stderr are redirected to corresponding child.stdin
, child.stdout
, and
child.stderr
streams on the ChildProcess
object. This is equivalent to
setting the options.stdio
equal to ['pipe', 'pipe', 'pipe']
.
For convenience, options.stdio
may be one of the following strings:
'pipe'
- equivalent to['pipe', 'pipe', 'pipe']
(the default)'ignore'
- equivalent to['ignore', 'ignore', 'ignore']
'inherit'
- equivalent to[process.stdin, process.stdout, process.stderr]
or[0,1,2]
Otherwise, the value of option.stdio
is an array where each index corresponds
to an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout,
and stderr, respectively. Additional fds can be specified to create additional
pipes between the parent and child. The value is one of the following:
'pipe'
- Create a pipe between the child process and the parent process. The parent end of the pipe is exposed to the parent as a property on thechild_process
object asChildProcess.stdio[fd]
. Pipes created for fds 0 - 2 are also available as ChildProcess.stdin, ChildProcess.stdout and ChildProcess.stderr, respectively.'ipc'
- Create an IPC channel for passing messages/file descriptors between parent and child. A ChildProcess may have at most one IPC stdio file descriptor. Setting this option enables the ChildProcess.send() method. If the child writes JSON messages to this file descriptor, theChildProcess.on('message')
event handler will be triggered in the parent. If the child is a Node.js process, the presence of an IPC channel will enableprocess.send()
,process.disconnect()
,process.on('disconnect')
, andprocess.on('message')
within the child.'ignore'
- Instructs Node.js to ignore the fd in the child. While Node.js will always open fds 0 - 2 for the processes it spawns, setting the fd to'ignore'
will cause Node.js to open/dev/null
and attach it to the child's fd.Stream
object - Share a readable or writable stream that refers to a tty, file, socket, or a pipe with the child process. The stream's underlying file descriptor is duplicated in the child process to the fd that corresponds to the index in thestdio
array. Note that the stream must have an underlying descriptor (file streams do not until the'open'
event has occurred).- Positive integer - The integer value is interpreted as a file descriptor
that is is currently open in the parent process. It is shared with the child
process, similar to how
Stream
objects can be shared. null
,undefined
- Use default value. For stdio fds 0, 1 and 2 (in other words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the default is'ignore'
.
Example:
const spawn = require('child_process').spawn;
// Child will use parent's stdios
spawn('prg', [], { stdio: 'inherit' });
// Spawn child sharing only stderr
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });
// Open an extra fd=4, to interact with programs presenting a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });
It is worth noting that when an IPC channel is established between the
parent and child processes, and the child is a Node.js process, the child
is launched with the IPC channel unreferenced (using unref()
) until the
child registers an event handler for the process.on('disconnected')
event.
This allows the child to exit normally without the process being held open
by the open IPC channel.
See also: child_process.exec()
and child_process.fork()
Synchronous Process Creation#
The child_process.spawnSync()
, child_process.execSync()
, and
child_process.execFileSync()
methods are synchronous and WILL block
the Node.js event loop, pausing execution of any additional code until the
spawned process exits.
Blocking calls like these are mostly useful for simplifying general purpose scripting tasks and for simplifying the loading/processing of application configuration at startup.
child_process.execFileSync(file[, args][, options])#
file
<String> The name or path of the executable file to runargs
<Array> List of string argumentsoptions
<Object>cwd
<String> Current working directory of the child processinput
<String> | <Buffer> The value which will be passed as stdin to the spawned process- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<Array> Child's stdio configuration. (Default: 'pipe')stderr
by default will be output to the parent process' stderr unlessstdio
is specified
env
<Object> Environment key-value pairsuid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)timeout
<Number> In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)killSignal
<String> The signal value to be used when the spawned process will be killed. (Default: 'SIGTERM')maxBuffer
<Number> largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killedencoding
<String> The encoding used for all stdio inputs and outputs. (Default: 'buffer')
- return: <Buffer> | <String> The stdout from the command
The child_process.execFileSync()
method is generally identical to
child_process.execFile()
with the exception that the method will not return
until the child process has fully closed. When a timeout has been encountered
and killSignal
is sent, the method won't return until the process has
completely exited. Note that if the child process intercepts and handles
the SIGTERM
signal and does not exit, the parent process will still wait
until the child process has exited.
If the process times out, or has a non-zero exit code, this method will
throw. The Error
object will contain the entire result from
child_process.spawnSync()
child_process.execSync(command[, options])#
command
<String> The command to runoptions
<Object>cwd
<String> Current working directory of the child processinput
<String> | <Buffer> The value which will be passed as stdin to the spawned process- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<Array> Child's stdio configuration. (Default: 'pipe')stderr
by default will be output to the parent process' stderr unlessstdio
is specified
env
<Object> Environment key-value pairsshell
<String> Shell to execute the command with (Default: '/bin/sh' on UNIX, 'cmd.exe' on Windows, The shell should understand the-c
switch on UNIX or/s /c
on Windows. On Windows, command line parsing should be compatible withcmd.exe
.)uid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)timeout
<Number> In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)killSignal
<String> The signal value to be used when the spawned process will be killed. (Default: 'SIGTERM')maxBuffer
<Number> largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killedencoding
<String> The encoding used for all stdio inputs and outputs. (Default: 'buffer')
- return: <Buffer> | <String> The stdout from the command
The child_process.execSync()
method is generally identical to
child_process.exec()
with the exception that the method will not return until
the child process has fully closed. When a timeout has been encountered and
killSignal
is sent, the method won't return until the process has completely
exited. Note that if the child process intercepts and handles the SIGTERM
signal and doesn't exit, the parent process will wait until the child
process has exited.
If the process times out, or has a non-zero exit code, this method will
throw. The Error
object will contain the entire result from
child_process.spawnSync()
child_process.spawnSync(command[, args][, options])#
command
<String> The command to runargs
<Array> List of string argumentsoptions
<Object>cwd
<String> Current working directory of the child processinput
<String> | <Buffer> The value which will be passed as stdin to the spawned process- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<Array> Child's stdio configuration.env
<Object> Environment key-value pairsuid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)timeout
<Number> In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)killSignal
<String> The signal value to be used when the spawned process will be killed. (Default: 'SIGTERM')maxBuffer
<Number> largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killedencoding
<String> The encoding used for all stdio inputs and outputs. (Default: 'buffer')shell
<Boolean> | <String> Iftrue
, runscommand
inside of a shell. Uses '/bin/sh' on UNIX, and 'cmd.exe' on Windows. A different shell can be specified as a string. The shell should understand the-c
switch on UNIX, or/s /c
on Windows. Defaults tofalse
(no shell).
- return: <Object>
pid
<Number> Pid of the child processoutput
<Array> Array of results from stdio outputstdout
<Buffer> | <String> The contents ofoutput[1]
stderr
<Buffer> | <String> The contents ofoutput[2]
status
<Number> The exit code of the child processsignal
<String> The signal used to kill the child processerror
<Error> The error object if the child process failed or timed out
The child_process.spawnSync()
method is generally identical to
child_process.spawn()
with the exception that the function will not return
until the child process has fully closed. When a timeout has been encountered
and killSignal
is sent, the method won't return until the process has
completely exited. Note that if the process intercepts and handles the
SIGTERM
signal and doesn't exit, the parent process will wait until the child
process has exited.
Class: ChildProcess#
Instances of the ChildProcess
class are EventEmitters
that represent
spawned child processes.
Instances of ChildProcess
are not intended to be created directly. Rather,
use the child_process.spawn()
, child_process.exec()
,
child_process.execFile()
, or child_process.fork()
methods to create
instances of ChildProcess
.
Event: 'close'#
The 'close'
event is emitted when the stdio streams of a child process have
been closed. This is distinct from the 'exit'
event, since multiple
processes might share the same stdio streams.
Event: 'disconnect'#
The 'disconnect'
event is emitted after calling the
ChildProcess.disconnect()
method in the parent or child process. After
disconnecting it is no longer possible to send or receive messages, and the
ChildProcess.connected
property is false.
Event: 'error'#
err
<Error> the error.
The 'error'
event is emitted whenever:
- The process could not be spawned, or
- The process could not be killed, or
- Sending a message to the child process failed.
Note that the 'exit'
event may or may not fire after an error has occurred.
If you are listening to both the 'exit'
and 'error'
events, it is important
to guard against accidentally invoking handler functions multiple times.
See also ChildProcess#kill()
and ChildProcess#send()
.
Event: 'exit'#
The 'exit'
event is emitted after the child process ends. If the process
exited, code
is the final exit code of the process, otherwise null
. If the
process terminated due to receipt of a signal, signal
is the string name of
the signal, otherwise null
. One of the two will always be non-null.
Note that when the 'exit'
event is triggered, child process stdio streams
might still be open.
Also, note that Node.js establishes signal handlers for SIGINT
and
SIGTERM
and Node.js processes will not terminate immediately due to receipt
of those signals. Rather, Node.js will perform a sequence of cleanup actions
and then will re-raise the handled signal.
See waitpid(2)
.
Event: 'message'#
message
<Object> a parsed JSON object or primitive value.sendHandle
<Handle> anet.Socket
ornet.Server
object, or undefined.
The 'message'
event is triggered when a child process uses process.send()
to send messages.
child.connected#
- <Boolean> Set to false after
.disconnect
is called
The child.connected
property indicates whether it is still possible to send
and receive messages from a child process. When child.connected
is false, it
is no longer possible to send or receive messages.
child.disconnect()#
Closes the IPC channel between parent and child, allowing the child to exit
gracefully once there are no other connections keeping it alive. After calling
this method the child.connected
and process.connected
properties in both
the parent and child (respectively) will be set to false
, and it will be no
longer possible to pass messages between the processes.
The 'disconnect'
event will be emitted when there are no messages in the
process of being received. This will most often be triggered immediately after
calling child.disconnect()
.
Note that when the child process is a Node.js instance (e.g. spawned using
child_process.fork()
), the process.disconnect()
method can be invoked
within the child process to close the IPC channel as well.
child.kill([signal])#
signal
<String>
The child.kill()
methods sends a signal to the child process. If no argument
is given, the process will be sent the 'SIGTERM'
signal. See signal(7)
for
a list of available signals.
const spawn = require('child_process').spawn;
const grep = spawn('grep', ['ssh']);
grep.on('close', (code, signal) => {
console.log(
`child process terminated due to receipt of signal ${signal}`);
});
// Send SIGHUP to process
grep.kill('SIGHUP');
The ChildProcess
object may emit an 'error'
event if the signal cannot be
delivered. Sending a signal to a child process that has already exited is not
an error but may have unforeseen consequences. Specifically, if the process
identifier (PID) has been reassigned to another process, the signal will be
delivered to that process instead which can have unexpected results.
Note that while the function is called kill
, the signal delivered to the
child process may not actually terminate the process.
See kill(2)
for reference.
Also note: on Linux, child processes of child processes will not be terminated
when attempting to kill their parent. This is likely to happen when running a
new process in a shell or with use of the shell
option of ChildProcess
, such
as in this example:
'use strict';
const spawn = require('child_process').spawn;
let child = spawn('sh', ['-c',
`node -e "setInterval(() => {
console.log(process.pid + 'is alive')
}, 500);"`
], {
stdio: ['inherit', 'inherit', 'inherit']
});
setTimeout(() => {
child.kill(); // does not terminate the node process in the shell
}, 2000);
child.pid#
- <Number> Integer
Returns the process identifier (PID) of the child process.
Example:
const spawn = require('child_process').spawn;
const grep = spawn('grep', ['ssh']);
console.log(`Spawned child pid: ${grep.pid}`);
grep.stdin.end();
child.send(message[, sendHandle[, options]][, callback])#
message
<Object>sendHandle
<Handle>options
<Object>callback
<Function>- Return: <Boolean>
When an IPC channel has been established between the parent and child (
i.e. when using child_process.fork()
), the child.send()
method can be
used to send messages to the child process. When the child process is a Node.js
instance, these messages can be received via the process.on('message')
event.
For example, in the parent script:
const cp = require('child_process');
const n = cp.fork(`${__dirname}/sub.js`);
n.on('message', (m) => {
console.log('PARENT got message:', m);
});
n.send({ hello: 'world' });
And then the child script, 'sub.js'
might look like this:
process.on('message', (m) => {
console.log('CHILD got message:', m);
});
process.send({ foo: 'bar' });
Child Node.js processes will have a process.send()
method of their own that
allows the child to send messages back to the parent.
There is a special case when sending a {cmd: 'NODE_foo'}
message. All messages
containing a NODE_
prefix in its cmd
property are considered to be reserved
for use within Node.js core and will not be emitted in the child's
process.on('message')
event. Rather, such messages are emitted using the
process.on('internalMessage')
event and are consumed internally by Node.js.
Applications should avoid using such messages or listening for
'internalMessage'
events as it is subject to change without notice.
The optional sendHandle
argument that may be passed to child.send()
is for
passing a TCP server or socket object to the child process. The child will
receive the object as the second argument passed to the callback function
registered on the process.on('message')
event.
The options
argument, if present, is an object used to parameterize the
sending of certain types of handles. options
supports the following
properties:
keepOpen
- A Boolean value that can be used when passing instances ofnet.Socket
. Whentrue
, the socket is kept open in the sending process. Defaults tofalse
.
The optional callback
is a function that is invoked after the message is
sent but before the child may have received it. The function is called with a
single argument: null
on success, or an Error
object on failure.
If no callback
function is provided and the message cannot be sent, an
'error'
event will be emitted by the ChildProcess
object. This can happen,
for instance, when the child process has already exited.
child.send()
will return false
if the channel has closed or when the
backlog of unsent messages exceeds a threshold that makes it unwise to send
more. Otherwise, the method returns true
. The callback
function can be
used to implement flow control.
Example: sending a server object#
The sendHandle
argument can be used, for instance, to pass the handle of
a TCP server object to the child process as illustrated in the example below:
const child = require('child_process').fork('child.js');
// Open up the server object and send the handle.
const server = require('net').createServer();
server.on('connection', (socket) => {
socket.end('handled by parent');
});
server.listen(1337, () => {
child.send('server', server);
});
The child would then receive the server object as:
process.on('message', (m, server) => {
if (m === 'server') {
server.on('connection', (socket) => {
socket.end('handled by child');
});
}
});
Once the server is now shared between the parent and child, some connections can be handled by the parent and some by the child.
While the example above uses a server created using the net
module, dgram
module servers use exactly the same workflow with the exceptions of listening on
a 'message'
event instead of 'connection'
and using server.bind
instead of
server.listen
. This is, however, currently only supported on UNIX platforms.
Example: sending a socket object#
Similarly, the sendHandler
argument can be used to pass the handle of a
socket to the child process. The example below spawns two children that each
handle connections with "normal" or "special" priority:
const normal = require('child_process').fork('child.js', ['normal']);
const special = require('child_process').fork('child.js', ['special']);
// Open up the server and send sockets to child
const server = require('net').createServer();
server.on('connection', (socket) => {
// If this is special priority
if (socket.remoteAddress === '74.125.127.100') {
special.send('socket', socket);
return;
}
// This is normal priority
normal.send('socket', socket);
});
server.listen(1337);
The child.js
would receive the socket handle as the second argument passed
to the event callback function:
process.on('message', (m, socket) => {
if (m === 'socket') {
socket.end(`Request handled with ${process.argv[2]} priority`);
}
});
Once a socket has been passed to a child, the parent is no longer capable of
tracking when the socket is destroyed. To indicate this, the .connections
property becomes null
. It is recommended not to use .maxConnections
when
this occurs.
Note: this function uses JSON.stringify()
internally to serialize the
message
.
child.stderr#
A Readable Stream
that represents the child process's stderr
.
If the child was spawned with stdio[2]
set to anything other than 'pipe'
,
then this will be undefined
.
child.stderr
is an alias for child.stdio[2]
. Both properties will refer to
the same value.
child.stdin#
A Writable Stream
that represents the child process's stdin
.
Note that if a child process waits to read all of its input, the child will not
continue until this stream has been closed via end()
.
If the child was spawned with stdio[0]
set to anything other than 'pipe'
,
then this will be undefined
.
child.stdin
is an alias for child.stdio[0]
. Both properties will refer to
the same value.
child.stdio#
A sparse array of pipes to the child process, corresponding with positions in
the stdio
option passed to child_process.spawn()
that have been set
to the value 'pipe'
. Note that child.stdio[0]
, child.stdio[1]
, and
child.stdio[2]
are also available as child.stdin
, child.stdout
, and
child.stderr
, respectively.
In the following example, only the child's fd 1
(stdout) is configured as a
pipe, so only the parent's child.stdio[1]
is a stream, all other values in
the array are null
.
const assert = require('assert');
const fs = require('fs');
const child_process = require('child_process');
const child = child_process.spawn('ls', {
stdio: [
0, // Use parents stdin for child
'pipe', // Pipe child's stdout to parent
fs.openSync('err.out', 'w') // Direct child's stderr to a file
]
});
assert.equal(child.stdio[0], null);
assert.equal(child.stdio[0], child.stdin);
assert(child.stdout);
assert.equal(child.stdio[1], child.stdout);
assert.equal(child.stdio[2], null);
assert.equal(child.stdio[2], child.stderr);
child.stdout#
A Readable Stream
that represents the child process's stdout
.
If the child was spawned with stdio[1]
set to anything other than 'pipe'
,
then this will be undefined
.
child.stdout
is an alias for child.stdio[1]
. Both properties will refer
to the same value.
maxBuffer
and Unicode#
It is important to keep in mind that the maxBuffer
option specifies the
largest number of octets allowed on stdout
or stderr
- if this value is
exceeded then the child process is terminated. This particularly impacts
output that includes multi-byte character encodings such as UTF-8 or UTF-16.
For instance, the following will output 13 UTF-8 encoded octets to stdout
although there are only 4 characters:
console.log('中文测试');
Cluster#
Stability: 2 - Stable
A single instance of Node.js runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node.js processes to handle the load.
The cluster module allows you to easily create child processes that all share server ports.
const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
// Fork workers.
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`worker ${worker.process.pid} died`);
});
} else {
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
}
Running Node.js will now share port 8000 between the workers:
$ NODE_DEBUG=cluster node server.js
23521,Master Worker 23524 online
23521,Master Worker 23526 online
23521,Master Worker 23523 online
23521,Master Worker 23528 online
Please note that, on Windows, it is not yet possible to set up a named pipe server in a worker.
How It Works#
The worker processes are spawned using the child_process.fork()
method,
so that they can communicate with the parent via IPC and pass server
handles back and forth.
The cluster module supports two methods of distributing incoming connections.
The first one (and the default one on all platforms except Windows), is the round-robin approach, where the master process listens on a port, accepts new connections and distributes them across the workers in a round-robin fashion, with some built-in smarts to avoid overloading a worker process.
The second approach is where the master process creates the listen socket and sends it to interested workers. The workers then accept incoming connections directly.
The second approach should, in theory, give the best performance. In practice however, distribution tends to be very unbalanced due to operating system scheduler vagaries. Loads have been observed where over 70% of all connections ended up in just two processes, out of a total of eight.
Because server.listen()
hands off most of the work to the master
process, there are three cases where the behavior between a normal
Node.js process and a cluster worker differs:
server.listen({fd: 7})
Because the message is passed to the master, file descriptor 7 in the parent will be listened on, and the handle passed to the worker, rather than listening to the worker's idea of what the number 7 file descriptor references.server.listen(handle)
Listening on handles explicitly will cause the worker to use the supplied handle, rather than talk to the master process. If the worker already has the handle, then it's presumed that you know what you are doing.server.listen(0)
Normally, this will cause servers to listen on a random port. However, in a cluster, each worker will receive the same "random" port each time they dolisten(0)
. In essence, the port is random the first time, but predictable thereafter. If you want to listen on a unique port, generate a port number based on the cluster worker ID.
There is no routing logic in Node.js, or in your program, and no shared state between the workers. Therefore, it is important to design your program such that it does not rely too heavily on in-memory data objects for things like sessions and login.
Because workers are all separate processes, they can be killed or re-spawned depending on your program's needs, without affecting other workers. As long as there are some workers still alive, the server will continue to accept connections. If no workers are alive, existing connections will be dropped and new connections will be refused. Node.js does not automatically manage the number of workers for you, however. It is your responsibility to manage the worker pool for your application's needs.
Class: Worker#
A Worker object contains all public information and method about a worker.
In the master it can be obtained using cluster.workers
. In a worker
it can be obtained using cluster.worker
.
Event: 'disconnect'#
Similar to the cluster.on('disconnect')
event, but specific to this worker.
cluster.fork().on('disconnect', () => {
// Worker has disconnected
});
Event: 'error'#
This event is the same as the one provided by child_process.fork()
.
In a worker you can also use process.on('error')
.
Event: 'exit'#
Similar to the cluster.on('exit')
event, but specific to this worker.
const worker = cluster.fork();
worker.on('exit', (code, signal) => {
if( signal ) {
console.log(`worker was killed by signal: ${signal}`);
} else if( code !== 0 ) {
console.log(`worker exited with error code: ${code}`);
} else {
console.log('worker success!');
}
});
Event: 'listening'#
address
<Object>
Similar to the cluster.on('listening')
event, but specific to this worker.
cluster.fork().on('listening', (address) => {
// Worker is listening
});
It is not emitted in the worker.
Event: 'message'#
message
<Object>
Similar to the cluster.on('message')
event, but specific to this worker.
This event is the same as the one provided by child_process.fork()
.
In a worker you can also use process.on('message')
.
As an example, here is a cluster that keeps count of the number of requests in the master process using the message system:
const cluster = require('cluster');
const http = require('http');
if (cluster.isMaster) {
// Keep track of http requests
var numReqs = 0;
setInterval(() => {
console.log('numReqs =', numReqs);
}, 1000);
// Count requests
function messageHandler(msg) {
if (msg.cmd && msg.cmd == 'notifyRequest') {
numReqs += 1;
}
}
// Start workers and listen for messages containing notifyRequest
const numCPUs = require('os').cpus().length;
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
Object.keys(cluster.workers).forEach((id) => {
cluster.workers[id].on('message', messageHandler);
});
} else {
// Worker processes have a http server.
http.Server((req, res) => {
res.writeHead(200);
res.end('hello world\n');
// notify master about the request
process.send({ cmd: 'notifyRequest' });
}).listen(8000);
}
Event: 'online'#
Similar to the cluster.on('online')
event, but specific to this worker.
cluster.fork().on('online', () => {
// Worker is online
});
It is not emitted in the worker.
worker.disconnect()#
In a worker, this function will close all servers, wait for the 'close'
event on
those servers, and then disconnect the IPC channel.
In the master, an internal message is sent to the worker causing it to call
.disconnect()
on itself.
Causes .suicide
to be set.
Note that after a server is closed, it will no longer accept new connections,
but connections may be accepted by any other listening worker. Existing
connections will be allowed to close as usual. When no more connections exist,
see server.close()
, the IPC channel to the worker will close allowing it to
die gracefully.
The above applies only to server connections, client connections are not automatically closed by workers, and disconnect does not wait for them to close before exiting.
Note that in a worker, process.disconnect
exists, but it is not this function,
it is disconnect
.
Because long living server connections may block workers from disconnecting, it
may be useful to send a message, so application specific actions may be taken to
close them. It also may be useful to implement a timeout, killing a worker if
the 'disconnect'
event has not been emitted after some time.
if (cluster.isMaster) {
var worker = cluster.fork();
var timeout;
worker.on('listening', (address) => {
worker.send('shutdown');
worker.disconnect();
timeout = setTimeout(() => {
worker.kill();
}, 2000);
});
worker.on('disconnect', () => {
clearTimeout(timeout);
});
} else if (cluster.isWorker) {
const net = require('net');
var server = net.createServer((socket) => {
// connections never end
});
server.listen(8000);
process.on('message', (msg) => {
if(msg === 'shutdown') {
// initiate graceful close of any connections to server
}
});
}
worker.id#
Each new worker is given its own unique id, this id is stored in the
id
.
While a worker is alive, this is the key that indexes it in cluster.workers
worker.isConnected()#
This function returns true
if the worker is connected to its master via its IPC
channel, false
otherwise. A worker is connected to its master after it's been
created. It is disconnected after the 'disconnect'
event is emitted.
worker.isDead()#
This function returns true
if the worker's process has terminated (either
because of exiting or being signaled). Otherwise, it returns false
.
worker.kill([signal='SIGTERM'])#
signal
<String> Name of the kill signal to send to the worker process.
This function will kill the worker. In the master, it does this by disconnecting
the worker.process
, and once disconnected, killing with signal
. In the
worker, it does it by disconnecting the channel, and then exiting with code 0
.
Causes .suicide
to be set.
This method is aliased as worker.destroy()
for backwards compatibility.
Note that in a worker, process.kill()
exists, but it is not this function,
it is kill
.
worker.process#
All workers are created using child_process.fork()
, the returned object
from this function is stored as .process
. In a worker, the global process
is stored.
See: Child Process module
Note that workers will call process.exit(0)
if the 'disconnect'
event occurs
on process
and .suicide
is not true
. This protects against accidental
disconnection.
worker.send(message[, sendHandle][, callback])#
message
<Object>sendHandle
<Handle>callback
<Function>- Return: Boolean
Send a message to a worker or master, optionally with a handle.
In the master this sends a message to a specific worker. It is identical to
ChildProcess.send()
.
In a worker this sends a message to the master. It is identical to
process.send()
.
This example will echo back all messages from the master:
if (cluster.isMaster) {
var worker = cluster.fork();
worker.send('hi there');
} else if (cluster.isWorker) {
process.on('message', (msg) => {
process.send(msg);
});
}
worker.suicide#
Set by calling .kill()
or .disconnect()
, until then it is undefined
.
The boolean worker.suicide
lets you distinguish between voluntary and accidental
exit, the master may choose not to respawn a worker based on this value.
cluster.on('exit', (worker, code, signal) => {
if (worker.suicide === true) {
console.log('Oh, it was just suicide\' – no need to worry').
}
});
// kill worker
worker.kill();
Event: 'disconnect'#
worker
<cluster.Worker>
Emitted after the worker IPC channel has disconnected. This can occur when a worker exits gracefully, is killed, or is disconnected manually (such as with worker.disconnect()).
There may be a delay between the 'disconnect'
and 'exit'
events. These events
can be used to detect if the process is stuck in a cleanup or if there are
long-living connections.
cluster.on('disconnect', (worker) => {
console.log(`The worker #${worker.id} has disconnected`);
});
Event: 'exit'#
worker
<cluster.Worker>code
<Number> the exit code, if it exited normally.signal
<String> the name of the signal (eg.'SIGHUP'
) that caused the process to be killed.
When any of the workers die the cluster module will emit the 'exit'
event.
This can be used to restart the worker by calling .fork()
again.
cluster.on('exit', (worker, code, signal) => {
console.log('worker %d died (%s). restarting...',
worker.process.pid, signal || code);
cluster.fork();
});
See child_process event: 'exit'.
Event: 'fork'#
worker
<cluster.Worker>
When a new worker is forked the cluster module will emit a 'fork'
event.
This can be used to log worker activity, and create your own timeout.
var timeouts = [];
function errorMsg() {
console.error('Something must be wrong with the connection ...');
}
cluster.on('fork', (worker) => {
timeouts[worker.id] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', (worker, address) => {
clearTimeout(timeouts[worker.id]);
});
cluster.on('exit', (worker, code, signal) => {
clearTimeout(timeouts[worker.id]);
errorMsg();
});
Event: 'listening'#
worker
<cluster.Worker>address
<Object>
After calling listen()
from a worker, when the 'listening'
event is emitted on
the server, a 'listening'
event will also be emitted on cluster
in the master.
The event handler is executed with two arguments, the worker
contains the worker
object and the address
object contains the following connection properties:
address
, port
and addressType
. This is very useful if the worker is listening
on more than one address.
cluster.on('listening', (worker, address) => {
console.log(
`A worker is now connected to ${address.address}:${address.port}`);
});
The addressType
is one of:
4
(TCPv4)6
(TCPv6)-1
(unix domain socket)"udp4"
or"udp6"
(UDP v4 or v6)
Event: 'message'#
worker
<cluster.Worker>message
<Object>handle
<undefined> | <Object>
Emitted when any worker receives a message.
See child_process event: 'message'.
Before Node.js v6.0, this event emitted only the message and the handle, but not the worker object, contrary to what the documentation stated.
If you need to support older versions and don't need the worker object, you can work around the discrepancy by checking the number of arguments:
cluster.on('message', function(worker, message, handle) {
if (arguments.length === 2) {
handle = message;
message = worker;
worker = undefined;
}
// ...
});
Event: 'online'#
worker
<cluster.Worker>
After forking a new worker, the worker should respond with an online message.
When the master receives an online message it will emit this event.
The difference between 'fork'
and 'online'
is that fork is emitted when the
master forks a worker, and 'online' is emitted when the worker is running.
cluster.on('online', (worker) => {
console.log('Yay, the worker responded after it was forked');
});
Event: 'setup'#
settings
<Object>
Emitted every time .setupMaster()
is called.
The settings
object is the cluster.settings
object at the time
.setupMaster()
was called and is advisory only, since multiple calls to
.setupMaster()
can be made in a single tick.
If accuracy is important, use cluster.settings
.
cluster.disconnect([callback])#
callback
<Function> called when all workers are disconnected and handles are closed
Calls .disconnect()
on each worker in cluster.workers
.
When they are disconnected all internal handles will be closed, allowing the master process to die gracefully if no other event is waiting.
The method takes an optional callback argument which will be called when finished.
This can only be called from the master process.
cluster.fork([env])#
env
<Object> Key/value pairs to add to worker process environment.- return <cluster.Worker>
Spawn a new worker process.
This can only be called from the master process.
cluster.isMaster#
True if the process is a master. This is determined
by the process.env.NODE_UNIQUE_ID
. If process.env.NODE_UNIQUE_ID
is
undefined, then isMaster
is true
.
cluster.isWorker#
True if the process is not a master (it is the negation of cluster.isMaster
).
cluster.schedulingPolicy#
The scheduling policy, either cluster.SCHED_RR
for round-robin or
cluster.SCHED_NONE
to leave it to the operating system. This is a
global setting and effectively frozen once you spawn the first worker
or call cluster.setupMaster()
, whatever comes first.
SCHED_RR
is the default on all operating systems except Windows.
Windows will change to SCHED_RR
once libuv is able to effectively
distribute IOCP handles without incurring a large performance hit.
cluster.schedulingPolicy
can also be set through the
NODE_CLUSTER_SCHED_POLICY
environment variable. Valid
values are "rr"
and "none"
.
cluster.settings#
- <Object>
execArgv
<Array> list of string arguments passed to the Node.js executable. (Default=process.execArgv
)exec
<String> file path to worker file. (Default=process.argv[1]
)args
<Array> string arguments passed to worker. (Default=process.argv.slice(2)
)silent
<Boolean> whether or not to send output to parent's stdio. (Default=false
)uid
<Number> Sets the user identity of the process. (See setuid(2).)gid
<Number> Sets the group identity of the process. (See setgid(2).)
After calling .setupMaster()
(or .fork()
) this settings object will contain
the settings, including the default values.
It is effectively frozen after being set, because .setupMaster()
can
only be called once.
This object is not supposed to be changed or set manually, by you.
cluster.setupMaster([settings])#
setupMaster
is used to change the default 'fork' behavior. Once called,
the settings will be present in cluster.settings
.
Note that:
- any settings changes only affect future calls to
.fork()
and have no effect on workers that are already running - The only attribute of a worker that cannot be set via
.setupMaster()
is theenv
passed to.fork()
- the defaults above apply to the first call only, the defaults for later
calls is the current value at the time of
cluster.setupMaster()
is called
Example:
const cluster = require('cluster');
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'https'],
silent: true
});
cluster.fork(); // https worker
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'http']
});
cluster.fork(); // http worker
This can only be called from the master process.
cluster.worker#
A reference to the current worker object. Not available in the master process.
const cluster = require('cluster');
if (cluster.isMaster) {
console.log('I am master');
cluster.fork();
cluster.fork();
} else if (cluster.isWorker) {
console.log(`I am worker #${cluster.worker.id}`);
}
cluster.workers#
A hash that stores the active worker objects, keyed by id
field. Makes it
easy to loop through all the workers. It is only available in the master
process.
A worker is removed from cluster.workers after the worker has disconnected and
exited. The order between these two events cannot be determined in advance.
However, it is guaranteed that the removal from the cluster.workers list happens
before last 'disconnect'
or 'exit'
event is emitted.
// Go through all workers
function eachWorker(callback) {
for (var id in cluster.workers) {
callback(cluster.workers[id]);
}
}
eachWorker((worker) => {
worker.send('big announcement to all workers');
});
Should you wish to reference a worker over a communication channel, using the worker's unique id is the easiest way to find the worker.
socket.on('data', (id) => {
var worker = cluster.workers[id];
});
Command Line Options#
Node.js comes with a wide variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.
To view this documentation as a manual page in your terminal, run man node
.
Synopsis#
node [options] [v8 options] [script.js | -e "script"] [arguments]
node debug [script.js | -e "script" | <host>:<port>] …
node --v8-options
Execute without arguments to start the REPL.
For more info about node debug
, please see the debugger documentation.
Options#
-v
, --version
#
Print node's version.
-h
, --help
#
Print node command line options. The output of this option is less detailed than this document.
-e
, --eval "script"
#
Evaluate the following argument as JavaScript. The modules which are
predefined in the REPL can also be used in script
.
-p
, --print "script"
#
Identical to -e
but prints the result.
-c
, --check
#
Syntax check the script without executing.
-i
, --interactive
#
Opens the REPL even if stdin does not appear to be a terminal.
-r
, --require module
#
Preload the specified module at startup.
Follows require()
's module resolution
rules. module
may be either a path to a file, or a node module name.
--no-deprecation
#
Silence deprecation warnings.
--trace-deprecation
#
Print stack traces for deprecations.
--throw-deprecation
#
Throw errors for deprecations.
--no-warnings
#
Silence all process warnings (including deprecations).
--trace-warnings
#
Print stack traces for process warnings (including deprecations).
--trace-sync-io
#
Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.
--zero-fill-buffers
#
Automatically zero-fills all newly allocated Buffer and SlowBuffer instances.
--track-heap-objects
#
Track heap object allocations for heap snapshots.
--prof-process
#
Process v8 profiler output generated using the v8 option --prof
.
--v8-options
#
Print v8 command line options.
--tls-cipher-list=list
#
Specify an alternative default TLS cipher list. (Requires Node.js to be built with crypto support. (Default))
--enable-fips
#
Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with
./configure --openssl-fips
)
--force-fips
#
Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.)
(Same requirements as --enable-fips
)
--icu-data-dir=file
#
Specify ICU data load path. (overrides NODE_ICU_DATA
)
Environment Variables#
NODE_DEBUG=module[,…]
#
','
-separated list of core modules that should print debug information.
NODE_PATH=path[:…]
#
':'
-separated list of directories prefixed to the module search path.
Note: on Windows, this is a ';'
-separated list instead.
NODE_DISABLE_COLORS=1
#
When set to 1
colors will not be used in the REPL.
NODE_ICU_DATA=file
#
Data path for ICU (Intl object) data. Will extend linked-in data when compiled with small-icu support.
NODE_REPL_HISTORY=file
#
Path to the file used to store the persistent REPL history. The default path is
~/.node_repl_history
, which is overridden by this variable. Setting the value
to an empty string (""
or " "
) disables persistent REPL history.
Console#
Stability: 2 - Stable
The console
module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
- A
Console
class with methods such asconsole.log()
,console.error()
andconsole.warn()
that can be used to write to any Node.js stream. - A global
console
instance configured to write tostdout
andstderr
. Because this object is global, it can be used without callingrequire('console')
.
Example using the global console
:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to stderr
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console
class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
While the API for the Console
class is designed fundamentally around the
browser console
object, the Console
in Node.js is not intended to
duplicate the browser's functionality exactly.
Asynchronous vs Synchronous Consoles#
The console functions are asynchronous unless the destination is a file. Disks are fast and operating systems normally employ write-back caching; it should be a very rare occurrence indeed that a write blocks, but it is possible.
Class: Console#
The Console
class can be used to create a simple logger with configurable
output streams and can be accessed using either require('console').Console
or console.Console
:
const Console = require('console').Console;
const Console = console.Console;
new Console(stdout[, stderr])#
Creates a new Console
by passing one or two writable stream instances.
stdout
is a writable stream to print log or info output. stderr
is used for warning or error output. If stderr
isn't passed, warning and error
output will be sent to stdout
.
const output = fs.createWriteStream('./stdout.log');
const errorOutput = fs.createWriteStream('./stderr.log');
// custom simple logger
const logger = new Console(output, errorOutput);
// use it like console
var count = 5;
logger.log('count: %d', count);
// in stdout.log: count 5
The global console
is a special Console
whose output is sent to
process.stdout
and process.stderr
. It is equivalent to calling:
new Console(process.stdout, process.stderr);
console.assert(value[, message][, ...])#
A simple assertion test that verifies whether value
is truthy. If it is not,
an AssertionError
is thrown. If provided, the error message
is formatted
using util.format()
and used as the error message.
console.assert(true, 'does nothing');
// OK
console.assert(false, 'Whoops %s', 'didn\'t work');
// AssertionError: Whoops didn't work
Note: the console.assert()
method is implemented differently in Node.js
than the console.assert()
method available in browsers.
Specifically, in browsers, calling console.assert()
with a falsy
assertion will cause the message
to be printed to the console without
interrupting execution of subsequent code. In Node.js, however, a falsy
assertion will cause an AssertionError
to be thrown.
Functionality approximating that implemented by browsers can be implemented
by extending Node.js' console
and overriding the console.assert()
method.
In the following example, a simple module is created that extends and overrides
the default behavior of console
in Node.js.
'use strict';
// Creates a simple extension of console with a
// new impl for assert without monkey-patching.
const myConsole = Object.setPrototypeOf({
assert(assertion, message, ...args) {
try {
console.assert(assertion, message, ...args);
} catch (err) {
console.error(err.stack);
}
}
}, console);
module.exports = myConsole;
This can then be used as a direct replacement for the built in console:
const console = require('./myConsole');
console.assert(false, 'this message will print, but no error thrown');
console.log('this will also print');
console.dir(obj[, options])#
Uses util.inspect()
on obj
and prints the resulting string to stdout
.
This function bypasses any custom inspect()
function defined on obj
. An
optional options
object may be passed to alter certain aspects of the
formatted string:
showHidden
- iftrue
then the object's non-enumerable and symbol properties will be shown too. Defaults tofalse
.depth
- tellsutil.inspect()
how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. Defaults to2
. To make it recurse indefinitely, passnull
.colors
- iftrue
, then the output will be styled with ANSI color codes. Defaults tofalse
. Colors are customizable; see customizingutil.inspect()
colors.
console.error([data][, ...])#
Prints to stderr
with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to
util.format()
).
const code = 5;
console.error('error #%d', code);
// Prints: error #5, to stderr
console.error('error', code);
// Prints: error 5, to stderr
If formatting elements (e.g. %d
) are not found in the first string then
util.inspect()
is called on each argument and the resulting string
values are concatenated. See util.format()
for more information.
console.info([data][, ...])#
The console.info()
function is an alias for console.log()
.
console.log([data][, ...])#
Prints to stdout
with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to
util.format()
).
var count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count: ', count);
// Prints: count: 5, to stdout
If formatting elements (e.g. %d
) are not found in the first string then
util.inspect()
is called on each argument and the resulting string
values are concatenated. See util.format()
for more information.
console.time(label)#
Starts a timer that can be used to compute the duration of an operation. Timers
are identified by a unique label
. Use the same label
when you call
console.timeEnd()
to stop the timer and output the elapsed time in
milliseconds to stdout. Timer durations are accurate to the sub-millisecond.
console.timeEnd(label)#
Stops a timer that was previously started by calling console.time()
and
prints the result to stdout:
console.time('100-elements');
for (var i = 0; i < 100; i++) {
;
}
console.timeEnd('100-elements');
// prints 100-elements: 225.438ms
console.trace(message[, ...])#
Prints to stderr
the string 'Trace :'
, followed by the util.format()
formatted message and stack trace to the current position in the code.
console.trace('Show me');
// Prints: (stack trace will vary based on where trace is called)
// Trace: Show me
// at repl:2:9
// at REPLServer.defaultEval (repl.js:248:27)
// at bound (domain.js:287:14)
// at REPLServer.runBound [as eval] (domain.js:300:12)
// at REPLServer.<anonymous> (repl.js:412:12)
// at emitOne (events.js:82:20)
// at REPLServer.emit (events.js:169:7)
// at REPLServer.Interface._onLine (readline.js:210:10)
// at REPLServer.Interface._line (readline.js:549:8)
// at REPLServer.Interface._ttyWrite (readline.js:826:14)
console.warn([data][, ...])#
The console.warn()
function is an alias for console.error()
.
Crypto#
Stability: 2 - Stable
The crypto
module provides cryptographic functionality that includes a set of
wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign and verify functions.
Use require('crypto')
to access this module.
const crypto = require('crypto');
const secret = 'abcdefg';
const hash = crypto.createHmac('sha256', secret)
.update('I love cupcakes')
.digest('hex');
console.log(hash);
// Prints:
// c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
Determining if crypto support is unavailable#
It is possible for Node.js to be built without including support for the
crypto
module. In such cases, calling require('crypto')
will result in an
error being thrown.
var crypto;
try {
crypto = require('crypto');
} catch (err) {
console.log('crypto support is disabled!');
}
Class: Certificate#
SPKAC is a Certificate Signing Request mechanism originally implemented by
Netscape and now specified formally as part of HTML5's keygen
element.
The crypto
module provides the Certificate
class for working with SPKAC
data. The most common usage is handling output generated by the HTML5
<keygen>
element. Node.js uses OpenSSL's SPKAC implementation internally.
new crypto.Certificate()#
Instances of the Certificate
class can be created using the new
keyword
or by calling crypto.Certificate()
as a function:
const crypto = require('crypto');
const cert1 = new crypto.Certificate();
const cert2 = crypto.Certificate();
certificate.exportChallenge(spkac)#
The spkac
data structure includes a public key and a challenge. The
certificate.exportChallenge()
returns the challenge component in the
form of a Node.js Buffer
. The spkac
argument can be either a string
or a Buffer
.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const challenge = cert.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints the challenge as a UTF8 string
certificate.exportPublicKey(spkac)#
The spkac
data structure includes a public key and a challenge. The
certificate.exportPublicKey()
returns the public key component in the
form of a Node.js Buffer
. The spkac
argument can be either a string
or a Buffer
.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const publicKey = cert.exportPublicKey(spkac);
console.log(publicKey);
// Prints the public key as <Buffer ...>
certificate.verifySpkac(spkac)#
Returns true
if the given spkac
data structure is valid, false
otherwise.
The spkac
argument must be a Node.js Buffer
.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
console.log(cert.verifySpkac(new Buffer(spkac)));
// Prints true or false
Class: Cipher#
Instances of the Cipher
class are used to encrypt data. The class can be
used in one of two ways:
- As a stream that is both readable and writable, where plain unencrypted data is written to produce encrypted data on the readable side, or
- Using the
cipher.update()
andcipher.final()
methods to produce the encrypted data.
The crypto.createCipher()
or crypto.createCipheriv()
methods are
used to create Cipher
instances. Cipher
objects are not to be created
directly using the new
keyword.
Example: Using Cipher
objects as streams:
const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
var encrypted = '';
cipher.on('readable', () => {
var data = cipher.read();
if (data)
encrypted += data.toString('hex');
});
cipher.on('end', () => {
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
});
cipher.write('some clear text data');
cipher.end();
Example: Using Cipher
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const cipher = crypto.createCipher('aes192', 'a password');
const input = fs.createReadStream('test.js');
const output = fs.createWriteStream('test.enc');
input.pipe(cipher).pipe(output);
Example: Using the cipher.update()
and cipher.final()
methods:
const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
var encrypted = cipher.update('some clear text data', 'utf8', 'hex');
encrypted += cipher.final('hex');
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
cipher.final([output_encoding])#
Returns any remaining enciphered contents. If output_encoding
parameter is one of 'binary'
, 'base64'
or 'hex'
, a string is returned.
