apache/docs/manual/handler.xml

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<manualpage metafile="handler.xml.meta">

  <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_imagemap</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>Handlers may also be configured explicitly,
    based on either filename extensions or on location,
    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_imagemap</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>