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<title>Filters - Apache HTTP Server</title>
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<p class="apache">Apache HTTP Server Version 2.0</p>
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<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/">Documentation</a> &gt; <a href="./">Version 2.0</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1>
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    <p>This document describes the use of filters in Apache.</p>
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<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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