If an output_encoding
is not provided, a Buffer
is returned.
Once the cipher.final()
method has been called, the Cipher
object can no
longer be used to encrypt data. Attempts to call cipher.final()
more than
once will result in an error being thrown.
cipher.setAAD(buffer)#
When using an authenticated encryption mode (only GCM
is currently
supported), the cipher.setAAD()
method sets the value used for the
additional authenticated data (AAD) input parameter.
cipher.getAuthTag()#
When using an authenticated encryption mode (only GCM
is currently
supported), the cipher.getAuthTag()
method returns a Buffer
containing
the authentication tag that has been computed from the given data.
The cipher.getAuthTag()
method should only be called after encryption has
been completed using the cipher.final()
method.
cipher.setAutoPadding(auto_padding=true)#
When using block encryption algorithms, the Cipher
class will automatically
add padding to the input data to the appropriate block size. To disable the
default padding call cipher.setAutoPadding(false)
.
When auto_padding
is false
, the length of the entire input data must be a
multiple of the cipher's block size or cipher.final()
will throw an Error.
Disabling automatic padding is useful for non-standard padding, for instance
using 0x0
instead of PKCS padding.
The cipher.setAutoPadding()
method must be called before cipher.final()
.
cipher.update(data[, input_encoding][, output_encoding])#
Updates the cipher with data
. If the input_encoding
argument is given,
it's value must be one of 'utf8'
, 'ascii'
, or 'binary'
and the data
argument is a string using the specified encoding. If the input_encoding
argument is not given, data
must be a Buffer
. If data
is a
Buffer
then input_encoding
is ignored.
The output_encoding
specifies the output format of the enciphered
data, and can be 'binary'
, 'base64'
or 'hex'
. If the output_encoding
is specified, a string using the specified encoding is returned. If no
output_encoding
is provided, a Buffer
is returned.
The cipher.update()
method can be called multiple times with new data until
cipher.final()
is called. Calling cipher.update()
after
cipher.final()
will result in an error being thrown.
Class: Decipher#
Instances of the Decipher
class are used to decrypt data. The class can be
used in one of two ways:
- As a stream that is both readable and writable, where plain encrypted data is written to produce unencrypted data on the readable side, or
- Using the
decipher.update()
anddecipher.final()
methods to produce the unencrypted data.
The crypto.createDecipher()
or crypto.createDecipheriv()
methods are
used to create Decipher
instances. Decipher
objects are not to be created
directly using the new
keyword.
Example: Using Decipher
objects as streams:
const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
var decrypted = '';
decipher.on('readable', () => {
var data = decipher.read();
if (data)
decrypted += data.toString('utf8');
});
decipher.on('end', () => {
console.log(decrypted);
// Prints: some clear text data
});
var encrypted = 'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
decipher.write(encrypted, 'hex');
decipher.end();
Example: Using Decipher
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const decipher = crypto.createDecipher('aes192', 'a password');
const input = fs.createReadStream('test.enc');
const output = fs.createWriteStream('test.js');
input.pipe(decipher).pipe(output);
Example: Using the decipher.update()
and decipher.final()
methods:
const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
var encrypted = 'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
var decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data
decipher.final([output_encoding])#
Returns any remaining deciphered contents. If output_encoding
parameter is one of 'binary'
, 'base64'
or 'hex'
, a string is returned.
If an output_encoding
is not provided, a Buffer
is returned.
Once the decipher.final()
method has been called, the Decipher
object can
no longer be used to decrypt data. Attempts to call decipher.final()
more
than once will result in an error being thrown.
decipher.setAAD(buffer)#
When using an authenticated encryption mode (only GCM
is currently
supported), the cipher.setAAD()
method sets the value used for the
additional authenticated data (AAD) input parameter.
decipher.setAuthTag(buffer)#
When using an authenticated encryption mode (only GCM
is currently
supported), the decipher.setAuthTag()
method is used to pass in the
received authentication tag. If no tag is provided, or if the cipher text
has been tampered with, decipher.final()
with throw, indicating that the
cipher text should be discarded due to failed authentication.
decipher.setAutoPadding(auto_padding=true)#
When data has been encrypted without standard block padding, calling
decipher.setAutoPadding(false)
will disable automatic padding to prevent
decipher.final()
from checking for and removing padding.
Turning auto padding off will only work if the input data's length is a multiple of the ciphers block size.
The decipher.setAutoPadding()
method must be called before
decipher.update()
.
decipher.update(data[, input_encoding][, output_encoding])#
Updates the decipher with data
. If the input_encoding
argument is given,
it's value must be one of 'binary'
, 'base64'
, or 'hex'
and the data
argument is a string using the specified encoding. If the input_encoding
argument is not given, data
must be a Buffer
. If data
is a
Buffer
then input_encoding
is ignored.
The output_encoding
specifies the output format of the enciphered
data, and can be 'binary'
, 'ascii'
or 'utf8'
. If the output_encoding
is specified, a string using the specified encoding is returned. If no
output_encoding
is provided, a Buffer
is returned.
The decipher.update()
method can be called multiple times with new data until
decipher.final()
is called. Calling decipher.update()
after
decipher.final()
will result in an error being thrown.
Class: DiffieHellman#
The DiffieHellman
class is a utility for creating Diffie-Hellman key
exchanges.
Instances of the DiffieHellman
class can be created using the
crypto.createDiffieHellman()
function.
const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createDiffieHellman(2048);
const alice_key = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createDiffieHellman(alice.getPrime(), alice.getGenerator());
const bob_key = bob.generateKeys();
// Exchange and generate the secret...
const alice_secret = alice.computeSecret(bob_key);
const bob_secret = bob.computeSecret(alice_key);
// OK
assert.equal(alice_secret.toString('hex'), bob_secret.toString('hex'));
diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])#
Computes the shared secret using other_public_key
as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using the specified input_encoding
, and secret is
encoded using specified output_encoding
. Encodings can be
'binary'
, 'hex'
, or 'base64'
. If the input_encoding
is not
provided, other_public_key
is expected to be a Buffer
.
If output_encoding
is given a string is returned; otherwise, a
Buffer
is returned.
diffieHellman.generateKeys([encoding])#
Generates private and public Diffie-Hellman key values, and returns
the public key in the specified encoding
. This key should be
transferred to the other party. Encoding can be 'binary'
, 'hex'
,
or 'base64'
. If encoding
is provided a string is returned; otherwise a
Buffer
is returned.
diffieHellman.getGenerator([encoding])#
Returns the Diffie-Hellman generator in the specified encoding
, which can
be 'binary'
, 'hex'
, or 'base64'
. If encoding
is provided a string is
returned; otherwise a Buffer
is returned.
diffieHellman.getPrime([encoding])#
Returns the Diffie-Hellman prime in the specified encoding
, which can
be 'binary'
, 'hex'
, or 'base64'
. If encoding
is provided a string is
returned; otherwise a Buffer
is returned.
diffieHellman.getPrivateKey([encoding])#
Returns the Diffie-Hellman private key in the specified encoding
,
which can be 'binary'
, 'hex'
, or 'base64'
. If encoding
is provided a
string is returned; otherwise a Buffer
is returned.
diffieHellman.getPublicKey([encoding])#
Returns the Diffie-Hellman public key in the specified encoding
, which
can be 'binary'
, 'hex'
, or 'base64'
. If encoding
is provided a
string is returned; otherwise a Buffer
is returned.
diffieHellman.setPrivateKey(private_key[, encoding])#
Sets the Diffie-Hellman private key. If the encoding
argument is provided
and is either 'binary'
, 'hex'
, or 'base64'
, private_key
is expected
to be a string. If no encoding
is provided, private_key
is expected
to be a Buffer
.
diffieHellman.setPublicKey(public_key[, encoding])#
Sets the Diffie-Hellman public key. If the encoding
argument is provided
and is either 'binary'
, 'hex'
or 'base64'
, public_key
is expected
to be a string. If no encoding
is provided, public_key
is expected
to be a Buffer
.
diffieHellman.verifyError#
A bit field containing any warnings and/or errors resulting from a check
performed during initialization of the DiffieHellman
object.
The following values are valid for this property (as defined in constants
module):
DH_CHECK_P_NOT_SAFE_PRIME
DH_CHECK_P_NOT_PRIME
DH_UNABLE_TO_CHECK_GENERATOR
DH_NOT_SUITABLE_GENERATOR
Class: ECDH#
The ECDH
class is a utility for creating Elliptic Curve Diffie-Hellman (ECDH)
key exchanges.
Instances of the ECDH
class can be created using the
crypto.createECDH()
function.
const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createECDH('secp521r1');
const alice_key = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createECDH('secp521r1');
const bob_key = bob.generateKeys();
// Exchange and generate the secret...
const alice_secret = alice.computeSecret(bob_key);
const bob_secret = bob.computeSecret(alice_key);
assert(alice_secret, bob_secret);
// OK
ecdh.computeSecret(other_public_key[, input_encoding][, output_encoding])#
Computes the shared secret using other_public_key
as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using specified input_encoding
, and the returned secret
is encoded using the specified output_encoding
. Encodings can be
'binary'
, 'hex'
, or 'base64'
. If the input_encoding
is not
provided, other_public_key
is expected to be a Buffer
.
If output_encoding
is given a string will be returned; otherwise a
Buffer
is returned.
ecdh.generateKeys([encoding[, format]])#
Generates private and public EC Diffie-Hellman key values, and returns
the public key in the specified format
and encoding
. This key should be
transferred to the other party.
The format
arguments specifies point encoding and can be 'compressed'
,
'uncompressed'
, or 'hybrid'
. If format
is not specified, the point will
be returned in 'uncompressed'
format.
The encoding
argument can be 'binary'
, 'hex'
, or 'base64'
. If
encoding
is provided a string is returned; otherwise a Buffer
is returned.
ecdh.getPrivateKey([encoding])#
Returns the EC Diffie-Hellman private key in the specified encoding
,
which can be 'binary'
, 'hex'
, or 'base64'
. If encoding
is provided
a string is returned; otherwise a Buffer
is returned.
ecdh.getPublicKey([encoding[, format]])#
Returns the EC Diffie-Hellman public key in the specified encoding
and
format
.
The format
argument specifies point encoding and can be 'compressed'
,
'uncompressed'
, or 'hybrid'
. If format
is not specified the point will be
returned in 'uncompressed'
format.
The encoding
argument can be 'binary'
, 'hex'
, or 'base64'
. If
encoding
is specified, a string is returned; otherwise a Buffer
is
returned.
ecdh.setPrivateKey(private_key[, encoding])#
Sets the EC Diffie-Hellman private key. The encoding
can be 'binary'
,
'hex'
or 'base64'
. If encoding
is provided, private_key
is expected
to be a string; otherwise private_key
is expected to be a Buffer
. If
private_key
is not valid for the curve specified when the ECDH
object was
created, an error is thrown. Upon setting the private key, the associated
public point (key) is also generated and set in the ECDH object.
ecdh.setPublicKey(public_key[, encoding])#
Stability: 0 - Deprecated
Sets the EC Diffie-Hellman public key. Key encoding can be 'binary'
,
'hex'
or 'base64'
. If encoding
is provided public_key
is expected to
be a string; otherwise a Buffer
is expected.
Note that there is not normally a reason to call this method because ECDH
only requires a private key and the other party's public key to compute the
shared secret. Typically either ecdh.generateKeys()
or
ecdh.setPrivateKey()
will be called. The ecdh.setPrivateKey()
method
attempts to generate the public point/key associated with the private key being
set.
Example (obtaining a shared secret):
const crypto = require('crypto');
const alice = crypto.createECDH('secp256k1');
const bob = crypto.createECDH('secp256k1');
// Note: This is a shortcut way to specify one of Alice's previous private
// keys. It would be unwise to use such a predictable private key in a real
// application.
alice.setPrivateKey(
crypto.createHash('sha256').update('alice', 'utf8').digest()
);
// Bob uses a newly generated cryptographically strong
// pseudorandom key pair bob.generateKeys();
const alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
// alice_secret and bob_secret should be the same shared secret value
console.log(alice_secret === bob_secret);
Class: Hash#
The Hash
class is a utility for creating hash digests of data. It can be
used in one of two ways:
- As a stream that is both readable and writable, where data is written to produce a computed hash digest on the readable side, or
- Using the
hash.update()
andhash.digest()
methods to produce the computed hash.
The crypto.createHash()
method is used to create Hash
instances. Hash
objects are not to be created directly using the new
keyword.
Example: Using Hash
objects as streams:
const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.on('readable', () => {
var data = hash.read();
if (data)
console.log(data.toString('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
});
hash.write('some data to hash');
hash.end();
Example: Using Hash
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream('test.js');
input.pipe(hash).pipe(process.stdout);
Example: Using the hash.update()
and hash.digest()
methods:
const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
hash.digest([encoding])#
Calculates the digest of all of the data passed to be hashed (using the
hash.update()
method). The encoding
can be 'hex'
, 'binary'
or
'base64'
. If encoding
is provided a string will be returned; otherwise
a Buffer
is returned.
The Hash
object can not be used again after hash.digest()
method has been
called. Multiple calls will cause an error to be thrown.
hash.update(data[, input_encoding])#
Updates the hash content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'binary'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Hmac#
The Hmac
Class is a utility for creating cryptographic HMAC digests. It can
be used in one of two ways:
- As a stream that is both readable and writable, where data is written to produce a computed HMAC digest on the readable side, or
- Using the
hmac.update()
andhmac.digest()
methods to produce the computed HMAC digest.
The crypto.createHmac()
method is used to create Hmac
instances. Hmac
objects are not to be created directly using the new
keyword.
Example: Using Hmac
objects as streams:
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.on('readable', () => {
var data = hmac.read();
if (data)
console.log(data.toString('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
});
hmac.write('some data to hash');
hmac.end();
Example: Using Hmac
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream('test.js');
input.pipe(hmac).pipe(process.stdout);
Example: Using the hmac.update()
and hmac.digest()
methods:
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.update('some data to hash');
console.log(hmac.digest('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
hmac.digest([encoding])#
Calculates the HMAC digest of all of the data passed using hmac.update()
.
The encoding
can be 'hex'
, 'binary'
or 'base64'
. If encoding
is
provided a string is returned; otherwise a Buffer
is returned;
The Hmac
object can not be used again after hmac.digest()
has been
called. Multiple calls to hmac.digest()
will result in an error being thrown.
hmac.update(data[, input_encoding])#
Updates the Hmac
content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'binary'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Sign#
The Sign
Class is a utility for generating signatures. It can be used in one
of two ways:
- As a writable stream, where data to be signed is written and the
sign.sign()
method is used to generate and return the signature, or - Using the
sign.update()
andsign.sign()
methods to produce the signature.
The crypto.createSign()
method is used to create Sign
instances. Sign
objects are not to be created directly using the new
keyword.
Example: Using Sign
objects as streams:
const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');
sign.write('some data to sign');
sign.end();
const private_key = getPrivateKeySomehow();
console.log(sign.sign(private_key, 'hex'));
// Prints the calculated signature
Example: Using the sign.update()
and sign.sign()
methods:
const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');
sign.update('some data to sign');
const private_key = getPrivateKeySomehow();
console.log(sign.sign(private_key, 'hex'));
// Prints the calculated signature
A [sign
][] instance can also be created by just passing in the digest
algorithm name, in which case OpenSSL will infer the full signature algorithm
from the type of the PEM-formatted private key, including algorithms that
do not have directly exposed name constants, e.g. 'ecdsa-with-SHA256'.
Example: signing using ECDSA with SHA256
const crypto = require('crypto');
const sign = crypto.createSign('sha256');
sign.update('some data to sign');
const private_key = '-----BEGIN EC PRIVATE KEY-----\n' +
'MHcCAQEEIF+jnWY1D5kbVYDNvxxo/Y+ku2uJPDwS0r/VuPZQrjjVoAoGCCqGSM49\n' +
'AwEHoUQDQgAEurOxfSxmqIRYzJVagdZfMMSjRNNhB8i3mXyIMq704m2m52FdfKZ2\n' +
'pQhByd5eyj3lgZ7m7jbchtdgyOF8Io/1ng==\n' +
'-----END EC PRIVATE KEY-----\n';
console.log(sign.sign(private_key).toString('hex'));
sign.sign(private_key[, output_format])#
Calculates the signature on all the data passed through using either
sign.update()
or sign.write()
.
The private_key
argument can be an object or a string. If private_key
is a
string, it is treated as a raw key with no passphrase. If private_key
is an
object, it is interpreted as a hash containing two properties:
The output_format
can specify one of 'binary'
, 'hex'
or 'base64'
. If
output_format
is provided a string is returned; otherwise a Buffer
is
returned.
The Sign
object can not be again used after sign.sign()
method has been
called. Multiple calls to sign.sign()
will result in an error being thrown.
sign.update(data[, input_encoding])#
Updates the Sign
content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'binary'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Verify#
The Verify
class is a utility for verifying signatures. It can be used in one
of two ways:
- As a writable stream where written data is used to validate against the supplied signature, or
Using the
verify.update()
andverify.verify()
methods to verify the signature.The
crypto.createSign()
method is used to createSign
instances.Sign
objects are not to be created directly using thenew
keyword.
Example: Using Verify
objects as streams:
const crypto = require('crypto');
const verify = crypto.createVerify('RSA-SHA256');
verify.write('some data to sign');
verify.end();
const public_key = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(sign.verify(public_key, signature));
// Prints true or false
Example: Using the verify.update()
and verify.verify()
methods:
const crypto = require('crypto');
const verify = crypto.createVerify('RSA-SHA256');
verify.update('some data to sign');
const public_key = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(public_key, signature));
// Prints true or false
verifier.update(data[, input_encoding])#
Updates the Verify
content with the given data
, the encoding of which
is given in input_encoding
and can be 'utf8'
, 'ascii'
or
'binary'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
then
input_encoding
is ignored.
This can be called many times with new data as it is streamed.
verifier.verify(object, signature[, signature_format])#
Verifies the provided data using the given object
and signature
.
The object
argument is a string containing a PEM encoded object, which can be
one an RSA public key, a DSA public key, or an X.509 certificate.
The signature
argument is the previously calculated signature for the data, in
the signature_format
which can be 'binary'
, 'hex'
or 'base64'
.
If a signature_format
is specified, the signature
is expected to be a
string; otherwise signature
is expected to be a Buffer
.
Returns true
or false
depending on the validity of the signature for
the data and public key.
The verifier
object can not be used again after verify.verify()
has been
called. Multiple calls to verify.verify()
will result in an error being
thrown.
crypto
module methods and properties#
crypto.DEFAULT_ENCODING#
The default encoding to use for functions that can take either strings
or buffers. The default value is 'buffer'
, which makes methods
default to Buffer
objects.
The crypto.DEFAULT_ENCODING
mechanism is provided for backwards compatibility
with legacy programs that expect 'binary'
to be the default encoding.
New applications should expect the default to be 'buffer'
. This property may
become deprecated in a future Node.js release.
crypto.fips#
Property for checking and controlling whether a FIPS compliant crypto provider is currently in use. Setting to true requires a FIPS build of Node.js.
crypto.createCipher(algorithm, password)#
Creates and returns a Cipher
object that uses the given algorithm
and
password
.
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The password
is used to derive the cipher key and initialization vector (IV).
The value must be either a 'binary'
encoded string or a Buffer
.
The implementation of crypto.createCipher()
derives keys using the OpenSSL
function EVP_BytesToKey
with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.
In line with OpenSSL's recommendation to use pbkdf2 instead of
EVP_BytesToKey
it is recommended that developers derive a key and IV on
their own using crypto.pbkdf2()
and to use crypto.createCipheriv()
to create the Cipher
object.
crypto.createCipheriv(algorithm, key, iv)#
Creates and returns a Cipher
object, with the given algorithm
, key
and
initialization vector (iv
).
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The key
is the raw key used by the algorithm
and iv
is an
initialization vector. Both arguments must be 'binary'
encoded strings or
buffers.
crypto.createCredentials(details)#
Stability: 0 - Deprecated: Use tls.createSecureContext()
instead.
The crypto.createCredentials()
method is a deprecated alias for creating
and returning a tls.SecureContext
object. The crypto.createCredentials()
method should not be used.
The optional details
argument is a hash object with keys:
pfx
: <String> | <Buffer> - PFX or PKCS12 encoded private key, certificate and CA certificateskey
: <String> - PEM encoded private keypassphrase
: <String> - passphrase for the private key or PFXcert
: <String> - PEM encoded certificateca
: <String> | <Array> - Either a string or array of strings of PEM encoded CA certificates to trust.crl
: <String> | <Array> - Either a string or array of strings of PEM encoded CRLs (Certificate Revocation List)ciphers
: <String> using the OpenSSL cipher list format describing the cipher algorithms to use or exclude.
If no 'ca' details are given, Node.js will use Mozilla's default publicly trusted list of CAs.
crypto.createDecipher(algorithm, password)#
Creates and returns a Decipher
object that uses the given algorithm
and
password
(key).
The implementation of crypto.createDecipher()
derives keys using the OpenSSL
function EVP_BytesToKey
with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.
In line with OpenSSL's recommendation to use pbkdf2 instead of
EVP_BytesToKey
it is recommended that developers derive a key and IV on
their own using crypto.pbkdf2()
and to use crypto.createDecipheriv()
to create the Decipher
object.
crypto.createDecipheriv(algorithm, key, iv)#
Creates and returns a Decipher
object that uses the given algorithm
, key
and initialization vector (iv
).
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The key
is the raw key used by the algorithm
and iv
is an
initialization vector. Both arguments must be 'binary'
encoded strings or
buffers.
crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])#
Creates a DiffieHellman
key exchange object using the supplied prime
and an
optional specific generator
.
The generator
argument can be a number, string, or Buffer
. If
generator
is not specified, the value 2
is used.
The prime_encoding
and generator_encoding
arguments can be 'binary'
,
'hex'
, or 'base64'
.
If prime_encoding
is specified, prime
is expected to be a string; otherwise
a Buffer
is expected.
If generator_encoding
is specified, generator
is expected to be a string;
otherwise either a number or Buffer
is expected.
crypto.createDiffieHellman(prime_length[, generator])#
Creates a DiffieHellman
key exchange object and generates a prime of
prime_length
bits using an optional specific numeric generator
.
If generator
is not specified, the value 2
is used.
crypto.createECDH(curve_name)#
Creates an Elliptic Curve Diffie-Hellman (ECDH
) key exchange object using a
predefined curve specified by the curve_name
string. Use
crypto.getCurves()
to obtain a list of available curve names. On recent
OpenSSL releases, openssl ecparam -list_curves
will also display the name
and description of each available elliptic curve.
crypto.createHash(algorithm)#
Creates and returns a Hash
object that can be used to generate hash digests
using the given algorithm
.
The algorithm
is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are 'sha256'
, 'sha512'
, etc.
On recent releases of OpenSSL, openssl list-message-digest-algorithms
will
display the available digest algorithms.
Example: generating the sha256 sum of a file
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream(filename);
input.on('readable', () => {
var data = input.read();
if (data)
hash.update(data);
else {
console.log(`${hash.digest('hex')} ${filename}`);
}
});
crypto.createHmac(algorithm, key)#
Creates and returns an Hmac
object that uses the given algorithm
and key
.
The algorithm
is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are 'sha256'
, 'sha512'
, etc.
On recent releases of OpenSSL, openssl list-message-digest-algorithms
will
display the available digest algorithms.
The key
is the HMAC key used to generate the cryptographic HMAC hash.
Example: generating the sha256 HMAC of a file
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream(filename);
input.on('readable', () => {
var data = input.read();
if (data)
hmac.update(data);
else {
console.log(`${hmac.digest('hex')} ${filename}`);
}
});
crypto.createSign(algorithm)#
Creates and returns a Sign
object that uses the given algorithm
. On
recent OpenSSL releases, openssl list-public-key-algorithms
will
display the available signing algorithms. One example is 'RSA-SHA256'
.
crypto.createVerify(algorithm)#
Creates and returns a Verify
object that uses the given algorithm. On
recent OpenSSL releases, openssl list-public-key-algorithms
will
display the available signing algorithms. One example is 'RSA-SHA256'
.
crypto.getCiphers()#
Returns an array with the names of the supported cipher algorithms.
Example:
const ciphers = crypto.getCiphers();
console.log(ciphers); // ['aes-128-cbc', 'aes-128-ccm', ...]
crypto.getCurves()#
Returns an array with the names of the supported elliptic curves.
Example:
const curves = crypto.getCurves();
console.log(curves); // ['secp256k1', 'secp384r1', ...]
crypto.getDiffieHellman(group_name)#
Creates a predefined DiffieHellman
key exchange object. The
supported groups are: 'modp1'
, 'modp2'
, 'modp5'
(defined in
RFC 2412, but see Caveats) and 'modp14'
, 'modp15'
,
'modp16'
, 'modp17'
, 'modp18'
(defined in RFC 3526). The
returned object mimics the interface of objects created by
crypto.createDiffieHellman()
, but will not allow changing
the keys (with diffieHellman.setPublicKey()
for example). The
advantage of using this method is that the parties do not have to
generate nor exchange a group modulus beforehand, saving both processor
and communication time.
Example (obtaining a shared secret):
const crypto = require('crypto');
const alice = crypto.getDiffieHellman('modp14');
const bob = crypto.getDiffieHellman('modp14');
alice.generateKeys();
bob.generateKeys();
const alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
/* alice_secret and bob_secret should be the same */
console.log(alice_secret == bob_secret);
crypto.getHashes()#
Returns an array with the names of the supported hash algorithms.
Example:
const hashes = crypto.getHashes();
console.log(hashes); // ['sha', 'sha1', 'sha1WithRSAEncryption', ...]
crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)#
Provides an asynchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by digest
is
applied to derive a key of the requested byte length (keylen
) from the
password
, salt
and iterations
.
The supplied callback
function is called with two arguments: err
and
derivedKey
. If an error occurs, err
will be set; otherwise err
will be
null. The successfully generated derivedKey
will be passed as a Buffer
.
The iterations
argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.
The salt
should also be as unique as possible. It is recommended that the
salts are random and their lengths are greater than 16 bytes. See
NIST SP 800-132 for details.
Example:
const crypto = require('crypto');
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, key) => {
if (err) throw err;
console.log(key.toString('hex')); // 'c5e478d...1469e50'
});
An array of supported digest functions can be retrieved using
crypto.getHashes()
.
crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)#
Provides a synchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by digest
is
applied to derive a key of the requested byte length (keylen
) from the
password
, salt
and iterations
.
If an error occurs an Error will be thrown, otherwise the derived key will be
returned as a Buffer
.
The iterations
argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.
The salt
should also be as unique as possible. It is recommended that the
salts are random and their lengths are greater than 16 bytes. See
NIST SP 800-132 for details.
Example:
const crypto = require('crypto');
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
console.log(key.toString('hex')); // 'c5e478d...1469e50'
An array of supported digest functions can be retrieved using
crypto.getHashes()
.
crypto.privateDecrypt(private_key, buffer)#
Decrypts buffer
with private_key
.
private_key
can be an object or a string. If private_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING
.
If private_key
is an object, it is interpreted as a hash object with the
keys:
key
: <String> - PEM encoded private keypassphrase
: <String> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:constants.RSA_NO_PADDING
constants.RSA_PKCS1_PADDING
constants.RSA_PKCS1_OAEP_PADDING
All paddings are defined in the constants
module.
crypto.privateEncrypt(private_key, buffer)#
Encrypts buffer
with private_key
.
private_key
can be an object or a string. If private_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_PADDING
.
If private_key
is an object, it is interpreted as a hash object with the
keys:
key
: <String> - PEM encoded private keypassphrase
: <String> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:constants.RSA_NO_PADDING
constants.RSA_PKCS1_PADDING
constants.RSA_PKCS1_OAEP_PADDING
All paddings are defined in the constants
module.
crypto.publicDecrypt(public_key, buffer)#
Decrypts buffer
with public_key
.
public_key
can be an object or a string. If public_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_PADDING
.
If public_key
is an object, it is interpreted as a hash object with the
keys:
key
: <String> - PEM encoded public keypassphrase
: <String> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:constants.RSA_NO_PADDING
constants.RSA_PKCS1_PADDING
constants.RSA_PKCS1_OAEP_PADDING
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
All paddings are defined in the constants
module.
crypto.publicEncrypt(public_key, buffer)#
Encrypts buffer
with public_key
.
public_key
can be an object or a string. If public_key
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING
.
If public_key
is an object, it is interpreted as a hash object with the
keys:
key
: <String> - PEM encoded public keypassphrase
: <String> - Optional passphrase for the private keypadding
: An optional padding value, one of the following:constants.RSA_NO_PADDING
constants.RSA_PKCS1_PADDING
constants.RSA_PKCS1_OAEP_PADDING
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
All paddings are defined in the constants
module.
crypto.randomBytes(size[, callback])#
Generates cryptographically strong pseudo-random data. The size
argument
is a number indicating the number of bytes to generate.
If a callback
function is provided, the bytes are generated asynchronously
and the callback
function is invoked with two arguments: err
and buf
.
If an error occurs, err
will be an Error object; otherwise it is null. The
buf
argument is a Buffer
containing the generated bytes.
// Asynchronous
const crypto = require('crypto');
crypto.randomBytes(256, (err, buf) => {
if (err) throw err;
console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`);
});
If the callback
function is not provided, the random bytes are generated
synchronously and returned as a Buffer
. An error will be thrown if
there is a problem generating the bytes.
// Synchronous
const buf = crypto.randomBytes(256);
console.log(
`${buf.length} bytes of random data: ${buf.toString('hex')}`);
The crypto.randomBytes()
method will block until there is sufficient entropy.
This should normally never take longer than a few milliseconds. The only time
when generating the random bytes may conceivably block for a longer period of
time is right after boot, when the whole system is still low on entropy.
crypto.setEngine(engine[, flags])#
Load and set the engine
for some or all OpenSSL functions (selected by flags).
engine
could be either an id or a path to the engine's shared library.
The optional flags
argument uses ENGINE_METHOD_ALL
by default. The flags
is a bit field taking one of or a mix of the following flags (defined in the
constants
module):
ENGINE_METHOD_RSA
ENGINE_METHOD_DSA
ENGINE_METHOD_DH
ENGINE_METHOD_RAND
ENGINE_METHOD_ECDH
ENGINE_METHOD_ECDSA
ENGINE_METHOD_CIPHERS
ENGINE_METHOD_DIGESTS
ENGINE_METHOD_STORE
ENGINE_METHOD_PKEY_METHS
ENGINE_METHOD_PKEY_ASN1_METHS
ENGINE_METHOD_ALL
ENGINE_METHOD_NONE
Notes#
Legacy Streams API (pre Node.js v0.10)#
The Crypto module was added to Node.js before there was the concept of a
unified Stream API, and before there were Buffer
objects for handling
binary data. As such, the many of the crypto
defined classes have methods not
typically found on other Node.js classes that implement the streams
API (e.g. update()
, final()
, or digest()
). Also, many methods accepted
and returned 'binary'
encoded strings by default rather than Buffers. This
default was changed after Node.js v0.8 to use Buffer
objects by default
instead.
Recent ECDH Changes#
Usage of ECDH
with non-dynamically generated key pairs has been simplified.
Now, ecdh.setPrivateKey()
can be called with a preselected private key
and the associated public point (key) will be computed and stored in the object.
This allows code to only store and provide the private part of the EC key pair.
ecdh.setPrivateKey()
now also validates that the private key is valid for
the selected curve.
The ecdh.setPublicKey()
method is now deprecated as its inclusion in the
API is not useful. Either a previously stored private key should be set, which
automatically generates the associated public key, or ecdh.generateKeys()
should be called. The main drawback of using ecdh.setPublicKey()
is that
it can be used to put the ECDH key pair into an inconsistent state.
Support for weak or compromised algorithms#
The crypto
module still supports some algorithms which are already
compromised and are not currently recommended for use. The API also allows
the use of ciphers and hashes with a small key size that are considered to be
too weak for safe use.
Users should take full responsibility for selecting the crypto algorithm and key size according to their security requirements.
Based on the recommendations of NIST SP 800-131A:
- MD5 and SHA-1 are no longer acceptable where collision resistance is required such as digital signatures.
- The key used with RSA, DSA and DH algorithms is recommended to have at least 2048 bits and that of the curve of ECDSA and ECDH at least 224 bits, to be safe to use for several years.
- The DH groups of
modp1
,modp2
andmodp5
have a key size smaller than 2048 bits and are not recommended.
See the reference for other recommendations and details.
Debugger#
Stability: 2 - Stable
Node.js includes a full-featured out-of-process debugging utility accessible
via a simple TCP-based protocol and built-in debugging client. To use it,
start Node.js with the debug
argument followed by the path to the script to
debug; a prompt will be displayed indicating successful launch of the debugger:
$ node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
1 x = 5;
2 setTimeout(() => {
3 debugger;
debug>
Node.js's debugger client does not yet support the full range of commands, but simple step and inspection are possible.
Inserting the statement debugger;
into the source code of a script will
enable a breakpoint at that position in the code.
For example, suppose myscript.js
is written as:
// myscript.js
x = 5;
setTimeout(() => {
debugger;
console.log('world');
}, 1000);
console.log('hello');
Once the debugger is run, a breakpoint will occur at line 4:
$ node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
1 x = 5;
2 setTimeout(() => {
3 debugger;
debug> cont
< hello
break in /home/indutny/Code/git/indutny/myscript.js:3
1 x = 5;
2 setTimeout(() => {
3 debugger;
4 console.log('world');
5 }, 1000);
debug> next
break in /home/indutny/Code/git/indutny/myscript.js:4
2 setTimeout(() => {
3 debugger;
4 console.log('world');
5 }, 1000);
6 console.log('hello');
debug> repl
Press Ctrl + C to leave debug repl
> x
5
> 2+2
4
debug> next
< world
break in /home/indutny/Code/git/indutny/myscript.js:5
3 debugger;
4 console.log('world');
5 }, 1000);
6 console.log('hello');
7
debug> quit
The repl
command allows code to be evaluated remotely. The next
command
steps over to the next line. Type help
to see what other commands are
available.
Pressing enter
without typing a command will repeat the previous debugger
command.
Watchers#
It is possible to watch expression and variable values while debugging. On every breakpoint, each expression from the watchers list will be evaluated in the current context and displayed immediately before the breakpoint's source code listing.
To begin watching an expression, type watch('my_expression')
. The command
watchers
will print the active watchers. To remove a watcher, type
unwatch('my_expression')
.
Commands reference#
Stepping#
cont
,c
- Continue executionnext
,n
- Step nextstep
,s
- Step inout
,o
- Step outpause
- Pause running code (like pause button in Developer Tools)
Breakpoints#
setBreakpoint()
,sb()
- Set breakpoint on current linesetBreakpoint(line)
,sb(line)
- Set breakpoint on specific linesetBreakpoint('fn()')
,sb(...)
- Set breakpoint on a first statement in functions bodysetBreakpoint('script.js', 1)
,sb(...)
- Set breakpoint on first line of script.jsclearBreakpoint('script.js', 1)
,cb(...)
- Clear breakpoint in script.js on line 1
It is also possible to set a breakpoint in a file (module) that isn't loaded yet:
$ ./node debug test/fixtures/break-in-module/main.js
< debugger listening on port 5858
connecting to port 5858... ok
break in test/fixtures/break-in-module/main.js:1
1 var mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
debug> setBreakpoint('mod.js', 23)
Warning: script 'mod.js' was not loaded yet.
1 var mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
debug> c
break in test/fixtures/break-in-module/mod.js:23
21
22 exports.hello = () => {
23 return 'hello from module';
24 };
25
debug>
Info#
backtrace
,bt
- Print backtrace of current execution framelist(5)
- List scripts source code with 5 line context (5 lines before and after)watch(expr)
- Add expression to watch listunwatch(expr)
- Remove expression from watch listwatchers
- List all watchers and their values (automatically listed on each breakpoint)repl
- Open debugger's repl for evaluation in debugging script's contextexec expr
- Execute an expression in debugging script's context
Execution control#
run
- Run script (automatically runs on debugger's start)restart
- Restart scriptkill
- Kill script
Various#
scripts
- List all loaded scriptsversion
- Display V8's version
Advanced Usage#
An alternative way of enabling and accessing the debugger is to start
Node.js with the --debug
command-line flag or by signaling an existing
Node.js process with SIGUSR1
.
Once a process has been set in debug mode this way, it can be connected to
using the Node.js debugger by either connecting to the pid
of the running
process or via URI reference to the listening debugger:
node debug -p <pid>
- Connects to the process via thepid
node debug <URI>
- Connects to the process via the URI such as localhost:5858
UDP / Datagram Sockets#
Stability: 2 - Stable
The dgram
module provides an implementation of UDP Datagram sockets.
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
var address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// server listening 0.0.0.0:41234
Class: dgram.Socket#
The dgram.Socket
object is an EventEmitter
that encapsulates the
datagram functionality.
New instances of dgram.Socket
are created using dgram.createSocket()
.
The new
keyword is not to be used to create dgram.Socket
instances.
Event: 'close'#
The 'close'
event is emitted after a socket is closed with close()
.
Once triggered, no new 'message'
events will be emitted on this socket.
Event: 'error'#
exception
<Error>
The 'error'
event is emitted whenever any error occurs. The event handler
function is passed a single Error object.
Event: 'listening'#
The 'listening'
event is emitted whenever a socket begins listening for
datagram messages. This occurs as soon as UDP sockets are created.
Event: 'message'#
The 'message'
event is emitted when a new datagram is available on a socket.
The event handler function is passed two arguments: msg
and rinfo
. The
msg
argument is a Buffer
and rinfo
is an object with the sender's
address information provided by the address
, family
and port
properties:
socket.on('message', (msg, rinfo) => {
console.log('Received %d bytes from %s:%d\n',
msg.length, rinfo.address, rinfo.port);
});
socket.addMembership(multicastAddress[, multicastInterface])#
Tells the kernel to join a multicast group at the given multicastAddress
using the IP_ADD_MEMBERSHIP
socket option. If the multicastInterface
argument is not specified, the operating system will try to add membership to
all valid networking interfaces.
socket.address()#
Returns an object containing the address information for a socket.
For UDP sockets, this object will contain address
, family
and port
properties.
socket.bind([port][, address][, callback])#
port
<Number> - Integer, Optionaladdress
<String>, Optionalcallback
<Function> with no parameters, Optional. Called when binding is complete.
For UDP sockets, causes the dgram.Socket
to listen for datagram messages on a
named port
and optional address
. If port
is not specified, the operating
system will attempt to bind to a random port. If address
is not specified,
the operating system will attempt to listen on all addresses. Once binding is
complete, a 'listening'
event is emitted and the optional callback
function
is called.
Note that specifying both a 'listening'
event listener and passing a
callback
to the socket.bind()
method is not harmful but not very
useful.
A bound datagram socket keeps the Node.js process running to receive datagram messages.
If binding fails, an 'error'
event is generated. In rare case (e.g.
attempting to bind with a closed socket), an Error
may be thrown.
Example of a UDP server listening on port 41234:
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
var address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// server listening 0.0.0.0:41234
socket.bind(options[, callback])#
options
<Object> - Required. Supports the following properties:callback
<Function> - Optional.
For UDP sockets, causes the dgram.Socket
to listen for datagram messages on a
named port
and optional address
that are passed as properties of an
options
object passed as the first argument. If port
is not specified, the
operating system will attempt to bind to a random port. If address
is not
specified, the operating system will attempt to listen on all addresses. Once
binding is complete, a 'listening'
event is emitted and the optional
callback
function is called.
The options
object may contain an additional exclusive
property that is
use when using dgram.Socket
objects with the [cluster
] module. When
exclusive
is set to false
(the default), cluster workers will use the same
underlying socket handle allowing connection handling duties to be shared.
When exclusive
is true
, however, the handle is not shared and attempted
port sharing results in an error.
An example socket listening on an exclusive port is shown below.
socket.bind({
address: 'localhost',
port: 8000,
exclusive: true
});
socket.close([callback])#
Close the underlying socket and stop listening for data on it. If a callback is
provided, it is added as a listener for the 'close'
event.
socket.dropMembership(multicastAddress[, multicastInterface])#
Instructs the kernel to leave a multicast group at multicastAddress
using the
IP_DROP_MEMBERSHIP
socket option. This method is automatically called by the
kernel when the socket is closed or the process terminates, so most apps will
never have reason to call this.
If multicastInterface
is not specified, the operating system will attempt to
drop membership on all valid interfaces.
socket.send(msg, [offset, length,] port, address[, callback])#
msg
<Buffer> | <String> | <Array> Message to be sentoffset
<Number> Integer. Optional. Offset in the buffer where the message starts.length
<Number> Integer. Optional. Number of bytes in the message.port
<Number> Integer. Destination port.address
<String> Destination hostname or IP address.callback
<Function> Called when the message has been sent. Optional.
Broadcasts a datagram on the socket. The destination port
and address
must
be specified.
The msg
argument contains the message to be sent.
Depending on its type, different behavior can apply. If msg
is a Buffer
,
the offset
and length
specify the offset within the Buffer
where the
message begins and the number of bytes in the message, respectively.
If msg
is a String
, then it is automatically converted to a Buffer
with 'utf8'
encoding. With messages that
contain multi-byte characters, offset
and length
will be calculated with
respect to byte length and not the character position.
If msg
is an array, offset
and length
must not be specified.
The address
argument is a string. If the value of address
is a host name,
DNS will be used to resolve the address of the host. If the address
is not
specified or is an empty string, '127.0.0.1'
or '::1'
will be used instead.
If the socket has not been previously bound with a call to bind
, the socket
is assigned a random port number and is bound to the "all interfaces" address
('0.0.0.0'
for udp4
sockets, '::0'
for udp6
sockets.)
An optional callback
function may be specified to as a way of reporting
DNS errors or for determining when it is safe to reuse the buf
object.
Note that DNS lookups delay the time to send for at least one tick of the
Node.js event loop.
The only way to know for sure that the datagram has been sent is by using a
callback
. If an error occurs and a callback
is given, the error will be
passed as the first argument to the callback
. If a callback
is not given,
the error is emitted as an 'error'
event on the socket
object.
Offset and length are optional, but if you specify one you would need to
specify the other. Also, they are supported only when the first
argument is a Buffer
.
Example of sending a UDP packet to a random port on localhost
;
const dgram = require('dgram');
const message = new Buffer('Some bytes');
const client = dgram.createSocket('udp4');
client.send(message, 41234, 'localhost', (err) => {
client.close();
});
Example of sending a UDP packet composed of multiple buffers to a random port on localhost
;
const dgram = require('dgram');
const buf1 = new Buffer('Some ');
const buf2 = new Buffer('bytes');
const client = dgram.createSocket('udp4');
client.send([buf1, buf2], 41234, 'localhost', (err) => {
client.close();
});
Sending multiple buffers might be faster or slower depending on your application and operating system: benchmark it. Usually it is faster.
A Note about UDP datagram size
The maximum size of an IPv4/v6
datagram depends on the MTU
(Maximum Transmission Unit) and on the Payload Length
field size.
The
Payload Length
field is16 bits
wide, which means that a normal payload exceed 64K octets including the internet header and data (65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header); this is generally true for loopback interfaces, but such long datagram messages are impractical for most hosts and networks.The
MTU
is the largest size a given link layer technology can support for datagram messages. For any link,IPv4
mandates a minimumMTU
of68
octets, while the recommendedMTU
for IPv4 is576
(typically recommended as theMTU
for dial-up type applications), whether they arrive whole or in fragments.For
IPv6
, the minimumMTU
is1280
octets, however, the mandatory minimum fragment reassembly buffer size is1500
octets. The value of68
octets is very small, since most current link layer technologies, like Ethernet, have a minimumMTU
of1500
.
