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      --><title>Filters - Apache HTTP Server</title><link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /><link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /><link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link href="./images/favicon.ico" rel="shortcut icon" /></head><body id="manual-page"><div id="page-header"><p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p><p class="apache">Apache HTTP Server Version 2.0</p><img alt="" src="./images/feather.gif" /></div><div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="./images/left.gif" /></a></div><div id="path"><a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs-project/">Documentation</a> &gt; <a href="./">Version 2.0</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1>
    <p>This document describes the use of filters in Apache.</p>
  </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div><div class="section"><h2><a name="filters" id="filters">Filters</a></h2>
    
    <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code></li><li><code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code></li><li><code class="module"><a href="./mod/mod_include.html">mod_include</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_mime.html#addinputfilter">AddInputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_mime.html#removeinputfilter">RemoveInputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code></li><li><code class="directive"><a href="./mod/mod_ext_filter.html#extfilterdefine">ExtFilterDefine</a></code></li><li><code class="directive"><a href="./mod/mod_ext_filter.html#extfilteroptions">ExtFilterOptions</a></code></li><li><code class="directive"><a href="./mod/core.html#setinputfilter">SetInputFilter</a></code></li><li><code class="directive"><a href="./mod/core.html#setoutputfilter">SetOutputFilter</a></code></li></ul></td></tr></table>
    
    <p>A <em>filter</em> is a process that is applied to data that
    is sent or received by the server. Data sent by clients to the
    server is processed by <em>input filters</em> while data sent
    by the server to the client is processed by <em>output
    filters</em>. Multiple filters can be applied to the data, and
    the order of the filters can be explicitly specified.</p>

    <p>Filters are used internally by Apache to perform functions such
    as chunking and byte-range request handling. In addition, modules
    can provide filters that are selectable using run-time
    configuration directives. The set of filters that apply to data
    can be manipulated with the
    <code class="directive"><a href="./mod/core.html#setinputfilter">SetInputFilter</a></code>,
    <code class="directive"><a href="./mod/core.html#setoutputfilter">SetOutputFilter</a></code>,
    <code class="directive"><a href="./mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>,
    <code class="directive"><a href="./mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>,
    <code class="directive"><a href="./mod/mod_mime.html#removeinputfilter">RemoveInputFilter</a></code>, and
    <code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code>
    directives.</p>

    <p>The following user-selectable filters are currently provided
    with the Apache HTTP Server distribution.</p>

    <dl>
      <dt>INCLUDES</dt>
      <dd>Server-Side Includes processing by <code class="module"><a href="./mod/mod_include.html">mod_include</a></code></dd>
      <dt>DEFLATE</dt>
      <dd>Compress output before sending it to the client using
          <code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code>
      </dd>
    </dl>

    <p>In addition, the module <code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code> allows
    for external programs to be defined as filters.</p>
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