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== Outdated egg!

This is an egg for CHICKEN 3, the unsupported old release.  You're almost certainly looking for [[/eggref/4/stream-cgi|the CHICKEN 4 version of this egg]], if it exists.

If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-4.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN.

[[tags:eggs web cgi streams eggspublicdomain]]
[[toc:]]

== Introduction

The stream-cgi egg is useful for creating applications that run under Common Gateway Interface.

You might find the [[html-stream]] egg useful.

== Examples

The following is a trivial CGI application.
You can call it using {{?name=alejo}} as its QUERY_STRING.

<enscript highlight=scheme>
(use stream-cgi html-stream)

(cgi-main
  (lambda (get post cookies)
    (stream-append
      (string->stream "Content-type: text/html\n\n")
      (let ((name (get 'name)))
        (if (null? name)
          (html-stream (html (body (p "Hello, stranger!"))))
          (html-stream
            (html
              (body (p "Hello, " (b (car name)))))))))))
</enscript>

This is another way to do the same:

<enscript highlight=scheme>
(use stream-cgi stream-ext)

(cgi-main
  (lambda (get post cookies)
    (with-output-to-stream
      (lambda ()
        (format #t "Content-type: text/html~%~%<html><body><p>")
        (let ((name (get 'name)))
          (if (null? name)
            (format #t "Hello, stranger!")
            (format #t "Hello, <b>~A</b>" (stream->string (car name)))))
        (format #t "</p></body></html>")))))
</enscript>

== Authors

The stream-cgi egg was created by [[Alejandro Forero Cuervo]] <azul@freaks-unidos.net>.

== License

The CGI egg for Chicken Scheme is in the public domain and may be reproduced or copied without
permission from its author.  Citation of the source is appreciated.

== Requirements

This egg depends on the following:

* [[srfi-40]]
* [[stream-ext]]

== Creating a CGI application

[procedure] (cgi-main proc)

Initializes internal structures, calls the
{{proc}} procedure and, after it returns, cleans things up.

{{proc}} is passed three argument:
procedures that can used to obtain information received by the CGI from, respectively:

# The {{QUERY_STRING}} (or {{<input>}} objects in HTML forms using method {{GET}})
# The contents uploaded through HTTP post requests.
# HTTP cookies.

The functions passed to {{proc}} receive one argument,
a symbol, and return a list with all its associated values as found on the inputs.
If no values are found, the empty list
is returned.  The values are returned as srfi-40 streams of characters;
values shorter than a given threshold are kept in memory while others
are stored in temporary files.  This allows the library to use a constant
amount of memory, regardless of the size of the contents received
through HTTP.

The functions passed to {{proc}} can not be called after
{{proc}} returns.
This is because they may depend on files that get removed
when {{proc}} returns.

{{proc}} must return a srfi-40 stream with the contents
to send to the browser, including HTTP headers;
the actual headers in the HTTP response are generated
by your web server.

Temporary files are created by the library by means of
{{(create-temporary-file "chicken-cgi-input")}}.
You probably want to make sure that the
{{TMPDIR}}, {{TEMP}} or {{TMP}}
environment variables are set to a meaningful directory,
such as {{/tmp}}, where the user your application
runs as (usually {{nobody}}) has write permissions.

== Version history

=== 1.4

* Implemented parsing of multipart/form-data.

=== 1.3

* Fixed bug in invocation of <code>hash-table-walk</code> [Thanks to Michal Dybizbanski]

=== 1.2

* Adapted to SRFI-69-compatible hash-tables

=== 1.1

* Simple bug fixes

=== 1.0

* First public release

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