It is impossible to know in advance the MTU of each link through which
a packet might travel. Sending a datagram greater than the receiver MTU
will
not work because the packet will get silently dropped without informing the
source that the data did not reach its intended recipient.
socket.setBroadcast(flag)#
flag
<Boolean>
Sets or clears the SO_BROADCAST
socket option. When set to true
, UDP
packets may be sent to a local interface's broadcast address.
socket.setMulticastLoopback(flag)#
flag
<Boolean>
Sets or clears the IP_MULTICAST_LOOP
socket option. When set to true
,
multicast packets will also be received on the local interface.
socket.setMulticastTTL(ttl)#
ttl
<Number> Integer
Sets the IP_MULTICAST_TTL
socket option. While TTL generally stands for
"Time to Live", in this context it specifies the number of IP hops that a
packet is allowed to travel through, specifically for multicast traffic. Each
router or gateway that forwards a packet decrements the TTL. If the TTL is
decremented to 0 by a router, it will not be forwarded.
The argument passed to to socket.setMulticastTTL()
is a number of hops
between 0 and 255. The default on most systems is 1
but can vary.
socket.setTTL(ttl)#
ttl
<Number> Integer
Sets the IP_TTL
socket option. While TTL generally stands for "Time to Live",
in this context it specifies the number of IP hops that a packet is allowed to
travel through. Each router or gateway that forwards a packet decrements the
TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.
Changing TTL values is typically done for network probes or when multicasting.
The argument to socket.setTTL()
is a number of hops between 1 and 255.
The default on most systems is 64 but can vary.
socket.ref()#
By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The socket.unref()
method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active. The socket.ref()
method adds the socket back to the reference
counting and restores the default behavior.
Calling socket.ref()
multiples times will have no additional effect.
The socket.ref()
method returns a reference to the socket so calls can be
chained.
socket.unref()#
By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The socket.unref()
method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active, allowing the process to exit even if the socket is still
listening.
Calling socket.unref()
multiple times will have no addition effect.
The socket.unref()
method returns a reference to the socket so calls can be
chained.
Change to asynchronous socket.bind()
behavior#
As of Node.js v0.10, dgram.Socket#bind()
changed to an asynchronous
execution model. Legacy code that assumes synchronous behavior, as in the
following example:
const s = dgram.createSocket('udp4');
s.bind(1234);
s.addMembership('224.0.0.114');
Must be changed to pass a callback function to the dgram.Socket#bind()
function:
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
dgram
module functions#
dgram.createSocket(options[, callback])#
options
<Object>callback
<Function> Attached as a listener to'message'
events.- Returns: <dgram.Socket>
Creates a dgram.Socket
object. The options
argument is an object that
should contain a type
field of either udp4
or udp6
and an optional
boolean reuseAddr
field.
When reuseAddr
is true
socket.bind()
will reuse the address, even if
another process has already bound a socket on it. reuseAddr
defaults to
false
. An optional callback
function can be passed specified which is added
as a listener for 'message'
events.
Once the socket is created, calling socket.bind()
will instruct the
socket to begin listening for datagram messages. When address
and port
are
not passed to socket.bind()
the method will bind the socket to the "all
interfaces" address on a random port (it does the right thing for both udp4
and udp6
sockets). The bound address and port can be retrieved using
socket.address().address
and socket.address().port
.
dgram.createSocket(type[, callback])#
type
<String> - Either 'udp4' or 'udp6'callback
<Function> - Attached as a listener to'message'
events. Optional- Returns: <dgram.Socket>
Creates a dgram.Socket
object of the specified type
. The type
argument
can be either udp4
or udp6
. An optional callback
function can be passed
which is added as a listener for 'message'
events.
Once the socket is created, calling socket.bind()
will instruct the
socket to begin listening for datagram messages. When address
and port
are
not passed to socket.bind()
the method will bind the socket to the "all
interfaces" address on a random port (it does the right thing for both udp4
and udp6
sockets). The bound address and port can be retrieved using
socket.address().address
and socket.address().port
.
DNS#
Stability: 2 - Stable
The dns
module contains functions belonging to two different categories:
1) Functions that use the underlying operating system facilities to perform
name resolution, and that do not necessarily perform any network communication.
This category contains only one function: dns.lookup()
. Developers
looking to perform name resolution in the same way that other applications on
the same operating system behave should use dns.lookup()
.
For example, looking up nodejs.org
.
const dns = require('dns');
dns.lookup('nodejs.org', (err, addresses, family) => {
console.log('addresses:', addresses);
});
2) Functions that connect to an actual DNS server to perform name resolution,
and that always use the network to perform DNS queries. This category
contains all functions in the dns
module except dns.lookup()
. These
functions do not use the same set of configuration files used by
dns.lookup()
(e.g. /etc/hosts
). These functions should be used by
developers who do not want to use the underlying operating system's facilities
for name resolution, and instead want to always perform DNS queries.
Below is an example that resolves 'nodejs.org'
then reverse resolves the IP
addresses that are returned.
const dns = require('dns');
dns.resolve4('nodejs.org', (err, addresses) => {
if (err) throw err;
console.log(`addresses: ${JSON.stringify(addresses)}`);
addresses.forEach((a) => {
dns.reverse(a, (err, hostnames) => {
if (err) {
throw err;
}
console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`);
});
});
});
There are subtle consequences in choosing one over the other, please consult the Implementation considerations section for more information.
dns.getServers()#
Returns an array of IP address strings that are being used for name resolution.
dns.lookup(hostname[, options], callback)#
Resolves a hostname (e.g. 'nodejs.org'
) into the first found A (IPv4) or
AAAA (IPv6) record. options
can be an object or integer. If options
is
not provided, then IPv4 and IPv6 addresses are both valid. If options
is
an integer, then it must be 4
or 6
.
Alternatively, options
can be an object containing these properties:
family
<Number> - The record family. If present, must be the integer4
or6
. If not provided, both IP v4 and v6 addresses are accepted.hints
: <Number> - If present, it should be one or more of the supportedgetaddrinfo
flags. Ifhints
is not provided, then no flags are passed togetaddrinfo
. Multiple flags can be passed throughhints
by logicallyOR
ing their values. See supportedgetaddrinfo
flags for more information on supported flags.all
: <Boolean> - Whentrue
, the callback returns all resolved addresses in an array, otherwise returns a single address. Defaults tofalse
.
All properties are optional. An example usage of options is shown below.
{
family: 4,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
all: false
}
The callback
function has arguments (err, address, family)
. address
is a
string representation of an IPv4 or IPv6 address. family
is either the
integer 4
or 6
and denotes the family of address
(not necessarily the
value initially passed to lookup
).
With the all
option set to true
, the arguments change to
(err, addresses)
, with addresses
being an array of objects with the
properties address
and family
.
On error, err
is an Error
object, where err.code
is the error code.
Keep in mind that err.code
will be set to 'ENOENT'
not only when
the hostname does not exist but also when the lookup fails in other ways
such as no available file descriptors.
dns.lookup()
does not necessarily have anything to do with the DNS protocol.
The implementation uses an operating system facility that can associate names
with addresses, and vice versa. This implementation can have subtle but
important consequences on the behavior of any Node.js program. Please take some
time to consult the Implementation considerations section before using
dns.lookup()
.
Supported getaddrinfo flags#
The following flags can be passed as hints to dns.lookup()
.
dns.ADDRCONFIG
: Returned address types are determined by the types of addresses supported by the current system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured. Loopback addresses are not considered.dns.V4MAPPED
: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. Note that it is not supported on some operating systems (e.g FreeBSD 10.1).
dns.lookupService(address, port, callback)#
Resolves the given address
and port
into a hostname and service using
the operating system's underlying getnameinfo
implementation.
If address
is not a valid IP address, a TypeError
will be thrown.
The port
will be coerced to a number. If it is not a legal port, a TypeError
will be thrown.
The callback has arguments (err, hostname, service)
. The hostname
and
service
arguments are strings (e.g. 'localhost'
and 'http'
respectively).
On error, err
is an Error
object, where err.code
is the error code.
const dns = require('dns');
dns.lookupService('127.0.0.1', 22, (err, hostname, service) => {
console.log(hostname, service);
// Prints: localhost ssh
});
dns.resolve(hostname[, rrtype], callback)#
Uses the DNS protocol to resolve a hostname (e.g. 'nodejs.org'
) into an
array of the record types specified by rrtype
.
Valid values for rrtype
are:
'A'
- IPV4 addresses, default'AAAA'
- IPV6 addresses'MX'
- mail exchange records'TXT'
- text records'SRV'
- SRV records'PTR'
- PTR records'NS'
- name server records'CNAME'
- canonical name records'SOA'
- start of authority record
The callback
function has arguments (err, addresses)
. When successful,
addresses
will be an array. The type of each item in addresses
is
determined by the record type, and described in the documentation for the
corresponding lookup methods.
On error, err
is an Error
object, where err.code
is
one of the error codes listed here.
dns.resolve4(hostname, callback)#
Uses the DNS protocol to resolve a IPv4 addresses (A
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv4 addresses (e.g.
['74.125.79.104', '74.125.79.105', '74.125.79.106']
).
dns.resolve6(hostname, callback)#
Uses the DNS protocol to resolve a IPv6 addresses (AAAA
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv6 addresses.
dns.resolveCname(hostname, callback)#
Uses the DNS protocol to resolve CNAME
records for the hostname
. The
addresses
argument passed to the callback
function
will contain an array of canonical name records available for the hostname
(e.g. ['bar.example.com']
).
dns.resolveMx(hostname, callback)#
Uses the DNS protocol to resolve mail exchange records (MX
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of objects containing both a priority
and exchange
property (e.g. [{priority: 10, exchange: 'mx.example.com'}, ...]
).
dns.resolveNs(hostname, callback)#
Uses the DNS protocol to resolve name server records (NS
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of name server records available for hostname
(e.g., ['ns1.example.com', 'ns2.example.com']
).
dns.resolveSoa(hostname, callback)#
Uses the DNS protocol to resolve a start of authority record (SOA
record) for
the hostname
. The addresses
argument passed to the callback
function will
be an object with the following properties:
nsname
hostmaster
serial
refresh
retry
expire
minttl
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
dns.resolveSrv(hostname, callback)#
Uses the DNS protocol to resolve service records (SRV
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of objects with the following properties:
priority
weight
port
name
{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
dns.resolvePtr(hostname, callback)#
Uses the DNS protocol to resolve pointer records (PTR
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of strings containing the reply records.
dns.resolveTxt(hostname, callback)#
Uses the DNS protocol to resolve text queries (TXT
records) for the
hostname
. The addresses
argument passed to the callback
function is
is a two-dimentional array of the text records available for hostname
(e.g.,
[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]
). Each sub-array contains TXT chunks of
one record. Depending on the use case, these could be either joined together or
treated separately.
dns.reverse(ip, callback)#
Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of hostnames.
The callback
function has arguments (err, hostnames)
, where hostnames
is an array of resolved hostnames for the given ip
.
On error, err
is an Error
object, where err.code
is
one of the DNS error codes.
dns.setServers(servers)#
Sets the IP addresses of the servers to be used when resolving. The servers
argument is an array of IPv4 or IPv6 addresses.
If a port specified on the address it will be removed.
An error will be thrown if an invalid address is provided.
The dns.setServers()
method must not be called while a DNS query is in
progress.
Error codes#
Each DNS query can return one of the following error codes:
dns.NODATA
: DNS server returned answer with no data.dns.FORMERR
: DNS server claims query was misformatted.dns.SERVFAIL
: DNS server returned general failure.dns.NOTFOUND
: Domain name not found.dns.NOTIMP
: DNS server does not implement requested operation.dns.REFUSED
: DNS server refused query.dns.BADQUERY
: Misformatted DNS query.dns.BADNAME
: Misformatted hostname.dns.BADFAMILY
: Unsupported address family.dns.BADRESP
: Misformatted DNS reply.dns.CONNREFUSED
: Could not contact DNS servers.dns.TIMEOUT
: Timeout while contacting DNS servers.dns.EOF
: End of file.dns.FILE
: Error reading file.dns.NOMEM
: Out of memory.dns.DESTRUCTION
: Channel is being destroyed.dns.BADSTR
: Misformatted string.dns.BADFLAGS
: Illegal flags specified.dns.NONAME
: Given hostname is not numeric.dns.BADHINTS
: Illegal hints flags specified.dns.NOTINITIALIZED
: c-ares library initialization not yet performed.dns.LOADIPHLPAPI
: Error loading iphlpapi.dll.dns.ADDRGETNETWORKPARAMS
: Could not find GetNetworkParams function.dns.CANCELLED
: DNS query cancelled.
Implementation considerations#
Although dns.lookup()
and the various dns.resolve*()/dns.reverse()
functions have the same goal of associating a network name with a network
address (or vice versa), their behavior is quite different. These differences
can have subtle but significant consequences on the behavior of Node.js
programs.
dns.lookup()
#
Under the hood, dns.lookup()
uses the same operating system facilities
as most other programs. For instance, dns.lookup()
will almost always
resolve a given name the same way as the ping
command. On most POSIX-like
operating systems, the behavior of the dns.lookup()
function can be
modified by changing settings in nsswitch.conf(5)
and/or resolv.conf(5)
,
but note that changing these files will change the behavior of all other
programs running on the same operating system.
Though the call to dns.lookup()
will be asynchronous from JavaScript's
perspective, it is implemented as a synchronous call to getaddrinfo(3)
that
runs on libuv's threadpool. Because libuv's threadpool has a fixed size, it
means that if for whatever reason the call to getaddrinfo(3)
takes a long
time, other operations that could run on libuv's threadpool (such as filesystem
operations) will experience degraded performance. In order to mitigate this
issue, one potential solution is to increase the size of libuv's threadpool by
setting the 'UV_THREADPOOL_SIZE'
environment variable to a value greater than
4
(its current default value). For more information on libuv's threadpool, see
the official libuv documentation.
dns.resolve()
, dns.resolve*()
and dns.reverse()
#
These functions are implemented quite differently than dns.lookup()
. They
do not use getaddrinfo(3)
and they always perform a DNS query on the
network. This network communication is always done asynchronously, and does not
use libuv's threadpool.
As a result, these functions cannot have the same negative impact on other
processing that happens on libuv's threadpool that dns.lookup()
can have.
They do not use the same set of configuration files than what dns.lookup()
uses. For instance, they do not use the configuration from /etc/hosts
.
Domain#
Stability: 0 - Deprecated
This module is pending deprecation. Once a replacement API has been finalized, this module will be fully deprecated. Most end users should not have cause to use this module. Users who absolutely must have the functionality that domains provide may rely on it for the time being but should expect to have to migrate to a different solution in the future.
Domains provide a way to handle multiple different IO operations as a
single group. If any of the event emitters or callbacks registered to a
domain emit an 'error'
event, or throw an error, then the domain object
will be notified, rather than losing the context of the error in the
process.on('uncaughtException')
handler, or causing the program to
exit immediately with an error code.
Warning: Don't Ignore Errors!#
Domain error handlers are not a substitute for closing down your process when an error occurs.
By the very nature of how throw
works in JavaScript, there is almost
never any way to safely "pick up where you left off", without leaking
references, or creating some other sort of undefined brittle state.
The safest way to respond to a thrown error is to shut down the process. Of course, in a normal web server, you might have many connections open, and it is not reasonable to abruptly shut those down because an error was triggered by someone else.
The better approach is to send an error response to the request that triggered the error, while letting the others finish in their normal time, and stop listening for new requests in that worker.
In this way, domain
usage goes hand-in-hand with the cluster module,
since the master process can fork a new worker when a worker
encounters an error. For Node.js programs that scale to multiple
machines, the terminating proxy or service registry can take note of
the failure, and react accordingly.
For example, this is not a good idea:
// XXX WARNING! BAD IDEA!
var d = require('domain').create();
d.on('error', (er) => {
// The error won't crash the process, but what it does is worse!
// Though we've prevented abrupt process restarting, we are leaking
// resources like crazy if this ever happens.
// This is no better than process.on('uncaughtException')!
console.log('error, but oh well', er.message);
});
d.run(() => {
require('http').createServer((req, res) => {
handleRequest(req, res);
}).listen(PORT);
});
By using the context of a domain, and the resilience of separating our program into multiple worker processes, we can react more appropriately, and handle errors with much greater safety.
// Much better!
const cluster = require('cluster');
const PORT = +process.env.PORT || 1337;
if (cluster.isMaster) {
// In real life, you'd probably use more than just 2 workers,
// and perhaps not put the master and worker in the same file.
//
// You can also of course get a bit fancier about logging, and
// implement whatever custom logic you need to prevent DoS
// attacks and other bad behavior.
//
// See the options in the cluster documentation.
//
// The important thing is that the master does very little,
// increasing our resilience to unexpected errors.
cluster.fork();
cluster.fork();
cluster.on('disconnect', (worker) => {
console.error('disconnect!');
cluster.fork();
});
} else {
// the worker
//
// This is where we put our bugs!
const domain = require('domain');
// See the cluster documentation for more details about using
// worker processes to serve requests. How it works, caveats, etc.
const server = require('http').createServer((req, res) => {
var d = domain.create();
d.on('error', (er) => {
console.error('error', er.stack);
// Note: we're in dangerous territory!
// By definition, something unexpected occurred,
// which we probably didn't want.
// Anything can happen now! Be very careful!
try {
// make sure we close down within 30 seconds
var killtimer = setTimeout(() => {
process.exit(1);
}, 30000);
// But don't keep the process open just for that!
killtimer.unref();
// stop taking new requests.
server.close();
// Let the master know we're dead. This will trigger a
// 'disconnect' in the cluster master, and then it will fork
// a new worker.
cluster.worker.disconnect();
// try to send an error to the request that triggered the problem
res.statusCode = 500;
res.setHeader('content-type', 'text/plain');
res.end('Oops, there was a problem!\n');
} catch (er2) {
// oh well, not much we can do at this point.
console.error('Error sending 500!', er2.stack);
}
});
// Because req and res were created before this domain existed,
// we need to explicitly add them.
// See the explanation of implicit vs explicit binding below.
d.add(req);
d.add(res);
// Now run the handler function in the domain.
d.run(() => {
handleRequest(req, res);
});
});
server.listen(PORT);
}
// This part isn't important. Just an example routing thing.
// You'd put your fancy application logic here.
function handleRequest(req, res) {
switch(req.url) {
case '/error':
// We do some async stuff, and then...
setTimeout(() => {
// Whoops!
flerb.bark();
});
break;
default:
res.end('ok');
}
}
Additions to Error objects#
Any time an Error
object is routed through a domain, a few extra fields
are added to it.
error.domain
The domain that first handled the error.error.domainEmitter
The event emitter that emitted an'error'
event with the error object.error.domainBound
The callback function which was bound to the domain, and passed an error as its first argument.error.domainThrown
A boolean indicating whether the error was thrown, emitted, or passed to a bound callback function.
Implicit Binding#
If domains are in use, then all new EventEmitter objects (including Stream objects, requests, responses, etc.) will be implicitly bound to the active domain at the time of their creation.
Additionally, callbacks passed to lowlevel event loop requests (such as to fs.open, or other callback-taking methods) will automatically be bound to the active domain. If they throw, then the domain will catch the error.
In order to prevent excessive memory usage, Domain objects themselves are not implicitly added as children of the active domain. If they were, then it would be too easy to prevent request and response objects from being properly garbage collected.
If you want to nest Domain objects as children of a parent Domain, then you must explicitly add them.
Implicit binding routes thrown errors and 'error'
events to the
Domain's 'error'
event, but does not register the EventEmitter on the
Domain, so domain.dispose()
will not shut down the EventEmitter.
Implicit binding only takes care of thrown errors and 'error'
events.
Explicit Binding#
Sometimes, the domain in use is not the one that ought to be used for a specific event emitter. Or, the event emitter could have been created in the context of one domain, but ought to instead be bound to some other domain.
For example, there could be one domain in use for an HTTP server, but perhaps we would like to have a separate domain to use for each request.
That is possible via explicit binding.
For example:
// create a top-level domain for the server
const domain = require('domain');
const http = require('http');
const serverDomain = domain.create();
serverDomain.run(() => {
// server is created in the scope of serverDomain
http.createServer((req, res) => {
// req and res are also created in the scope of serverDomain
// however, we'd prefer to have a separate domain for each request.
// create it first thing, and add req and res to it.
var reqd = domain.create();
reqd.add(req);
reqd.add(res);
reqd.on('error', (er) => {
console.error('Error', er, req.url);
try {
res.writeHead(500);
res.end('Error occurred, sorry.');
} catch (er) {
console.error('Error sending 500', er, req.url);
}
});
}).listen(1337);
});
domain.create()#
- return: <Domain>
Returns a new Domain object.
Class: Domain#
The Domain class encapsulates the functionality of routing errors and uncaught exceptions to the active Domain object.
Domain is a child class of EventEmitter
. To handle the errors that it
catches, listen to its 'error'
event.
domain.run(fn[, arg][, ...])#
fn
<Function>
Run the supplied function in the context of the domain, implicitly binding all event emitters, timers, and lowlevel requests that are created in that context. Optionally, arguments can be passed to the function.
This is the most basic way to use a domain.
Example:
const domain = require('domain');
const fs = require('fs');
const d = domain.create();
d.on('error', (er) => {
console.error('Caught error!', er);
});
d.run(() => {
process.nextTick(() => {
setTimeout(() => { // simulating some various async stuff
fs.open('non-existent file', 'r', (er, fd) => {
if (er) throw er;
// proceed...
});
}, 100);
});
});
In this example, the d.on('error')
handler will be triggered, rather
than crashing the program.
domain.members#
An array of timers and event emitters that have been explicitly added to the domain.
domain.add(emitter)#
emitter
<EventEmitter> | <Timer> emitter or timer to be added to the domain
Explicitly adds an emitter to the domain. If any event handlers called by
the emitter throw an error, or if the emitter emits an 'error'
event, it
will be routed to the domain's 'error'
event, just like with implicit
binding.
This also works with timers that are returned from setInterval()
and
setTimeout()
. If their callback function throws, it will be caught by
the domain 'error' handler.
If the Timer or EventEmitter was already bound to a domain, it is removed from that one, and bound to this one instead.
domain.remove(emitter)#
emitter
<EventEmitter> | <Timer> emitter or timer to be removed from the domain
The opposite of domain.add(emitter)
. Removes domain handling from the
specified emitter.
domain.bind(callback)#
callback
<Function> The callback function- return: <Function> The bound function
The returned function will be a wrapper around the supplied callback
function. When the returned function is called, any errors that are
thrown will be routed to the domain's 'error'
event.
Example#
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.bind((er, data) => {
// if this throws, it will also be passed to the domain
return cb(er, data ? JSON.parse(data) : null);
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
domain.intercept(callback)#
callback
<Function> The callback function- return: <Function> The intercepted function
This method is almost identical to domain.bind(callback)
. However, in
addition to catching thrown errors, it will also intercept Error
objects sent as the first argument to the function.
In this way, the common if (err) return callback(err);
pattern can be replaced
with a single error handler in a single place.
Example#
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.intercept((data) => {
// note, the first argument is never passed to the
// callback since it is assumed to be the 'Error' argument
// and thus intercepted by the domain.
// if this throws, it will also be passed to the domain
// so the error-handling logic can be moved to the 'error'
// event on the domain instead of being repeated throughout
// the program.
return cb(null, JSON.parse(data));
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
domain.enter()#
The enter
method is plumbing used by the run
, bind
, and intercept
methods to set the active domain. It sets domain.active
and process.domain
to the domain, and implicitly pushes the domain onto the domain stack managed
by the domain module (see domain.exit()
for details on the domain stack). The
call to enter
delimits the beginning of a chain of asynchronous calls and I/O
operations bound to a domain.
Calling enter
changes only the active domain, and does not alter the domain
itself. enter
and exit
can be called an arbitrary number of times on a
single domain.
If the domain on which enter
is called has been disposed, enter
will return
without setting the domain.
domain.exit()#
The exit
method exits the current domain, popping it off the domain stack.
Any time execution is going to switch to the context of a different chain of
asynchronous calls, it's important to ensure that the current domain is exited.
The call to exit
delimits either the end of or an interruption to the chain
of asynchronous calls and I/O operations bound to a domain.
If there are multiple, nested domains bound to the current execution context,
exit
will exit any domains nested within this domain.
Calling exit
changes only the active domain, and does not alter the domain
itself. enter
and exit
can be called an arbitrary number of times on a
single domain.
If the domain on which exit
is called has been disposed, exit
will return
without exiting the domain.
domain.dispose()#
Stability: 0 - Deprecated. Please recover from failed IO actions explicitly via error event handlers set on the domain.
Once dispose
has been called, the domain will no longer be used by callbacks
bound into the domain via run
, bind
, or intercept
, and a 'dispose'
event
is emitted.
Errors#
Applications running in Node.js will generally experience four categories of errors:
- Standard JavaScript errors such as:
- <EvalError> : thrown when a call to
eval()
fails. - <SyntaxError> : thrown in response to improper JavaScript language syntax.
- <RangeError> : thrown when a value is not within an expected range
- <ReferenceError> : thrown when using undefined variables
- <TypeError> : thrown when passing arguments of the wrong type
- <URIError> : thrown when a global URI handling function is misused.
- <EvalError> : thrown when a call to
- System errors triggered by underlying operating system constraints such as attempting to open a file that does not exist, attempting to send data over a closed socket, etc;
- And User-specified errors triggered by application code.
- Assertion Errors are a special class of error that can be triggered whenever
Node.js detects an exceptional logic violation that should never occur. These
are raised typically by the
assert
module.
All JavaScript and System errors raised by Node.js inherit from, or are instances of, the standard JavaScript <Error> class and are guaranteed to provide at least the properties available on that class.
Error Propagation and Interception#
Node.js supports several mechanisms for propagating and handling errors that occur while an application is running. How these errors are reported and handled depends entirely on the type of Error and the style of the API that is called.
All JavaScript errors are handled as exceptions that immediately generate
and throw an error using the standard JavaScript throw
mechanism. These
are handled using the try / catch
construct provided by the JavaScript
language.
// Throws with a ReferenceError because z is undefined
try {
const m = 1;
const n = m + z;
} catch (err) {
// Handle the error here.
}
Any use of the JavaScript throw
mechanism will raise an exception that
must be handled using try / catch
or the Node.js process will exit
immediately.
With few exceptions, Synchronous APIs (any blocking method that does not
accept a callback
function, such as fs.readFileSync
), will use throw
to report errors.
Errors that occur within Asynchronous APIs may be reported in multiple ways:
Most asynchronous methods that accept a
callback
function will accept anError
object passed as the first argument to that function. If that first argument is notnull
and is an instance ofError
, then an error occurred that should be handled.const fs = require('fs'); fs.readFile('a file that does not exist', (err, data) => { if (err) { console.error('There was an error reading the file!', err); return; } // Otherwise handle the data });
When an asynchronous method is called on an object that is an
EventEmitter
, errors can be routed to that object's'error'
event.const net = require('net'); const connection = net.connect('localhost'); // Adding an 'error' event handler to a stream: connection.on('error', (err) => { // If the connection is reset by the server, or if it can't // connect at all, or on any sort of error encountered by // the connection, the error will be sent here. console.error(err); }); connection.pipe(process.stdout);
A handful of typically asynchronous methods in the Node.js API may still use the
throw
mechanism to raise exceptions that must be handled usingtry / catch
. There is no comprehensive list of such methods; please refer to the documentation of each method to determine the appropriate error handling mechanism required.
The use of the 'error'
event mechanism is most common for stream-based
and event emitter-based APIs, which themselves represent a series of
asynchronous operations over time (as opposed to a single operation that may
pass or fail).
For all EventEmitter
objects, if an 'error'
event handler is not
provided, the error will be thrown, causing the Node.js process to report an
unhandled exception and crash unless either: The domain
module is used
appropriately or a handler has been registered for the
process.on('uncaughtException')
event.
const EventEmitter = require('events');
const ee = new EventEmitter();
setImmediate(() => {
// This will crash the process because no 'error' event
// handler has been added.
ee.emit('error', new Error('This will crash'));
});
Errors generated in this way cannot be intercepted using try / catch
as
they are thrown after the calling code has already exited.
Developers must refer to the documentation for each method to determine exactly how errors raised by those methods are propagated.
Node.js style callbacks#
Most asynchronous methods exposed by the Node.js core API follow an idiomatic
pattern referred to as a "Node.js style callback". With this pattern, a
callback function is passed to the method as an argument. When the operation
either completes or an error is raised, the callback function is called with
the Error object (if any) passed as the first argument. If no error was raised,
the first argument will be passed as null
.
const fs = require('fs');
function nodeStyleCallback(err, data) {
if (err) {
console.error('There was an error', err);
return;
}
console.log(data);
}
fs.readFile('/some/file/that/does-not-exist', nodeStyleCallback);
fs.readFile('/some/file/that/does-exist', nodeStyleCallback)
The JavaScript try / catch
mechanism cannot be used to intercept errors
generated by asynchronous APIs. A common mistake for beginners is to try to
use throw
inside a Node.js style callback:
// THIS WILL NOT WORK:
const fs = require('fs');
try {
fs.readFile('/some/file/that/does-not-exist', (err, data) => {
// mistaken assumption: throwing here...
if (err) {
throw err;
}
});
} catch(err) {
// This will not catch the throw!
console.log(err);
}
This will not work because the callback function passed to fs.readFile()
is
called asynchronously. By the time the callback has been called, the
surrounding code (including the try { } catch(err) { }
block will have
already exited. Throwing an error inside the callback can crash the Node.js
process in most cases. If domains are enabled, or a handler has been
registered with process.on('uncaughtException')
, such errors can be
intercepted.
Class: Error#
A generic JavaScript Error
object that does not denote any specific
circumstance of why the error occurred. Error
objects capture a "stack trace"
detailing the point in the code at which the Error
was instantiated, and may
provide a text description of the error.
All errors generated by Node.js, including all System and JavaScript errors,
will either be instances of, or inherit from, the Error
class.
new Error(message)#
Creates a new Error
object and sets the error.message
property to the
provided text message. If an object is passed as message
, the text message
is generated by calling message.toString()
. The error.stack
property will
represent the point in the code at which new Error()
was called. Stack traces
are dependent on V8's stack trace API. Stack traces extend only to either
(a) the beginning of synchronous code execution, or (b) the number of frames
given by the property Error.stackTraceLimit
, whichever is smaller.
Error.captureStackTrace(targetObject[, constructorOpt])#
Creates a .stack
property on targetObject
, which when accessed returns
a string representing the location in the code at which
Error.captureStackTrace()
was called.
const myObject = {};
Error.captureStackTrace(myObject);
myObject.stack // similar to `new Error().stack`
The first line of the trace, instead of being prefixed with ErrorType:
message
, will be the result of calling targetObject.toString()
.
The optional constructorOpt
argument accepts a function. If given, all frames
above constructorOpt
, including constructorOpt
, will be omitted from the
generated stack trace.
The constructorOpt
argument is useful for hiding implementation
details of error generation from an end user. For instance:
function MyError() {
Error.captureStackTrace(this, MyError);
}
// Without passing MyError to captureStackTrace, the MyError
// frame would should up in the .stack property. by passing
// the constructor, we omit that frame and all frames above it.
new MyError().stack
Error.stackTraceLimit#
The Error.stackTraceLimit
property specifies the number of stack frames
collected by a stack trace (whether generated by new Error().stack
or
Error.captureStackTrace(obj)
).
The default value is 10
but may be set to any valid JavaScript number. Changes
will affect any stack trace captured after the value has been changed.
If set to a non-number value, or set to a negative number, stack traces will not capture any frames.
error.message#
Returns the string description of error as set by calling new Error(message)
.
The message
passed to the constructor will also appear in the first line of
the stack trace of the Error
, however changing this property after the
Error
object is created may not change the first line of the stack trace.
const err = new Error('The message');
console.log(err.message);
// Prints: The message
error.stack#
Returns a string describing the point in the code at which the Error
was
instantiated.
For example:
Error: Things keep happening!
at /home/gbusey/file.js:525:2
at Frobnicator.refrobulate (/home/gbusey/business-logic.js:424:21)
at Actor.<anonymous> (/home/gbusey/actors.js:400:8)
at increaseSynergy (/home/gbusey/actors.js:701:6)
The first line is formatted as <error class name>: <error message>
, and
is followed by a series of stack frames (each line beginning with "at ").
Each frame describes a call site within the code that lead to the error being
generated. V8 attempts to display a name for each function (by variable name,
function name, or object method name), but occasionally it will not be able to
find a suitable name. If V8 cannot determine a name for the function, only
location information will be displayed for that frame. Otherwise, the
determined function name will be displayed with location information appended
in parentheses.
It is important to note that frames are only generated for JavaScript
functions. If, for example, execution synchronously passes through a C++ addon
function called cheetahify
, which itself calls a JavaScript function, the
frame representing the cheetahify
call will not be present in the stack
traces:
const cheetahify = require('./native-binding.node');
function makeFaster() {
// cheetahify *synchronously* calls speedy.
cheetahify(function speedy() {
throw new Error('oh no!');
});
}
makeFaster(); // will throw:
// /home/gbusey/file.js:6
// throw new Error('oh no!');
// ^
// Error: oh no!
// at speedy (/home/gbusey/file.js:6:11)
// at makeFaster (/home/gbusey/file.js:5:3)
// at Object.<anonymous> (/home/gbusey/file.js:10:1)
// at Module._compile (module.js:456:26)
// at Object.Module._extensions..js (module.js:474:10)
// at Module.load (module.js:356:32)
// at Function.Module._load (module.js:312:12)
// at Function.Module.runMain (module.js:497:10)
// at startup (node.js:119:16)
// at node.js:906:3
The location information will be one of:
native
, if the frame represents a call internal to V8 (as in[].forEach
).plain-filename.js:line:column
, if the frame represents a call internal to Node.js./absolute/path/to/file.js:line:column
, if the frame represents a call in a user program, or its dependencies.
The string representing the stack trace is lazily generated when the
error.stack
property is accessed.
The number of frames captured by the stack trace is bounded by the smaller of
Error.stackTraceLimit
or the number of available frames on the current event
loop tick.
System-level errors are generated as augmented Error
instances, which are
detailed here.
Class: RangeError#
A subclass of Error
that indicates that a provided argument was not within the
set or range of acceptable values for a function; whether that is a numeric
range, or outside the set of options for a given function parameter.
For example:
require('net').connect(-1);
// throws RangeError, port should be > 0 && < 65536
Node.js will generate and throw RangeError
instances immediately as a form
of argument validation.
Class: ReferenceError#
A subclass of Error
that indicates that an attempt is being made to access a
variable that is not defined. Such errors commonly indicate typos in code, or
an otherwise broken program.
While client code may generate and propagate these errors, in practice, only V8 will do so.
doesNotExist;
// throws ReferenceError, doesNotExist is not a variable in this program.
ReferenceError
instances will have an error.arguments
property whose value
is an array containing a single element: a string representing the variable
that was not defined.
const assert = require('assert');
try {
doesNotExist;
} catch(err) {
assert(err.arguments[0], 'doesNotExist');
}
Unless an application is dynamically generating and running code,
ReferenceError
instances should always be considered a bug in the code
or its dependencies.
Class: SyntaxError#
A subclass of Error
that indicates that a program is not valid JavaScript.
These errors may only be generated and propagated as a result of code
evaluation. Code evaluation may happen as a result of eval
, Function
,
require
, or vm. These errors are almost always indicative of a broken
program.
try {
require('vm').runInThisContext('binary ! isNotOk');
} catch(err) {
// err will be a SyntaxError
}
SyntaxError
instances are unrecoverable in the context that created them –
they may only be caught by other contexts.
Class: TypeError#
A subclass of Error
that indicates that a provided argument is not an
allowable type. For example, passing a function to a parameter which expects a
string would be considered a TypeError.
require('url').parse(() => { });
// throws TypeError, since it expected a string
Node.js will generate and throw TypeError
instances immediately as a form
of argument validation.
Exceptions vs. Errors#
A JavaScript exception is a value that is thrown as a result of an invalid
operation or as the target of a throw
statement. While it is not required
that these values are instances of Error
or classes which inherit from
Error
, all exceptions thrown by Node.js or the JavaScript runtime will be
instances of Error.
Some exceptions are unrecoverable at the JavaScript layer. Such exceptions
will always cause the Node.js process to crash. Examples include assert()
checks or abort()
calls in the C++ layer.
System Errors#
System errors are generated when exceptions occur within the program's runtime environment. Typically, these are operational errors that occur when an application violates an operating system constraint such as attempting to read a file that does not exist or when the user does not have sufficient permissions.
System errors are typically generated at the syscall level: an exhaustive list
of error codes and their meanings is available by running man 2 intro
or
man 3 errno
on most Unices; or online.
In Node.js, system errors are represented as augmented Error
objects with
added properties.
Class: System Error#
error.code#
error.errno#
Returns a string representing the error code, which is always E
followed by
a sequence of capital letters, and may be referenced in man 2 intro
.
The properties error.code
and error.errno
are aliases of one another and
return the same value.
error.syscall#
Returns a string describing the syscall that failed.
Common System Errors#
This list is not exhaustive, but enumerates many of the common system errors encountered when writing a Node.js program. An exhaustive list may be found here.
EACCES
(Permission denied): An attempt was made to access a file in a way forbidden by its file access permissions.EADDRINUSE
(Address already in use): An attempt to bind a server (net
,http
, orhttps
) to a local address failed due to another server on the local system already occupying that address.ECONNREFUSED
(Connection refused): No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host.ECONNRESET
(Connection reset by peer): A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote socket due to a timeout or reboot. Commonly encountered via thehttp
andnet
modules.EEXIST
(File exists): An existing file was the target of an operation that required that the target not exist.EISDIR
(Is a directory): An operation expected a file, but the given pathname was a directory.EMFILE
(Too many open files in system): Maximum number of file descriptors allowable on the system has been reached, and requests for another descriptor cannot be fulfilled until at least one has been closed. This is encountered when opening many files at once in parallel, especially on systems (in particular, OS X) where there is a low file descriptor limit for processes. To remedy a low limit, runulimit -n 2048
in the same shell that will run the Node.js process.ENOENT
(No such file or directory): Commonly raised byfs
operations to indicate that a component of the specified pathname does not exist -- no entity (file or directory) could be found by the given path.ENOTDIR
(Not a directory): A component of the given pathname existed, but was not a directory as expected. Commonly raised byfs.readdir
.ENOTEMPTY
(Directory not empty): A directory with entries was the target of an operation that requires an empty directory -- usuallyfs.unlink
.EPERM
(Operation not permitted): An attempt was made to perform an operation that requires elevated privileges.EPIPE
(Broken pipe): A write on a pipe, socket, or FIFO for which there is no process to read the data. Commonly encountered at thenet
andhttp
layers, indicative that the remote side of the stream being written to has been closed.ETIMEDOUT
(Operation timed out): A connect or send request failed because the connected party did not properly respond after a period of time. Usually encountered byhttp
ornet
-- often a sign that asocket.end()
was not properly called.
Events#
Stability: 2 - Stable
Much of the Node.js core API is built around an idiomatic asynchronous event-driven architecture in which certain kinds of objects (called "emitters") periodically emit named events that cause Function objects ("listeners") to be called.
For instance: a net.Server
object emits an event each time a peer
connects to it; a fs.ReadStream
emits an event when the file is opened;
a stream emits an event whenever data is available to be read.
All objects that emit events are instances of the EventEmitter
class. These
objects expose an eventEmitter.on()
function that allows one or more
Functions to be attached to named events emitted by the object. Typically,
event names are camel-cased strings but any valid JavaScript property key
can be used.
When the EventEmitter
object emits an event, all of the Functions attached
to that specific event are called synchronously. Any values returned by the
called listeners are ignored and will be discarded.
The following example shows a simple EventEmitter
instance with a single
listener. The eventEmitter.on()
method is used to register listeners, while
the eventEmitter.emit()
method is used to trigger the event.
const EventEmitter = require('events');
const util = require('util');
function MyEmitter() {
EventEmitter.call(this);
}
util.inherits(MyEmitter, EventEmitter);
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
Any object can become an EventEmitter
through inheritance. The example above
uses the traditional Node.js style prototypical inheritance using
the util.inherits()
method. It is, however, possible to use ES6 classes as
well:
const EventEmitter = require('events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');
Passing arguments and this
to listeners#
The eventEmitter.emit()
method allows an arbitrary set of arguments to be
passed to the listener functions. It is important to keep in mind that when an
ordinary listener function is called by the EventEmitter
, the standard this
keyword is intentionally set to reference the EventEmitter
to which the
listener is attached.
const myEmitter = new MyEmitter();
myEmitter.on('event', function(a, b) {
console.log(a, b, this);
// Prints:
// a b MyEmitter {
// domain: null,
// _events: { event: [Function] },
// _eventsCount: 1,
// _maxListeners: undefined }
});
myEmitter.emit('event', 'a', 'b');
It is possible to use ES6 Arrow Functions as listeners, however, when doing so,
the this
keyword will no longer reference the EventEmitter
instance:
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
console.log(a, b, this);
// Prints: a b {}
});
myEmitter.emit('event', 'a', 'b');
Asynchronous vs. Synchronous#
The EventListener
calls all listeners synchronously in the order in which
they were registered. This is important to ensure the proper sequencing of
events and to avoid race conditions or logic errors. When appropriate,
listener functions can switch to an asynchronous mode of operation using
the setImmediate()
or process.nextTick()
methods:
const myEmitter = new MyEmitter();
myEmitter.on('event', (a, b) => {
setImmediate(() => {
console.log('this happens asynchronously');
});
});
myEmitter.emit('event', 'a', 'b');
Handling events only once#
When a listener is registered using the eventEmitter.on()
method, that
listener will be invoked every time the named event is emitted.
const myEmitter = new MyEmitter();
var m = 0;
myEmitter.on('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Prints: 2
Using the eventEmitter.once()
method, it is possible to register a listener
that is immediately unregistered after it is called.
const myEmitter = new MyEmitter();
var m = 0;
myEmitter.once('event', () => {
console.log(++m);
});
myEmitter.emit('event');
// Prints: 1
myEmitter.emit('event');
// Ignored
Error events#
When an error occurs within an EventEmitter
instance, the typical action is
for an 'error'
event to be emitted. These are treated as a special case
within Node.js.
If an EventEmitter
does not have at least one listener registered for the
'error'
event, and an 'error'
event is emitted, the error is thrown, a
stack trace is printed, and the Node.js process exits.
const myEmitter = new MyEmitter();
myEmitter.emit('error', new Error('whoops!'));
// Throws and crashes Node.js
To guard against crashing the Node.js process, developers can either register
a listener for the process.on('uncaughtException')
event or use the
domain
module (Note, however, that the domain
module has been
deprecated).
const myEmitter = new MyEmitter();
process.on('uncaughtException', (err) => {
console.log('whoops! there was an error');
});
myEmitter.emit('error', new Error('whoops!'));
// Prints: whoops! there was an error
As a best practice, developers should always register listeners for the
'error'
event:
const myEmitter = new MyEmitter();
myEmitter.on('error', (err) => {
console.log('whoops! there was an error');
});
myEmitter.emit('error', new Error('whoops!'));
// Prints: whoops! there was an error
Class: EventEmitter#
The EventEmitter
class is defined and exposed by the events
module:
const EventEmitter = require('events');
All EventEmitters emit the event 'newListener'
when new listeners are
added and 'removeListener'
when a listener is removed.
Event: 'newListener'#
eventName
<String> | <Symbol> The name of the event being listened forlistener
<Function> The event handler function
The EventEmitter
instance will emit it's own 'newListener'
event before
a listener is added to it's internal array of listeners.
Listeners registered for the 'newListener'
event will be passed the event
name and a reference to the listener being added.
