Node:Server-side scripts, Next:, Up:XML tools



Writing web-server-side Kawa scripts

You can compile a Kawa program (written in any supported Kawa language, including Scheme, BRL, KRL, or XQuery), and run it as either servlet engine (using a web server that supports servlets), or as a "CGI script" on most web servers.

In either case, the result of evaluating the top-level expressions becomes the HTTP response that the servlet sends back to the browser. The result is typically an HTML/XML element code object; Kawa will automatically format the result as appropriate for the type. The initial result values may be special "response header values", as created by the response-header function. Kawa will use the response header values to set various required and optional fields of the HTTP response. Note that response-header does not actually do anything until it is "printed" to the standard output. Note also that if a "Content-Type" response value is printed that controls the formatting of the following non-response-header values.

Here is a simple program hello.scm:

     (require 'http) ; Required for Scheme, though not BRL/KRL.
     (response-content-type 'text/html) ; Optional
     (make-element 'p
       "The request URL was: " (request-url))
     (make-element 'p
       (let ((query (request-query-string)))
         (if query
           (values-append "The query string was: " query)
           "There was no query string.")))
     #\newline ; emit a new-line at the end
     

The same program using KRL is shorter:

     <p>The request URL was: [(request-url)]</p>,
     <p>[(let ((query (request-query-string)))
         (if query
           (begin ]The query string was: [query)
           ]There was no query string.[))]</p>
     

You can also use XQuery:

     <p>The request URL was: {request-url()}</p>
     <p>{let $query := request-query-string() return
         if ($query)
         then ("The query string was: ",$query)
         else "There was no query string."}</p>
     

Either way, you compile your program to a servlet:

     kawa --servlet -C hello.scm
     
or:
     kawa --servlet --krl -C hello.krl
     
or:
     kawa --servlet --xquery -C hello.xql
     

The next two sections will explain how you can install this script as either a servlet or a CGI script.