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   8 <title>Filters - Apache HTTP Server</title>
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  14 <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>
  15 <p class="apache">Apache HTTP Server Version 2.3</p>
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  19 <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 2.3</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1>
  20 <div class="toplang">
  21 <p><span>Available Languages: </span><a href="./en/filter.html" title="English">&nbsp;en&nbsp;</a> |
  22 <a href="./es/filter.html" hreflang="es" rel="alternate" title="Español">&nbsp;es&nbsp;</a> |
  23 <a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
  24 <a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  25 <a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
  26 <a href="./tr/filter.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
  27 </div>
  28
  29     <p>This document describes the use of filters in Apache.</p>
  30   </div>
  31 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#intro">Filtering in Apache 2</a></li>
  32 <li><img alt="" src="./images/down.gif" /> <a href="#smart">Smart Filtering</a></li>
  33 <li><img alt="" src="./images/down.gif" /> <a href="#using">Using Filters</a></li>
  34 </ul></div>
  35 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
  36 <div class="section">
  37 <h2><a name="intro" id="intro">Filtering in Apache 2</a></h2>
  38
  39     <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code></li><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><li><code class="module"><a href="./mod/mod_charset_lite.html">mod_charset_lite</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_filter.html#filterchain">FilterChain</a></code></li><li><code class="directive"><a href="./mod/mod_filter.html#filterdeclare">FilterDeclare</a></code></li><li><code class="directive"><a href="./mod/mod_filter.html#filterprotocol">FilterProtocol</a></code></li><li><code class="directive"><a href="./mod/mod_filter.html#filterprovider">FilterProvider</a></code></li><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>
  40
  41 <p>The Filter Chain is available in Apache 2.0 and higher,
  42 and enables applications to process incoming and outgoing data
  43 in a highly flexible and configurable manner, regardless of
  44 where the data comes from.  We can pre-process incoming data,
  45 and post-process outgoing data, at will.  This is basically
  46 independent of the traditional request processing phases.</p>
  47 <p class="figure">
  48 <img src="images/filter_arch.png" width="569" height="392" alt="Filters can be chained, in a Data Axis orthogonal to request processing" />
  49 </p>
  50 <p>Some examples of filtering in the standard Apache distribution are:</p>
  51 <ul>
  52 <li><code class="module"><a href="./mod/mod_include.html">mod_include</a></code>, implements server-side includes.</li>
  53 <li><code class="module"><a href="./mod/mod_ssl.html">mod_ssl</a></code>, implements SSL encryption (https).</li>
  54 <li><code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code>, implements compression/decompression on the fly.</li>
  55 <li><code class="module"><a href="./mod/mod_charset_lite.html">mod_charset_lite</a></code>, transcodes between different character sets.</li>
  56 <li><code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code>, runs an external program as a filter.</li>
  57 </ul>
  58 <p>Apache also uses a number of filters internally to perform
  59 functions like chunking and byte-range handling.</p>
  60
  61 <p>A wider range of applications are implemented by third-party filter
  62 modules available from <a href="http://modules.apache.org/">modules.apache.org</a> and
  63 elsewhere.  A few of these are:</p>
  64
  65 <ul>
  66 <li>HTML and XML processing and rewriting</li>
  67 <li>XSLT transforms and XIncludes</li>
  68 <li>XML Namespace support</li>
  69 <li>File Upload handling and decoding of HTML Forms</li>
  70 <li>Image processing</li>
  71 <li>Protection of vulnerable applications such as PHP scripts</li>
  72 <li>Text search-and-replace editing</li>
  73 </ul>
  74 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
  75 <div class="section">
  76 <h2><a name="smart" id="smart">Smart Filtering</a></h2>
  77
  78 <p class="figure">
  79 <img src="images/mod_filter_new.png" width="423" height="331" alt="Smart filtering applies different filter providers according to the state of request processing" />
  80 </p>
  81 <p><code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code>, included in Apache 2.1 and later,
  82 enables the filter chain to be configured dynamically at run time.
  83 So for example you can set up a proxy to rewrite
  84 HTML with an HTML filter and JPEG images with a completely
  85 separate filter, despite the proxy having no prior information
  86 about what the origin server will send.  This works by using a
  87 filter harness, that dispatches to different providers according
  88 to the actual contents at runtime.  Any filter may be either
  89 inserted directly in the chain and run unconditionally, or
  90 used as a provider and inserted dynamically.  For example,</p>
  91 <ul>
  92 <li>an HTML processing filter will only run if the content is
  93 text/html or application/xhtml+xml</li>
  94 <li>A compression filter will only run if the input is a
  95 compressible type and not already compressed</li>
  96 <li>A charset conversion filter will be inserted if a text
  97 document is not already in the desired charset</li>
  98 </ul>
  99 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
 100 <div class="section">
 101 <h2><a name="using" id="using">Using Filters</a></h2>
 102
 103 <p>There are two ways to use filtering: Simple and Dynamic.
 104 In general, you should use one or the other; mixing them can
 105 have unexpected consequences (although simple Input filtering
 106 can be mixed freely with either simple or dynamic Output filtering).</p>
 107 <p>The Simple Way is the only way to configure input filters, and is
 108 sufficient for output filters where you need a static filter chain.
 109 Relevant directives are
 110     <code class="directive"><a href="./mod/core.html#setinputfilter">SetInputFilter</a></code>,
 111     <code class="directive"><a href="./mod/core.html#setoutputfilter">SetOutputFilter</a></code>,
 112     <code class="directive"><a href="./mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>,
 113     <code class="directive"><a href="./mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>,
 114     <code class="directive"><a href="./mod/mod_mime.html#removeinputfilter">RemoveInputFilter</a></code>, and
 115     <code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code>.</p>
 116
 117 <p>The Dynamic Way enables both static and flexible, dynamic configuration
 118 of output filters, as discussed in the <code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code> page.
 119 Relevant directives are
 120     <code class="directive"><a href="./mod/mod_filter.html#filterchain">FilterChain</a></code>,
 121     <code class="directive"><a href="./mod/mod_filter.html#filterdeclare">FilterDeclare</a></code>, and
 122     <code class="directive"><a href="./mod/mod_filter.html#filterprovider">FilterProvider</a></code>.</p>
 123
 124 <p>One further directive <code class="directive"><a href="./mod/core.html#addoutputfilterbytype">AddOutputFilterByType</a></code> is still supported,
 125 but may be problematic and is now deprecated.  Use dynamic
 126 configuration instead.</p>
 127
 128   </div></div>
 129 <div class="bottomlang">
 130 <p><span>Available Languages: </span><a href="./en/filter.html" title="English">&nbsp;en&nbsp;</a> |
 131 <a href="./es/filter.html" hreflang="es" rel="alternate" title="Español">&nbsp;es&nbsp;</a> |
 132 <a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
 133 <a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 134 <a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
 135 <a href="./tr/filter.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 136 </div><div id="footer">
 137 <p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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