The fact that the event is triggered before adding the listener has a subtle
but important side effect: any additional listeners registered to the same
name
within the 'newListener'
callback will be inserted before the
listener that is in the process of being added.
const myEmitter = new MyEmitter();
// Only do this once so we don't loop forever
myEmitter.once('newListener', (event, listener) => {
if (event === 'event') {
// Insert a new listener in front
myEmitter.on('event', () => {
console.log('B');
});
}
});
myEmitter.on('event', () => {
console.log('A');
});
myEmitter.emit('event');
// Prints:
// B
// A
Event: 'removeListener'#
eventName
<String> | <Symbol> The event namelistener
<Function> The event handler function
The 'removeListener'
event is emitted after a listener is removed.
EventEmitter.listenerCount(emitter, eventName)#
Stability: 0 - Deprecated: Use emitter.listenerCount()
instead.
A class method that returns the number of listeners for the given eventName
registered on the given emitter
.
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(EventEmitter.listenerCount(myEmitter, 'event'));
// Prints: 2
EventEmitter.defaultMaxListeners#
By default, a maximum of 10
listeners can be registered for any single
event. This limit can be changed for individual EventEmitter
instances
using the emitter.setMaxListeners(n)
method. To change the default
for all EventEmitter
instances, the EventEmitter.defaultMaxListeners
property can be used.
Take caution when setting the EventEmitter.defaultMaxListeners
because the
change effects all EventEmitter
instances, including those created before
the change is made. However, calling emitter.setMaxListeners(n)
still has
precedence over EventEmitter.defaultMaxListeners
.
Note that this is not a hard limit. The EventEmitter
instance will allow
more listeners to be added but will output a trace warning to stderr indicating
that a possible EventEmitter memory leak
has been detected. For any single
EventEmitter
, the emitter.getMaxListeners()
and emitter.setMaxListeners()
methods can be used to temporarily avoid this warning:
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
// do stuff
emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});
emitter.addListener(eventName, listener)#
Alias for emitter.on(eventName, listener)
.
emitter.emit(eventName[, arg1][, arg2][, ...])#
Synchronously calls each of the listeners registered for the event named
eventName
, in the order they were registered, passing the supplied arguments
to each.
Returns true
if the event had listeners, false
otherwise.
emitter.eventNames()#
Returns an array listing the events for which the emitter has registered listeners. The values in the array will be strings or Symbols.
const EventEmitter = require('events');
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myErr.eventNames());
// Prints ['foo', 'bar', Symbol('symbol')]
emitter.getMaxListeners()#
Returns the current max listener value for the EventEmitter
which is either
set by emitter.setMaxListeners(n)
or defaults to
EventEmitter.defaultMaxListeners
.
emitter.listenerCount(eventName)#
eventName
<Value> The name of the event being listened for
Returns the number of listeners listening to the event named eventName
.
emitter.listeners(eventName)#
Returns a copy of the array of listeners for the event named eventName
.
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
emitter.on(eventName, listener)#
Adds the listener
function to the end of the listeners array for the
event named eventName
. No checks are made to see if the listener
has
already been added. Multiple calls passing the same combination of eventName
and listener
will result in the listener
being added, and called, multiple
times.
server.on('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter
so calls can be chained.
emitter.once(eventName, listener)#
Adds a one time listener
function for the event named eventName
. This
listener is invoked only the next time eventName
is triggered, after which
it is removed.
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter
so calls can be chained.
emitter.removeAllListeners([eventName])#
Removes all listeners, or those of the specified eventName
.
Note that it is bad practice to remove listeners added elsewhere in the code,
particularly when the EventEmitter
instance was created by some other
component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter
so calls can be chained.
emitter.removeListener(eventName, listener)#
Removes the specified listener
from the listener array for the event named
eventName
.
var callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
removeListener
will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified eventName
, then removeListener
must be
called multiple times to remove each instance.
Note that once an event has been emitted, all listeners attached to it at the
time of emitting will be called in order. This implies that any removeListener()
or removeAllListeners()
calls after emitting and before the last listener
finishes execution will not remove them from emit()
in progress. Subsequent
events will behave as expected.
const myEmitter = new MyEmitter();
var callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
var callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered after the listener
being removed. This will not impact the order in which listeners are called,
but it will means that any copies of the listener array as returned by
the emitter.listeners()
method will need to be recreated.
Returns a reference to the EventEmitter
so calls can be chained.
emitter.setMaxListeners(n)#
By default EventEmitters will print a warning if more than 10
listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. Obviously, not all events should be limited to just 10 listeners.
The emitter.setMaxListeners()
method allows the limit to be modified for this
specific EventEmitter
instance. The value can be set to Infinity
(or 0
)
for to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter
so calls can be chained.
File System#
Stability: 2 - Stable
File I/O is provided by simple wrappers around standard POSIX functions. To
use this module do require('fs')
. All the methods have asynchronous and
synchronous forms.
The asynchronous form always takes a completion callback as its last argument.
The arguments passed to the completion callback depend on the method, but the
first argument is always reserved for an exception. If the operation was
completed successfully, then the first argument will be null
or undefined
.
When using the synchronous form any exceptions are immediately thrown. You can use try/catch to handle exceptions or allow them to bubble up.
Here is an example of the asynchronous version:
const fs = require('fs');
fs.unlink('/tmp/hello', (err) => {
if (err) throw err;
console.log('successfully deleted /tmp/hello');
});
Here is the synchronous version:
const fs = require('fs');
fs.unlinkSync('/tmp/hello');
console.log('successfully deleted /tmp/hello');
With the asynchronous methods there is no guaranteed ordering. So the following is prone to error:
fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
console.log('renamed complete');
});
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
It could be that fs.stat
is executed before fs.rename
.
The correct way to do this is to chain the callbacks.
fs.rename('/tmp/hello', '/tmp/world', (err) => {
if (err) throw err;
fs.stat('/tmp/world', (err, stats) => {
if (err) throw err;
console.log(`stats: ${JSON.stringify(stats)}`);
});
});
In busy processes, the programmer is strongly encouraged to use the asynchronous versions of these calls. The synchronous versions will block the entire process until they complete--halting all connections.
The relative path to a filename can be used. Remember, however, that this path
will be relative to process.cwd()
.
Most fs functions let you omit the callback argument. If you do, a default
callback is used that rethrows errors. To get a trace to the original call
site, set the NODE_DEBUG
environment variable:
$ cat script.js
function bad() {
require('fs').readFile('/');
}
bad();
$ env NODE_DEBUG=fs node script.js
fs.js:66
throw err;
^
Error: EISDIR, read
at rethrow (fs.js:61:21)
at maybeCallback (fs.js:79:42)
at Object.fs.readFile (fs.js:153:18)
at bad (/path/to/script.js:2:17)
at Object.<anonymous> (/path/to/script.js:5:1)
<etc.>
Buffer API#
fs
functions support passing and receiving paths as both strings
and Buffers. The latter is intended to make it possible to work with
filesystems that allow for non-UTF-8 filenames. For most typical
uses, working with paths as Buffers will be unnecessary, as the string
API converts to and from UTF-8 automatically.
Note that on certain file systems (such as NTFS and HFS+) filenames
will always be encoded as UTF-8. On such file systems, passing
non-UTF-8 encoded Buffers to fs
functions will not work as expected.
Class: fs.FSWatcher#
Objects returned from fs.watch()
are of this type.
Event: 'change'#
Emitted when something changes in a watched directory or file.
See more details in fs.watch()
.
The filename
argument may not be provided depending on operating system
support. If filename
is provided, it will be provided as a Buffer
if
fs.watch()
is called with it's encoding
option set to 'buffer'
, otherwise
filename
will be a string.
fs.watch('./tmp', {encoding: 'buffer'}, (event, filename) => {
if (filename)
console.log(filename);
// Prints: <Buffer ...>
});
Event: 'error'#
error
<Error>
Emitted when an error occurs.
watcher.close()#
Stop watching for changes on the given fs.FSWatcher
.
Class: fs.ReadStream#
ReadStream
is a Readable Stream.
Event: 'open'#
fd
<Integer> Integer file descriptor used by the ReadStream.
Emitted when the ReadStream's file is opened.
readStream.path#
The path to the file the stream is reading from as specified in the first
argument to fs.createReadStream()
. If path
is passed as a string, then
readStream.path
will be a string. If path
is passed as a Buffer
, then
readStream.path
will be a Buffer
.
Class: fs.Stats#
Objects returned from fs.stat()
, fs.lstat()
and fs.fstat()
and their
synchronous counterparts are of this type.
stats.isFile()
stats.isDirectory()
stats.isBlockDevice()
stats.isCharacterDevice()
stats.isSymbolicLink()
(only valid withfs.lstat()
)stats.isFIFO()
stats.isSocket()
For a regular file util.inspect(stats)
would return a string very
similar to this:
{
dev: 2114,
ino: 48064969,
mode: 33188,
nlink: 1,
uid: 85,
gid: 100,
rdev: 0,
size: 527,
blksize: 4096,
blocks: 8,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT
}
Please note that atime
, mtime
, birthtime
, and ctime
are
instances of Date
object and to compare the values of
these objects you should use appropriate methods. For most general
uses getTime()
will return the number of
milliseconds elapsed since 1 January 1970 00:00:00 UTC and this
integer should be sufficient for any comparison, however there are
additional methods which can be used for displaying fuzzy information.
More details can be found in the MDN JavaScript Reference
page.
Stat Time Values#
The times in the stat object have the following semantics:
atime
"Access Time" - Time when file data last accessed. Changed by themknod(2)
,utimes(2)
, andread(2)
system calls.mtime
"Modified Time" - Time when file data last modified. Changed by themknod(2)
,utimes(2)
, andwrite(2)
system calls.ctime
"Change Time" - Time when file status was last changed (inode data modification). Changed by thechmod(2)
,chown(2)
,link(2)
,mknod(2)
,rename(2)
,unlink(2)
,utimes(2)
,read(2)
, andwrite(2)
system calls.birthtime
"Birth Time" - Time of file creation. Set once when the file is created. On filesystems where birthtime is not available, this field may instead hold either thectime
or1970-01-01T00:00Z
(ie, unix epoch timestamp0
). Note that this value may be greater thanatime
ormtime
in this case. On Darwin and other FreeBSD variants, also set if theatime
is explicitly set to an earlier value than the currentbirthtime
using theutimes(2)
system call.
Prior to Node v0.12, the ctime
held the birthtime
on Windows
systems. Note that as of v0.12, ctime
is not "creation time", and
on Unix systems, it never was.
Class: fs.WriteStream#
WriteStream
is a Writable Stream.
Event: 'open'#
fd
<Integer> Integer file descriptor used by the WriteStream.
Emitted when the WriteStream's file is opened.
writeStream.bytesWritten#
The number of bytes written so far. Does not include data that is still queued for writing.
writeStream.path#
The path to the file the stream is writing to as specified in the first
argument to fs.createWriteStream()
. If path
is passed as a string, then
writeStream.path
will be a string. If path
is passed as a Buffer
, then
writeStream.path
will be a Buffer
.
fs.access(path[, mode], callback)#
path
<String> | <Buffer>mode
<Integer>callback
<Function>
Tests a user's permissions for the file specified by path
. mode
is an
optional integer that specifies the accessibility checks to be performed. The
following constants define the possible values of mode
. It is possible to
create a mask consisting of the bitwise OR of two or more values.
fs.F_OK
- File is visible to the calling process. This is useful for determining if a file exists, but says nothing aboutrwx
permissions. Default if nomode
is specified.fs.R_OK
- File can be read by the calling process.fs.W_OK
- File can be written by the calling process.fs.X_OK
- File can be executed by the calling process. This has no effect on Windows (will behave likefs.F_OK
).
The final argument, callback
, is a callback function that is invoked with
a possible error argument. If any of the accessibility checks fail, the error
argument will be populated. The following example checks if the file
/etc/passwd
can be read and written by the current process.
fs.access('/etc/passwd', fs.R_OK | fs.W_OK, (err) => {
console.log(err ? 'no access!' : 'can read/write');
});
fs.accessSync(path[, mode])#
Synchronous version of fs.access()
. This throws if any accessibility checks
fail, and does nothing otherwise.
fs.appendFile(file, data[, options], callback)#
Asynchronously append data to a file, creating the file if it does not yet exist.
data
can be a string or a buffer.
Example:
fs.appendFile('message.txt', 'data to append', (err) => {
if (err) throw err;
console.log('The "data to append" was appended to file!');
});
If options
is a string, then it specifies the encoding. Example:
fs.appendFile('message.txt', 'data to append', 'utf8', callback);
Any specified file descriptor has to have been opened for appending.
Note: Specified file descriptors will not be closed automatically.
fs.appendFileSync(file, data[, options])#
The synchronous version of fs.appendFile()
. Returns undefined
.
fs.chmod(path, mode, callback)#
path
<String> | <Buffer>mode
<Integer>callback
<Function>
Asynchronous chmod(2). No arguments other than a possible exception are given to the completion callback.
fs.chmodSync(path, mode)#
Synchronous chmod(2). Returns undefined
.
fs.chown(path, uid, gid, callback)#
path
<String> | <Buffer>uid
<Integer>gid
<Integer>callback
<Function>
Asynchronous chown(2). No arguments other than a possible exception are given to the completion callback.
fs.chownSync(path, uid, gid)#
Synchronous chown(2). Returns undefined
.
fs.close(fd, callback)#
fd
<Integer>callback
<Function>
Asynchronous close(2). No arguments other than a possible exception are given to the completion callback.
fs.closeSync(fd)#
fd
<Integer>
Synchronous close(2). Returns undefined
.
fs.createReadStream(path[, options])#
Returns a new ReadStream
object. (See Readable Stream).
Be aware that, unlike the default value set for highWaterMark
on a
readable stream (16 kb), the stream returned by this method has a
default value of 64 kb for the same parameter.
options
is an object or string with the following defaults:
{
flags: 'r',
encoding: null,
fd: null,
mode: 0o666,
autoClose: true
}
options
can include start
and end
values to read a range of bytes from
the file instead of the entire file. Both start
and end
are inclusive and
start at 0. The encoding
can be any one of those accepted by Buffer
.
If fd
is specified, ReadStream
will ignore the path
argument and will use
the specified file descriptor. This means that no 'open'
event will be emitted.
Note that fd
should be blocking; non-blocking fd
s should be passed to
net.Socket
.
If autoClose
is false, then the file descriptor won't be closed, even if
there's an error. It is your responsibility to close it and make sure
there's no file descriptor leak. If autoClose
is set to true (default
behavior), on error
or end
the file descriptor will be closed
automatically.
mode
sets the file mode (permission and sticky bits), but only if the
file was created.
An example to read the last 10 bytes of a file which is 100 bytes long:
fs.createReadStream('sample.txt', {start: 90, end: 99});
If options
is a string, then it specifies the encoding.
fs.createWriteStream(path[, options])#
Returns a new WriteStream
object. (See Writable Stream).
options
is an object or string with the following defaults:
{
flags: 'w',
defaultEncoding: 'utf8',
fd: null,
mode: 0o666,
autoClose: true
}
options
may also include a start
option to allow writing data at
some position past the beginning of the file. Modifying a file rather
than replacing it may require a flags
mode of r+
rather than the
default mode w
. The defaultEncoding
can be any one of those accepted by Buffer
.
If autoClose
is set to true (default behavior) on error
or end
the file descriptor will be closed automatically. If autoClose
is false,
then the file descriptor won't be closed, even if there's an error.
It is your responsibility to close it and make sure
there's no file descriptor leak.
Like ReadStream
, if fd
is specified, WriteStream
will ignore the
path
argument and will use the specified file descriptor. This means that no
'open'
event will be emitted. Note that fd
should be blocking; non-blocking
fd
s should be passed to net.Socket
.
If options
is a string, then it specifies the encoding.
fs.exists(path, callback)#
Stability: 0 - Deprecated: Usefs.stat()
orfs.access()
instead.
path
<String> | <Buffer>callback
<Function>
Test whether or not the given path exists by checking with the file system.
Then call the callback
argument with either true or false. Example:
fs.exists('/etc/passwd', (exists) => {
console.log(exists ? 'it\'s there' : 'no passwd!');
});
fs.exists()
should not be used to check if a file exists before calling
fs.open()
. Doing so introduces a race condition since other processes may
change the file's state between the two calls. Instead, user code should
call fs.open()
directly and handle the error raised if the file is
non-existent.
fs.existsSync(path)#
Stability: 0 - Deprecated: Usefs.statSync()
orfs.accessSync()
instead.
Synchronous version of fs.exists()
.
Returns true
if the file exists, false
otherwise.
fs.fchmod(fd, mode, callback)#
fd
<Integer>mode
<Integer>callback
<Function>
Asynchronous fchmod(2). No arguments other than a possible exception are given to the completion callback.
fs.fchmodSync(fd, mode)#
fd
<Integer>mode
<Integer>
Synchronous fchmod(2). Returns undefined
.
fs.fchown(fd, uid, gid, callback)#
fd
<Integer>uid
<Integer>gid
<Integer>callback
<Function>
Asynchronous fchown(2). No arguments other than a possible exception are given to the completion callback.
fs.fchownSync(fd, uid, gid)#
fd
<Integer>uid
<Integer>gid
<Integer>
Synchronous fchown(2). Returns undefined
.
fs.fdatasync(fd, callback)#
fd
<Integer>callback
<Function>
Asynchronous fdatasync(2). No arguments other than a possible exception are given to the completion callback.
fs.fdatasyncSync(fd)#
fd
<Integer>
Synchronous fdatasync(2). Returns undefined
.
fs.fstat(fd, callback)#
fd
<Integer>callback
<Function>
Asynchronous fstat(2). The callback gets two arguments (err, stats)
where
stats
is a fs.Stats
object. fstat()
is identical to stat()
, except that
the file to be stat-ed is specified by the file descriptor fd
.
fs.fstatSync(fd)#
fd
<Integer>
Synchronous fstat(2). Returns an instance of fs.Stats
.
fs.fsync(fd, callback)#
fd
<Integer>callback
<Function>
Asynchronous fsync(2). No arguments other than a possible exception are given to the completion callback.
fs.fsyncSync(fd)#
fd
<Integer>
Synchronous fsync(2). Returns undefined
.
fs.ftruncate(fd, len, callback)#
fd
<Integer>len
<Integer>callback
<Function>
Asynchronous ftruncate(2). No arguments other than a possible exception are given to the completion callback.
fs.ftruncateSync(fd, len)#
fd
<Integer>len
<Integer>
Synchronous ftruncate(2). Returns undefined
.
fs.futimes(fd, atime, mtime, callback)#
fd
<Integer>atime
<Integer>mtime
<Integer>callback
<Function>
Change the file timestamps of a file referenced by the supplied file descriptor.
fs.futimesSync(fd, atime, mtime)#
fd
<Integer>atime
<Integer>mtime
<Integer>
Synchronous version of fs.futimes()
. Returns undefined
.
fs.lchmod(path, mode, callback)#
path
<String> | <Buffer>mode
<Integer>callback
<Function>
Asynchronous lchmod(2). No arguments other than a possible exception are given to the completion callback.
Only available on Mac OS X.
fs.lchmodSync(path, mode)#
Synchronous lchmod(2). Returns undefined
.
fs.lchown(path, uid, gid, callback)#
path
<String> | <Buffer>uid
<Integer>gid
<Integer>callback
<Function>
Asynchronous lchown(2). No arguments other than a possible exception are given to the completion callback.
fs.lchownSync(path, uid, gid)#
Synchronous lchown(2). Returns undefined
.
fs.link(srcpath, dstpath, callback)#
srcpath
<String> | <Buffer>dstpath
<String> | <Buffer>callback
<Function>
Asynchronous link(2). No arguments other than a possible exception are given to the completion callback.
fs.linkSync(srcpath, dstpath)#
Synchronous link(2). Returns undefined
.
fs.lstat(path, callback)#
path
<String> | <Buffer>callback
<Function>
Asynchronous lstat(2). The callback gets two arguments (err, stats)
where
stats
is a fs.Stats
object. lstat()
is identical to stat()
, except that if
path
is a symbolic link, then the link itself is stat-ed, not the file that it
refers to.
fs.lstatSync(path)#
Synchronous lstat(2). Returns an instance of fs.Stats
.
fs.mkdir(path[, mode], callback)#
path
<String> | <Buffer>mode
<Integer>callback
<Function>
Asynchronous mkdir(2). No arguments other than a possible exception are given
to the completion callback. mode
defaults to 0o777
.
fs.mkdirSync(path[, mode])#
Synchronous mkdir(2). Returns undefined
.
fs.mkdtemp(prefix, callback)#
Creates a unique temporary directory.
Generates six random characters to be appended behind a required
prefix
to create a unique temporary directory.
The created folder path is passed as a string to the callback's second parameter.
Example:
fs.mkdtemp('/tmp/foo-', (err, folder) => {
console.log(folder);
// Prints: /tmp/foo-itXde2
});
fs.mkdtempSync(template)#
The synchronous version of [fs.mkdtemp()
][]. Returns the created
folder path.
fs.open(path, flags[, mode], callback)#
path
<String> | <Buffer>flags
<String> | <Number>mode
<Integer>callback
<Function>
Asynchronous file open. See open(2). flags
can be:
'r'
- Open file for reading. An exception occurs if the file does not exist.'r+'
- Open file for reading and writing. An exception occurs if the file does not exist.'rs'
- Open file for reading in synchronous mode. Instructs the operating system to bypass the local file system cache.This is primarily useful for opening files on NFS mounts as it allows you to skip the potentially stale local cache. It has a very real impact on I/O performance so don't use this flag unless you need it.
Note that this doesn't turn
fs.open()
into a synchronous blocking call. If that's what you want then you should be usingfs.openSync()
'rs+'
- Open file for reading and writing, telling the OS to open it synchronously. See notes for'rs'
about using this with caution.'w'
- Open file for writing. The file is created (if it does not exist) or truncated (if it exists).'wx'
- Like'w'
but fails ifpath
exists.'w+'
- Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).'wx+'
- Like'w+'
but fails ifpath
exists.'a'
- Open file for appending. The file is created if it does not exist.'ax'
- Like'a'
but fails ifpath
exists.'a+'
- Open file for reading and appending. The file is created if it does not exist.'ax+'
- Like'a+'
but fails ifpath
exists.
mode
sets the file mode (permission and sticky bits), but only if the file was
created. It defaults to 0666
, readable and writable.
The callback gets two arguments (err, fd)
.
The exclusive flag 'x'
(O_EXCL
flag in open(2)) ensures that path
is newly
created. On POSIX systems, path
is considered to exist even if it is a symlink
to a non-existent file. The exclusive flag may or may not work with network file
systems.
flags
can also be a number as documented by open(2); commonly used constants
are available from require('constants')
. On Windows, flags are translated to
their equivalent ones where applicable, e.g. O_WRONLY
to FILE_GENERIC_WRITE
,
or O_EXCL|O_CREAT
to CREATE_NEW
, as accepted by CreateFileW.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
fs.openSync(path, flags[, mode])#
Synchronous version of fs.open()
. Returns an integer representing the file
descriptor.
fs.read(fd, buffer, offset, length, position, callback)#
fd
<Integer>buffer
<String> | <Buffer>offset
<Integer>length
<Integer>position
<Integer>callback
<Function>
Read data from the file specified by fd
.
buffer
is the buffer that the data will be written to.
offset
is the offset in the buffer to start writing at.
length
is an integer specifying the number of bytes to read.
position
is an integer specifying where to begin reading from in the file.
If position
is null
, data will be read from the current file position.
The callback is given the three arguments, (err, bytesRead, buffer)
.
fs.readdir(path[, options], callback)#
Asynchronous readdir(3). Reads the contents of a directory.
The callback gets two arguments (err, files)
where files
is an array of
the names of the files in the directory excluding '.'
and '..'
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the filenames passed to the callback. If the encoding
is set to 'buffer'
,
the filenames returned will be passed as Buffer
objects.
fs.readdirSync(path[, options])#
Synchronous readdir(3). Returns an array of filenames excluding '.'
and
'..'
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the filenames passed to the callback. If the encoding
is set to 'buffer'
,
the filenames returned will be passed as Buffer
objects.
fs.readFile(file[, options], callback)#
Asynchronously reads the entire contents of a file. Example:
fs.readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
The callback is passed two arguments (err, data)
, where data
is the
contents of the file.
If no encoding is specified, then the raw buffer is returned.
If options
is a string, then it specifies the encoding. Example:
fs.readFile('/etc/passwd', 'utf8', callback);
Any specified file descriptor has to support reading.
Note: Specified file descriptors will not be closed automatically.
fs.readFileSync(file[, options])#
Synchronous version of fs.readFile
. Returns the contents of the file
.
If the encoding
option is specified then this function returns a
string. Otherwise it returns a buffer.
fs.readlink(path[, options], callback)#
Asynchronous readlink(2). The callback gets two arguments (err,
linkString)
.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the link path passed to the callback. If the encoding
is set to 'buffer'
,
the link path returned will be passed as a Buffer
object.
fs.readlinkSync(path[, options])#
Synchronous readlink(2). Returns the symbolic link's string value.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the link path passed to the callback. If the encoding
is set to 'buffer'
,
the link path returned will be passed as a Buffer
object.
fs.realpath(path[, options], callback)#
Asynchronous realpath(2). The callback
gets two arguments (err,
resolvedPath)
. May use process.cwd
to resolve relative paths.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the path passed to the callback. If the encoding
is set to 'buffer'
,
the path returned will be passed as a Buffer
object.
fs.readSync(fd, buffer, offset, length, position)#
Synchronous version of fs.read()
. Returns the number of bytesRead
.
fs.realpathSync(path[, options])#
Synchronous realpath(2). Returns the resolved path.
The optional options
argument can be a string specifying an encoding, or an
object with an encoding
property specifying the character encoding to use for
the path passed to the callback. If the encoding
is set to 'buffer'
,
the path returned will be passed as a Buffer
object.
fs.rename(oldPath, newPath, callback)#
oldPath
<String> | <Buffer>newPath
<String> | <Buffer>callback
<Function>
Asynchronous rename(2). No arguments other than a possible exception are given to the completion callback.
fs.renameSync(oldPath, newPath)#
Synchronous rename(2). Returns undefined
.
fs.rmdir(path, callback)#
path
<String> | <Buffer>callback
<Function>
Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback.
fs.rmdirSync(path)#
Synchronous rmdir(2). Returns undefined
.
fs.stat(path, callback)#
path
<String> | <Buffer>callback
<Function>
Asynchronous stat(2). The callback gets two arguments (err, stats)
where
stats
is a fs.Stats
object. See the fs.Stats
section for more
information.
fs.statSync(path)#
Synchronous stat(2). Returns an instance of fs.Stats
.
fs.symlink(target, path[, type], callback)#
Asynchronous symlink(2). No arguments other than a possible exception are given
to the completion callback.
The type
argument can be set to 'dir'
, 'file'
, or 'junction'
(default
is 'file'
) and is only available on Windows (ignored on other platforms).
Note that Windows junction points require the destination path to be absolute. When using
'junction'
, the target
argument will automatically be normalized to absolute path.
Here is an example below:
fs.symlink('./foo', './new-port');
It creates a symbolic link named "new-port" that points to "foo".
fs.symlinkSync(target, path[, type])#
Synchronous symlink(2). Returns undefined
.
fs.truncate(path, len, callback)#
path
<String> | <Buffer>len
<Integer>callback
<Function>
Asynchronous truncate(2). No arguments other than a possible exception are
given to the completion callback. A file descriptor can also be passed as the
first argument. In this case, fs.ftruncate()
is called.
fs.truncateSync(path, len)#
Synchronous truncate(2). Returns undefined
.
fs.unlink(path, callback)#
path
<String> | <Buffer>callback
<Function>
Asynchronous unlink(2). No arguments other than a possible exception are given to the completion callback.
fs.unlinkSync(path)#
Synchronous unlink(2). Returns undefined
.
fs.unwatchFile(filename[, listener])#
filename
<String> | <Buffer>listener
<Function>
Stop watching for changes on filename
. If listener
is specified, only that
particular listener is removed. Otherwise, all listeners are removed and you
have effectively stopped watching filename
.
Calling fs.unwatchFile()
with a filename that is not being watched is a
no-op, not an error.
Note: fs.watch()
is more efficient than fs.watchFile()
and fs.unwatchFile()
.
fs.watch()
should be used instead of fs.watchFile()
and fs.unwatchFile()
when possible.
fs.utimes(path, atime, mtime, callback)#
path
<String> | <Buffer>atime
<Integer>mtime
<Integer>callback
<Function>
Change file timestamps of the file referenced by the supplied path.
Note: the arguments atime
and mtime
of the following related functions does
follow the below rules:
- If the value is a numberable string like
'123456789'
, the value would get converted to corresponding number. - If the value is
NaN
orInfinity
, the value would get converted toDate.now()
.
fs.utimesSync(path, atime, mtime)#
Synchronous version of fs.utimes()
. Returns undefined
.
fs.watch(filename[, options][, listener])#
filename
<String> | <Buffer>options
<String> | <Object>persistent
<Boolean> Indicates whether the process should continue to run as long as files are being watched. default =true
recursive
<Boolean> Indicates whether all subdirectories should be watched, or only the current directory. The applies when a directory is specified, and only on supported platforms (See Caveats). default =false
encoding
<String> Specifies the character encoding to be used for the filename passed to the listener. default ='utf8'
listener
<Function>
Watch for changes on filename
, where filename
is either a file or a
directory. The returned object is a fs.FSWatcher
.
The second argument is optional. If options
is provided as a string, it
specifies the encoding
. Otherwise options
should be passed as an object.
The listener callback gets two arguments (event, filename)
. event
is either
'rename'
or 'change'
, and filename
is the name of the file which triggered
the event.
Caveats#
The fs.watch
API is not 100% consistent across platforms, and is
unavailable in some situations.
The recursive option is only supported on OS X and Windows.
Availability#
This feature depends on the underlying operating system providing a way to be notified of filesystem changes.
- On Linux systems, this uses
inotify
. - On BSD systems, this uses
kqueue
. - On OS X, this uses
kqueue
for files and 'FSEvents' for directories. - On SunOS systems (including Solaris and SmartOS), this uses
event ports
. - On Windows systems, this feature depends on
ReadDirectoryChangesW
.
If the underlying functionality is not available for some reason, then
fs.watch
will not be able to function. For example, watching files or
directories on network file systems (NFS, SMB, etc.) often doesn't work
reliably or at all.
You can still use fs.watchFile
, which uses stat polling, but it is slower and
less reliable.
Inodes#
On Linux and OS X systems, fs.watch()
resolves the path to an inode and
watches the inode. If the watched path is deleted and recreated, it is assigned
a new inode. The watch will emit an event for the delete but will continue
watching the original inode. Events for the new inode will not be emitted.
This is expected behavior.
Filename Argument#
Providing filename
argument in the callback is only supported on Linux and
Windows. Even on supported platforms, filename
is not always guaranteed to
be provided. Therefore, don't assume that filename
argument is always
provided in the callback, and have some fallback logic if it is null.
fs.watch('somedir', (event, filename) => {
console.log(`event is: ${event}`);
if (filename) {
console.log(`filename provided: ${filename}`);
} else {
console.log('filename not provided');
}
});
fs.watchFile(filename[, options], listener)#
filename
<String> | <Buffer>options
<Object>persistent
<Boolean>interval
<Integer>
listener
<Function>
Watch for changes on filename
. The callback listener
will be called each
time the file is accessed.
The options
argument may be omitted. If provided, it should be an object. The
options
object may contain a boolean named persistent
that indicates
whether the process should continue to run as long as files are being watched.
The options
object may specify an interval
property indicating how often the
target should be polled in milliseconds. The default is
{ persistent: true, interval: 5007 }
.
The listener
gets two arguments the current stat object and the previous
stat object:
fs.watchFile('message.text', (curr, prev) => {
console.log(`the current mtime is: ${curr.mtime}`);
console.log(`the previous mtime was: ${prev.mtime}`);
});
These stat objects are instances of fs.Stat
.
If you want to be notified when the file was modified, not just accessed,
you need to compare curr.mtime
and prev.mtime
.
Note: when an fs.watchFile
operation results in an ENOENT
error, it will
invoke the listener once, with all the fields zeroed (or, for dates, the Unix
Epoch). In Windows, blksize
and blocks
fields will be undefined
, instead
of zero. If the file is created later on, the listener will be called again,
with the latest stat objects. This is a change in functionality since v0.10.
Note: fs.watch()
is more efficient than fs.watchFile
and fs.unwatchFile
.
fs.watch
should be used instead of fs.watchFile
and fs.unwatchFile
when possible.
fs.write(fd, buffer, offset, length[, position], callback)#
fd
<Integer>buffer
<String> | <Buffer>offset
<Integer>length
<Integer>position
<Integer>callback
<Function>
Write buffer
to the file specified by fd
.
offset
and length
determine the part of the buffer to be written.
position
refers to the offset from the beginning of the file where this data
should be written. If typeof position !== 'number'
, the data will be written
at the current position. See pwrite(2).
The callback will be given three arguments (err, written, buffer)
where
written
specifies how many bytes were written from buffer
.
Note that it is unsafe to use fs.write
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
fs.write(fd, data[, position[, encoding]], callback)#
fd
<Integer>data
<String> | <Buffer>position
<Integer>encoding
<String>callback
<Function>
Write data
to the file specified by fd
. If data
is not a Buffer instance
then the value will be coerced to a string.
position
refers to the offset from the beginning of the file where this data
should be written. If typeof position !== 'number'
the data will be written at
the current position. See pwrite(2).
encoding
is the expected string encoding.
The callback will receive the arguments (err, written, string)
where written
specifies how many bytes the passed string required to be written. Note that
bytes written is not the same as string characters. See Buffer.byteLength
.
Unlike when writing buffer
, the entire string must be written. No substring
may be specified. This is because the byte offset of the resulting data may not
be the same as the string offset.
Note that it is unsafe to use fs.write
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
fs.writeFile(file, data[, options], callback)#
Asynchronously writes data to a file, replacing the file if it already exists.
data
can be a string or a buffer.
The encoding
option is ignored if data
is a buffer. It defaults
to 'utf8'
.
Example:
fs.writeFile('message.txt', 'Hello Node.js', (err) => {
if (err) throw err;
console.log('It\'s saved!');
});
If options
is a string, then it specifies the encoding. Example:
fs.writeFile('message.txt', 'Hello Node.js', 'utf8', callback);
Any specified file descriptor has to support writing.
Note that it is unsafe to use fs.writeFile
multiple times on the same file
without waiting for the callback. For this scenario,
fs.createWriteStream
is strongly recommended.
Note: Specified file descriptors will not be closed automatically.
fs.writeFileSync(file, data[, options])#
The synchronous version of fs.writeFile()
. Returns undefined
.
fs.writeSync(fd, buffer, offset, length[, position])#
fs.writeSync(fd, data[, position[, encoding]])#
Synchronous versions of fs.write()
. Returns the number of bytes written.
Global Objects#
These objects are available in all modules. Some of these objects aren't actually in the global scope but in the module scope - this will be noted.
Class: Buffer#
Used to handle binary data. See the buffer section.
__dirname#
The name of the directory that the currently executing script resides in.
Example: running node example.js
from /Users/mjr
console.log(__dirname);
// /Users/mjr
__dirname
isn't actually a global but rather local to each module.
For instance, given two modules: a
and b
, where b
is a dependency of
a
and there is a directory structure of:
/Users/mjr/app/a.js
/Users/mjr/app/node_modules/b/b.js
References to __dirname
within b.js
will return
/Users/mjr/app/node_modules/b
while references to __dirname
within a.js
will return /Users/mj/app
.
__filename#
The filename of the code being executed. This is the resolved absolute path of this code file. For a main program this is not necessarily the same filename used in the command line. The value inside a module is the path to that module file.
Example: running node example.js
from /Users/mjr
console.log(__filename);
// /Users/mjr/example.js
__filename
isn't actually a global but rather local to each module.
clearImmediate(immediateObject)#
clearImmediate
is described in the timers section.
clearInterval(intervalObject)#
clearInterval
is described in the timers section.
clearTimeout(timeoutObject)#
clearTimeout
is described in the timers section.
console#
Used to print to stdout and stderr. See the console
section.
exports#
A reference to the module.exports
that is shorter to type.
See module system documentation for details on when to use exports
and
when to use module.exports
.
exports
isn't actually a global but rather local to each module.
See the module system documentation for more information.
global#
- <Object> The global namespace object.
In browsers, the top-level scope is the global scope. That means that in
browsers if you're in the global scope var something
will define a global
variable. In Node.js this is different. The top-level scope is not the global
scope; var something
inside an Node.js module will be local to that module.
module#
A reference to the current module. In particular
module.exports
is used for defining what a module exports and makes
available through require()
.
module
isn't actually a global but rather local to each module.
See the module system documentation for more information.
process#
The process object. See the process
object section.
require()#
To require modules. See the Modules section. require
isn't actually a
global but rather local to each module.
require.cache#
Modules are cached in this object when they are required. By deleting a key
value from this object, the next require
will reload the module. Note that
this does not apply to native addons, for which reloading will result in an
Error.
require.extensions#
Stability: 0 - Deprecated
Instruct require
on how to handle certain file extensions.
Process files with the extension .sjs
as .js
:
require.extensions['.sjs'] = require.extensions['.js'];
Deprecated In the past, this list has been used to load non-JavaScript modules into Node.js by compiling them on-demand. However, in practice, there are much better ways to do this, such as loading modules via some other Node.js program, or compiling them to JavaScript ahead of time.
Since the Module system is locked, this feature will probably never go away. However, it may have subtle bugs and complexities that are best left untouched.
require.resolve()#
Use the internal require()
machinery to look up the location of a module,
but rather than loading the module, just return the resolved filename.
setImmediate(callback[, arg][, ...])#
setImmediate
is described in the timers section.
setInterval(callback, delay[, arg][, ...])#
setInterval
is described in the timers section.
setTimeout(callback, delay[, arg][, ...])#
setTimeout
is described in the timers section.
HTTP#
Stability: 2 - Stable
To use the HTTP server and client one must require('http')
.
The HTTP interfaces in Node.js are designed to support many features of the protocol which have been traditionally difficult to use. In particular, large, possibly chunk-encoded, messages. The interface is careful to never buffer entire requests or responses--the user is able to stream data.
HTTP message headers are represented by an object like this:
{ 'content-length': '123',
'content-type': 'text/plain',
'connection': 'keep-alive',
'host': 'mysite.com',
'accept': '*/*' }
Keys are lowercased. Values are not modified.
In order to support the full spectrum of possible HTTP applications, Node.js's HTTP API is very low-level. It deals with stream handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body.
See message.headers
for details on how duplicate headers are handled.
The raw headers as they were received are retained in the rawHeaders
property, which is an array of [key, value, key2, value2, ...]
. For
example, the previous message header object might have a rawHeaders
list like the following:
[ 'ConTent-Length', '123456',
'content-LENGTH', '123',
'content-type', 'text/plain',
'CONNECTION', 'keep-alive',
'Host', 'mysite.com',
'accepT', '*/*' ]
Class: http.Agent#
The HTTP Agent is used for pooling sockets used in HTTP client requests.
The HTTP Agent also defaults client requests to using Connection:keep-alive. If no pending HTTP requests are waiting on a socket to become free the socket is closed. This means that Node.js's pool has the benefit of keep-alive when under load but still does not require developers to manually close the HTTP clients using KeepAlive.
If you opt into using HTTP KeepAlive, you can create an Agent object
with that flag set to true
. (See the constructor options.)
Then, the Agent will keep unused sockets in a pool for later use. They
will be explicitly marked so as to not keep the Node.js process running.
However, it is still a good idea to explicitly destroy()
KeepAlive
agents when they are no longer in use, so that the Sockets will be shut
down.
Sockets are removed from the agent's pool when the socket emits either
a 'close'
event or a special 'agentRemove'
event. This means that if
you intend to keep one HTTP request open for a long time and don't
want it to stay in the pool you can do something along the lines of:
http.get(options, (res) => {
// Do stuff
}).on('socket', (socket) => {
socket.emit('agentRemove');
});
Alternatively, you could just opt out of pooling entirely using
agent:false
:
http.get({
hostname: 'localhost',
port: 80,
path: '/',
agent: false // create a new agent just for this one request
}, (res) => {
// Do stuff with response
})
new Agent(options)#
options
<Object> Set of configurable options to set on the agent. Can have the following fields:keepAlive
<Boolean> Keep sockets around in a pool to be used by other requests in the future. Default =false
keepAliveMsecs
<Integer> When using HTTP KeepAlive, how often to send TCP KeepAlive packets over sockets being kept alive. Default =1000
. Only relevant ifkeepAlive
is set totrue
.maxSockets
<Number> Maximum number of sockets to allow per host. Default =Infinity
.maxFreeSockets
<Number> Maximum number of sockets to leave open in a free state. Only relevant ifkeepAlive
is set totrue
. Default =256
.
The default http.globalAgent
that is used by http.request()
has all
of these values set to their respective defaults.
To configure any of them, you must create your own http.Agent
object.
const http = require('http');
var keepAliveAgent = new http.Agent({ keepAlive: true });
options.agent = keepAliveAgent;
http.request(options, onResponseCallback);
agent.createConnection(options[, callback])#
Produces a socket/stream to be used for HTTP requests.
By default, this function is the same as net.createConnection()
. However,
custom Agents may override this method in case greater flexibility is desired.
A socket/stream can be supplied in one of two ways: by returning the
socket/stream from this function, or by passing the socket/stream to callback
.
callback
has a signature of (err, stream)
.
agent.destroy()#
Destroy any sockets that are currently in use by the agent.
It is usually not necessary to do this. However, if you are using an agent with KeepAlive enabled, then it is best to explicitly shut down the agent when you know that it will no longer be used. Otherwise, sockets may hang open for quite a long time before the server terminates them.
agent.freeSockets#
An object which contains arrays of sockets currently awaiting use by the Agent when HTTP KeepAlive is used. Do not modify.
agent.getName(options)#
Get a unique name for a set of request options, to determine whether a
connection can be reused. In the http agent, this returns
host:port:localAddress
. In the https agent, the name includes the
CA, cert, ciphers, and other HTTPS/TLS-specific options that determine
socket reusability.
Options:
host
: A domain name or IP address of the server to issue the request to.port
: Port of remote server.localAddress
: Local interface to bind for network connections when issuing the request.
agent.maxFreeSockets#
By default set to 256. For Agents supporting HTTP KeepAlive, this sets the maximum number of sockets that will be left open in the free state.
agent.maxSockets#
By default set to Infinity. Determines how many concurrent sockets the agent can have open per origin. Origin is either a 'host:port' or 'host:port:localAddress' combination.
agent.requests#
An object which contains queues of requests that have not yet been assigned to sockets. Do not modify.
agent.sockets#
An object which contains arrays of sockets currently in use by the Agent. Do not modify.
Class: http.ClientRequest#
This object is created internally and returned from http.request()
. It
represents an in-progress request whose header has already been queued. The
header is still mutable using the setHeader(name, value)
, getHeader(name)
,
removeHeader(name)
API. The actual header will be sent along with the first
data chunk or when closing the connection.
To get the response, add a listener for 'response'
to the request object.
'response'
will be emitted from the request object when the response
headers have been received. The 'response'
event is executed with one
argument which is an instance of http.IncomingMessage
.
During the 'response'
event, one can add listeners to the
response object; particularly to listen for the 'data'
event.
If no 'response'
handler is added, then the response will be
entirely discarded. However, if you add a 'response'
event handler,
then you must consume the data from the response object, either by
calling response.read()
whenever there is a 'readable'
event, or
by adding a 'data'
handler, or by calling the .resume()
method.
Until the data is consumed, the 'end'
event will not fire. Also, until
the data is read it will consume memory that can eventually lead to a
'process out of memory' error.
Note: Node.js does not check whether Content-Length and the length of the body which has been transmitted are equal or not.
