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  <title>Apache's Handler Use</title>

  <summary>
    <p>This document describes the use of Apache's Handlers.</p>
  </summary>

  <section id="definition">
    <title>What is a Handler</title>
    <related>
      <modulelist>
        <module>mod_actions</module>
        <module>mod_asis</module>
        <module>mod_cgi</module>
        <module>mod_imap</module>
        <module>mod_info</module>
        <module>mod_mime</module>
        <module>mod_negotiation</module>
        <module>mod_status</module>
     </modulelist>
      <directivelist>
        <directive module="mod_actions">Action</directive>
        <directive module="mod_mime">AddHandler</directive>
        <directive module="mod_mime">RemoveHandler</directive>
        <directive module="core">SetHandler</directive>
      </directivelist>
    </related>
    

    <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 <directive 
    module="mod_actions">Action</directive> 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>

      <li><strong>send-as-is</strong>: Send file with HTTP headers
      as is. (<module>mod_asis</module>)</li>

      <li><strong>cgi-script</strong>: Treat the file as a CGI
      script. (<module>mod_cgi</module>)</li>

      <li><strong>imap-file</strong>: Parse as an imagemap rule
      file. (<module>mod_imap</module>)</li>

      <li><strong>server-info</strong>: Get the server's
      configuration information. (<module>mod_info</module>)</li>

      <li><strong>server-status</strong>: Get the server's status
      report. (<module>mod_status</module>)</li>

      <li><strong>type-map</strong>: Parse as a type map file for
      content negotiation. (<module>mod_negotiation</module>)</li>
    </ul>
  </section>
  <section id="examples">
    <title>Examples</title>

    <section id="example1">
      <title>Modifying static content using a CGI script</title>

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

      <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>
 
    </section>
    <section id="example2">
      <title>Files with HTTP headers</title>

      <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>

      <example>
        &lt;Directory /web/htdocs/asis&gt;<br/>
        SetHandler send-as-is<br/>
        &lt;/Directory&gt;
      </example>
      
    </section>
  </section>
  <section id="programmer">
    <title>Programmer's Note</title>

    <p>In order to implement the handler features, an addition has
    been made to the <a href="developer/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>

    <example>
      char *handler
    </example>

    <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>
  </section>
</manualpage>





