<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
<TITLE>Apache's Handler Use</TITLE>
</HEAD>

<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
<BODY
 BGCOLOR="#FFFFFF"
 TEXT="#000000"
 LINK="#0000FF"
 VLINK="#000080"
 ALINK="#FF0000"
>
<!--#include virtual="header.html" -->
<H1 ALIGN="CENTER">Apache's Handler Use</H1>

<ul>
<li><a href="#definition">What is a Handler</a></li>
<li><a href="#examples">Examples</a></li>
<li><a href="#programmer">Programmer's Note</a></li>
</ul>

<hr>
<H2><a name="definition">What is a Handler</a></H2>

<table border="1">
<tr><td valign="top">
<strong>Related Modules</strong><br><br>

<a href="mod/mod_actions.html">mod_actions</a><br>
<A HREF="mod/mod_asis.html">mod_asis</A><br>
<A HREF="mod/mod_cgi.html">mod_cgi</A><br>
<A HREF="mod/mod_imap.html">mod_imap</A><br>
<A HREF="mod/mod_info.html">mod_info</A><br>
<a href="mod/mod_mime.html">mod_mime</a><br>
<A HREF="mod/mod_negotiation.html">mod_negotiation</A><br>
<A HREF="mod/mod_status.html">mod_status</A><br>
</td>
<td valign="top">
<strong>Related Directives</strong><br><br>

<a href="mod/mod_actions.html#action">Action</a><br>
<A HREF="mod/mod_mime.html#addhandler">AddHandler</A><br>
<a href="mod/mod_mime.html#removehandler">RemoveHandler</a><br>
<A HREF="mod/mod_mime.html#sethandler">SetHandler</A><br>
</td>
</tr></table>


<P>A "handler" is an internal Apache representation of the action to be
performed when a file is called. Generally, files have implicit
handlers, based on the file type. Normally, all files are simply
served by the server, but certain file types are "handled"
separately.</P>

<P>Apache 1.1 adds the ability to use handlers explicitly. Based on
either filename extensions or on location, handlers can be specified
without relation to file type. This is advantageous both because it is
a more elegant solution, and because it also allows for both a type
<STRONG>and</STRONG> a handler to be associated with a file. (See also
<A HREF="mod/mod_mime.html#multipleext">Files with Multiple
Extensions</A>.)</p>

<P>Handlers can either be built into the server or included in a module,
or they can be added with the <A
HREF="mod/mod_actions.html#action">Action</A> directive. The built-in
handlers in the standard distribution are as follows:</P>

<UL>
<LI><STRONG>default-handler</STRONG>:
    Send the file using the <CODE>default_handler()</CODE>, which is the 
    handler used by default to handle static content.
    (core)
<LI><STRONG>send-as-is</STRONG>:
    Send file with HTTP headers as is.
    (<A HREF="mod/mod_asis.html">mod_asis</A>)
<LI><STRONG>cgi-script</STRONG>:
    Treat the file as a CGI script.
    (<A HREF="mod/mod_cgi.html">mod_cgi</A>)
<LI><STRONG>imap-file</STRONG>:
    Parse as an imagemap rule file.
    (<A HREF="mod/mod_imap.html">mod_imap</A>)
<LI><STRONG>server-info</STRONG>:
    Get the server's configuration information.
    (<A HREF="mod/mod_info.html">mod_info</A>)
<LI><STRONG>server-status</STRONG>:
    Get the server's status report.
    (<A HREF="mod/mod_status.html">mod_status</A>)
<LI><STRONG>type-map</STRONG>:
    Parse as a type map file for content negotiation.
    (<A HREF="mod/mod_negotiation.html">mod_negotiation</A>)
</UL>

<hr>

<h2><a name="examples">Examples</a></h2>

<h3>Modifying static content using a CGI script</h3>

<p>The following directives will cause requests for files with the
<code>html</code> extension to trigger the launch of the
<code>footer.pl</code> CGI script.</p>

<pre>
     Action add-footer /cgi-bin/footer.pl
     AddHandler add-footer .html
</pre>

<p>Then the CGI script is responsible for sending the originally
requested document (pointed to by the <code>PATH_TRANSLATED</code>
environment variable) and making whatever modifications or additions
are desired.</p>

<h3>Files with HTTP headers</h3>

<p>The following directives will enable the <code>send-as-is</code>
handler, which is used for files which contain their own HTTP headers.
All files in the <code>/web/htdocs/asis/</code> directory will be
processed by the <code>send-as-is</code> handler, regardless of their
filename extensions.</p>

<pre>
    &lt;Directory /web/htdocs/asis&gt;
    SetHandler send-as-is
    &lt;/Directory&gt;
</pre>

<hr>

<H2><a name="programmer">Programmer's Note</a></H2>

<P>In order to implement the handler features, an addition has been
made to the <A HREF="misc/API.html">Apache API</A> that you may wish to
make use of. Specifically, a new record has been added to the
<CODE>request_rec</CODE> structure:</P>
<PRE>
    char *handler
</PRE>
<P>If you wish to have your module engage a handler, you need only to
set <CODE>r-&gt;handler</CODE> to the name of the handler at any time
prior to the <CODE>invoke_handler</CODE> stage of the
request. Handlers are implemented as they were before, albeit using
the handler name instead of a content type. While it is not
necessary, the naming convention for handlers is to use a
dash-separated word, with no slashes, so as to not invade the media
type name-space.</P>

<!--#include virtual="footer.html" -->
</BODY>
</HTML>