The request implements the Writable Stream interface. This is an
EventEmitter
with the following events:
Event: 'abort'#
function () { }
Emitted when the request has been aborted by the client. This event is only
emitted on the first call to abort()
.
Event: 'checkExpectation'#
function (request, response) { }
Emitted each time a request with an http Expect header is received, where the value is not 100-continue. If this event isn't listened for, the server will automatically respond with a 417 Expectation Failed as appropriate.
Note that when this event is emitted and handled, the request
event will
not be emitted.
Event: 'connect'#
function (response, socket, head) { }
Emitted each time a server responds to a request with a CONNECT
method. If this
event isn't being listened for, clients receiving a CONNECT
method will have
their connections closed.
A client server pair that show you how to listen for the 'connect'
event.
const http = require('http');
const net = require('net');
const url = require('url');
// Create an HTTP tunneling proxy
var proxy = http.createServer( (req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('okay');
});
proxy.on('connect', (req, cltSocket, head) => {
// connect to an origin server
var srvUrl = url.parse(`http://${req.url}`);
var srvSocket = net.connect(srvUrl.port, srvUrl.hostname, () => {
cltSocket.write('HTTP/1.1 200 Connection Established\r\n' +
'Proxy-agent: Node.js-Proxy\r\n' +
'\r\n');
srvSocket.write(head);
srvSocket.pipe(cltSocket);
cltSocket.pipe(srvSocket);
});
});
// now that proxy is running
proxy.listen(1337, '127.0.0.1', () => {
// make a request to a tunneling proxy
var options = {
port: 1337,
hostname: '127.0.0.1',
method: 'CONNECT',
path: 'www.google.com:80'
};
var req = http.request(options);
req.end();
req.on('connect', (res, socket, head) => {
console.log('got connected!');
// make a request over an HTTP tunnel
socket.write('GET / HTTP/1.1\r\n' +
'Host: www.google.com:80\r\n' +
'Connection: close\r\n' +
'\r\n');
socket.on('data', (chunk) => {
console.log(chunk.toString());
});
socket.on('end', () => {
proxy.close();
});
});
});
Event: 'continue'#
function () { }
Emitted when the server sends a '100 Continue' HTTP response, usually because the request contained 'Expect: 100-continue'. This is an instruction that the client should send the request body.
Event: 'response'#
function (response) { }
Emitted when a response is received to this request. This event is emitted only
once. The response
argument will be an instance of http.IncomingMessage
.
Event: 'socket'#
function (socket) { }
Emitted after a socket is assigned to this request.
Event: 'upgrade'#
function (response, socket, head) { }
Emitted each time a server responds to a request with an upgrade. If this event isn't being listened for, clients receiving an upgrade header will have their connections closed.
A client server pair that show you how to listen for the 'upgrade'
event.
const http = require('http');
// Create an HTTP server
var srv = http.createServer( (req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('okay');
});
srv.on('upgrade', (req, socket, head) => {
socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
'Upgrade: WebSocket\r\n' +
'Connection: Upgrade\r\n' +
'\r\n');
socket.pipe(socket); // echo back
});
// now that server is running
srv.listen(1337, '127.0.0.1', () => {
// make a request
var options = {
port: 1337,
hostname: '127.0.0.1',
headers: {
'Connection': 'Upgrade',
'Upgrade': 'websocket'
}
};
var req = http.request(options);
req.end();
req.on('upgrade', (res, socket, upgradeHead) => {
console.log('got upgraded!');
socket.end();
process.exit(0);
});
});
request.abort()#
Marks the request as aborting. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed.
request.end([data][, encoding][, callback])#
Finishes sending the request. If any parts of the body are
unsent, it will flush them to the stream. If the request is
chunked, this will send the terminating '0\r\n\r\n'
.
If data
is specified, it is equivalent to calling
response.write(data, encoding)
followed by request.end(callback)
.
If callback
is specified, it will be called when the request stream
is finished.
request.flushHeaders()#
Flush the request headers.
For efficiency reasons, Node.js normally buffers the request headers until you
call request.end()
or write the first chunk of request data. It then tries
hard to pack the request headers and data into a single TCP packet.
That's usually what you want (it saves a TCP round-trip) but not when the first
data isn't sent until possibly much later. request.flushHeaders()
lets you bypass
the optimization and kickstart the request.
request.setNoDelay([noDelay])#
Once a socket is assigned to this request and is connected
socket.setNoDelay()
will be called.
request.setSocketKeepAlive([enable][, initialDelay])#
Once a socket is assigned to this request and is connected
socket.setKeepAlive()
will be called.
request.setTimeout(timeout[, callback])#
Once a socket is assigned to this request and is connected
socket.setTimeout()
will be called.
timeout
<Number> Milliseconds before a request is considered to be timed out.callback
<Function> Optional function to be called when a timeout occurs. Same as binding to thetimeout
event.
request.write(chunk[, encoding][, callback])#
Sends a chunk of the body. By calling this method
many times, the user can stream a request body to a
server--in that case it is suggested to use the
['Transfer-Encoding', 'chunked']
header line when
creating the request.
The chunk
argument should be a Buffer
or a string.
The encoding
argument is optional and only applies when chunk
is a string.
Defaults to 'utf8'
.
The callback
argument is optional and will be called when this chunk of data
is flushed.
Returns request
.
Class: http.Server#
This class inherits from net.Server
and has the following additional events:
Event: 'checkContinue'#
function (request, response) { }
Emitted each time a request with an http Expect: 100-continue is received. If this event isn't listened for, the server will automatically respond with a 100 Continue as appropriate.
Handling this event involves calling response.writeContinue()
if the client
should continue to send the request body, or generating an appropriate HTTP
response (e.g., 400 Bad Request) if the client should not continue to send the
request body.
Note that when this event is emitted and handled, the 'request'
event will
not be emitted.
Event: 'clientError'#
function (exception, socket) { }
If a client connection emits an 'error'
event, it will be forwarded here.
Listener of this event is responsible for closing/destroying the underlying
socket. For example, one may wish to more gracefully close the socket with an
HTTP '400 Bad Request' response instead of abruptly severing the connection.
Default behavior is to destroy the socket immediately on malformed request.
socket
is the net.Socket
object that the error originated from.
const http = require('http');
const server = http.createServer((req, res) => {
res.end();
});
server.on('clientError', (err, socket) => {
socket.end('HTTP/1.1 400 Bad Request\r\n\r\n');
});
server.listen(8000);
When the 'clientError'
event occurs, there is no request
or response
object, so any HTTP response sent, including response headers and payload,
must be written directly to the socket
object. Care must be taken to
ensure the response is a properly formatted HTTP response message.
Event: 'close'#
function () { }
Emitted when the server closes.
Event: 'connect'#
function (request, socket, head) { }
Emitted each time a client requests a http CONNECT
method. If this event isn't
listened for, then clients requesting a CONNECT
method will have their
connections closed.
request
is the arguments for the http request, as it is in the request event.socket
is the network socket between the server and client.head
is an instance of Buffer, the first packet of the tunneling stream, this may be empty.
After this event is emitted, the request's socket will not have a 'data'
event listener, meaning you will need to bind to it in order to handle data
sent to the server on that socket.
Event: 'connection'#
function (socket) { }
When a new TCP stream is established. socket
is an object of type
net.Socket
. Usually users will not want to access this event. In
particular, the socket will not emit 'readable'
events because of how
the protocol parser attaches to the socket. The socket
can also be
accessed at request.connection
.
Event: 'request'#
function (request, response) { }
Emitted each time there is a request. Note that there may be multiple requests
per connection (in the case of keep-alive connections).
request
is an instance of http.IncomingMessage
and response
is
an instance of http.ServerResponse
.
Event: 'upgrade'#
function (request, socket, head) { }
Emitted each time a client requests a http upgrade. If this event isn't listened for, then clients requesting an upgrade will have their connections closed.
request
is the arguments for the http request, as it is in the request event.socket
is the network socket between the server and client.head
is an instance of Buffer, the first packet of the upgraded stream, this may be empty.
After this event is emitted, the request's socket will not have a 'data'
event listener, meaning you will need to bind to it in order to handle data
sent to the server on that socket.
server.close([callback])#
Stops the server from accepting new connections. See net.Server.close()
.
server.listen(handle[, callback])#
handle
<Object>callback
<Function>
The handle
object can be set to either a server or socket (anything
with an underlying _handle
member), or a {fd: <n>}
object.
This will cause the server to accept connections on the specified handle, but it is presumed that the file descriptor or handle has already been bound to a port or domain socket.
Listening on a file descriptor is not supported on Windows.
This function is asynchronous. The last parameter callback
will be added as
a listener for the 'listening'
event. See also net.Server.listen()
.
Returns server
.
server.listen(path[, callback])#
Start a UNIX socket server listening for connections on the given path
.
This function is asynchronous. The last parameter callback
will be added as
a listener for the 'listening'
event. See also net.Server.listen(path)
.
server.listen(port[, hostname][, backlog][, callback])#
Begin accepting connections on the specified port
and hostname
. If the
hostname
is omitted, the server will accept connections on any IPv6 address
(::
) when IPv6 is available, or any IPv4 address (0.0.0.0
) otherwise. A
port value of zero will assign a random port.
To listen to a unix socket, supply a filename instead of port and hostname.
Backlog is the maximum length of the queue of pending connections.
The actual length will be determined by your OS through sysctl settings such as
tcp_max_syn_backlog
and somaxconn
on linux. The default value of this
parameter is 511 (not 512).
This function is asynchronous. The last parameter callback
will be added as
a listener for the 'listening'
event. See also net.Server.listen(port)
.
server.listening#
A Boolean indicating whether or not the server is listening for connections.
server.maxHeadersCount#
Limits maximum incoming headers count, equal to 1000 by default. If set to 0 - no limit will be applied.
server.setTimeout(msecs, callback)#
msecs
<Number>callback
<Function>
Sets the timeout value for sockets, and emits a 'timeout'
event on
the Server object, passing the socket as an argument, if a timeout
occurs.
If there is a 'timeout'
event listener on the Server object, then it
will be called with the timed-out socket as an argument.
By default, the Server's timeout value is 2 minutes, and sockets are
destroyed automatically if they time out. However, if you assign a
callback to the Server's 'timeout'
event, then you are responsible
for handling socket timeouts.
Returns server
.
server.timeout#
- <Number> Default = 120000 (2 minutes)
The number of milliseconds of inactivity before a socket is presumed to have timed out.
Note that the socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections.
Set to 0 to disable any kind of automatic timeout behavior on incoming connections.
Class: http.ServerResponse#
This object is created internally by a HTTP server--not by the user. It is
passed as the second parameter to the 'request'
event.
The response implements the Writable Stream interface. This is an
EventEmitter
with the following events:
Event: 'close'#
function () { }
Indicates that the underlying connection was terminated before
response.end()
was called or able to flush.
Event: 'finish'#
function () { }
Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the client has received anything yet.
After this event, no more events will be emitted on the response object.
response.addTrailers(headers)#
This method adds HTTP trailing headers (a header but at the end of the message) to the response.
Trailers will only be emitted if chunked encoding is used for the response; if it is not (e.g., if the request was HTTP/1.0), they will be silently discarded.
Note that HTTP requires the Trailer
header to be sent if you intend to
emit trailers, with a list of the header fields in its value. E.g.,
response.writeHead(200, { 'Content-Type': 'text/plain',
'Trailer': 'Content-MD5' });
response.write(fileData);
response.addTrailers({'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667'});
response.end();
Attempting to set a header field name or value that contains invalid characters
will result in a TypeError
being thrown.
response.end([data][, encoding][, callback])#
This method signals to the server that all of the response headers and body
have been sent; that server should consider this message complete.
The method, response.end()
, MUST be called on each response.
If data
is specified, it is equivalent to calling
response.write(data, encoding)
followed by response.end(callback)
.
If callback
is specified, it will be called when the response stream
is finished.
response.finished#
Boolean value that indicates whether the response has completed. Starts
as false
. After response.end()
executes, the value will be true
.
response.getHeader(name)#
Reads out a header that's already been queued but not sent to the client. Note that the name is case insensitive. This can only be called before headers get implicitly flushed.
Example:
var contentType = response.getHeader('content-type');
response.headersSent#
Boolean (read-only). True if headers were sent, false otherwise.
response.removeHeader(name)#
Removes a header that's queued for implicit sending.
Example:
response.removeHeader('Content-Encoding');
response.sendDate#
When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true.
This should only be disabled for testing; HTTP requires the Date header in responses.
response.setHeader(name, value)#
Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here if you need to send multiple headers with the same name.
Example:
response.setHeader('Content-Type', 'text/html');
or
response.setHeader('Set-Cookie', ['type=ninja', 'language=javascript']);
Attempting to set a header field name or value that contains invalid characters
will result in a TypeError
being thrown.
When headers have been set with response.setHeader()
, they will be merged with
any headers passed to response.writeHead()
, with the headers passed to
response.writeHead()
given precedence.
// returns content-type = text/plain
const server = http.createServer((req,res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('ok');
});
response.setTimeout(msecs, callback)#
msecs
<Number>callback
<Function>
Sets the Socket's timeout value to msecs
. If a callback is
provided, then it is added as a listener on the 'timeout'
event on
the response object.
If no 'timeout'
listener is added to the request, the response, or
the server, then sockets are destroyed when they time out. If you
assign a handler on the request, the response, or the server's
'timeout'
events, then it is your responsibility to handle timed out
sockets.
Returns response
.
response.statusCode#
When using implicit headers (not calling response.writeHead()
explicitly),
this property controls the status code that will be sent to the client when
the headers get flushed.
Example:
response.statusCode = 404;
After response header was sent to the client, this property indicates the status code which was sent out.
response.statusMessage#
When using implicit headers (not calling response.writeHead()
explicitly), this property
controls the status message that will be sent to the client when the headers get
flushed. If this is left as undefined
then the standard message for the status
code will be used.
Example:
response.statusMessage = 'Not found';
After response header was sent to the client, this property indicates the status message which was sent out.
response.write(chunk[, encoding][, callback])#
If this method is called and response.writeHead()
has not been called,
it will switch to implicit header mode and flush the implicit headers.
This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.
chunk
can be a string or a buffer. If chunk
is a string,
the second parameter specifies how to encode it into a byte stream.
By default the encoding
is 'utf8'
. The last parameter callback
will be called when this chunk of data is flushed.
Note: This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used.
The first time response.write()
is called, it will send the buffered
header information and the first body to the client. The second time
response.write()
is called, Node.js assumes you're going to be streaming
data, and sends that separately. That is, the response is buffered up to the
first chunk of body.
Returns true
if the entire data was flushed successfully to the kernel
buffer. Returns false
if all or part of the data was queued in user memory.
'drain'
will be emitted when the buffer is free again.
response.writeContinue()#
Sends a HTTP/1.1 100 Continue message to the client, indicating that
the request body should be sent. See the 'checkContinue'
event on Server
.
response.writeHead(statusCode[, statusMessage][, headers])#
Sends a response header to the request. The status code is a 3-digit HTTP
status code, like 404
. The last argument, headers
, are the response headers.
Optionally one can give a human-readable statusMessage
as the second
argument.
Example:
var body = 'hello world';
response.writeHead(200, {
'Content-Length': body.length,
'Content-Type': 'text/plain' });
This method must only be called once on a message and it must
be called before response.end()
is called.
If you call response.write()
or response.end()
before calling this,
the implicit/mutable headers will be calculated and call this function for you.
When headers have been set with response.setHeader()
, they will be merged with
any headers passed to response.writeHead()
, with the headers passed to
response.writeHead()
given precedence.
// returns content-type = text/plain
const server = http.createServer((req,res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('ok');
});
Note that Content-Length is given in bytes not characters. The above example
works because the string 'hello world'
contains only single byte characters.
If the body contains higher coded characters then Buffer.byteLength()
should be used to determine the number of bytes in a given encoding.
And Node.js does not check whether Content-Length and the length of the body
which has been transmitted are equal or not.
Attempting to set a header field name or value that contains invalid characters
will result in a TypeError
being thrown.
Class: http.IncomingMessage#
An IncomingMessage
object is created by http.Server
or
http.ClientRequest
and passed as the first argument to the 'request'
and 'response'
event respectively. It may be used to access response status,
headers and data.
It implements the Readable Stream interface, as well as the following additional events, methods, and properties.
Event: 'close'#
function () { }
Indicates that the underlying connection was closed.
Just like 'end'
, this event occurs only once per response.
message.headers#
The request/response headers object.
Key-value pairs of header names and values. Header names are lower-cased. Example:
// Prints something like:
//
// { 'user-agent': 'curl/7.22.0',
// host: '127.0.0.1:8000',
// accept: '*/*' }
console.log(request.headers);
Duplicates in raw headers are handled in the following ways, depending on the header name:
- Duplicates of
age
,authorization
,content-length
,content-type
,etag
,expires
,from
,host
,if-modified-since
,if-unmodified-since
,last-modified
,location
,max-forwards
,proxy-authorization
,referer
,retry-after
, oruser-agent
are discarded. set-cookie
is always an array. Duplicates are added to the array.- For all other headers, the values are joined together with ', '.
message.httpVersion#
In case of server request, the HTTP version sent by the client. In the case of
client response, the HTTP version of the connected-to server.
Probably either '1.1'
or '1.0'
.
Also message.httpVersionMajor
is the first integer and
message.httpVersionMinor
is the second.
message.method#
Only valid for request obtained from http.Server
.
The request method as a string. Read only. Example:
'GET'
, 'DELETE'
.
message.rawHeaders#
The raw request/response headers list exactly as they were received.
Note that the keys and values are in the same list. It is not a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values.
Header names are not lowercased, and duplicates are not merged.
// Prints something like:
//
// [ 'user-agent',
// 'this is invalid because there can be only one',
// 'User-Agent',
// 'curl/7.22.0',
// 'Host',
// '127.0.0.1:8000',
// 'ACCEPT',
// '*/*' ]
console.log(request.rawHeaders);
message.rawTrailers#
The raw request/response trailer keys and values exactly as they were
received. Only populated at the 'end'
event.
message.setTimeout(msecs, callback)#
msecs
<Number>callback
<Function>
Calls message.connection.setTimeout(msecs, callback)
.
Returns message
.
message.statusCode#
Only valid for response obtained from http.ClientRequest
.
The 3-digit HTTP response status code. E.G. 404
.
message.statusMessage#
Only valid for response obtained from http.ClientRequest
.
The HTTP response status message (reason phrase). E.G. OK
or Internal Server Error
.
message.socket#
The net.Socket
object associated with the connection.
With HTTPS support, use request.socket.getPeerCertificate()
to obtain the
client's authentication details.
message.trailers#
The request/response trailers object. Only populated at the 'end'
event.
message.url#
Only valid for request obtained from http.Server
.
Request URL string. This contains only the URL that is present in the actual HTTP request. If the request is:
GET /status?name=ryan HTTP/1.1\r\n
Accept: text/plain\r\n
\r\n
Then request.url
will be:
'/status?name=ryan'
If you would like to parse the URL into its parts, you can use
require('url').parse(request.url)
. Example:
$ node
> require('url').parse('/status?name=ryan')
{
href: '/status?name=ryan',
search: '?name=ryan',
query: 'name=ryan',
pathname: '/status'
}
If you would like to extract the params from the query string,
you can use the require('querystring').parse
function, or pass
true
as the second argument to require('url').parse
. Example:
$ node
> require('url').parse('/status?name=ryan', true)
{
href: '/status?name=ryan',
search: '?name=ryan',
query: {name: 'ryan'},
pathname: '/status'
}
http.METHODS#
A list of the HTTP methods that are supported by the parser.
http.STATUS_CODES#
A collection of all the standard HTTP response status codes, and the
short description of each. For example, http.STATUS_CODES[404] === 'Not
Found'
.
http.createClient([port][, host])#
Stability: 0 - Deprecated: Use http.request()
instead.
Constructs a new HTTP client. port
and host
refer to the server to be
connected to.
http.createServer([requestListener])#
Returns a new instance of http.Server
.
The requestListener
is a function which is automatically
added to the 'request'
event.
http.get(options[, callback])#
Since most requests are GET requests without bodies, Node.js provides this
convenience method. The only difference between this method and http.request()
is that it sets the method to GET and calls req.end()
automatically.
Example:
http.get('http://www.google.com/index.html', (res) => {
console.log(`Got response: ${res.statusCode}`);
// consume response body
res.resume();
}).on('error', (e) => {
console.log(`Got error: ${e.message}`);
});
http.globalAgent#
Global instance of Agent which is used as the default for all http client requests.
http.request(options[, callback])#
Node.js maintains several connections per server to make HTTP requests. This function allows one to transparently issue requests.
options
can be an object or a string. If options
is a string, it is
automatically parsed with url.parse()
.
Options:
protocol
: Protocol to use. Defaults to'http:'
.host
: A domain name or IP address of the server to issue the request to. Defaults to'localhost'
.hostname
: Alias forhost
. To supporturl.parse()
hostname
is preferred overhost
.family
: IP address family to use when resolvinghost
andhostname
. Valid values are4
or6
. When unspecified, both IP v4 and v6 will be used.port
: Port of remote server. Defaults to 80.localAddress
: Local interface to bind for network connections.socketPath
: Unix Domain Socket (use one of host:port or socketPath).method
: A string specifying the HTTP request method. Defaults to'GET'
.path
: Request path. Defaults to'/'
. Should include query string if any. E.G.'/index.html?page=12'
. An exception is thrown when the request path contains illegal characters. Currently, only spaces are rejected but that may change in the future.headers
: An object containing request headers.auth
: Basic authentication i.e.'user:password'
to compute an Authorization header.agent
: ControlsAgent
behavior. When an Agent is used request will default toConnection: keep-alive
. Possible values:undefined
(default): usehttp.globalAgent
for this host and port.Agent
object: explicitly use the passed inAgent
.false
: opts out of connection pooling with an Agent, defaults request toConnection: close
.
createConnection
: A function that produces a socket/stream to use for the request when theagent
option is not used. This can be used to avoid creating a custom Agent class just to override the defaultcreateConnection
function. Seeagent.createConnection()
for more details.
The optional callback
parameter will be added as a one time listener for
the 'response'
event.
http.request()
returns an instance of the http.ClientRequest
class. The ClientRequest
instance is a writable stream. If one needs to
upload a file with a POST request, then write to the ClientRequest
object.
Example:
var postData = querystring.stringify({
'msg' : 'Hello World!'
});
var options = {
hostname: 'www.google.com',
port: 80,
path: '/upload',
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded',
'Content-Length': postData.length
}
};
var req = http.request(options, (res) => {
console.log(`STATUS: ${res.statusCode}`);
console.log(`HEADERS: ${JSON.stringify(res.headers)}`);
res.setEncoding('utf8');
res.on('data', (chunk) => {
console.log(`BODY: ${chunk}`);
});
res.on('end', () => {
console.log('No more data in response.')
})
});
req.on('error', (e) => {
console.log(`problem with request: ${e.message}`);
});
// write data to request body
req.write(postData);
req.end();
Note that in the example req.end()
was called. With http.request()
one
must always call req.end()
to signify that you're done with the request -
even if there is no data being written to the request body.
If any error is encountered during the request (be that with DNS resolution,
TCP level errors, or actual HTTP parse errors) an 'error'
event is emitted
on the returned request object. As with all 'error'
events, if no listeners
are registered the error will be thrown.
There are a few special headers that should be noted.
Sending a 'Connection: keep-alive' will notify Node.js that the connection to the server should be persisted until the next request.
Sending a 'Content-length' header will disable the default chunked encoding.
Sending an 'Expect' header will immediately send the request headers. Usually, when sending 'Expect: 100-continue', you should both set a timeout and listen for the
'continue'
event. See RFC2616 Section 8.2.3 for more information.Sending an Authorization header will override using the
auth
option to compute basic authentication.
HTTPS#
Stability: 2 - Stable
HTTPS is the HTTP protocol over TLS/SSL. In Node.js this is implemented as a separate module.
Class: https.Agent#
An Agent object for HTTPS similar to http.Agent
. See https.request()
for more information.
Class: https.Server#
This class is a subclass of tls.Server
and emits events same as
http.Server
. See http.Server
for more information.
server.setTimeout(msecs, callback)#
server.timeout#
See http.Server#timeout
.
https.createServer(options[, requestListener])#
Returns a new HTTPS web server object. The options
is similar to
tls.createServer()
. The requestListener
is a function which is
automatically added to the 'request'
event.
Example:
// curl -k https://localhost:8000/
const https = require('https');
const fs = require('fs');
const options = {
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
Or
const https = require('https');
const fs = require('fs');
const options = {
pfx: fs.readFileSync('server.pfx')
};
https.createServer(options, (req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
server.close([callback])#
See http.close()
for details.
server.listen(handle[, callback])#
server.listen(path[, callback])#
server.listen(port[, host][, backlog][, callback])#
See http.listen()
for details.
https.get(options, callback)#
Like http.get()
but for HTTPS.
options
can be an object or a string. If options
is a string, it is
automatically parsed with url.parse()
.
Example:
const https = require('https');
https.get('https://encrypted.google.com/', (res) => {
console.log('statusCode: ', res.statusCode);
console.log('headers: ', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
}).on('error', (e) => {
console.error(e);
});
https.globalAgent#
Global instance of https.Agent
for all HTTPS client requests.
https.request(options, callback)#
Makes a request to a secure web server.
options
can be an object or a string. If options
is a string, it is
automatically parsed with url.parse()
.
All options from http.request()
are valid.
Example:
const https = require('https');
var options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET'
};
var req = https.request(options, (res) => {
console.log('statusCode: ', res.statusCode);
console.log('headers: ', res.headers);
res.on('data', (d) => {
process.stdout.write(d);
});
});
req.end();
req.on('error', (e) => {
console.error(e);
});
The options argument has the following options
host
: A domain name or IP address of the server to issue the request to. Defaults to'localhost'
.hostname
: Alias forhost
. To supporturl.parse()
hostname
is preferred overhost
.family
: IP address family to use when resolvinghost
andhostname
. Valid values are4
or6
. When unspecified, both IP v4 and v6 will be used.port
: Port of remote server. Defaults to 443.localAddress
: Local interface to bind for network connections.socketPath
: Unix Domain Socket (use one of host:port or socketPath).method
: A string specifying the HTTP request method. Defaults to'GET'
.path
: Request path. Defaults to'/'
. Should include query string if any. E.G.'/index.html?page=12'
. An exception is thrown when the request path contains illegal characters. Currently, only spaces are rejected but that may change in the future.headers
: An object containing request headers.auth
: Basic authentication i.e.'user:password'
to compute an Authorization header.agent
: ControlsAgent
behavior. When an Agent is used request will default toConnection: keep-alive
. Possible values:undefined
(default): useglobalAgent
for this host and port.Agent
object: explicitly use the passed inAgent
.false
: opts out of connection pooling with an Agent, defaults request toConnection: close
.
The following options from tls.connect()
can also be specified. However, a
globalAgent
silently ignores these.
pfx
: Certificate, Private key and CA certificates to use for SSL. Defaultnull
.key
: Private key to use for SSL. Defaultnull
.passphrase
: A string of passphrase for the private key or pfx. Defaultnull
.cert
: Public x509 certificate to use. Defaultnull
.ca
: A string,Buffer
or array of strings orBuffer
s of trusted certificates in PEM format. If this is omitted several well known "root" CAs will be used, like VeriSign. These are used to authorize connections.ciphers
: A string describing the ciphers to use or exclude. Consult https://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.rejectUnauthorized
: Iftrue
, the server certificate is verified against the list of supplied CAs. An'error'
event is emitted if verification fails. Verification happens at the connection level, before the HTTP request is sent. Defaulttrue
.secureProtocol
: The SSL method to use, e.g.SSLv3_method
to force SSL version 3. The possible values depend on your installation of OpenSSL and are defined in the constantSSL_METHODS
.servername
: Servername for SNI (Server Name Indication) TLS extension.
In order to specify these options, use a custom Agent
.
Example:
var options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
options.agent = new https.Agent(options);
var req = https.request(options, (res) => {
...
}
Alternatively, opt out of connection pooling by not using an Agent
.
Example:
var options = {
hostname: 'encrypted.google.com',
port: 443,
path: '/',
method: 'GET',
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem'),
agent: false
};
var req = https.request(options, (res) => {
...
}
Modules#
Stability: 3 - Locked
Node.js has a simple module loading system. In Node.js, files and modules are
in one-to-one correspondence. As an example, foo.js
loads the module
circle.js
in the same directory.
The contents of foo.js
:
const circle = require('./circle.js');
console.log( `The area of a circle of radius 4 is ${circle.area(4)}`);
The contents of circle.js
:
const PI = Math.PI;
exports.area = (r) => PI * r * r;
exports.circumference = (r) => 2 * PI * r;
The module circle.js
has exported the functions area()
and
circumference()
. To add functions and objects to the root of your module,
you can add them to the special exports
object.
Variables local to the module will be private, as though the module was wrapped
in a function. In this example the variable PI
is private to circle.js
.
If you want the root of your module's export to be a function (such as a
constructor) or if you want to export a complete object in one assignment
instead of building it one property at a time, assign it to module.exports
instead of exports
.
Below, bar.js
makes use of the square
module, which exports a constructor:
const square = require('./square.js');
var mySquare = square(2);
console.log(`The area of my square is ${mySquare.area()}`);
The square
module is defined in square.js
:
// assigning to exports will not modify module, must use module.exports
module.exports = (width) => {
return {
area: () => width * width
};
}
The module system is implemented in the require("module")
module.
Accessing the main module#
When a file is run directly from Node.js, require.main
is set to its
module
. That means that you can determine whether a file has been run
directly by testing
require.main === module
For a file foo.js
, this will be true
if run via node foo.js
, but
false
if run by require('./foo')
.
Because module
provides a filename
property (normally equivalent to
__filename
), the entry point of the current application can be obtained
by checking require.main.filename
.
Addenda: Package Manager Tips#
The semantics of Node.js's require()
function were designed to be general
enough to support a number of reasonable directory structures. Package manager
programs such as dpkg
, rpm
, and npm
will hopefully find it possible to
build native packages from Node.js modules without modification.
Below we give a suggested directory structure that could work:
Let's say that we wanted to have the folder at
/usr/lib/node/<some-package>/<some-version>
hold the contents of a
specific version of a package.
Packages can depend on one another. In order to install package foo
, you
may have to install a specific version of package bar
. The bar
package
may itself have dependencies, and in some cases, these dependencies may even
collide or form cycles.
Since Node.js looks up the realpath
of any modules it loads (that is,
resolves symlinks), and then looks for their dependencies in the node_modules
folders as described here, this
situation is very simple to resolve with the following architecture:
/usr/lib/node/foo/1.2.3/
- Contents of thefoo
package, version 1.2.3./usr/lib/node/bar/4.3.2/
- Contents of thebar
package thatfoo
depends on./usr/lib/node/foo/1.2.3/node_modules/bar
- Symbolic link to/usr/lib/node/bar/4.3.2/
./usr/lib/node/bar/4.3.2/node_modules/*
- Symbolic links to the packages thatbar
depends on.
Thus, even if a cycle is encountered, or if there are dependency conflicts, every module will be able to get a version of its dependency that it can use.
When the code in the foo
package does require('bar')
, it will get the
version that is symlinked into /usr/lib/node/foo/1.2.3/node_modules/bar
.
Then, when the code in the bar
package calls require('quux')
, it'll get
the version that is symlinked into
/usr/lib/node/bar/4.3.2/node_modules/quux
.
Furthermore, to make the module lookup process even more optimal, rather
than putting packages directly in /usr/lib/node
, we could put them in
/usr/lib/node_modules/<name>/<version>
. Then Node.js will not bother
looking for missing dependencies in /usr/node_modules
or /node_modules
.
In order to make modules available to the Node.js REPL, it might be useful to
also add the /usr/lib/node_modules
folder to the $NODE_PATH
environment
variable. Since the module lookups using node_modules
folders are all
relative, and based on the real path of the files making the calls to
require()
, the packages themselves can be anywhere.
All Together...#
To get the exact filename that will be loaded when require()
is called, use
the require.resolve()
function.
Putting together all of the above, here is the high-level algorithm in pseudocode of what require.resolve does:
require(X) from module at path Y
1. If X is a core module,
a. return the core module
b. STOP
2. If X begins with './' or '/' or '../'
a. LOAD_AS_FILE(Y + X)
b. LOAD_AS_DIRECTORY(Y + X)
3. LOAD_NODE_MODULES(X, dirname(Y))
4. THROW "not found"
LOAD_AS_FILE(X)
1. If X is a file, load X as JavaScript text. STOP
2. If X.js is a file, load X.js as JavaScript text. STOP
3. If X.json is a file, parse X.json to a JavaScript Object. STOP
4. If X.node is a file, load X.node as binary addon. STOP
LOAD_AS_DIRECTORY(X)
1. If X/package.json is a file,
a. Parse X/package.json, and look for "main" field.
b. let M = X + (json main field)
c. LOAD_AS_FILE(M)
2. If X/index.js is a file, load X/index.js as JavaScript text. STOP
3. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP
4. If X/index.node is a file, load X/index.node as binary addon. STOP
LOAD_NODE_MODULES(X, START)
1. let DIRS=NODE_MODULES_PATHS(START)
2. for each DIR in DIRS:
a. LOAD_AS_FILE(DIR/X)
b. LOAD_AS_DIRECTORY(DIR/X)
NODE_MODULES_PATHS(START)
1. let PARTS = path split(START)
2. let I = count of PARTS - 1
3. let DIRS = []
4. while I >= 0,
a. if PARTS[I] = "node_modules" CONTINUE
c. DIR = path join(PARTS[0 .. I] + "node_modules")
b. DIRS = DIRS + DIR
c. let I = I - 1
5. return DIRS
Caching#
Modules are cached after the first time they are loaded. This means
(among other things) that every call to require('foo')
will get
exactly the same object returned, if it would resolve to the same file.
Multiple calls to require('foo')
may not cause the module code to be
executed multiple times. This is an important feature. With it,
"partially done" objects can be returned, thus allowing transitive
dependencies to be loaded even when they would cause cycles.
If you want to have a module execute code multiple times, then export a function, and call that function.
Module Caching Caveats#
Modules are cached based on their resolved filename. Since modules may
resolve to a different filename based on the location of the calling
module (loading from node_modules
folders), it is not a guarantee
that require('foo')
will always return the exact same object, if it
would resolve to different files.
Additionally, on case-insensitive file systems or operating systems, different
resolved filenames can point to the same file, but the cache will still treat
them as different modules and will reload the file multiple times. For example,
require('./foo')
and require('./FOO')
return two different objects,
irrespective of whether or not ./foo
and ./FOO
are the same file.
Core Modules#
Node.js has several modules compiled into the binary. These modules are described in greater detail elsewhere in this documentation.
The core modules are defined within Node.js's source and are located in the
lib/
folder.
Core modules are always preferentially loaded if their identifier is
passed to require()
. For instance, require('http')
will always
return the built in HTTP module, even if there is a file by that name.
Cycles#
When there are circular require()
calls, a module might not have finished
executing when it is returned.
Consider this situation:
a.js
:
console.log('a starting');
exports.done = false;
const b = require('./b.js');
console.log('in a, b.done = %j', b.done);
exports.done = true;
console.log('a done');
b.js
:
console.log('b starting');
exports.done = false;
const a = require('./a.js');
console.log('in b, a.done = %j', a.done);
exports.done = true;
console.log('b done');
main.js
:
console.log('main starting');
const a = require('./a.js');
const b = require('./b.js');
console.log('in main, a.done=%j, b.done=%j', a.done, b.done);
When main.js
loads a.js
, then a.js
in turn loads b.js
. At that
point, b.js
tries to load a.js
. In order to prevent an infinite
loop, an unfinished copy of the a.js
exports object is returned to the
b.js
module. b.js
then finishes loading, and its exports
object is
provided to the a.js
module.
By the time main.js
has loaded both modules, they're both finished.
The output of this program would thus be:
$ node main.js
main starting
a starting
b starting
in b, a.done = false
b done
in a, b.done = true
a done
in main, a.done=true, b.done=true
If you have cyclic module dependencies in your program, make sure to plan accordingly.
File Modules#
If the exact filename is not found, then Node.js will attempt to load the
required filename with the added extensions: .js
, .json
, and finally
.node
.
.js
files are interpreted as JavaScript text files, and .json
files are
parsed as JSON text files. .node
files are interpreted as compiled addon
modules loaded with dlopen
.
A required module prefixed with '/'
is an absolute path to the file. For
example, require('/home/marco/foo.js')
will load the file at
/home/marco/foo.js
.
A required module prefixed with './'
is relative to the file calling
require()
. That is, circle.js
must be in the same directory as foo.js
for
require('./circle')
to find it.
Without a leading '/', './', or '../' to indicate a file, the module must
either be a core module or is loaded from a node_modules
folder.
If the given path does not exist, require()
will throw an Error
with its
code
property set to 'MODULE_NOT_FOUND'
.
Folders as Modules#
It is convenient to organize programs and libraries into self-contained
directories, and then provide a single entry point to that library.
There are three ways in which a folder may be passed to require()
as
an argument.
The first is to create a package.json
file in the root of the folder,
which specifies a main
module. An example package.json file might
look like this:
{ "name" : "some-library",
"main" : "./lib/some-library.js" }
If this was in a folder at ./some-library
, then
require('./some-library')
would attempt to load
./some-library/lib/some-library.js
.
This is the extent of Node.js's awareness of package.json files.
Note: If the file specified by the "main"
entry of package.json
is missing
and can not be resolved, Node.js will report the entire module as missing with
the default error:
Error: Cannot find module 'some-library'
If there is no package.json file present in the directory, then Node.js
will attempt to load an index.js
or index.node
file out of that
directory. For example, if there was no package.json file in the above
example, then require('./some-library')
would attempt to load:
./some-library/index.js
./some-library/index.node
Loading from node_modules
Folders#
If the module identifier passed to require()
is not a native module,
and does not begin with '/'
, '../'
, or './'
, then Node.js starts at the
parent directory of the current module, and adds /node_modules
, and
attempts to load the module from that location. Node will not append
node_modules
to a path already ending in node_modules
.
If it is not found there, then it moves to the parent directory, and so on, until the root of the file system is reached.
For example, if the file at '/home/ry/projects/foo.js'
called
require('bar.js')
, then Node.js would look in the following locations, in
this order:
/home/ry/projects/node_modules/bar.js
/home/ry/node_modules/bar.js
/home/node_modules/bar.js
/node_modules/bar.js
This allows programs to localize their dependencies, so that they do not clash.
You can require specific files or sub modules distributed with a module by
including a path suffix after the module name. For instance
require('example-module/path/to/file')
would resolve path/to/file
relative to where example-module
is located. The suffixed path follows the
same module resolution semantics.
Loading from the global folders#
If the NODE_PATH
environment variable is set to a colon-delimited list
of absolute paths, then Node.js will search those paths for modules if they
are not found elsewhere. (Note: On Windows, NODE_PATH
is delimited by
semicolons instead of colons.)
NODE_PATH
was originally created to support loading modules from
varying paths before the current module resolution algorithm was frozen.
NODE_PATH
is still supported, but is less necessary now that the Node.js
ecosystem has settled on a convention for locating dependent modules.
Sometimes deployments that rely on NODE_PATH
show surprising behavior
when people are unaware that NODE_PATH
must be set. Sometimes a
module's dependencies change, causing a different version (or even a
different module) to be loaded as the NODE_PATH
is searched.
Additionally, Node.js will search in the following locations:
- 1:
$HOME/.node_modules
- 2:
$HOME/.node_libraries
- 3:
$PREFIX/lib/node
Where $HOME
is the user's home directory, and $PREFIX
is Node.js's
configured node_prefix
.
These are mostly for historic reasons. You are highly encouraged
to place your dependencies locally in node_modules
folders. They
will be loaded faster, and more reliably.
The module
Object#
In each module, the module
free variable is a reference to the object
representing the current module. For convenience, module.exports
is
also accessible via the exports
module-global. module
isn't actually
a global but rather local to each module.
module.children#
The module objects required by this one.
module.exports#
The module.exports
object is created by the Module system. Sometimes this is
not acceptable; many want their module to be an instance of some class. To do
this, assign the desired export object to module.exports
. Note that assigning
the desired object to exports
will simply rebind the local exports
variable,
which is probably not what you want to do.
For example suppose we were making a module called a.js
const EventEmitter = require('events');
module.exports = new EventEmitter();
// Do some work, and after some time emit
// the 'ready' event from the module itself.
setTimeout(() => {
module.exports.emit('ready');
}, 1000);
Then in another file we could do
const a = require('./a');
a.on('ready', () => {
console.log('module a is ready');
});
Note that assignment to module.exports
must be done immediately. It cannot be
done in any callbacks. This does not work:
x.js:
setTimeout(() => {
module.exports = { a: 'hello' };
}, 0);
y.js:
const x = require('./x');
console.log(x.a);
exports alias#
The exports
variable that is available within a module starts as a reference
to module.exports
. As with any variable, if you assign a new value to it, it
is no longer bound to the previous value.
To illustrate the behavior, imagine this hypothetical implementation of
require()
:
function require(...) {
// ...
((module, exports) => {
// Your module code here
exports = some_func; // re-assigns exports, exports is no longer
// a shortcut, and nothing is exported.
module.exports = some_func; // makes your module export 0
})(module, module.exports);
return module;
}
As a guideline, if the relationship between exports
and module.exports
seems like magic to you, ignore exports
and only use module.exports
.
module.filename#
The fully resolved filename to the module.
module.id#
The identifier for the module. Typically this is the fully resolved filename.
module.loaded#
Whether or not the module is done loading, or is in the process of loading.
module.parent#
- <Object> Module object
The module that first required this one.
module.require(id)#
The module.require
method provides a way to load a module as if
require()
was called from the original module.
Note that in order to do this, you must get a reference to the module
object. Since require()
returns the module.exports
, and the module
is
typically only available within a specific module's code, it must be
explicitly exported in order to be used.
net#
Stability: 2 - Stable
The net
module provides you with an asynchronous network wrapper. It contains
functions for creating both servers and clients (called streams). You can include
this module with require('net');
.
Class: net.Server#
This class is used to create a TCP or local server.
net.Server
is an EventEmitter
with the following events:
Event: 'close'#
Emitted when the server closes. Note that if connections exist, this event is not emitted until all connections are ended.
Event: 'connection'#
- <net.Socket> The connection object
Emitted when a new connection is made. socket
is an instance of
net.Socket
.
Event: 'error'#
Emitted when an error occurs. The 'close'
event will be called directly
following this event. See example in discussion of server.listen
.
Event: 'listening'#
Emitted when the server has been bound after calling server.listen
.
server.address()#
Returns the bound address, the address family name and port of the server
as reported by the operating system.
Useful to find which port was assigned when giving getting an OS-assigned address.
Returns an object with three properties, e.g.
{ port: 12346, family: 'IPv4', address: '127.0.0.1' }
Example:
var server = net.createServer((socket) => {
socket.end('goodbye\n');
}).on('error', (err) => {
// handle errors here
throw err;
});
// grab a random port.
server.listen(() => {
address = server.address();
console.log('opened server on %j', address);
});
Don't call server.address()
until the 'listening'
event has been emitted.
server.close([callback])#
Stops the server from accepting new connections and keeps existing
connections. This function is asynchronous, the server is finally
closed when all connections are ended and the server emits a 'close'
event.
The optional callback
will be called once the 'close'
event occurs. Unlike
that event, it will be called with an Error as its only argument if the server
was not open when it was closed.
server.connections#
Stability: 0 - Deprecated: Use server.getConnections()
instead.
The number of concurrent connections on the server.
This becomes null
when sending a socket to a child with
child_process.fork()
. To poll forks and get current number of active
connections use asynchronous server.getConnections
instead.
server.getConnections(callback)#
Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks.
Callback should take two arguments err
and count
.
server.listen(handle[, backlog][, callback])#
handle
<Object>backlog
<Number>callback
<Function>
The handle
object can be set to either a server or socket (anything
with an underlying _handle
member), or a {fd: <n>}
object.
This will cause the server to accept connections on the specified handle, but it is presumed that the file descriptor or handle has already been bound to a port or domain socket.
Listening on a file descriptor is not supported on Windows.
This function is asynchronous. When the server has been bound,
'listening'
event will be emitted.
The last parameter callback
will be added as a listener for the
'listening'
event.
The parameter backlog
behaves the same as in
server.listen(port[, hostname][, backlog][, callback])
.
server.listen(options[, callback])#
The port
, host
, and backlog
properties of options
, as well as the
optional callback function, behave as they do on a call to
server.listen(port[, hostname][, backlog][, callback])
.
Alternatively, the path
option can be used to specify a UNIX socket.
If exclusive
is false
(default), then cluster workers will use the same
underlying handle, allowing connection handling duties to be shared. When
exclusive
is true
, the handle is not shared, and attempted port sharing
results in an error. An example which listens on an exclusive port is
shown below.
server.listen({
host: 'localhost',
port: 80,
exclusive: true
});
server.listen(path[, backlog][, callback])#
path
<String>backlog
<Number>callback
<Function>
Start a local socket server listening for connections on the given path
.
This function is asynchronous. When the server has been bound,
'listening'
event will be emitted. The last parameter callback
will be added as a listener for the 'listening'
event.
On UNIX, the local domain is usually known as the UNIX domain. The path is a filesystem path name. It is subject to the same naming conventions and permissions checks as would be done on file creation, will be visible in the filesystem, and will persist until unlinked.
On Windows, the local domain is implemented using a named pipe. The path must
refer to an entry in \\?\pipe\
or \\.\pipe\
. Any characters are permitted,
but the latter may do some processing of pipe names, such as resolving ..
sequences. Despite appearances, the pipe name space is flat. Pipes will not
persist, they are removed when the last reference to them is closed. Do not
forget JavaScript string escaping requires paths to be specified with
double-backslashes, such as:
net.createServer().listen(
path.join('\\\\?\\pipe', process.cwd(), 'myctl'))
The parameter backlog
behaves the same as in
server.listen(port[, hostname][, backlog][, callback])
.
server.listen(port[, hostname][, backlog][, callback])#
Begin accepting connections on the specified port
and hostname
. If the
hostname
is omitted, the server will accept connections on any IPv6 address
(::
) when IPv6 is available, or any IPv4 address (0.0.0.0
) otherwise. A
port value of zero will assign a random port.
Backlog is the maximum length of the queue of pending connections.
The actual length will be determined by your OS through sysctl settings such as
tcp_max_syn_backlog
and somaxconn
on linux. The default value of this
parameter is 511 (not 512).
This function is asynchronous. When the server has been bound,
'listening'
event will be emitted. The last parameter callback
will be added as a listener for the 'listening'
event.
One issue some users run into is getting EADDRINUSE
errors. This means that
another server is already running on the requested port. One way of handling this
would be to wait a second and then try again. This can be done with
server.on('error', (e) => {
if (e.code == 'EADDRINUSE') {
console.log('Address in use, retrying...');
setTimeout(() => {
server.close();
server.listen(PORT, HOST);
}, 1000);
}
});
(Note: All sockets in Node.js set SO_REUSEADDR
already)
server.listening#
A Boolean indicating whether or not the server is listening for connections.
server.maxConnections#
Set this property to reject connections when the server's connection count gets high.
It is not recommended to use this option once a socket has been sent to a child
with child_process.fork()
.
server.ref()#
Opposite of unref
, calling ref
on a previously unref
d server will not
let the program exit if it's the only server left (the default behavior). If
the server is ref
d calling ref
again will have no effect.
Returns server
.
server.unref()#
Calling unref
on a server will allow the program to exit if this is the only
active server in the event system. If the server is already unref
d calling
unref
again will have no effect.
Returns server
.
Class: net.Socket#
This object is an abstraction of a TCP or local socket. net.Socket
instances implement a duplex Stream interface. They can be created by the
user and used as a client (with connect()
) or they can be created by Node.js
and passed to the user through the 'connection'
event of a server.
new net.Socket(options)#
Construct a new socket object.
options
is an object with the following defaults:
{
fd: null,
allowHalfOpen: false,
readable: false,
writable: false
}
fd
allows you to specify the existing file descriptor of socket.
Set readable
and/or writable
to true
to allow reads and/or writes on this
socket (NOTE: Works only when fd
is passed).
About allowHalfOpen
, refer to createServer()
and 'end'
event.
net.Socket
instances are EventEmitter
with the following events:
Event: 'close'#
had_error
<Boolean>true
if the socket had a transmission error.
Emitted once the socket is fully closed. The argument had_error
is a boolean
which says if the socket was closed due to a transmission error.
Event: 'connect'#
Emitted when a socket connection is successfully established.
See connect()
.
Event: 'data'#
Emitted when data is received. The argument data
will be a Buffer
or
String
. Encoding of data is set by socket.setEncoding()
.
(See the Readable Stream section for more information.)
Note that the data will be lost if there is no listener when a Socket
emits a 'data'
event.
Event: 'drain'#
Emitted when the write buffer becomes empty. Can be used to throttle uploads.
See also: the return values of socket.write()
Event: 'end'#
Emitted when the other end of the socket sends a FIN packet.
By default (allowHalfOpen == false
) the socket will destroy its file
descriptor once it has written out its pending write queue. However, by
setting allowHalfOpen == true
the socket will not automatically end()
its side allowing the user to write arbitrary amounts of data, with the
caveat that the user is required to end()
their side now.
Event: 'error'#
Emitted when an error occurs. The 'close'
event will be called directly
following this event.
Event: 'lookup'#
Emitted after resolving the hostname but before connecting. Not applicable to UNIX sockets.
err
<Error> | <Null> The error object. Seedns.lookup()
.address
<String> The IP address.family
<String> | <Null> The address type. Seedns.lookup()
.host
<String> The hostname.
Event: 'timeout'#
Emitted if the socket times out from inactivity. This is only to notify that the socket has been idle. The user must manually close the connection.
See also: socket.setTimeout()
socket.address()#
Returns the bound address, the address family name and port of the
socket as reported by the operating system. Returns an object with
three properties, e.g.
{ port: 12346, family: 'IPv4', address: '127.0.0.1' }
socket.bufferSize#
net.Socket
has the property that socket.write()
always works. This is to
help users get up and running quickly. The computer cannot always keep up
with the amount of data that is written to a socket - the network connection
simply might be too slow. Node.js will internally queue up the data written to a
socket and send it out over the wire when it is possible. (Internally it is
polling on the socket's file descriptor for being writable).
The consequence of this internal buffering is that memory may grow. This property shows the number of characters currently buffered to be written. (Number of characters is approximately equal to the number of bytes to be written, but the buffer may contain strings, and the strings are lazily encoded, so the exact number of bytes is not known.)
Users who experience large or growing bufferSize
should attempt to
"throttle" the data flows in their program with pause()
and resume()
.
socket.bytesRead#
The amount of received bytes.
socket.bytesWritten#
The amount of bytes sent.
socket.connect(options[, connectListener])#
Opens the connection for a given socket.
For TCP sockets, options
argument should be an object which specifies:
port
: Port the client should connect to (Required).host
: Host the client should connect to. Defaults to'localhost'
.localAddress
: Local interface to bind to for network connections.localPort
: Local port to bind to for network connections.family
: Version of IP stack. Defaults to4
.hints
:dns.lookup()
hints. Defaults to0
.lookup
: Custom lookup function. Defaults todns.lookup
.
For local domain sockets, options
argument should be an object which
specifies:
path
: Path the client should connect to (Required).
Normally this method is not needed, as net.createConnection
opens the
socket. Use this only if you are implementing a custom Socket.
This function is asynchronous. When the 'connect'
event is emitted the
socket is established. If there is a problem connecting, the 'connect'
event
will not be emitted, the 'error'
event will be emitted with the exception.
The connectListener
parameter will be added as a listener for the
'connect'
event.
socket.connect(path[, connectListener])#
socket.connect(port[, host][, connectListener])#
As socket.connect(options\[, connectListener\])
,
with options either as either {port: port, host: host}
or {path: path}
.
socket.destroy()#
Ensures that no more I/O activity happens on this socket. Only necessary in case of errors (parse error or so).
socket.end([data][, encoding])#
Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.
If data
is specified, it is equivalent to calling
socket.write(data, encoding)
followed by socket.end()
.
socket.localAddress#
The string representation of the local IP address the remote client is
connecting on. For example, if you are listening on '0.0.0.0'
and the
client connects on '192.168.1.1'
, the value would be '192.168.1.1'
.
socket.localPort#
The numeric representation of the local port. For example,
80
or 21
.
socket.pause()#
Pauses the reading of data. That is, 'data'
events will not be emitted.
Useful to throttle back an upload.
socket.ref()#
Opposite of unref
, calling ref
on a previously unref
d socket will not
let the program exit if it's the only socket left (the default behavior). If
the socket is ref
d calling ref
again will have no effect.
Returns socket
.
socket.remoteAddress#
The string representation of the remote IP address. For example,
'74.125.127.100'
or '2001:4860:a005::68'
. Value may be undefined
if
the socket is destroyed (for example, if the client disconnected).
socket.remoteFamily#
The string representation of the remote IP family. 'IPv4'
or 'IPv6'
.
socket.remotePort#
The numeric representation of the remote port. For example,
80
or 21
.
socket.resume()#
Resumes reading after a call to pause()
.
socket.setEncoding([encoding])#
Set the encoding for the socket as a Readable Stream. See
stream.setEncoding()
for more information.
socket.setKeepAlive([enable][, initialDelay])#
Enable/disable keep-alive functionality, and optionally set the initial
delay before the first keepalive probe is sent on an idle socket.
enable
defaults to false
.
Set initialDelay
(in milliseconds) to set the delay between the last
data packet received and the first keepalive probe. Setting 0 for
initialDelay will leave the value unchanged from the default
(or previous) setting. Defaults to 0
.
Returns socket
.
socket.setNoDelay([noDelay])#
Disables the Nagle algorithm. By default TCP connections use the Nagle
algorithm, they buffer data before sending it off. Setting true
for
noDelay
will immediately fire off data each time socket.write()
is called.
noDelay
defaults to true
.
Returns socket
.
socket.setTimeout(timeout[, callback])#
Sets the socket to timeout after timeout
milliseconds of inactivity on
the socket. By default net.Socket
do not have a timeout.
When an idle timeout is triggered the socket will receive a 'timeout'
event but the connection will not be severed. The user must manually end()
or destroy()
the socket.
If timeout
is 0, then the existing idle timeout is disabled.
The optional callback
parameter will be added as a one time listener for the
'timeout'
event.
Returns socket
.
socket.unref()#
Calling unref
on a socket will allow the program to exit if this is the only
active socket in the event system. If the socket is already unref
d calling
unref
again will have no effect.
Returns socket
.
socket.write(data[, encoding][, callback])#
Sends data on the socket. The second parameter specifies the encoding in the case of a string--it defaults to UTF8 encoding.
Returns true
if the entire data was flushed successfully to the kernel
buffer. Returns false
if all or part of the data was queued in user memory.
'drain'
will be emitted when the buffer is again free.
The optional callback
parameter will be executed when the data is finally
written out - this may not be immediately.
net.connect(options[, connectListener])#
A factory function, which returns a new net.Socket
and automatically
connects with the supplied options
.
The options are passed to both the net.Socket
constructor and the
socket.connect
method.
The connectListener
parameter will be added as a listener for the
'connect'
event once.
Here is an example of a client of the previously described echo server:
const net = require('net');
const client = net.connect({port: 8124}, () => {
// 'connect' listener
console.log('connected to server!');
client.write('world!\r\n');
});
client.on('data', (data) => {
console.log(data.toString());
client.end();
});
client.on('end', () => {
console.log('disconnected from server');
});
To connect on the socket /tmp/echo.sock
the second line would just be
changed to
const client = net.connect({path: '/tmp/echo.sock'});
net.connect(path[, connectListener])#
A factory function, which returns a new unix net.Socket
and automatically
connects to the supplied path
.
The connectListener
parameter will be added as a listener for the
'connect'
event once.
net.connect(port[, host][, connectListener])#
A factory function, which returns a new net.Socket
and automatically
connects to the supplied port
and host
.
If host
is omitted, 'localhost'
will be assumed.
The connectListener
parameter will be added as a listener for the
'connect'
event once.
net.createConnection(options[, connectListener])#
A factory function, which returns a new net.Socket
and automatically
connects with the supplied options
.
The options are passed to both the net.Socket
constructor and the
socket.connect
method.
The connectListener
parameter will be added as a listener for the
'connect'
event once.
Here is an example of a client of the previously described echo server:
const net = require('net');
const client = net.createConnection({port: 8124}, () => {
//'connect' listener
console.log('connected to server!');
client.write('world!\r\n');
});
client.on('data', (data) => {
console.log(data.toString());
client.end();
});
client.on('end', () => {
console.log('disconnected from server');
});
To connect on the socket /tmp/echo.sock
the second line would just be
changed to
const client = net.connect({path: '/tmp/echo.sock'});
net.createConnection(path[, connectListener])#
A factory function, which returns a new unix net.Socket
and automatically
connects to the supplied path
.
The connectListener
parameter will be added as a listener for the
'connect'
event once.
net.createConnection(port[, host][, connectListener])#
A factory function, which returns a new net.Socket
and automatically
connects to the supplied port
and host
.
If host
is omitted, 'localhost'
will be assumed.
The connectListener
parameter will be added as a listener for the
'connect'
event once.
net.createServer([options][, connectionListener])#
Creates a new server. The connectionListener
argument is
automatically set as a listener for the 'connection'
event.
options
is an object with the following defaults:
{
allowHalfOpen: false,
pauseOnConnect: false
}
If allowHalfOpen
is true
, then the socket won't automatically send a FIN
packet when the other end of the socket sends a FIN packet. The socket becomes
non-readable, but still writable. You should call the end()
method explicitly.
See 'end'
event for more information.
If pauseOnConnect
is true
, then the socket associated with each incoming
connection will be paused, and no data will be read from its handle. This allows
connections to be passed between processes without any data being read by the
original process. To begin reading data from a paused socket, call resume()
.
Here is an example of an echo server which listens for connections on port 8124:
const net = require('net');
const server = net.createServer((c) => {
// 'connection' listener
console.log('client connected');
c.on('end', () => {
console.log('client disconnected');
});
c.write('hello\r\n');
c.pipe(c);
});
server.on('error', (err) => {
throw err;
});
server.listen(8124, () => {
console.log('server bound');
});
Test this by using telnet
:
telnet localhost 8124
To listen on the socket /tmp/echo.sock
the third line from the last would
just be changed to
server.listen('/tmp/echo.sock', () => {
console.log('server bound');
});
Use nc
to connect to a UNIX domain socket server:
nc -U /tmp/echo.sock
net.isIP(input)#
Tests if input is an IP address. Returns 0 for invalid strings, returns 4 for IP version 4 addresses, and returns 6 for IP version 6 addresses.
net.isIPv4(input)#
Returns true if input is a version 4 IP address, otherwise returns false.
net.isIPv6(input)#
Returns true if input is a version 6 IP address, otherwise returns false.
OS#
Stability: 2 - Stable
Provides a few basic operating-system related utility functions.
Use require('os')
to access this module.
os.EOL#
A constant defining the appropriate End-of-line marker for the operating system.
os.arch()#
Returns the operating system CPU architecture. Possible values are 'x64'
,
'arm'
and 'ia32'
. Returns the value of process.arch
.
os.cpus()#
Returns an array of objects containing information about each CPU/core installed: model, speed (in MHz), and times (an object containing the number of milliseconds the CPU/core spent in: user, nice, sys, idle, and irq).
Example inspection of os.cpus:
[ { model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 252020,
nice: 0,
sys: 30340,
idle: 1070356870,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 306960,
nice: 0,
sys: 26980,
idle: 1071569080,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 248450,
nice: 0,
sys: 21750,
idle: 1070919370,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 256880,
nice: 0,
sys: 19430,
idle: 1070905480,
irq: 20 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 511580,
nice: 20,
sys: 40900,
idle: 1070842510,
irq: 0 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 291660,
nice: 0,
sys: 34360,
idle: 1070888000,
irq: 10 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 308260,
nice: 0,
sys: 55410,
idle: 1071129970,
irq: 880 } },
{ model: 'Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz',
speed: 2926,
times:
{ user: 266450,
nice: 1480,
sys: 34920,
idle: 1072572010,
irq: 30 } } ]
Note that since nice
values are UNIX centric in Windows the nice
values of
all processors are always 0.
os.endianness()#
Returns the endianness of the CPU. Possible values are 'BE'
for big endian
or 'LE'
for little endian.
os.freemem()#
Returns the amount of free system memory in bytes.
os.homedir()#
Returns the home directory of the current user.
os.hostname()#
Returns the hostname of the operating system.
os.loadavg()#
Returns an array containing the 1, 5, and 15 minute load averages.
The load average is a measure of system activity, calculated by the operating system and expressed as a fractional number. As a rule of thumb, the load average should ideally be less than the number of logical CPUs in the system.
The load average is a very UNIX-y concept; there is no real equivalent on
Windows platforms. That is why this function always returns [0, 0, 0]
on
Windows.
os.networkInterfaces()#
Get a list of network interfaces:
{ lo:
[ { address: '127.0.0.1',
netmask: '255.0.0.0',
family: 'IPv4',
mac: '00:00:00:00:00:00',
internal: true },
{ address: '::1',
netmask: 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff',
family: 'IPv6',
mac: '00:00:00:00:00:00',
internal: true } ],
eth0:
[ { address: '192.168.1.108',
netmask: '255.255.255.0',
family: 'IPv4',
mac: '01:02:03:0a:0b:0c',
internal: false },
{ address: 'fe80::a00:27ff:fe4e:66a1',
netmask: 'ffff:ffff:ffff:ffff::',
family: 'IPv6',
mac: '01:02:03:0a:0b:0c',
internal: false } ] }
Note that due to the underlying implementation this will only return network interfaces that have been assigned an address.
os.platform()#
Returns the operating system platform. Possible values are 'darwin'
,
'freebsd'
, 'linux'
, 'sunos'
or 'win32'
. Returns the value of
process.platform
.
os.release()#
Returns the operating system release.
os.tmpdir()#
Returns the operating system's default directory for temporary files.
os.totalmem()#
Returns the total amount of system memory in bytes.
os.type()#
Returns the operating system name. For example 'Linux'
on Linux, 'Darwin'
on OS X and 'Windows_NT'
on Windows.
os.uptime()#
Returns the system uptime in seconds.
os.userInfo(options)#
Returns a subset of the password file entry for the current effective user. The
returned object includes the username
, uid
, gid
, shell
, and homedir
.
On Windows, the uid
and gid
fields are -1
, and shell
is null
.
The value of homedir
returned by userInfo()
comes directly from the
operating system. This differs from the result of os.homedir()
, which queries
several environment variables for the home directory before falling back to the
operating system response.
Path#
Stability: 2 - Stable
This module contains utilities for handling and transforming file paths. The file system is not consulted to check whether paths are valid.
Use require('path')
to use this module. The following methods are provided:
path.basename(path[, ext])#
Return the last portion of a path, similar to the Unix basename
command.
path
must be a string. ext
, if given, must also be a string.
Examples:
path.basename('/foo/bar/baz/asdf/quux.html')
// returns 'quux.html'
path.basename('/foo/bar/baz/asdf/quux.html', '.html')
// returns 'quux'
path.delimiter#
The platform-specific path delimiter, ;
or ':'
.
An example on *nix:
console.log(process.env.PATH)
// '/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin'
process.env.PATH.split(path.delimiter)
// returns ['/usr/bin', '/bin', '/usr/sbin', '/sbin', '/usr/local/bin']
An example on Windows:
console.log(process.env.PATH)
// 'C:\Windows\system32;C:\Windows;C:\Program Files\node\'
process.env.PATH.split(path.delimiter)
// returns ['C:\\Windows\\system32', 'C:\\Windows', 'C:\\Program Files\\node\\']
path.dirname(path)#
Return the directory name of a path, similar to the Unix dirname
command.
path
must be a string.
Example:
path.dirname('/foo/bar/baz/asdf/quux')
// returns '/foo/bar/baz/asdf'
path.extname(path)#
Return the extension of the path, from the last '.' to end of string
in the last portion of the path. If there is no '.' in the last portion
of the path or the first character of it is '.', then it returns
an empty string. path
must be a string.
Examples:
path.extname('index.html')
// returns '.html'
path.extname('index.coffee.md')
// returns '.md'
path.extname('index.')
// returns '.'
path.extname('index')
// returns ''
path.extname('.index')
// returns ''
path.format(pathObject)#
Returns a path string from an object. This is the opposite of path.parse
.
If pathObject
has dir
and base
properties, the returned string will
be a concatenation of the dir
property, the platform-dependent path separator,
and the base
property.
If the dir
property is not supplied, the root
property will be used as the
dir
property. However, it will be assumed that the root
property already
ends with the platform-dependent path separator. In this case, the returned
string will be the concatenation of the root
property and the base
property.
If both the dir
and the root
properties are not supplied, then the returned
string will be the contents of the base
property.
If the base
property is not supplied, a concatenation of the name
property
and the ext
property will be used as the base
property.
Examples:
Some Posix system examples:
// If `dir` and `base` are provided, `dir` + platform separator + `base`
// will be returned.
path.format({
dir: '/home/user/dir',
base: 'file.txt'
});
// returns '/home/user/dir/file.txt'
// `root` will be used if `dir` is not specified.
// `name` + `ext` will be used if `base` is not specified.
// If only `root` is provided or `dir` is equal to `root` then the
// platform separator will not be included.
path.format({
root: '/',
base: 'file.txt'
});
// returns '/file.txt'
path.format({
dir: '/',
root: '/',
name: 'file',
ext: '.txt'
});
// returns '/file.txt'
// `base` will be returned if `dir` or `root` are not provided.
path.format({
base: 'file.txt'
});
// returns 'file.txt'
An example on Windows:
path.format({
root : "C:\\",
dir : "C:\\path\\dir",
base : "file.txt",
ext : ".txt",
name : "file"
})
// returns 'C:\\path\\dir\\file.txt'
path.isAbsolute(path)#
Determines whether path
is an absolute path. An absolute path will always
resolve to the same location, regardless of the working directory. path
must
be a string.
Examples on *nix:
path.isAbsolute('/foo/bar') // true
path.isAbsolute('/baz/..') // true
path.isAbsolute('qux/') // false
path.isAbsolute('.') // false
Examples on Windows:
path.isAbsolute('//server') // true
path.isAbsolute('C:/foo/..') // true
path.isAbsolute('bar\\baz') // false
path.isAbsolute('.') // false
Note: If the path string passed as parameter is a zero-length string, unlike
other path module functions, it will be used as-is and false
will be
returned.
path.join([path1][, path2][, ...])#
Join all arguments together and normalize the resulting path.
All arguments must be strings. In v0.8, non-string arguments were silently ignored. In v0.10 and up, an exception is thrown.
Examples:
path.join('/foo', 'bar', 'baz/asdf', 'quux', '..')
// returns '/foo/bar/baz/asdf'
path.join('foo', {}, 'bar')
// throws exception
TypeError: Arguments to path.join must be strings
Note: If the arguments to join
have zero-length strings, unlike other path
module functions, they will be ignored. If the joined path string is a
zero-length string then '.'
will be returned, which represents the
current working directory.
path.normalize(path)#
Normalize a path, taking care of '..'
and '.'
parts. path
must be a
string.
When multiple slashes are found, they're replaced by a single one; when the path contains a trailing slash, it is preserved. On Windows backslashes are used.
Example:
path.normalize('/foo/bar//baz/asdf/quux/..')
// returns '/foo/bar/baz/asdf'
Note: If the path string passed as argument is a zero-length string then '.'
will be returned, which represents the current working directory.
path.parse(path)#
Returns an object from a path. path
must be a string.
An example on *nix:
path.parse('/home/user/dir/file.txt')
// returns
// {
// root : "/",
// dir : "/home/user/dir",
// base : "file.txt",
// ext : ".txt",
// name : "file"
// }
An example on Windows:
path.parse('C:\\path\\dir\\index.html')
// returns
// {
// root : "C:\\",
// dir : "C:\\path\\dir",
// base : "index.html",
// ext : ".html",
// name : "index"
// }
path.posix#
Provide access to aforementioned path
methods but always interact in a posix
compatible way.
path.relative(from, to)#
Solve the relative path from from
to to
. from
and to
must be strings.
At times we have two absolute paths, and we need to derive the relative
path from one to the other. This is actually the reverse transform of
path.resolve
, which means we see that:
path.resolve(from, path.relative(from, to)) == path.resolve(to)
Examples:
path.relative('C:\\orandea\\test\\aaa', 'C:\\orandea\\impl\\bbb')
// returns '..\\..\\impl\\bbb'
path.relative('/data/orandea/test/aaa', '/data/orandea/impl/bbb')
// returns '../../impl/bbb'
Note: If the arguments to relative
have zero-length strings then the current
working directory will be used instead of the zero-length strings. If
both the paths are the same then a zero-length string will be returned.
path.resolve([from ...], to)#
Resolves to
to an absolute path. All arguments must be strings.
If to
isn't already absolute from
arguments are prepended in right to left
order, until an absolute path is found. If after using all from
paths still
no absolute path is found, the current working directory is used as well. The
resulting path is normalized, and trailing slashes are removed unless the path
gets resolved to the root directory. Empty string from
arguments are
ignored.
Another way to think of it is as a sequence of cd
commands in a shell.
path.resolve('foo/bar', '/tmp/file/', '..', 'a/../subfile')
Is similar to:
cd foo/bar
cd /tmp/file/
cd ..
cd a/../subfile
pwd
The difference is that the different paths don't need to exist and may also be files.
Examples:
path.resolve('/foo/bar', './baz')
// returns '/foo/bar/baz'
path.resolve('/foo/bar', '/tmp/file/')
// returns '/tmp/file'
path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif')
// if currently in /home/myself/node, it returns
// '/home/myself/node/wwwroot/static_files/gif/image.gif'
path.sep#
The platform-specific file separator. '\\'
or '/'
.
An example on *nix:
'foo/bar/baz'.split(path.sep)
// returns ['foo', 'bar', 'baz']
An example on Windows:
'foo\\bar\\baz'.split(path.sep)
// returns ['foo', 'bar', 'baz']
path.win32#
Provide access to aforementioned path
methods but always interact in a win32
compatible way.
process#
The process
object is a global object and can be accessed from anywhere.
It is an instance of EventEmitter
.
Event: 'beforeExit'#
This event is emitted when Node.js empties its event loop and has nothing else
to schedule. Normally, Node.js exits when there is no work scheduled, but a
listener for 'beforeExit'
can make asynchronous calls, and cause Node.js to
continue.
'beforeExit'
is not emitted for conditions causing explicit termination, such
as process.exit()
or uncaught exceptions, and should not be used as an
alternative to the 'exit'
event unless the intention is to schedule more work.
Event: 'exit'#
Emitted when the process is about to exit. There is no way to prevent the
exiting of the event loop at this point, and once all 'exit'
listeners have
finished running the process will exit. Therefore you must only perform
synchronous operations in this handler. This is a good hook to perform
checks on the module's state (like for unit tests). The callback takes one
argument, the code the process is exiting with.
This event is only emitted when Node.js exits explicitly by process.exit() or implicitly by the event loop draining.
Example of listening for 'exit'
:
process.on('exit', (code) => {
// do *NOT* do this
setTimeout(() => {
console.log('This will not run');
}, 0);
console.log('About to exit with code:', code);
});
Event: 'message'#
message
<Object> a parsed JSON object or primitive valuesendHandle
<Handle object> anet.Socket
ornet.Server
object, or undefined.
Messages sent by ChildProcess.send()
are obtained using the 'message'
event on the child's process object.
Event: 'rejectionHandled'#
Emitted whenever a Promise was rejected and an error handler was attached to it
(for example with .catch()
) later than after an event loop turn. This event
is emitted with the following arguments:
p
the promise that was previously emitted in an'unhandledRejection'
event, but which has now gained a rejection handler.
There is no notion of a top level for a promise chain at which rejections can
always be handled. Being inherently asynchronous in nature, a promise rejection
can be handled at a future point in time — possibly much later than the
event loop turn it takes for the 'unhandledRejection'
event to be emitted.
Another way of stating this is that, unlike in synchronous code where there is
an ever-growing list of unhandled exceptions, with promises there is a
growing-and-shrinking list of unhandled rejections. In synchronous code, the
'uncaughtException'
event tells you when the list of unhandled exceptions
grows. And in asynchronous code, the 'unhandledRejection'
event tells you
when the list of unhandled rejections grows, while the 'rejectionHandled'
event tells you when the list of unhandled rejections shrinks.
For example using the rejection detection hooks in order to keep a map of all the rejected promise reasons at a given time:
const unhandledRejections = new Map();
process.on('unhandledRejection', (reason, p) => {
unhandledRejections.set(p, reason);
});
process.on('rejectionHandled', (p) => {
unhandledRejections.delete(p);
});
This map will grow and shrink over time, reflecting rejections that start unhandled and then become handled. You could record the errors in some error log, either periodically (probably best for long-running programs, allowing you to clear the map, which in the case of a very buggy program could grow indefinitely) or upon process exit (more convenient for scripts).
Event: 'uncaughtException'#
The 'uncaughtException'
event is emitted when an exception bubbles all the
way back to the event loop. By default, Node.js handles such exceptions by
printing the stack trace to stderr and exiting. Adding a handler for the
'uncaughtException'
event overrides this default behavior.
For example:
process.on('uncaughtException', (err) => {
console.log(`Caught exception: ${err}`);
});
setTimeout(() => {
console.log('This will still run.');
}, 500);
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');
Warning: Using 'uncaughtException'
correctly#
Note that 'uncaughtException'
is a crude mechanism for exception handling
intended to be used only as a last resort. The event should not be used as
an equivalent to On Error Resume Next
. Unhandled exceptions inherently mean
that an application is in an undefined state. Attempting to resume application
code without properly recovering from the exception can cause additional
unforeseen and unpredictable issues.
Exceptions thrown from within the event handler will not be caught. Instead the process will exit with a non zero exit code and the stack trace will be printed. This is to avoid infinite recursion.
Attempting to resume normally after an uncaught exception can be similar to pulling out of the power cord when upgrading a computer -- nine out of ten times nothing happens - but the 10th time, the system becomes corrupted.
The correct use of 'uncaughtException'
is to perform synchronous cleanup
of allocated resources (e.g. file descriptors, handles, etc) before shutting
down the process. It is not safe to resume normal operation after
'uncaughtException'
.
Event: 'unhandledRejection'#
Emitted whenever a Promise
is rejected and no error handler is attached to
the promise within a turn of the event loop. When programming with promises
exceptions are encapsulated as rejected promises. Such promises can be caught
and handled using promise.catch(...)
and rejections are propagated through
a promise chain. This event is useful for detecting and keeping track of
promises that were rejected whose rejections were not handled yet. This event
is emitted with the following arguments:
reason
the object with which the promise was rejected (usually anError
instance).p
the promise that was rejected.
Here is an example that logs every unhandled rejection to the console
process.on('unhandledRejection', (reason, p) => {
console.log("Unhandled Rejection at: Promise ", p, " reason: ", reason);
// application specific logging, throwing an error, or other logic here
});
For example, here is a rejection that will trigger the 'unhandledRejection'
event:
somePromise.then((res) => {
return reportToUser(JSON.pasre(res)); // note the typo (`pasre`)
}); // no `.catch` or `.then`
Here is an example of a coding pattern that will also trigger
'unhandledRejection'
:
function SomeResource() {
// Initially set the loaded status to a rejected promise
this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}
var resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turn
In cases like this, you may not want to track the rejection as a developer
error like you would for other 'unhandledRejection'
events. To address
this, you can either attach a dummy .catch(() => { })
handler to
resource.loaded
, preventing the 'unhandledRejection'
event from being
emitted, or you can use the 'rejectionHandled'
event.
Event: 'warning'#
Emitted whenever Node.js emits a process warning.
A process warning is similar to an error in that it describes exceptional conditions that are being brought to the user's attention. However, warnings are not part of the normal Node.js and JavaScript error handling flow. Node.js can emit warnings whenever it detects bad coding practices that could lead to sub-optimal application performance, bugs or security vulnerabilities.
The event handler for 'warning'
events is called with a single warning
argument whose value is an Error
object. There are three key properties that
describe the warning:
name
- The name of the warning (currentlyWarning
by default).message
- A system-provided description of the warning.stack
- A stack trace to the location in the code where the warning was issued.
process.on('warning', (warning) => {
console.warn(warning.name); // Print the warning name
console.warn(warning.message); // Print the warning message
console.warn(warning.stack); // Print the stack trace
});
By default, Node.js will print process warnings to stderr
. The --no-warnings
command-line option can be used to suppress the default console output but the
'warning'
event will still be emitted by the process
object.
The following example illustrates the warning that is printed to stderr
when
too many listeners have been added to an event
$ node
> event.defaultMaxListeners = 1;
> process.on('foo', () => {});
> process.on('foo', () => {});
> (node:38638) Warning: Possible EventEmitter memory leak detected. 2 foo
... listeners added. Use emitter.setMaxListeners() to increase limit
In contrast, the following example turns off the default warning output and
adds a custom handler to the 'warning'
event:
$ node --no-warnings
> var p = process.on('warning', (warning) => console.warn('Do not do that!'));
> event.defaultMaxListeners = 1;
> process.on('foo', () => {});
> process.on('foo', () => {});
> Do not do that!
The --trace-warnings
command-line option can be used to have the default
console output for warnings include the full stack trace of the warning.
Emitting custom warnings#
The process.emitWarning()
method can be used to issue
custom or application specific warnings.
// Emit a warning using a string...
process.emitWarning('Something happened!');
// Prints: (node 12345) Warning: Something happened!
// Emit a warning using an object...
process.emitWarning('Something Happened!', 'CustomWarning');
// Prints: (node 12345) CustomWarning: Something happened!
// Emit a warning using a custom Error object...
class CustomWarning extends Error {
constructor(message) {
super(message);
this.name = 'CustomWarning';
Error.captureStackTrace(this, CustomWarning);
}
}
const myWarning = new CustomWarning('Something happened!');
process.emitWarning(myWarning);
// Prints: (node 12345) CustomWarning: Something happened!
Emitting custom deprecation warnings#
Custom deprecation warnings can be emitted by setting the name
of a custom
warning to DeprecationWarning
. For instance:
process.emitWarning('This API is deprecated', 'DeprecationWarning');
Or,
const err = new Error('This API is deprecated');
err.name = 'DeprecationWarning';
process.emitWarning(err);
Launching Node.js using the --throw-deprecation
command line flag will
cause custom deprecation warnings to be thrown as exceptions.
Using the --trace-deprecation
command line flag will cause the custom
deprecation to be printed to stderr
along with the stack trace.
Using the --no-deprecation
command line flag will suppress all reporting
of the custom deprecation.
The *-deprecation
command line flags only affect warnings that use the name
DeprecationWarning
.
Exit Codes#
Node.js will normally exit with a 0
status code when no more async
operations are pending. The following status codes are used in other
cases:
1
Uncaught Fatal Exception - There was an uncaught exception, and it was not handled by a domain or an'uncaughtException'
event handler.2
- Unused (reserved by Bash for builtin misuse)3
Internal JavaScript Parse Error - The JavaScript source code internal in Node.js's bootstrapping process caused a parse error. This is extremely rare, and generally can only happen during development of Node.js itself.4
Internal JavaScript Evaluation Failure - The JavaScript source code internal in Node.js's bootstrapping process failed to return a function value when evaluated. This is extremely rare, and generally can only happen during development of Node.js itself.5
Fatal Error - There was a fatal unrecoverable error in V8. Typically a message will be printed to stderr with the prefixFATAL ERROR
.6
Non-function Internal Exception Handler - There was an uncaught exception, but the internal fatal exception handler function was somehow set to a non-function, and could not be called.7
Internal Exception Handler Run-Time Failure - There was an uncaught exception, and the internal fatal exception handler function itself threw an error while attempting to handle it. This can happen, for example, if aprocess.on('uncaughtException')
ordomain.on('error')
handler throws an error.8
- Unused. In previous versions of Node.js, exit code 8 sometimes indicated an uncaught exception.9
- Invalid Argument - Either an unknown option was specified, or an option requiring a value was provided without a value.10
Internal JavaScript Run-Time Failure - The JavaScript source code internal in Node.js's bootstrapping process threw an error when the bootstrapping function was called. This is extremely rare, and generally can only happen during development of Node.js itself.12
Invalid Debug Argument - The--debug
and/or--debug-brk
options were set, but an invalid port number was chosen.>128
Signal Exits - If Node.js receives a fatal signal such asSIGKILL
orSIGHUP
, then its exit code will be128
plus the value of the signal code. This is a standard Unix practice, since exit codes are defined to be 7-bit integers, and signal exits set the high-order bit, and then contain the value of the signal code.
Signal Events#
Emitted when the processes receives a signal. See sigaction(2) for a list of
standard POSIX signal names such as SIGINT
, SIGHUP
, etc.
Example of listening for SIGINT
:
// Start reading from stdin so we don't exit.
process.stdin.resume();
process.on('SIGINT', () => {
console.log('Got SIGINT. Press Control-D to exit.');
});
An easy way to send the SIGINT
signal is with Control-C
in most terminal
programs.
Note:
SIGUSR1
is reserved by Node.js to start the debugger. It's possible to install a listener but that won't stop the debugger from starting.SIGTERM
andSIGINT
have default handlers on non-Windows platforms that resets the terminal mode before exiting with code128 + signal number
. If one of these signals has a listener installed, its default behavior will be removed (Node.js will no longer exit).SIGPIPE
is ignored by default. It can have a listener installed.SIGHUP
is generated on Windows when the console window is closed, and on other platforms under various similar conditions, see signal(7). It can have a listener installed, however Node.js will be unconditionally terminated by Windows about 10 seconds later. On non-Windows platforms, the default behavior ofSIGHUP
is to terminate Node.js, but once a listener has been installed its default behavior will be removed.SIGTERM
is not supported on Windows, it can be listened on.SIGINT
from the terminal is supported on all platforms, and can usually be generated withCTRL+C
(though this may be configurable). It is not generated when terminal raw mode is enabled.SIGBREAK
is delivered on Windows whenCTRL+BREAK
is pressed, on non-Windows platforms it can be listened on, but there is no way to send or generate it.SIGWINCH
is delivered when the console has been resized. On Windows, this will only happen on write to the console when the cursor is being moved, or when a readable tty is used in raw mode.SIGKILL
cannot have a listener installed, it will unconditionally terminate Node.js on all platforms.SIGSTOP
cannot have a listener installed.
Note that Windows does not support sending Signals, but Node.js offers some
emulation with process.kill()
, and child_process.kill()
. Sending signal 0
can be used to test for the existence of a process. Sending SIGINT
,
SIGTERM
, and SIGKILL
cause the unconditional termination of the target
process.
process.abort()#
This causes Node.js to emit an abort. This will cause Node.js to exit and generate a core file.
process.arch#
What processor architecture you're running on: 'arm'
, 'ia32'
, or 'x64'
.
console.log('This processor architecture is ' + process.arch);
process.argv#
An array containing the command line arguments. The first element will be 'node', the second element will be the name of the JavaScript file. The next elements will be any additional command line arguments.
// print process.argv
process.argv.forEach((val, index, array) => {
console.log(`${index}: ${val}`);
});
This will generate:
$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four
process.chdir(directory)#
Changes the current working directory of the process or throws an exception if that fails.
console.log(`Starting directory: ${process.cwd()}`);
try {
process.chdir('/tmp');
console.log(`New directory: ${process.cwd()}`);
}
catch (err) {
console.log(`chdir: ${err}`);
}
process.config#
An Object containing the JavaScript representation of the configure options
that were used to compile the current Node.js executable. This is the same as
the config.gypi
file that was produced when running the ./configure
script.
An example of the possible output looks like:
{
target_defaults:
{ cflags: [],
default_configuration: 'Release',
defines: [],
include_dirs: [],
libraries: [] },
variables:
{
host_arch: 'x64',
node_install_npm: 'true',
node_prefix: '',
node_shared_cares: 'false',
node_shared_http_parser: 'false',
node_shared_libuv: 'false',
node_shared_zlib: 'false',
node_use_dtrace: 'false',
node_use_openssl: 'true',
node_shared_openssl: 'false',
strict_aliasing: 'true',
target_arch: 'x64',
v8_use_snapshot: 'true'
}
}
process.connected#
- <Boolean> Set to false after
process.disconnect()
is called
If process.connected
is false, it is no longer possible to send messages.
process.cwd()#
Returns the current working directory of the process.
console.log(`Current directory: ${process.cwd()}`);
process.disconnect()#
Close the IPC channel to the parent process, allowing this child to exit gracefully once there are no other connections keeping it alive.
Identical to the parent process's ChildProcess.disconnect()
.
If Node.js was not spawned with an IPC channel, process.disconnect()
will be
undefined.
process.env#
An object containing the user environment. See environ(7).
An example of this object looks like:
{ TERM: 'xterm-256color',
SHELL: '/usr/local/bin/bash',
USER: 'maciej',
PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
PWD: '/Users/maciej',
EDITOR: 'vim',
SHLVL: '1',
HOME: '/Users/maciej',
LOGNAME: 'maciej',
_: '/usr/local/bin/node' }
You can write to this object, but changes won't be reflected outside of your process. That means that the following won't work:
$ node -e 'process.env.foo = "bar"' && echo $foo
But this will:
process.env.foo = 'bar';
console.log(process.env.foo);
Assigning a property on process.env
will implicitly convert the value
to a string.
Example:
process.env.test = null;
console.log(process.env.test);
// => 'null'
process.env.test = undefined;
console.log(process.env.test);
// => 'undefined'
Use delete
to delete a property from process.env
.
Example:
process.env.TEST = 1;
delete process.env.TEST;
console.log(process.env.TEST);
// => undefined
process.emitWarning(warning[, name][, ctor])#
warning
<String> | <Error> The warning to emit.name
<String> Whenwarning
is a String,name
is the name to use for the warning. Default:Warning
.ctor
<Function> Whenwarning
is a String,ctor
is an optional function used to limit the generated stack trace. Defaultprocess.emitWarning
The process.emitWarning()
method can be used to emit custom or application
specific process warnings. These can be listened for by adding a handler to the
process.on('warning')
event.
// Emit a warning using a string...
process.emitWarning('Something happened!');
// Emits: (node: 56338) Warning: Something happened!
// Emit a warning using a string and a name...
process.emitWarning('Something Happened!', 'CustomWarning');
// Emits: (node:56338) CustomWarning: Something Happened!
In each of the previous examples, an Error
object is generated internally by
process.emitWarning()
and passed through to the
process.on('warning')
event.
process.on('warning', (warning) => {
console.warn(warning.name);
console.warn(warning.message);
console.warn(warning.stack);
});
If warning
is passed as an Error
object, it will be passed through to the
process.on('warning')
event handler unmodified (and the optional name
and ctor
arguments will be ignored):
// Emit a warning using an Error object...
const myWarning = new Error('Warning! Something happened!');
myWarning.name = 'CustomWarning';
process.emitWarning(myWarning);
// Emits: (node:56338) CustomWarning: Warning! Something Happened!
A TypeError
is thrown if warning
is anything other than a string or Error
object.
Note that while process warnings use Error
objects, the process warning
mechanism is not a replacement for normal error handling mechanisms.
The following additional handling is implemented if the warning name
is
DeprecationWarning
:
- If the
--throw-deprecation
command-line flag is used, the deprecation warning is thrown as an exception rather than being emitted as an event. - If the
--no-deprecation
command-line flag is used, the deprecation warning is suppressed. - If the
--trace-deprecation
command-line flag is used, the deprecation warning is printed tostderr
along with the full stack trace.
Avoiding duplicate warnings#
As a best practice, warnings should be emitted only once per process. To do
so, it is recommended to place the emitWarning()
behind a simple boolean
flag as illustrated in the example below:
var warned = false;
function emitMyWarning() {
if (!warned) {
process.emitWarning('Only warn once!');
warned = true;
}
}
emitMyWarning();
// Emits: (node: 56339) Warning: Only warn once!
emitMyWarning();
// Emits nothing
process.execArgv#
This is the set of Node.js-specific command line options from the
executable that started the process. These options do not show up in
process.argv
, and do not include the Node.js executable, the name of
the script, or any options following the script name. These options
are useful in order to spawn child processes with the same execution
environment as the parent.
Example:
$ node --harmony script.js --version
results in process.execArgv:
['--harmony']
and process.argv:
['/usr/local/bin/node', 'script.js', '--version']
process.execPath#
This is the absolute pathname of the executable that started the process.
Example:
/usr/local/bin/node
process.exit([code])#
Ends the process with the specified code
. If omitted, exit uses the
'success' code 0
.
To exit with a 'failure' code:
process.exit(1);
The shell that executed Node.js should see the exit code as 1.
process.exitCode#
A number which will be the process exit code, when the process either
exits gracefully, or is exited via process.exit()
without specifying
a code.
Specifying a code to process.exit(code)
will override any previous
setting of process.exitCode
.
process.getegid()#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Gets the effective group identity of the process. (See getegid(2).) This is the numerical group id, not the group name.
if (process.getegid) {
console.log(`Current gid: ${process.getegid()}`);
}
process.geteuid()#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Gets the effective user identity of the process. (See geteuid(2).) This is the numerical userid, not the username.
if (process.geteuid) {
console.log(`Current uid: ${process.geteuid()}`);
}
process.getgid()#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Gets the group identity of the process. (See getgid(2).) This is the numerical group id, not the group name.
if (process.getgid) {
console.log(`Current gid: ${process.getgid()}`);
}
process.getgroups()#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Returns an array with the supplementary group IDs. POSIX leaves it unspecified if the effective group ID is included but Node.js ensures it always is.
process.getuid()#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Gets the user identity of the process. (See getuid(2).) This is the numerical userid, not the username.
if (process.getuid) {
console.log(`Current uid: ${process.getuid()}`);
}
process.hrtime()#
Returns the current high-resolution real time in a [seconds, nanoseconds]
tuple Array. It is relative to an arbitrary time in the past. It is not
related to the time of day and therefore not subject to clock drift. The
primary use is for measuring performance between intervals.
You may pass in the result of a previous call to process.hrtime()
to get
a diff reading, useful for benchmarks and measuring intervals:
var time = process.hrtime();
// [ 1800216, 25 ]
setTimeout(() => {
var diff = process.hrtime(time);
// [ 1, 552 ]
console.log('benchmark took %d nanoseconds', diff[0] * 1e9 + diff[1]);
// benchmark took 1000000527 nanoseconds
}, 1000);
process.initgroups(user, extra_group)#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Reads /etc/group and initializes the group access list, using all groups of
which the user is a member. This is a privileged operation, meaning you need
to be root or have the CAP_SETGID
capability.
user
is a user name or user ID. extra_group
is a group name or group ID.
Some care needs to be taken when dropping privileges. Example:
console.log(process.getgroups()); // [ 0 ]
process.initgroups('bnoordhuis', 1000); // switch user
console.log(process.getgroups()); // [ 27, 30, 46, 1000, 0 ]
process.setgid(1000); // drop root gid
console.log(process.getgroups()); // [ 27, 30, 46, 1000 ]
process.kill(pid[, signal])#
Send a signal to a process. pid
is the process id and signal
is the
string describing the signal to send. Signal names are strings like
SIGINT
or SIGHUP
. If omitted, the signal will be SIGTERM
.
See Signal Events and kill(2) for more information.
Will throw an error if target does not exist, and as a special case, a signal
of 0
can be used to test for the existence of a process. Windows platforms
will throw an error if the pid
is used to kill a process group.
Note that even though the name of this function is process.kill
, it is really
just a signal sender, like the kill
system call. The signal sent may do
something other than kill the target process.
Example of sending a signal to yourself:
process.on('SIGHUP', () => {
console.log('Got SIGHUP signal.');
});
setTimeout(() => {
console.log('Exiting.');
process.exit(0);
}, 100);
process.kill(process.pid, 'SIGHUP');
Note: When SIGUSR1 is received by Node.js it starts the debugger, see Signal Events.
process.mainModule#
Alternate way to retrieve require.main
. The difference is that if the main
module changes at runtime, require.main
might still refer to the original main
module in modules that were required before the change occurred. Generally it's
safe to assume that the two refer to the same module.
As with require.main
, it will be undefined
if there was no entry script.
process.memoryUsage()#
Returns an object describing the memory usage of the Node.js process measured in bytes.
const util = require('util');
console.log(util.inspect(process.memoryUsage()));
This will generate:
{ rss: 4935680,
heapTotal: 1826816,
heapUsed: 650472 }
heapTotal
and heapUsed
refer to V8's memory usage.
process.nextTick(callback[, arg][, ...])#
callback
<Function>
Once the current event loop turn runs to completion, call the callback function.
This is not a simple alias to setTimeout(fn, 0)
, it's much more
efficient. It runs before any additional I/O events (including
timers) fire in subsequent ticks of the event loop.
console.log('start');
process.nextTick(() => {
console.log('nextTick callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// nextTick callback
This is important in developing APIs where you want to give the user the chance to assign event handlers after an object has been constructed, but before any I/O has occurred.
function MyThing(options) {
this.setupOptions(options);
process.nextTick(() => {
this.startDoingStuff();
});
}
var thing = new MyThing();
thing.getReadyForStuff();
// thing.startDoingStuff() gets called now, not before.
It is very important for APIs to be either 100% synchronous or 100% asynchronous. Consider this example:
// WARNING! DO NOT USE! BAD UNSAFE HAZARD!
function maybeSync(arg, cb) {
if (arg) {
cb();
return;
}
fs.stat('file', cb);
}
This API is hazardous. If you do this:
maybeSync(true, () => {
foo();
});
bar();
then it's not clear whether foo()
or bar()
will be called first.
This approach is much better:
function definitelyAsync(arg, cb) {
if (arg) {
process.nextTick(cb);
return;
}
fs.stat('file', cb);
}
Note: the nextTick queue is completely drained on each pass of the
event loop before additional I/O is processed. As a result,
recursively setting nextTick callbacks will block any I/O from
happening, just like a while(true);
loop.
process.pid#
The PID of the process.
console.log(`This process is pid ${process.pid}`);
process.platform#
What platform you're running on:
'darwin'
, 'freebsd'
, 'linux'
, 'sunos'
or 'win32'
console.log(`This platform is ${process.platform}`);
process.release#
An Object containing metadata related to the current release, including URLs for the source tarball and headers-only tarball.
process.release
contains the following properties:
name
: a string with a value that will always be'node'
for Node.js. For legacy io.js releases, this will be'io.js'
.sourceUrl
: a complete URL pointing to a .tar.gz file containing the source of the current release.headersUrl
: a complete URL pointing to a .tar.gz file containing only the header files for the current release. This file is significantly smaller than the full source file and can be used for compiling add-ons against Node.js.libUrl
: a complete URL pointing to an node.lib file matching the architecture and version of the current release. This file is used for compiling add-ons against Node.js. This property is only present on Windows builds of Node.js and will be missing on all other platforms.
e.g.
{ name: 'node',
sourceUrl: 'https://nodejs.org/download/release/v4.0.0/node-v4.0.0.tar.gz',
headersUrl: 'https://nodejs.org/download/release/v4.0.0/node-v4.0.0-headers.tar.gz',
libUrl: 'https://nodejs.org/download/release/v4.0.0/win-x64/node.lib' }
In custom builds from non-release versions of the source tree, only the
name
property may be present. The additional properties should not be
relied upon to exist.
process.send(message[, sendHandle[, options]][, callback])#
message
<Object>sendHandle
<Handle object>options
<Object>callback
<Function>- Return: <Boolean>
When Node.js is spawned with an IPC channel attached, it can send messages to its
parent process using process.send()
. Each will be received as a
'message'
event on the parent's ChildProcess
object.
Note: this function uses JSON.stringify()
internally to serialize the message
.
If Node.js was not spawned with an IPC channel, process.send()
will be undefined.
process.setegid(id)#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Sets the effective group identity of the process. (See setegid(2).) This accepts either a numerical ID or a groupname string. If a groupname is specified, this method blocks while resolving it to a numerical ID.
if (process.getegid && process.setegid) {
console.log(`Current gid: ${process.getegid()}`);
try {
process.setegid(501);
console.log(`New gid: ${process.getegid()}`);
}
catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
process.seteuid(id)#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Sets the effective user identity of the process. (See seteuid(2).) This accepts either a numerical ID or a username string. If a username is specified, this method blocks while resolving it to a numerical ID.
if (process.geteuid && process.seteuid) {
console.log(`Current uid: ${process.geteuid()}`);
try {
process.seteuid(501);
console.log(`New uid: ${process.geteuid()}`);
}
catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
process.setgid(id)#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Sets the group identity of the process. (See setgid(2).) This accepts either a numerical ID or a groupname string. If a groupname is specified, this method blocks while resolving it to a numerical ID.
if (process.getgid && process.setgid) {
console.log(`Current gid: ${process.getgid()}`);
try {
process.setgid(501);
console.log(`New gid: ${process.getgid()}`);
}
catch (err) {
console.log(`Failed to set gid: ${err}`);
}
}
process.setgroups(groups)#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Sets the supplementary group IDs. This is a privileged operation, meaning you
need to be root or have the CAP_SETGID
capability.
The list can contain group IDs, group names or both.
process.setuid(id)#
Note: this function is only available on POSIX platforms (i.e. not Windows, Android)
Sets the user identity of the process. (See setuid(2).) This accepts either a numerical ID or a username string. If a username is specified, this method blocks while resolving it to a numerical ID.
if (process.getuid && process.setuid) {
console.log(`Current uid: ${process.getuid()}`);
try {
process.setuid(501);
console.log(`New uid: ${process.getuid()}`);
}
catch (err) {
console.log(`Failed to set uid: ${err}`);
}
}
process.stderr#
A writable stream to stderr (on fd 2
).
process.stderr
and process.stdout
are unlike other streams in Node.js in
that they cannot be closed (end()
will throw), they never emit the finish
event and that writes can block when output is redirected to a file (although
disks are fast and operating systems normally employ write-back caching so it
should be a very rare occurrence indeed.)
process.stdin#
A Readable Stream
for stdin (on fd 0
).
Example of opening standard input and listening for both events:
process.stdin.setEncoding('utf8');
process.stdin.on('readable', () => {
var chunk = process.stdin.read();
if (chunk !== null) {
process.stdout.write(`data: ${chunk}`);
}
});
process.stdin.on('end', () => {
process.stdout.write('end');
});
As a Stream, process.stdin
can also be used in "old" mode that is compatible
with scripts written for node.js prior to v0.10.
For more information see Stream compatibility.
In "old" Streams mode the stdin stream is paused by default, so one
must call process.stdin.resume()
to read from it. Note also that calling
process.stdin.resume()
itself would switch stream to "old" mode.
If you are starting a new project you should prefer a more recent "new" Streams mode over "old" one.
process.stdout#
A Writable Stream
to stdout
(on fd 1
).
For example, a console.log
equivalent could look like this:
console.log = (msg) => {
process.stdout.write(`${msg}\n`);
};
process.stderr
and process.stdout
are unlike other streams in Node.js in
that they cannot be closed (end()
will throw), they never emit the 'finish'
event and that writes can block when output is redirected to a file (although
disks are fast and operating systems normally employ write-back caching so it
should be a very rare occurrence indeed.)
To check if Node.js is being run in a TTY context, read the isTTY
property
on process.stderr
, process.stdout
, or process.stdin
:
$ node -p "Boolean(process.stdin.isTTY)"
true
$ echo "foo" | node -p "Boolean(process.stdin.isTTY)"
false
$ node -p "Boolean(process.stdout.isTTY)"
true
$ node -p "Boolean(process.stdout.isTTY)" | cat
false
See the tty docs for more information.
process.title#
Getter/setter to set what is displayed in ps
.
When used as a setter, the maximum length is platform-specific and probably short.
On Linux and OS X, it's limited to the size of the binary name plus the length of the command line arguments because it overwrites the argv memory.
v0.8 allowed for longer process title strings by also overwriting the environ memory but that was potentially insecure/confusing in some (rather obscure) cases.
process.umask([mask])#
Sets or reads the process's file mode creation mask. Child processes inherit
the mask from the parent process. Returns the old mask if mask
argument is
given, otherwise returns the current mask.
const newmask = 0o022;
const oldmask = process.umask(newmask);
console.log(
`Changed umask from ${oldmask.toString(8)} to ${newmask.toString(8)}`
);
process.uptime()#
Number of seconds Node.js has been running.
process.version#
A compiled-in property that exposes NODE_VERSION
.
console.log(`Version: ${process.version}`);
process.versions#
A property exposing version strings of Node.js and its dependencies.
console.log(process.versions);
Will print something like:
{ http_parser: '2.3.0',
node: '1.1.1',
v8: '4.1.0.14',
uv: '1.3.0',
zlib: '1.2.8',
ares: '1.10.0-DEV',
modules: '43',
icu: '55.1',
openssl: '1.0.1k' }
punycode#
Stability: 2 - Stable
Punycode.js is bundled with Node.js v0.6.2+. Use require('punycode')
to
access it. (To use it with other Node.js versions, use npm to install the
punycode
module first.)
punycode.decode(string)#
Converts a Punycode string of ASCII-only symbols to a string of Unicode symbols.
// decode domain name parts
punycode.decode('maana-pta'); // 'mañana'
punycode.decode('--dqo34k'); // '☃-⌘'
punycode.encode(string)#
Converts a string of Unicode symbols to a Punycode string of ASCII-only symbols.
// encode domain name parts
punycode.encode('mañana'); // 'maana-pta'
punycode.encode('☃-⌘'); // '--dqo34k'
punycode.toASCII(domain)#
Converts a Unicode string representing a domain name to Punycode. Only the non-ASCII parts of the domain name will be converted, i.e. it doesn't matter if you call it with a domain that's already in ASCII.
// encode domain names
punycode.toASCII('mañana.com'); // 'xn--maana-pta.com'
punycode.toASCII('☃-⌘.com'); // 'xn----dqo34k.com'
punycode.toUnicode(domain)#
Converts a Punycode string representing a domain name to Unicode. Only the Punycoded parts of the domain name will be converted, i.e. it doesn't matter if you call it on a string that has already been converted to Unicode.
// decode domain names
punycode.toUnicode('xn--maana-pta.com'); // 'mañana.com'
punycode.toUnicode('xn----dqo34k.com'); // '☃-⌘.com'
punycode.ucs2#
punycode.ucs2.decode(string)#
Creates an array containing the numeric code point values of each Unicode symbol in the string. While JavaScript uses UCS-2 internally, this function will convert a pair of surrogate halves (each of which UCS-2 exposes as separate characters) into a single code point, matching UTF-16.
punycode.ucs2.decode('abc'); // [0x61, 0x62, 0x63]
// surrogate pair for U+1D306 tetragram for centre:
punycode.ucs2.decode('\uD834\uDF06'); // [0x1D306]
punycode.ucs2.encode(codePoints)#
Creates a string based on an array of numeric code point values.
punycode.ucs2.encode([0x61, 0x62, 0x63]); // 'abc'
punycode.ucs2.encode([0x1D306]); // '\uD834\uDF06'
punycode.version#
A string representing the current Punycode.js version number.
Query String#
Stability: 2 - Stable
This module provides utilities for dealing with query strings. It provides the following methods:
querystring.escape#
The escape function used by querystring.stringify
,
provided so that it could be overridden if necessary.
querystring.parse(str[, sep][, eq][, options])#
Deserialize a query string to an object.
Optionally override the default separator ('&'
) and assignment ('='
)
characters.
Options object may contain maxKeys
property (equal to 1000 by default), it'll
be used to limit processed keys. Set it to 0 to remove key count limitation.
Options object may contain decodeURIComponent
property (querystring.unescape
by default),
it can be used to decode a non-utf8
encoding string if necessary.
Example:
querystring.parse('foo=bar&baz=qux&baz=quux&corge')
// returns { foo: 'bar', baz: ['qux', 'quux'], corge: '' }
// Suppose gbkDecodeURIComponent function already exists,
// it can decode `gbk` encoding string
querystring.parse('w=%D6%D0%CE%C4&foo=bar', null, null,
{ decodeURIComponent: gbkDecodeURIComponent })
// returns { w: '中文', foo: 'bar' }
querystring.stringify(obj[, sep][, eq][, options])#
Serialize an object to a query string.
Optionally override the default separator ('&'
) and assignment ('='
)
characters.
Options object may contain encodeURIComponent
property (querystring.escape
by default),
it can be used to encode string with non-utf8
encoding if necessary.
Example:
querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' })
// returns 'foo=bar&baz=qux&baz=quux&corge='
querystring.stringify({foo: 'bar', baz: 'qux'}, ';', ':')
// returns 'foo:bar;baz:qux'
// Suppose gbkEncodeURIComponent function already exists,
// it can encode string with `gbk` encoding
querystring.stringify({ w: '中文', foo: 'bar' }, null, null,
{ encodeURIComponent: gbkEncodeURIComponent })
// returns 'w=%D6%D0%CE%C4&foo=bar'
querystring.unescape#
The unescape function used by querystring.parse
,
provided so that it could be overridden if necessary.
It will try to use decodeURIComponent
in the first place,
but if that fails it falls back to a safer equivalent that
doesn't throw on malformed URLs.
Readline#
Stability: 2 - Stable
To use this module, do require('readline')
. Readline allows reading of a
stream (such as process.stdin
) on a line-by-line basis.
Note that once you've invoked this module, your Node.js program will not terminate until you've closed the interface. Here's how to allow your program to gracefully exit:
const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
rl.question('What do you think of Node.js? ', (answer) => {
// TODO: Log the answer in a database
console.log('Thank you for your valuable feedback:', answer);
rl.close();
});
Class: Interface#
The class that represents a readline interface with an input and output stream.
rl.close()#
Closes the Interface
instance, relinquishing control on the input
and
output
streams. The 'close'
event will also be emitted.
rl.pause()#
Pauses the readline input
stream, allowing it to be resumed later if needed.
Note that this doesn't immediately pause the stream of events. Several events may
be emitted after calling pause
, including line
.
rl.prompt([preserveCursor])#
Readies readline for input from the user, putting the current setPrompt
options on a new line, giving the user a new spot to write. Set preserveCursor
to true
to prevent the cursor placement being reset to 0
.
This will also resume the input
stream used with createInterface
if it has
been paused.
If output
is set to null
or undefined
when calling createInterface
, the
prompt is not written.
rl.question(query, callback)#
Prepends the prompt with query
and invokes callback
with the user's
response. Displays the query to the user, and then invokes callback
with the user's response after it has been typed.
This will also resume the input
stream used with createInterface
if
it has been paused.
If output
is set to null
or undefined
when calling createInterface
,
nothing is displayed.
Example usage:
rl.question('What is your favorite food?', (answer) => {
console.log(`Oh, so your favorite food is ${answer}`);
});
rl.resume()#
Resumes the readline input
stream.
rl.setPrompt(prompt)#
Sets the prompt, for example when you run node
on the command line, you see
>
, which is Node.js's prompt.
rl.write(data[, key])#
Writes data
to output
stream, unless output
is set to null
or
undefined
when calling createInterface
. key
is an object literal to
represent a key sequence; available if the terminal is a TTY.
This will also resume the input
stream if it has been paused.
Example:
rl.write('Delete me!');
// Simulate ctrl+u to delete the line written previously
rl.write(null, {ctrl: true, name: 'u'});
Events#
Event: 'close'#
function () {}
Emitted when close()
is called.
Also emitted when the input
stream receives its 'end'
event. The Interface
instance should be considered "finished" once this is emitted. For example, when
the input
stream receives ^D
, respectively known as EOT
.
This event is also called if there is no SIGINT
event listener present when
the input
stream receives a ^C
, respectively known as SIGINT
.
Event: 'line'#
function (line) {}
Emitted whenever the input
stream receives an end of line (\n
, \r
, or
\r\n
), usually received when the user hits enter, or return. This is a good
hook to listen for user input.
Example of listening for 'line'
:
rl.on('line', (cmd) => {
console.log(`You just typed: ${cmd}`);
});
Event: 'pause'#
function () {}
Emitted whenever the input
stream is paused.
Also emitted whenever the input
stream is not paused and receives the
SIGCONT
event. (See events SIGTSTP
and SIGCONT
)
Example of listening for 'pause'
:
rl.on('pause', () => {
console.log('Readline paused.');
});
Event: 'resume'#
function () {}
Emitted whenever the input
stream is resumed.
Example of listening for 'resume'
:
rl.on('resume', () => {
console.log('Readline resumed.');
});
Event: 'SIGCONT'#
function () {}
This does not work on Windows.
Emitted whenever the input
stream is sent to the background with ^Z
,
respectively known as SIGTSTP
, and then continued with fg(1)
. This event
only emits if the stream was not paused before sending the program to the
background.
Example of listening for SIGCONT
:
rl.on('SIGCONT', () => {
// `prompt` will automatically resume the stream
rl.prompt();
});
Event: 'SIGINT'#
function () {}
Emitted whenever the input
stream receives a ^C
, respectively known as
SIGINT
. If there is no SIGINT
event listener present when the input
stream receives a SIGINT
, pause
will be triggered.
Example of listening for SIGINT
:
rl.on('SIGINT', () => {
rl.question('Are you sure you want to exit?', (answer) => {
if (answer.match(/^y(es)?$/i)) rl.pause();
});
});
Event: 'SIGTSTP'#
function () {}
This does not work on Windows.
Emitted whenever the input
stream receives a ^Z
, respectively known as
SIGTSTP
. If there is no SIGTSTP
event listener present when the input
stream receives a SIGTSTP
, the program will be sent to the background.
When the program is resumed with fg
, the 'pause'
and SIGCONT
events will be
emitted. You can use either to resume the stream.
The 'pause'
and SIGCONT
events will not be triggered if the stream was paused
before the program was sent to the background.
Example of listening for SIGTSTP
:
rl.on('SIGTSTP', () => {
// This will override SIGTSTP and prevent the program from going to the
// background.
console.log('Caught SIGTSTP.');
});
Example: Tiny CLI#
Here's an example of how to use all these together to craft a tiny command line interface:
const readline = require('readline');
const rl = readline.createInterface(process.stdin, process.stdout);
rl.setPrompt('OHAI> ');
rl.prompt();
rl.on('line', (line) => {
switch(line.trim()) {
case 'hello':
console.log('world!');
break;
default:
console.log('Say what? I might have heard `' + line.trim() + '`');
break;
}
rl.prompt();
}).on('close', () => {
console.log('Have a great day!');
process.exit(0);
});
Example: Read File Stream Line-by-Line#
A common case for readline
's input
option is to pass a filesystem readable
stream to it. This is how one could craft line-by-line parsing of a file:
const readline = require('readline');
const fs = require('fs');
const rl = readline.createInterface({
input: fs.createReadStream('sample.txt')
});
rl.on('line', (line) => {
console.log('Line from file:', line);
});
readline.clearLine(stream, dir)#
Clears current line of given TTY stream in a specified direction.
dir
should have one of following values:
-1
- to the left from cursor1
- to the right from cursor0
- the entire line
readline.clearScreenDown(stream)#
Clears the screen from the current position of the cursor down.
readline.createInterface(options)#
Creates a readline Interface
instance. Accepts an options
Object that takes
the following values:
input
- the readable stream to listen to (Required).output
- the writable stream to write readline data to (Optional).completer
- an optional function that is used for Tab autocompletion. See below for an example of using this.terminal
- passtrue
if theinput
andoutput
streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Defaults to checkingisTTY
on theoutput
stream upon instantiation.historySize
- maximum number of history lines retained. Defaults to30
.
The completer
function is given the current line entered by the user, and
is supposed to return an Array with 2 entries:
An Array with matching entries for the completion.
The substring that was used for the matching.
Which ends up looking something like:
[[substr1, substr2, ...], originalsubstring]
.
Example:
function completer(line) {
var completions = '.help .error .exit .quit .q'.split(' ')
var hits = completions.filter((c) => { return c.indexOf(line) == 0 })
// show all completions if none found
return [hits.length ? hits : completions, line]
}
Also completer
can be run in async mode if it accepts two arguments:
function completer(linePartial, callback) {
callback(null, [['123'], linePartial]);
}
createInterface
is commonly used with process.stdin
and
process.stdout
in order to accept user input:
const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
Once you have a readline instance, you most commonly listen for the
'line'
event.
If terminal
is true
for this instance then the output
stream will get
the best compatibility if it defines an output.columns
property, and fires
a 'resize'
event on the output
if/when the columns ever change
(process.stdout
does this automatically when it is a TTY).
readline.cursorTo(stream, x, y)#
Move cursor to the specified position in a given TTY stream.
readline.emitKeypressEvents(stream)#
Causes stream
to begin emitting 'keypress'
events corresponding to its
input.
readline.moveCursor(stream, dx, dy)#
Move cursor relative to it's current position in a given TTY stream.
REPL#
Stability: 2 - Stable
A Read-Eval-Print-Loop (REPL) is available both as a standalone program and easily includable in other programs. The REPL provides a way to interactively run JavaScript and see the results. It can be used for debugging, testing, or just trying things out.
By executing node
without any arguments from the command-line you will be
dropped into the REPL. It has simplistic emacs line-editing.
$ node
Type '.help' for options.
> a = [ 1, 2, 3];
[ 1, 2, 3 ]
> a.forEach((v) => {
... console.log(v);
... });
1
2
3
For advanced line-editors, start Node.js with the environmental variable
NODE_NO_READLINE=1
. This will start the main and debugger REPL in canonical
terminal settings which will allow you to use with rlwrap
.
For example, you could add this to your bashrc file:
alias node="env NODE_NO_READLINE=1 rlwrap node"
Environment Variable Options#
The built-in repl (invoked by running node
or node -i
) may be controlled
via the following environment variables:
NODE_REPL_HISTORY
- When a valid path is given, persistent REPL history will be saved to the specified file rather than.node_repl_history
in the user's home directory. Setting this value to""
will disable persistent REPL history. Whitespace will be trimmed from the value.NODE_REPL_HISTORY_SIZE
- Defaults to1000
. Controls how many lines of history will be persisted if history is available. Must be a positive number.NODE_REPL_MODE
- May be any ofsloppy
,strict
, ormagic
. Defaults tomagic
, which will automatically run "strict mode only" statements in strict mode.
Persistent History#
By default, the REPL will persist history between node
REPL sessions by saving
to a .node_repl_history
file in the user's home directory. This can be
disabled by setting the environment variable NODE_REPL_HISTORY=""
.
NODE_REPL_HISTORY_FILE#
Stability: 0 - Deprecated: Use NODE_REPL_HISTORY
instead.
Previously in Node.js/io.js v2.x, REPL history was controlled by using a
NODE_REPL_HISTORY_FILE
environment variable, and the history was saved in JSON
format. This variable has now been deprecated, and your REPL history will
automatically be converted to using plain text. The new file will be saved to
either your home directory, or a directory defined by the NODE_REPL_HISTORY
variable, as documented here.
REPL Features#
Inside the REPL, Control+D will exit. Multi-line expressions can be input. Tab completion is supported for both global and local variables.
Core modules will be loaded on-demand into the environment. For example,
accessing fs
will require()
the fs
module as global.fs
.
The special variable _
(underscore) contains the result of the last expression.
> [ 'a', 'b', 'c' ]
[ 'a', 'b', 'c' ]
> _.length
3
> _ += 1
4
Explicitly setting _
will disable this behavior until the context is reset.
The REPL provides access to any variables in the global scope. You can expose
a variable to the REPL explicitly by assigning it to the context
object
associated with each REPLServer
. For example:
// repl_test.js
const repl = require('repl');
var msg = 'message';
repl.start('> ').context.m = msg;
Things in the context
object appear as local within the REPL:
$ node repl_test.js
> m
'message'
There are a few special REPL commands:
.break
- While inputting a multi-line expression, sometimes you get lost or just don't care about completing it..break
will start over..clear
- Resets thecontext
object to an empty object and clears any multi-line expression..exit
- Close the I/O stream, which will cause the REPL to exit..help
- Show this list of special commands..save
- Save the current REPL session to a file.save ./file/to/save.js
.load
- Load a file into the current REPL session..load ./file/to/load.js
The following key combinations in the REPL have these special effects:
<ctrl>C
- Similar to the.break
keyword. Terminates the current command. Press twice on a blank line to forcibly exit.<ctrl>D
- Similar to the.exit
keyword.<tab>
- Show both global and local(scope) variables
Customizing Object displays in the REPL#
The REPL module internally uses
util.inspect()
, when printing values. However, util.inspect
delegates the
call to the object's inspect()
function, if it has one. You can read more
about this delegation here.
For example, if you have defined an inspect()
function on an object, like this:
> var obj = {foo: 'this will not show up in the inspect() output'};
undefined
> obj.inspect = () => {
... return {bar: 'baz'};
... };
[Function]
and try to print obj
in REPL, it will invoke the custom inspect()
function:
> obj
{bar: 'baz'}
Class: REPLServer#
This inherits from Readline Interface with the following events:
Event: 'exit'#
function () {}
Emitted when the user exits the REPL in any of the defined ways. Namely, typing
.exit
at the repl, pressing Ctrl+C twice to signal SIGINT
, or pressing Ctrl+D
to signal 'end'
on the input
stream.
Example of listening for exit
:
replServer.on('exit', () => {
console.log('Got "exit" event from repl!');
process.exit();
});
Event: 'reset'#
function (context) {}
Emitted when the REPL's context is reset. This happens when you type .clear
.
If you start the repl with { useGlobal: true }
then this event will never
be emitted.
Example of listening for reset
:
// Extend the initial repl context.
var replServer = repl.start({ options ... });
someExtension.extend(r.context);
// When a new context is created extend it as well.
replServer.on('reset', (context) => {
console.log('repl has a new context');
someExtension.extend(context);
});
replServer.defineCommand(keyword, cmd)#
keyword
<String>cmd
<Object> | <Function>
Makes a command available in the REPL. The command is invoked by typing a .
followed by the keyword. The cmd
is an object with the following values:
help
- help text to be displayed when.help
is entered (Optional).action
- a function to execute, potentially taking in a string argument, when the command is invoked, bound to the REPLServer instance (Required).
If a function is provided instead of an object for cmd
, it is treated as the
action
.
Example of defining a command:
// repl_test.js
const repl = require('repl');
var replServer = repl.start();
replServer.defineCommand('sayhello', {
help: 'Say hello',
action: function(name) {
this.write(`Hello, ${name}!\n`);
this.displayPrompt();
}
});
Example of invoking that command from the REPL:
> .sayhello Node.js User
Hello, Node.js User!
replServer.displayPrompt([preserveCursor])#
preserveCursor
<Boolean>
Like readline.prompt
except also adding indents with ellipses when inside
blocks. The preserveCursor
argument is passed to readline.prompt
. This is
used primarily with defineCommand
. It's also used internally to render each
prompt line.
repl.start(options)#
Returns and starts a REPLServer
instance, that inherits from
Readline Interface. Accepts an "options" Object that takes
the following values:
prompt
- the prompt andstream
for all I/O. Defaults to>
.input
- the readable stream to listen to. Defaults toprocess.stdin
.output
- the writable stream to write readline data to. Defaults toprocess.stdout
.terminal
- passtrue
if thestream
should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Defaults to checkingisTTY
on theoutput
stream upon instantiation.eval
- function that will be used to eval each given line. Defaults to an async wrapper foreval()
. See below for an example of a customeval
.useColors
- a boolean which specifies whether or not thewriter
function should output colors. If a differentwriter
function is set then this does nothing. Defaults to the repl'sterminal
value.useGlobal
- if set totrue
, then the repl will use theglobal
object, instead of running scripts in a separate context. Defaults tofalse
.ignoreUndefined
- if set totrue
, then the repl will not output the return value of command if it'sundefined
. Defaults tofalse
.writer
- the function to invoke for each command that gets evaluated which returns the formatting (including coloring) to display. Defaults toutil.inspect
.replMode
- controls whether the repl runs all commands in strict mode, default mode, or a hybrid mode ("magic" mode.) Acceptable values are:repl.REPL_MODE_SLOPPY
- run commands in sloppy mode.repl.REPL_MODE_STRICT
- run commands in strict mode. This is equivalent to prefacing every repl statement with'use strict'
.repl.REPL_MODE_MAGIC
- attempt to run commands in default mode. If they fail to parse, re-try in strict mode.
You can use your own eval
function if it has following signature:
function eval(cmd, context, filename, callback) {
callback(null, result);
}
On tab completion, eval
will be called with .scope
as an input string. It
is expected to return an array of scope names to be used for the auto-completion.
Multiple REPLs may be started against the same running instance of Node.js. Each will share the same global object but will have unique I/O.
Here is an example that starts a REPL on stdin, a Unix socket, and a TCP socket:
const net = require('net');
const repl = require('repl');
var connections = 0;
repl.start({
prompt: 'Node.js via stdin> ',
input: process.stdin,
output: process.stdout
});
net.createServer((socket) => {
connections += 1;
repl.start({
prompt: 'Node.js via Unix socket> ',
input: socket,
output: socket
}).on('exit', () => {
socket.end();
})
}).listen('/tmp/node-repl-sock');
net.createServer((socket) => {
connections += 1;
repl.start({
prompt: 'Node.js via TCP socket> ',
input: socket,
output: socket
}).on('exit', () => {
socket.end();
});
}).listen(5001);
Running this program from the command line will start a REPL on stdin. Other
REPL clients may connect through the Unix socket or TCP socket. telnet
is useful
for connecting to TCP sockets, and socat
can be used to connect to both Unix and
TCP sockets.
By starting a REPL from a Unix socket-based server instead of stdin, you can connect to a long-running Node.js process without restarting it.
For an example of running a "full-featured" (terminal
) REPL over
a net.Server
and net.Socket
instance, see: https://gist.github.com/2209310
For an example of running a REPL instance over curl(1)
,
see: https://gist.github.com/2053342
Stream#
Stability: 2 - Stable
A stream is an abstract interface implemented by various objects in
Node.js. For example a request to an HTTP server is a
stream, as is process.stdout
. Streams are readable, writable, or both. All
streams are instances of EventEmitter
.
You can load the Stream base classes by doing require('stream')
.
There are base classes provided for Readable streams, Writable
streams, Duplex streams, and Transform streams.
This document is split up into 3 sections:
- The first section explains the parts of the API that you need to be aware of to use streams in your programs.
- The second section explains the parts of the API that you need to use if you implement your own custom streams yourself. The API is designed to make this easy for you to do.
- The third section goes into more depth about how streams work, including some of the internal mechanisms and functions that you should probably not modify unless you definitely know what you are doing.
API for Stream Consumers#
Streams can be either Readable, Writable, or both (Duplex).
All streams are EventEmitters, but they also have other custom methods and properties depending on whether they are Readable, Writable, or Duplex.
If a stream is both Readable and Writable, then it implements all of the methods and events. So, a Duplex or Transform stream is fully described by this API, though their implementation may be somewhat different.
It is not necessary to implement Stream interfaces in order to consume streams in your programs. If you are implementing streaming interfaces in your own program, please also refer to API for Stream Implementors.
Almost all Node.js programs, no matter how simple, use Streams in some way. Here is an example of using Streams in an Node.js program:
const http = require('http');
var server = http.createServer( (req, res) => {
// req is an http.IncomingMessage, which is a Readable Stream
// res is an http.ServerResponse, which is a Writable Stream
var body = '';
// we want to get the data as utf8 strings
// If you don't set an encoding, then you'll get Buffer objects
req.setEncoding('utf8');
// Readable streams emit 'data' events once a listener is added
req.on('data', (chunk) => {
body += chunk;
});
// the end event tells you that you have entire body
req.on('end', () => {
try {
var data = JSON.parse(body);
} catch (er) {
// uh oh! bad json!
res.statusCode = 400;
return res.end(`error: ${er.message}`);
}
// write back something interesting to the user:
res.write(typeof data);
res.end();
});
});
server.listen(1337);
// $ curl localhost:1337 -d '{}'
// object
// $ curl localhost:1337 -d '"foo"'
// string
// $ curl localhost:1337 -d 'not json'
// error: Unexpected token o
Class: stream.Duplex#
Duplex streams are streams that implement both the Readable and Writable interfaces.
Examples of Duplex streams include:
Class: stream.Readable#
The Readable stream interface is the abstraction for a source of data that you are reading from. In other words, data comes out of a Readable stream.
A Readable stream will not start emitting data until you indicate that you are ready to receive it.
Readable streams have two "modes": a flowing mode and a paused
mode. When in flowing mode, data is read from the underlying system
and provided to your program as fast as possible. In paused mode, you
must explicitly call stream.read()
to get chunks of data out.
Streams start out in paused mode.
Note: If no data event handlers are attached, and there are no
stream.pipe()
destinations, and the stream is switched into flowing
mode, then data will be lost.
You can switch to flowing mode by doing any of the following:
- Adding a
'data'
event handler to listen for data. - Calling the
stream.resume()
method to explicitly open the flow. - Calling the
stream.pipe()
method to send the data to a Writable.
You can switch back to paused mode by doing either of the following:
- If there are no pipe destinations, by calling the
stream.pause()
method. - If there are pipe destinations, by removing any
'data'
event handlers, and removing all pipe destinations by calling thestream.unpipe()
method.
Note that, for backwards compatibility reasons, removing 'data'
event handlers will not automatically pause the stream. Also, if
there are piped destinations, then calling stream.pause()
will
not guarantee that the stream will remain paused once those
destinations drain and ask for more data.
Examples of readable streams include:
- HTTP responses, on the client
- HTTP requests, on the server
- fs read streams
- zlib streams
- crypto streams
- TCP sockets
- child process stdout and stderr
process.stdin
Event: 'close'#
Emitted when the stream and any of its underlying resources (a file descriptor, for example) have been closed. The event indicates that no more events will be emitted, and no further computation will occur.
Not all streams will emit the 'close'
event.
Event: 'data'#
Attaching a 'data'
event listener to a stream that has not been
explicitly paused will switch the stream into flowing mode. Data will
then be passed as soon as it is available.
If you just want to get all the data out of the stream as fast as possible, this is the best way to do so.
var readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log('got %d bytes of data', chunk.length);
});
Event: 'end'#
This event fires when there will be no more data to read.
Note that the 'end'
event will not fire unless the data is
completely consumed. This can be done by switching into flowing mode,
or by calling stream.read()
repeatedly until you get to the
end.
var readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log('got %d bytes of data', chunk.length);
});
readable.on('end', () => {
console.log('there will be no more data.');
});
Event: 'error'#
Emitted if there was an error receiving data.
Event: 'readable'#
When a chunk of data can be read from the stream, it will emit a
'readable'
event.
In some cases, listening for a 'readable'
event will cause some data
to be read into the internal buffer from the underlying system, if it
hadn't already.
var readable = getReadableStreamSomehow();
readable.on('readable', () => {
// there is some data to read now
});
Once the internal buffer is drained, a 'readable'
event will fire
again when more data is available.
The 'readable'
event is not emitted in the "flowing" mode with the
sole exception of the last one, on end-of-stream.
The 'readable'
event indicates that the stream has new information:
either new data is available or the end of the stream has been reached.
In the former case, stream.read()
will return that data. In the
latter case, stream.read()
will return null. For instance, in
the following example, foo.txt
is an empty file:
const fs = require('fs');
var rr = fs.createReadStream('foo.txt');
rr.on('readable', () => {
console.log('readable:', rr.read());
});
rr.on('end', () => {
console.log('end');
});
The output of running this script is:
$ node test.js
readable: null
end
readable.isPaused()#
- Return: <Boolean>
This method returns whether or not the readable
has been explicitly
paused by client code (using stream.pause()
without a
corresponding stream.resume()
).
var readable = new stream.Readable
readable.isPaused() // === false
readable.pause()
readable.isPaused() // === true
readable.resume()
readable.isPaused() // === false
readable.pause()#
- Return:
this
This method will cause a stream in flowing mode to stop emitting
'data'
events, switching out of flowing mode. Any data that becomes
available will remain in the internal buffer.
var readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
console.log('got %d bytes of data', chunk.length);
readable.pause();
console.log('there will be no more data for 1 second');
setTimeout(() => {
console.log('now data will start flowing again');
readable.resume();
}, 1000);
});
readable.pipe(destination[, options])#
destination
<stream.Writable> The destination for writing dataoptions
<Object> Pipe optionsend
<Boolean> End the writer when the reader ends. Default =true
This method pulls all the data out of a readable stream, and writes it to the supplied destination, automatically managing the flow so that the destination is not overwhelmed by a fast readable stream.
Multiple destinations can be piped to safely.
var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt'
readable.pipe(writable);
This function returns the destination stream, so you can set up pipe chains like so:
var r = fs.createReadStream('file.txt');
var z = zlib.createGzip();
var w = fs.createWriteStream('file.txt.gz');
r.pipe(z).pipe(w);
For example, emulating the Unix cat
command:
process.stdin.pipe(process.stdout);
By default stream.end()
is called on the destination when the
source stream emits 'end'
, so that destination
is no longer writable.
Pass { end: false }
as options
to keep the destination stream open.
This keeps writer
open so that "Goodbye" can be written at the
end.
reader.pipe(writer, { end: false });
reader.on('end', () => {
writer.end('Goodbye\n');
});
Note that process.stderr
and process.stdout
are never closed until
the process exits, regardless of the specified options.
readable.read([size])#
The read()
method pulls some data out of the internal buffer and
returns it. If there is no data available, then it will return
null
.
If you pass in a size
argument, then it will return that many
bytes. If size
bytes are not available, then it will return null
,
unless we've ended, in which case it will return the data remaining
in the buffer.
If you do not specify a size
argument, then it will return all the
data in the internal buffer.
This method should only be called in paused mode. In flowing mode, this method is called automatically until the internal buffer is drained.
var readable = getReadableStreamSomehow();
readable.on('readable', () => {
var chunk;
while (null !== (chunk = readable.read())) {
console.log('got %d bytes of data', chunk.length);
}
});
If this method returns a data chunk, then it will also trigger the
emission of a 'data'
event.
Note that calling stream.read([size])
after the 'end'
event has been triggered will return null
. No runtime error will be raised.
readable.resume()#
- Return:
this
This method will cause the readable stream to resume emitting 'data'
events.
This method will switch the stream into flowing mode. If you do not
want to consume the data from a stream, but you do want to get to
its 'end'
event, you can call stream.resume()
to open
the flow of data.
var readable = getReadableStreamSomehow();
readable.resume();
readable.on('end', () => {
console.log('got to the end, but did not read anything');
});
readable.setEncoding(encoding)#
encoding
<String> The encoding to use.- Return:
this
Call this function to cause the stream to return strings of the specified
encoding instead of Buffer objects. For example, if you do
readable.setEncoding('utf8')
, then the output data will be interpreted as
UTF-8 data, and returned as strings. If you do readable.setEncoding('hex')
,
then the data will be encoded in hexadecimal string format.
This properly handles multi-byte characters that would otherwise be
potentially mangled if you simply pulled the Buffers directly and
called buf.toString(encoding)
on them. If you want to read the data
as strings, always use this method.
Also you can disable any encoding at all with readable.setEncoding(null)
.
This approach is very useful if you deal with binary data or with large
multi-byte strings spread out over multiple chunks.
var readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', (chunk) => {
assert.equal(typeof chunk, 'string');
console.log('got %d characters of string data', chunk.length);
});
readable.unpipe([destination])#
destination
<stream.Writable> Optional specific stream to unpipe
This method will remove the hooks set up for a previous stream.pipe()
call.
If the destination is not specified, then all pipes are removed.
If the destination is specified, but no pipe is set up for it, then this is a no-op.
var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second
readable.pipe(writable);
setTimeout(() => {
console.log('stop writing to file.txt');
readable.unpipe(writable);
console.log('manually close the file stream');
writable.end();
}, 1000);
readable.unshift(chunk)#
This is useful in certain cases where a stream is being consumed by a parser, which needs to "un-consume" some data that it has optimistically pulled out of the source, so that the stream can be passed on to some other party.
Note that stream.unshift(chunk)
cannot be called after the 'end'
event
has been triggered; a runtime error will be raised.
If you find that you must often call stream.unshift(chunk)
in your
programs, consider implementing a Transform stream instead. (See API
for Stream Implementors.)
// Pull off a header delimited by \n\n
// use unshift() if we get too much
// Call the callback with (error, header, stream)
const StringDecoder = require('string_decoder').StringDecoder;
function parseHeader(stream, callback) {
stream.on('error', callback);
stream.on('readable', onReadable);
var decoder = new StringDecoder('utf8');
var header = '';
function onReadable() {
var chunk;
while (null !== (chunk = stream.read())) {
var str = decoder.write(chunk);
if (str.match(/\n\n/)) {
// found the header boundary
var split = str.split(/\n\n/);
header += split.shift();
var remaining = split.join('\n\n');
var buf = new Buffer(remaining, 'utf8');
if (buf.length)
stream.unshift(buf);
stream.removeListener('error', callback);
stream.removeListener('readable', onReadable);
// now the body of the message can be read from the stream.
callback(null, header, stream);
} else {
// still reading the header.
header += str;
}
}
}
}
Note that, unlike stream.push(chunk)
, stream.unshift(chunk)
will not end the reading process by resetting the internal reading state of the
stream. This can cause unexpected results if unshift()
is called during a
read (i.e. from within a stream._read()
implementation on a
custom stream). Following the call to unshift()
with an immediate
stream.push('')
will reset the reading state appropriately,
however it is best to simply avoid calling unshift()
while in the process of
performing a read.
readable.wrap(stream)#
stream
<Stream> An "old style" readable stream
Versions of Node.js prior to v0.10 had streams that did not implement the entire Streams API as it is today. (See Compatibility for more information.)
If you are using an older Node.js library that emits 'data'
events and
has a stream.pause()
method that is advisory only, then you
can use the wrap()
method to create a Readable stream that uses the old
stream as its data source.
You will very rarely ever need to call this function, but it exists as a convenience for interacting with old Node.js programs and libraries.
For example:
const OldReader = require('./old-api-module.js').OldReader;
const Readable = require('stream').Readable;
const oreader = new OldReader;
const myReader = new Readable().wrap(oreader);
myReader.on('readable', () => {
myReader.read(); // etc.
});
Class: stream.Transform#
Transform streams are Duplex streams where the output is in some way computed from the input. They implement both the Readable and Writable interfaces.
Examples of Transform streams include:
Class: stream.Writable#
The Writable stream interface is an abstraction for a destination that you are writing data to.
Examples of writable streams include:
- HTTP requests, on the client
- HTTP responses, on the server
- fs write streams
- zlib streams
- crypto streams
- TCP sockets
- child process stdin
process.stdout
,process.stderr
Event: 'drain'#
If a stream.write(chunk)
call returns false
, then the
'drain'
event will indicate when it is appropriate to begin writing more data
to the stream.
// Write the data to the supplied writable stream one million times.
// Be attentive to back-pressure.
function writeOneMillionTimes(writer, data, encoding, callback) {
var i = 1000000;
write();
function write() {
var ok = true;
do {
i -= 1;
if (i === 0) {
// last time!
writer.write(data, encoding, callback);
} else {
// see if we should continue, or wait
// don't pass the callback, because we're not done yet.
ok = writer.write(data, encoding);
}
} while (i > 0 && ok);
if (i > 0) {
// had to stop early!
// write some more once it drains
writer.once('drain', write);
}
}
}
Event: 'error'#
Emitted if there was an error when writing or piping data.
Event: 'finish'#
When the stream.end()
method has been called, and all data has
been flushed to the underlying system, this event is emitted.
var writer = getWritableStreamSomehow();
for (var i = 0; i < 100; i ++) {
writer.write('hello, #${i}!\n');
}
writer.end('this is the end\n');
writer.on('finish', () => {
console.error('all writes are now complete.');
});
Event: 'pipe'#
src
<stream.Readable> source stream that is piping to this writable
This is emitted whenever the stream.pipe()
method is called on a readable
stream, adding this writable to its set of destinations.
var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('pipe', (src) => {
console.error('something is piping into the writer');
assert.equal(src, reader);
});
reader.pipe(writer);
Event: 'unpipe'#
This is emitted whenever the stream.unpipe()
method is called on a
readable stream, removing this writable from its set of destinations.
var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('unpipe', (src) => {
console.error('something has stopped piping into the writer');
assert.equal(src, reader);
});
reader.pipe(writer);
reader.unpipe(writer);
writable.cork()#
Forces buffering of all writes.
Buffered data will be flushed either at stream.uncork()
or at
stream.end()
call.
writable.end([chunk][, encoding][, callback])#
chunk
<String> | <Buffer> Optional data to writeencoding
<String> The encoding, ifchunk
is a Stringcallback
<Function> Optional callback for when the stream is finished
Call this method when no more data will be written to the stream. If supplied,
the callback is attached as a listener on the 'finish'
event.
Calling stream.write()
after calling
stream.end()
will raise an error.
// write 'hello, ' and then end with 'world!'
var file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');
// writing more now is not allowed!
writable.setDefaultEncoding(encoding)#
encoding
<String> The new default encoding
Sets the default encoding for a writable stream.
writable.uncork()#
Flush all data, buffered since stream.cork()
call.
writable.write(chunk[, encoding][, callback])#
chunk
<String> | <Buffer> The data to writeencoding
<String> The encoding, ifchunk
is a Stringcallback
<Function> Callback for when this chunk of data is flushed- Returns: <Boolean>
true
if the data was handled completely.
This method writes some data to the underlying system, and calls the
supplied callback once the data has been fully handled. If an error
occurs, the callback may or may not be called with the error as its
first argument. To detect write errors, listen for the 'error'
event.
The return value indicates if you should continue writing right now.
If the data had to be buffered internally, then it will return
false
. Otherwise, it will return true
.
This return value is strictly advisory. You MAY continue to write,
even if it returns false
. However, writes will be buffered in
memory, so it is best not to do this excessively. Instead, wait for
the 'drain'
event before writing more data.
API for Stream Implementors#
To implement any sort of stream, the pattern is the same:
- Extend the appropriate parent class in your own subclass. (The
util.inherits()
method is particularly helpful for this.) - Call the appropriate parent class constructor in your constructor, to be sure that the internal mechanisms are set up properly.
- Implement one or more specific methods, as detailed below.
The class to extend and the method(s) to implement depend on the sort of stream class you are writing:
Use-case |
Class |
Method(s) to implement |
---|---|---|
Reading only |
||
Writing only |
||
Reading and writing |
||
Operate on written data, then read the result |
In your implementation code, it is very important to never call the methods described in API for Stream Consumers. Otherwise, you can potentially cause adverse side effects in programs that consume your streaming interfaces.
Class: stream.Duplex#
A "duplex" stream is one that is both Readable and Writable, such as a TCP socket connection.
Note that stream.Duplex
is an abstract class designed to be extended
with an underlying implementation of the stream._read(size)
and stream._write(chunk, encoding, callback)
methods as you
would with a Readable or Writable stream class.
Since JavaScript doesn't have multiple prototypal inheritance, this class
prototypally inherits from Readable, and then parasitically from Writable. It is
thus up to the user to implement both the low-level
stream._read(n)
method as well as the low-level
stream._write(chunk, encoding, callback)
method on extension
duplex classes.
new stream.Duplex(options)#
options
<Object> Passed to both Writable and Readable constructors. Also has the following fields:allowHalfOpen
<Boolean> Default =true
. If set tofalse
, then the stream will automatically end the readable side when the writable side ends and vice versa.readableObjectMode
<Boolean> Default =false
. SetsobjectMode
for readable side of the stream. Has no effect ifobjectMode
istrue
.writableObjectMode
<Boolean> Default =false
. SetsobjectMode
for writable side of the stream. Has no effect ifobjectMode
istrue
.
In classes that extend the Duplex class, make sure to call the constructor so that the buffering settings can be properly initialized.
Class: stream.PassThrough#
This is a trivial implementation of a Transform stream that simply passes the input bytes across to the output. Its purpose is mainly for examples and testing, but there are occasionally use cases where it can come in handy as a building block for novel sorts of streams.
Class: stream.Readable#
stream.Readable
is an abstract class designed to be extended with an
underlying implementation of the stream._read(size)
method.
Please see API for Stream Consumers for how to consume streams in your programs. What follows is an explanation of how to implement Readable streams in your programs.
new stream.Readable(options)#
options
<Object>highWaterMark
<Number> The maximum number of bytes to store in the internal buffer before ceasing to read from the underlying resource. Default =16384
(16kb), or16
forobjectMode
streamsencoding
<String> If specified, then buffers will be decoded to strings using the specified encoding. Default =null
objectMode
<Boolean> Whether this stream should behave as a stream of objects. Meaning thatstream.read(n)
returns a single value instead of a Buffer of size n. Default =false
read
<Function> Implementation for thestream._read()
method.
In classes that extend the Readable class, make sure to call the Readable constructor so that the buffering settings can be properly initialized.
readable._read(size)#
size
<Number> Number of bytes to read asynchronously
Note: Implement this method, but do NOT call it directly.
This method is prefixed with an underscore because it is internal to the class that defines it and should only be called by the internal Readable class methods. All Readable stream implementations must provide a _read method to fetch data from the underlying resource.
When _read()
is called, if data is available from the resource, the _read()
implementation should start pushing that data into the read queue by calling
this.push(dataChunk)
. _read()
should continue reading from
the resource and pushing data until push returns false
, at which point it
should stop reading from the resource. Only when _read()
is called again after
it has stopped should it start reading more data from the resource and pushing
that data onto the queue.
Note: once the _read()
method is called, it will not be called again until
the stream.push()
method is called.
The size
argument is advisory. Implementations where a "read" is a
single call that returns data can use this to know how much data to
fetch. Implementations where that is not relevant, such as TCP or
TLS, may ignore this argument, and simply provide data whenever it
becomes available. There is no need, for example to "wait" until
size
bytes are available before calling stream.push(chunk)
.
readable.push(chunk[, encoding])#
Note: This method should be called by Readable implementors, NOT by consumers of Readable streams.
If a value other than null is passed, The push()
method adds a chunk of data
into the queue for subsequent stream processors to consume. If null
is
passed, it signals the end of the stream (EOF), after which no more data
can be written.
The data added with push()
can be pulled out by calling the
stream.read()
method when the 'readable'
event fires.
This API is designed to be as flexible as possible. For example, you may be wrapping a lower-level source which has some sort of pause/resume mechanism, and a data callback. In those cases, you could wrap the low-level source object by doing something like this:
// source is an object with readStop() and readStart() methods,
// and an `ondata` member that gets called when it has data, and
// an `onend` member that gets called when the data is over.
util.inherits(SourceWrapper, Readable);
function SourceWrapper(options) {
Readable.call(this, options);
this._source = getLowlevelSourceObject();
// Every time there's data, we push it into the internal buffer.
this._source.ondata = (chunk) => {
// if push() returns false, then we need to stop reading from source
if (!this.push(chunk))
this._source.readStop();
};
// When the source ends, we push the EOF-signaling `null` chunk
this._source.onend = () => {
this.push(null);
};
}
// _read will be called when the stream wants to pull more data in
// the advisory size argument is ignored in this case.
SourceWrapper.prototype._read = function(size) {
this._source.readStart();
};
Example: A Counting Stream#
This is a basic example of a Readable stream. It emits the numerals from 1 to 1,000,000 in ascending order, and then ends.
const Readable = require('stream').Readable;
const util = require('util');
util.inherits(Counter, Readable);
function Counter(opt) {
Readable.call(this, opt);
this._max = 1000000;
this._index = 1;
}
Counter.prototype._read = function() {
var i = this._index++;
if (i > this._max)
this.push(null);
else {
var str = '' + i;
var buf = new Buffer(str, 'ascii');
this.push(buf);
}
};
Example: SimpleProtocol v1 (Sub-optimal)#
This is similar to the parseHeader
function described
here, but implemented as a custom stream.
Also, note that this implementation does not convert the incoming data to a
string.
However, this would be better implemented as a Transform stream. See SimpleProtocol v2 for a better implementation.
// A parser for a simple data protocol.
// The "header" is a JSON object, followed by 2 \n characters, and
// then a message body.
//
// NOTE: This can be done more simply as a Transform stream!
// Using Readable directly for this is sub-optimal. See the
// alternative example below under the Transform section.
const Readable = require('stream').Readable;
const util = require('util');
util.inherits(SimpleProtocol, Readable);
function SimpleProtocol(source, options) {
if (!(this instanceof SimpleProtocol))
return new SimpleProtocol(source, options);
Readable.call(this, options);
this._inBody = false;
this._sawFirstCr = false;
// source is a readable stream, such as a socket or file
this._source = source;
source.on('end', () => {
this.push(null);
});
// give it a kick whenever the source is readable
// read(0) will not consume any bytes
source.on('readable', () => {
this.read(0);
});
this._rawHeader = [];
this.header = null;
}
SimpleProtocol.prototype._read = function(n) {
if (!this._inBody) {
var chunk = this._source.read();
// if the source doesn't have data, we don't have data yet.
if (chunk === null)
return this.push('');
// check if the chunk has a \n\n
var split = -1;
for (var i = 0; i < chunk.length; i++) {
if (chunk[i] === 10) { // '\n'
if (this._sawFirstCr) {
split = i;
break;
} else {
this._sawFirstCr = true;
}
} else {
this._sawFirstCr = false;
}
}
if (split === -1) {
// still waiting for the \n\n
// stash the chunk, and try again.
this._rawHeader.push(chunk);
this.push('');
} else {
this._inBody = true;
var h = chunk.slice(0, split);
this._rawHeader.push(h);
var header = Buffer.concat(this._rawHeader).toString();
try {
this.header = JSON.parse(header);
} catch (er) {
this.emit('error', new Error('invalid simple protocol data'));
return;
}
// now, because we got some extra data, unshift the rest
// back into the read queue so that our consumer will see it.
var b = chunk.slice(split);
this.unshift(b);
// calling unshift by itself does not reset the reading state
// of the stream; since we're inside _read, doing an additional
// push('') will reset the state appropriately.
this.push('');
// and let them know that we are done parsing the header.
this.emit('header', this.header);
}
} else {
// from there on, just provide the data to our consumer.
// careful not to push(null), since that would indicate EOF.
var chunk = this._source.read();
if (chunk) this.push(chunk);
}
};
// Usage:
// var parser = new SimpleProtocol(source);
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.
Class: stream.Transform#
A "transform" stream is a duplex stream where the output is causally connected in some way to the input, such as a zlib stream or a crypto stream.
There is no requirement that the output be the same size as the input, the same number of chunks, or arrive at the same time. For example, a Hash stream will only ever have a single chunk of output which is provided when the input is ended. A zlib stream will produce output that is either much smaller or much larger than its input.
Rather than implement the stream._read()
and
stream._write()
methods, Transform classes must implement the
stream._transform()
method, and may optionally
also implement the stream._flush()
method. (See below.)
new stream.Transform(options)#
options
<Object> Passed to both Writable and Readable constructors. Also has the following fields:transform
<Function> Implementation for thestream._transform()
method.flush
<Function> Implementation for thestream._flush()
method.
In classes that extend the Transform class, make sure to call the constructor so that the buffering settings can be properly initialized.
Events: 'finish' and 'end'#
The 'finish'
and 'end'
events are from the parent Writable
and Readable classes respectively. The 'finish'
event is fired after
stream.end()
is called and all chunks have been processed by
stream._transform()
, 'end'
is fired after all data has
been output which is after the callback in stream._flush()
has been called.
transform._flush(callback)#
callback
<Function> Call this function (optionally with an error argument) when you are done flushing any remaining data.
Note: This function MUST NOT be called directly. It MAY be implemented by child classes, and if so, will be called by the internal Transform class methods only.
In some cases, your transform operation may need to emit a bit more
data at the end of the stream. For example, a Zlib
compression
stream will store up some internal state so that it can optimally
compress the output. At the end, however, it needs to do the best it
can with what is left, so that the data will be complete.
In those cases, you can implement a _flush()
method, which will be
called at the very end, after all the written data is consumed, but
before emitting 'end'
to signal the end of the readable side. Just
like with stream._transform()
, call
transform.push(chunk)
zero or more times, as appropriate, and call callback
when the flush operation is complete.
This method is prefixed with an underscore because it is internal to the class that defines it, and should not be called directly by user programs. However, you are expected to override this method in your own extension classes.
transform._transform(chunk, encoding, callback)#
chunk
<Buffer> | <String> The chunk to be transformed. Will always be a buffer unless thedecodeStrings
option was set tofalse
.encoding
<String> If the chunk is a string, then this is the encoding type. If chunk is a buffer, then this is the special value - 'buffer', ignore it in this case.callback
<Function> Call this function (optionally with an error argument and data) when you are done processing the supplied chunk.
Note: This function MUST NOT be called directly. It should be implemented by child classes, and called by the internal Transform class methods only.
All Transform stream implementations must provide a _transform()
method to accept input and produce output.
_transform()
should do whatever has to be done in this specific
Transform class, to handle the bytes being written, and pass them off
to the readable portion of the interface. Do asynchronous I/O,
process things, and so on.
Call transform.push(outputChunk)
0 or more times to generate output
from this input chunk, depending on how much data you want to output
as a result of this chunk.
Call the callback function only when the current chunk is completely consumed. Note that there may or may not be output as a result of any particular input chunk. If you supply a second argument to the callback it will be passed to the push method. In other words the following are equivalent:
transform.prototype._transform = function (data, encoding, callback) {
this.push(data);
callback();
};
transform.prototype._transform = function (data, encoding, callback) {
callback(null, data);
};
This method is prefixed with an underscore because it is internal to the class that defines it, and should not be called directly by user programs. However, you are expected to override this method in your own extension classes.
Example: SimpleProtocol
parser v2#
The example here of a simple
protocol parser can be implemented simply by using the higher level
Transform stream class, similar to the parseHeader
and SimpleProtocol
v1
examples.
In this example, rather than providing the input as an argument, it would be piped into the parser, which is a more idiomatic Node.js stream approach.
const util = require('util');
const Transform = require('stream').Transform;
util.inherits(SimpleProtocol, Transform);
function SimpleProtocol(options) {
if (!(this instanceof SimpleProtocol))
return new SimpleProtocol(options);
Transform.call(this, options);
this._inBody = false;
this._sawFirstCr = false;
this._rawHeader = [];
this.header = null;
}
SimpleProtocol.prototype._transform = function(chunk, encoding, done) {
if (!this._inBody) {
// check if the chunk has a \n\n
var split = -1;
for (var i = 0; i < chunk.length; i++) {
if (chunk[i] === 10) { // '\n'
if (this._sawFirstCr) {
split = i;
break;
} else {
this._sawFirstCr = true;
}
} else {
this._sawFirstCr = false;
}
}
if (split === -1) {
// still waiting for the \n\n
// stash the chunk, and try again.
this._rawHeader.push(chunk);
} else {
this._inBody = true;
var h = chunk.slice(0, split);
this._rawHeader.push(h);
var header = Buffer.concat(this._rawHeader).toString();
try {
this.header = JSON.parse(header);
} catch (er) {
this.emit('error', new Error('invalid simple protocol data'));
return;
}
// and let them know that we are done parsing the header.
this.emit('header', this.header);
// now, because we got some extra data, emit this first.
this.push(chunk.slice(split));
}
} else {
// from there on, just provide the data to our consumer as-is.
this.push(chunk);
}
done();
};
// Usage:
// var parser = new SimpleProtocol();
// source.pipe(parser)
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.
Class: stream.Writable#
stream.Writable
is an abstract class designed to be extended with an
underlying implementation of the
stream._write(chunk, encoding, callback)
method.
Please see API for Stream Consumers for how to consume writable streams in your programs. What follows is an explanation of how to implement Writable streams in your programs.
new stream.Writable(options)#
options
<Object>highWaterMark
<Number> Buffer level whenstream.write()
starts returningfalse
. Default =16384
(16kb), or16
forobjectMode
streams.decodeStrings
<Boolean> Whether or not to decode strings into Buffers before passing them tostream._write()
. Default =true
objectMode
<Boolean> Whether or not thestream.write(anyObj)
is a valid operation. If set you can write arbitrary data instead of onlyBuffer
/String
data. Default =false
write
<Function> Implementation for thestream._write()
method.writev
<Function> Implementation for thestream._writev()
method.
In classes that extend the Writable class, make sure to call the constructor so that the buffering settings can be properly initialized.
writable._write(chunk, encoding, callback)#
chunk
<Buffer> | <String> The chunk to be written. Will always be a buffer unless thedecodeStrings
option was set tofalse
.encoding
<String> If the chunk is a string, then this is the encoding type. If chunk is a buffer, then this is the special value - 'buffer', ignore it in this case.callback
<Function> Call this function (optionally with an error argument) when you are done processing the supplied chunk.
All Writable stream implementations must provide a
stream._write()
method to send data to the underlying
resource.
Note: This function MUST NOT be called directly. It should be implemented by child classes, and called by the internal Writable class methods only.
Call the callback using the standard callback(error)
pattern to
signal that the write completed successfully or with an error.
If the decodeStrings
flag is set in the constructor options, then
chunk
may be a string rather than a Buffer, and encoding
will
indicate the sort of string that it is. This is to support
implementations that have an optimized handling for certain string
data encodings. If you do not explicitly set the decodeStrings
option to false
, then you can safely ignore the encoding
argument,
and assume that chunk
will always be a Buffer.
This method is prefixed with an underscore because it is internal to the class that defines it, and should not be called directly by user programs. However, you are expected to override this method in your own extension classes.
writable._writev(chunks, callback)#
chunks
<Array> The chunks to be written. Each chunk has following format:{ chunk: ..., encoding: ... }
.callback
<Function> Call this function (optionally with an error argument) when you are done processing the supplied chunks.
Note: This function MUST NOT be called directly. It may be implemented by child classes, and called by the internal Writable class methods only.
This function is completely optional to implement. In most cases it is unnecessary. If implemented, it will be called with all the chunks that are buffered in the write queue.
Simplified Constructor API#
In simple cases there is now the added benefit of being able to construct a stream without inheritance.
This can be done by passing the appropriate methods as constructor options:
Examples:
Duplex#
var duplex = new stream.Duplex({
read: function(n) {
// sets this._read under the hood
// push data onto the read queue, passing null
// will signal the end of the stream (EOF)
this.push(chunk);
},
write: function(chunk, encoding, next) {
// sets this._write under the hood
// An optional error can be passed as the first argument
next()
}
});
// or
var duplex = new stream.Duplex({
read: function(n) {
// sets this._read under the hood
// push data onto the read queue, passing null
// will signal the end of the stream (EOF)
this.push(chunk);
},
writev: function(chunks, next) {
// sets this._writev under the hood
// An optional error can be passed as the first argument
next()
}
});
Readable#
var readable = new stream.Readable({
read: function(n) {
// sets this._read under the hood
// push data onto the read queue, passing null
// will signal the end of the stream (EOF)
this.push(chunk);
}
});
Transform#
var transform = new stream.Transform({
transform: function(chunk, encoding, next) {
// sets this._transform under the hood
// generate output as many times as needed
// this.push(chunk);
// call when the current chunk is consumed
next();
},
flush: function(done) {
// sets this._flush under the hood
// generate output as many times as needed
// this.push(chunk);
done();
}
});
Writable#
var writable = new stream.Writable({
write: function(chunk, encoding, next) {
// sets this._write under the hood
// An optional error can be passed as the first argument
next()
}
});
// or
var writable = new stream.Writable({
writev: function(chunks, next) {
// sets this._writev under the hood
// An optional error can be passed as the first argument
next()
}
});
Streams: Under the Hood#
Buffering#
Both Writable and Readable streams will buffer data on an internal
object which can be retrieved from _writableState.getBuffer()
or
_readableState.buffer
, respectively.
The amount of data that will potentially be buffered depends on the
highWaterMark
option which is passed into the constructor.
Buffering in Readable streams happens when the implementation calls
stream.push(chunk)
. If the consumer of the Stream does not
call stream.read()
, then the data will sit in the internal
queue until it is consumed.
Buffering in Writable streams happens when the user calls
stream.write(chunk)
repeatedly, even when it returns false
.
The purpose of streams, especially with the stream.pipe()
method, is to
limit the buffering of data to acceptable levels, so that sources and
destinations of varying speed will not overwhelm the available memory.
Compatibility with Older Node.js Versions#
In versions of Node.js prior to v0.10, the Readable stream interface was simpler, but also less powerful and less useful.
- Rather than waiting for you to call the
stream.read()
method,'data'
events would start emitting immediately. If you needed to do some I/O to decide how to handle data, then you had to store the chunks in some kind of buffer so that they would not be lost. - The
stream.pause()
method was advisory, rather than guaranteed. This meant that you still had to be prepared to receive'data'
events even when the stream was in a paused state.
In Node.js v0.10, the Readable class was added.
For backwards compatibility with older Node.js programs, Readable streams
switch into "flowing mode" when a 'data'
event handler is added, or
when the stream.resume()
method is called. The effect is
that, even if you are not using the new stream.read()
method
and 'readable'
event, you no longer have to worry about losing
'data'
chunks.
Most programs will continue to function normally. However, this introduces an edge case in the following conditions:
- No
'data'
event handler is added. - The
stream.resume()
method is never called. - The stream is not piped to any writable destination.
For example, consider the following code:
// WARNING! BROKEN!
net.createServer((socket) => {
// we add an 'end' method, but never consume the data
socket.on('end', () => {
// It will never get here.
socket.end('I got your message (but didnt read it)\n');
});
}).listen(1337);
In versions of Node.js prior to v0.10, the incoming message data would be simply discarded. However, in Node.js v0.10 and beyond, the socket will remain paused forever.
The workaround in this situation is to call the
stream.resume()
method to start the flow of data:
// Workaround
net.createServer((socket) => {
socket.on('end', () => {
socket.end('I got your message (but didnt read it)\n');
});
// start the flow of data, discarding it.
socket.resume();
}).listen(1337);
In addition to new Readable streams switching into flowing mode,
pre-v0.10 style streams can be wrapped in a Readable class using the
stream.wrap()
method.
Object Mode#
Normally, Streams operate on Strings and Buffers exclusively.
Streams that are in object mode can emit generic JavaScript values other than Buffers and Strings.
A Readable stream in object mode will always return a single item from
a call to stream.read(size)
, regardless of what the size
argument is.
A Writable stream in object mode will always ignore the encoding
argument to stream.write(data, encoding)
.
The special value null
still retains its special value for object
mode streams. That is, for object mode readable streams, null
as a
return value from stream.read()
indicates that there is no more
data, and stream.push(null)
will signal the end of stream data
(EOF
).
No streams in Node.js core are object mode streams. This pattern is only used by userland streaming libraries.
You should set objectMode
in your stream child class constructor on
the options object. Setting objectMode
mid-stream is not safe.
For Duplex streams objectMode
can be set exclusively for readable or
writable side with readableObjectMode
and writableObjectMode
respectively. These options can be used to implement parsers and
serializers with Transform streams.
const util = require('util');
const StringDecoder = require('string_decoder').StringDecoder;
const Transform = require('stream').Transform;
util.inherits(JSONParseStream, Transform);
// Gets \n-delimited JSON string data, and emits the parsed objects
function JSONParseStream() {
if (!(this instanceof JSONParseStream))
return new JSONParseStream();
Transform.call(this, { readableObjectMode : true });
this._buffer = '';
this._decoder = new StringDecoder('utf8');
}
JSONParseStream.prototype._transform = function(chunk, encoding, cb) {
this._buffer += this._decoder.write(chunk);
// split on newlines
var lines = this._buffer.split(/\r?\n/);
// keep the last partial line buffered
this._buffer = lines.pop();
for (var l = 0; l < lines.length; l++) {
var line = lines[l];
try {
var obj = JSON.parse(line);
} catch (er) {
this.emit('error', er);
return;
}
// push the parsed object out to the readable consumer
this.push(obj);
}
cb();
};
JSONParseStream.prototype._flush = function(cb) {
// Just handle any leftover
var rem = this._buffer.trim();
if (rem) {
try {
var obj = JSON.parse(rem);
} catch (er) {
this.emit('error', er);
return;
}
// push the parsed object out to the readable consumer
this.push(obj);
}
cb();
};
stream.read(0)
#
There are some cases where you want to trigger a refresh of the
underlying readable stream mechanisms, without actually consuming any
data. In that case, you can call stream.read(0)
, which will always
return null.
If the internal read buffer is below the highWaterMark
, and the
stream is not currently reading, then calling stream.read(0)
will trigger
a low-level stream._read()
call.
There is almost never a need to do this. However, you will see some cases in Node.js's internals where this is done, particularly in the Readable stream class internals.
stream.push('')
#
Pushing a zero-byte string or Buffer (when not in Object mode) has an
interesting side effect. Because it is a call to
stream.push()
, it will end the reading
process. However, it
does not add any data to the readable buffer, so there's nothing for
a user to consume.
Very rarely, there are cases where you have no data to provide now,
but the consumer of your stream (or, perhaps, another bit of your own
code) will know when to check again, by calling stream.read(0)
.
In those cases, you may call stream.push('')
.
So far, the only use case for this functionality is in the
tls.CryptoStream
class, which is deprecated in Node.js/io.js v1.0. If you
find that you have to use stream.push('')
, please consider another
approach, because it almost certainly indicates that something is
horribly wrong.
StringDecoder#
Stability: 2 - Stable
To use this module, do require('string_decoder')
. StringDecoder decodes a
buffer to a string. It is a simple interface to buffer.toString()
but provides
additional support for utf8.
const StringDecoder = require('string_decoder').StringDecoder;
const decoder = new StringDecoder('utf8');
const cent = new Buffer([0xC2, 0xA2]);
console.log(decoder.write(cent));
const euro = new Buffer([0xE2, 0x82, 0xAC]);
console.log(decoder.write(euro));
Class: StringDecoder#
Accepts a single argument, encoding
which defaults to 'utf8'
.
decoder.end()#
Returns any trailing bytes that were left in the buffer.
decoder.write(buffer)#
Returns a decoded string.
Timers#
Stability: 3 - Locked
All of the timer functions are globals. You do not need to require()
this module in order to use them.
clearImmediate(immediateObject)#
Stops an immediateObject
, as created by setImmediate
, from triggering.
clearInterval(intervalObject)#
Stops an intervalObject
, as created by setInterval
, from triggering.
clearTimeout(timeoutObject)#
Prevents a timeoutObject
, as created by setTimeout
, from triggering.
ref()#
If a timer was previously unref()
d, then ref()
can be called to explicitly
request the timer hold the program open. If the timer is already ref
d calling
ref
again will have no effect.
Returns the timer.
setImmediate(callback[, arg][, ...])#
Schedules "immediate" execution of callback
after I/O events'
callbacks and before timers set by setTimeout
and setInterval
are
triggered. Returns an immediateObject
for possible use with
clearImmediate
. Additional optional arguments may be passed to the
callback.
Callbacks for immediates are queued in the order in which they were created. The entire callback queue is processed every event loop iteration. If an immediate is queued from inside an executing callback, that immediate won't fire until the next event loop iteration.
If callback
is not a function setImmediate()
will throw immediately.
setInterval(callback, delay[, arg][, ...])#
Schedules repeated execution of callback
every delay
milliseconds.
Returns a intervalObject
for possible use with clearInterval
. Additional
optional arguments may be passed to the callback.
To follow browser behavior, when using delays larger than 2147483647
milliseconds (approximately 25 days) or less than 1, Node.js will use 1 as the
delay
.
If callback
is not a function setInterval()
will throw immediately.
setTimeout(callback, delay[, arg][, ...])#
Schedules execution of a one-time callback
after delay
milliseconds.
Returns a timeoutObject
for possible use with clearTimeout
. Additional
optional arguments may be passed to the callback.
The callback will likely not be invoked in precisely delay
milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.
To follow browser behavior, when using delays larger than 2147483647
milliseconds (approximately 25 days) or less than 1, the timeout is executed
immediately, as if the delay
was set to 1.
If callback
is not a function setTimeout()
will throw immediately.
unref()#
The opaque value returned by setTimeout
and setInterval
also has the
method timer.unref()
which allows the creation of a timer that is active but
if it is the only item left in the event loop, it won't keep the program
running. If the timer is already unref
d calling unref
again will have no
effect.
In the case of setTimeout
, unref
creates a separate timer that will
wakeup the event loop, creating too many of these may adversely effect event
loop performance -- use wisely.
Returns the timer.
TLS (SSL)#
Stability: 2 - Stable
Use require('tls')
to access this module.
The tls
module uses OpenSSL to provide Transport Layer Security and/or
Secure Socket Layer: encrypted stream communication.
TLS/SSL is a public/private key infrastructure. Each client and each server must have a private key. A private key is created like this:
openssl genrsa -out ryans-key.pem 2048
All servers and some clients need to have a certificate. Certificates are public keys signed by a Certificate Authority or self-signed. The first step to getting a certificate is to create a "Certificate Signing Request" (CSR) file. This is done with:
openssl req -new -sha256 -key ryans-key.pem -out ryans-csr.pem
To create a self-signed certificate with the CSR, do this:
openssl x509 -req -in ryans-csr.pem -signkey ryans-key.pem -out ryans-cert.pem
Alternatively you can send the CSR to a Certificate Authority for signing.
For Perfect Forward Secrecy, it is required to generate Diffie-Hellman parameters:
openssl dhparam -outform PEM -out dhparam.pem 2048
To create a .pfx or .p12, do this:
openssl pkcs12 -export -in agent5-cert.pem -inkey agent5-key.pem \
-certfile ca-cert.pem -out agent5.pfx
in
: certificateinkey
: private keycertfile
: all CA certs concatenated in one file likecat ca1-cert.pem ca2-cert.pem > ca-cert.pem
ALPN, NPN and SNI#
ALPN (Application-Layer Protocol Negotiation Extension), NPN (Next Protocol Negotiation) and, SNI (Server Name Indication) are TLS handshake extensions:
- ALPN/NPN - Allows the use of one TLS server for multiple protocols (HTTP, SPDY, HTTP/2)
- SNI - Allows the use of one TLS server for multiple hostnames with different SSL certificates.
Client-initiated renegotiation attack mitigation#
The TLS protocol lets the client renegotiate certain aspects of the TLS session. Unfortunately, session renegotiation requires a disproportionate amount of server-side resources, which makes it a potential vector for denial-of-service attacks.
To mitigate this, renegotiation is limited to three times every 10 minutes. An
error is emitted on the tls.TLSSocket
instance when the threshold is
exceeded. These limits are configurable:
tls.CLIENT_RENEG_LIMIT
: renegotiation limit, default is 3.tls.CLIENT_RENEG_WINDOW
: renegotiation window in seconds, default is 10 minutes.
Do not change the defaults without a full understanding of the implications.
To test the server, connect to it with openssl s_client -connect address:port
and tap R<CR>
(i.e., the letter R
followed by a carriage return) a few
times.
Modifying the Default TLS Cipher suite#
Node.js is built with a default suite of enabled and disabled TLS ciphers. Currently, the default cipher suite is:
ECDHE-RSA-AES128-GCM-SHA256:
ECDHE-ECDSA-AES128-GCM-SHA256:
ECDHE-RSA-AES256-GCM-SHA384:
ECDHE-ECDSA-AES256-GCM-SHA384:
DHE-RSA-AES128-GCM-SHA256:
ECDHE-RSA-AES128-SHA256:
DHE-RSA-AES128-SHA256:
ECDHE-RSA-AES256-SHA384:
DHE-RSA-AES256-SHA384:
ECDHE-RSA-AES256-SHA256:
DHE-RSA-AES256-SHA256:
HIGH:
!aNULL:
!eNULL:
!EXPORT:
!DES:
!RC4:
!MD5:
!PSK:
!SRP:
!CAMELLIA
This default can be overriden entirely using the --tls-cipher-list
command
line switch. For instance, the following makes
ECDHE-RSA-AES128-GCM-SHA256:!RC4
the default TLS cipher suite:
node --tls-cipher-list="ECDHE-RSA-AES128-GCM-SHA256:!RC4"
Note that the default cipher suite included within Node.js has been carefully
selected to reflect current security best practices and risk mitigation.
Changing the default cipher suite can have a significant impact on the security
of an application. The --tls-cipher-list
switch should by used only if
absolutely necessary.
Perfect Forward Secrecy#
The term "Forward Secrecy" or "Perfect Forward Secrecy" describes a feature of key-agreement (i.e., key-exchange) methods. Practically it means that even if the private key of a server is compromised, communication can only be decrypted by eavesdroppers if they manage to obtain the key-pair specifically generated for each session.
This is achieved by randomly generating a key pair for key-agreement on every handshake (in contrast to using the same key for all sessions). Methods implementing this technique, thus offering Perfect Forward Secrecy, are called "ephemeral".
Currently two methods are commonly used to achieve Perfect Forward Secrecy (note the character "E" appended to the traditional abbreviations):
- DHE - An ephemeral version of the Diffie Hellman key-agreement protocol.
- ECDHE - An ephemeral version of the Elliptic Curve Diffie Hellman key-agreement protocol.
Ephemeral methods may have some performance drawbacks, because key generation is expensive.
Class: CryptoStream#
Stability: 0 - Deprecated: Use tls.TLSSocket
instead.
This is an encrypted stream.
cryptoStream.bytesWritten#
A proxy to the underlying socket's bytesWritten accessor, this will return the total bytes written to the socket, including the TLS overhead.
Class: SecurePair#
Returned by tls.createSecurePair.
Event: 'secure'#
This event is emitted from the SecurePair once the pair has successfully established a secure connection.
As with checking for the server secureConnection
event, pair.cleartext.authorized
should be inspected to confirm whether the
certificate used is properly authorized.
Class: tls.Server#
This class is a subclass of net.Server
and has the same methods on it.
Instead of accepting only raw TCP connections, this accepts encrypted
connections using TLS or SSL.
Event: 'tlsClientError'#
function (exception, tlsSocket) { }
When a client connection emits an 'error'
event before a secure connection is
established it will be forwarded here.
tlsSocket
is the tls.TLSSocket
that the error originated from.
Event: 'newSession'#
function (sessionId, sessionData, callback) { }
Emitted on creation of a TLS session. May be used to store sessions in external
storage. callback
must be invoked eventually, otherwise no data will be
sent or received from the secure connection.
NOTE: adding this event listener will only have an effect on connections established after the addition of the event listener.
Event: 'OCSPRequest'#
function (certificate, issuer, callback) { }
Emitted when the client sends a certificate status request. The server's
current certificate can be parsed to obtain the OCSP URL and certificate ID;
after obtaining an OCSP response callback(null, resp)
is then invoked, where
resp
is a Buffer
instance. Both certificate
and issuer
are Buffer
DER-representations of the primary and issuer's certificates. They can be used
to obtain the OCSP certificate ID and OCSP endpoint URL.
Alternatively, callback(null, null)
may be called, meaning that there was no
OCSP response.
Calling callback(err)
will result in a socket.destroy(err)
call.
Typical flow:
- Client connects to the server and sends an
'OCSPRequest'
to it (via status info extension in ClientHello). - Server receives the request and invokes the
'OCSPRequest'
event listener if present. - Server extracts the OCSP URL from either the
certificate
orissuer
and performs an OCSP request to the CA. - Server receives
OCSPResponse
from the CA and sends it back to the client via thecallback
argument - Client validates the response and either destroys the socket or performs a handshake.
NOTE: issuer
could be null
if the certificate is self-signed or if the
issuer is not in the root certificates list. (An issuer may be provided via the
ca
option.)
NOTE: adding this event listener will only have an effect on connections established after the addition of the event listener.
NOTE: An npm module like asn1.js may be used to parse the certificates.
Event: 'resumeSession'#
function (sessionId, callback) { }
Emitted when the client wants to resume the previous TLS session. The event
listener may perform a lookup in external storage using the given sessionId
and invoke callback(null, sessionData)
once finished. If the session can't be
resumed (i.e., doesn't exist in storage) one may call callback(null, null)
.
Calling callback(err)
will terminate incoming connection and destroy the
socket.
NOTE: adding this event listener will only have an effect on connections established after the addition of the event listener.
Here's an example for using TLS session resumption:
var tlsSessionStore = {};
server.on('newSession', (id, data, cb) => {
tlsSessionStore[id.toString('hex')] = data;
cb();
});
server.on('resumeSession', (id, cb) => {
cb(null, tlsSessionStore[id.toString('hex')] || null);
});
Event: 'secureConnection'#
function (tlsSocket) {}
This event is emitted after the handshaking process for a new connection has
successfully completed. The argument is an instance of tls.TLSSocket
and
has all the common stream methods and events.
socket.authorized
is a boolean value which indicates if the
client has been verified by one of the supplied certificate authorities for the
server. If socket.authorized
is false, then socket.authorizationError
is
set to describe how authorization failed. Implied but worth mentioning:
depending on the settings of the TLS server, unauthorized connections may
be accepted.
socket.npnProtocol
is a string containing the selected NPN protocol
and socket.alpnProtocol
is a string containing the selected ALPN
protocol. When both NPN and ALPN extensions are received, ALPN takes
precedence over NPN and the next protocol is selected by ALPN. When
ALPN has no selected protocol, this returns false.
socket.servername
is a string containing the server name requested with
SNI.
server.addContext(hostname, context)#
Add secure context that will be used if the client request's SNI hostname
matches the supplied hostname
(wildcards can be used). context
can contain
key
, cert
, ca
or any other properties from
tls.createSecureContext()
options
argument.
server.address()#
Returns the bound address, the address family name, and port of the
server as reported by the operating system. See net.Server.address()
for
more information.
server.close([callback])#
Stops the server from accepting new connections. This function is
asynchronous, the server is finally closed when the server emits a 'close'
event. Optionally, you can pass a callback to listen for the 'close'
event.
server.connections#
The number of concurrent connections on the server.
server.getTicketKeys()#
Returns a Buffer
instance holding the keys currently used for
encryption/decryption of the TLS Session Tickets
server.listen(port[, hostname][, callback])#
Begin accepting connections on the specified port
and hostname
. If the
hostname
is omitted, the server will accept connections on any IPv6 address
(::
) when IPv6 is available, or any IPv4 address (0.0.0.0
) otherwise. A
port value of zero will assign a random port.
This function is asynchronous. The last parameter callback
will be called
when the server has been bound.
See net.Server
for more information.
server.setTicketKeys(keys)#
Updates the keys for encryption/decryption of the TLS Session Tickets.
NOTE: the buffer should be 48 bytes long. See ticketKeys
option in
tls.createServer for
more information on how it is used.
NOTE: the change is effective only for future server connections. Existing or currently pending server connections will use the previous keys.
server.maxConnections#
Set this property to reject connections when the server's connection count exceeds the specified threshold.
Class: tls.TLSSocket#
This is a wrapped version of net.Socket
that does transparent encryption
of written data and all required TLS negotiation.
This instance implements the duplex Stream interface. It has all the common stream methods and events.
Methods that return TLS connection metadata (e.g.
tls.TLSSocket.getPeerCertificate()
will only return data while the
connection is open.
new tls.TLSSocket(socket[, options])#
Construct a new TLSSocket object from an existing TCP socket.
socket
is an instance of net.Socket
options
is an optional object that might contain following properties: