1<?xml version="1.0" encoding="ISO-8859-1"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- 4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 5 This file is generated from xml source: DO NOT EDIT 6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7 --> 8<title>Filters - Apache HTTP Server</title> 9<link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> 10<link href="/style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> 11<link href="/style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="/style/css/prettify.css" /> 12<script src="/style/scripts/prettify.min.js" type="text/javascript"> 13</script> 14 15<link href="/images/favicon.ico" rel="shortcut icon" /></head> 16<body id="manual-page"><div id="page-header"> 17<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p> 18<p class="apache">Apache HTTP Server Version 2.4</p> 19<img alt="" src="/images/feather.gif" /></div> 20<div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div> 21<div id="path"> 22<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.4</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1> 23<div class="toplang"> 24<p><span>Available Languages: </span><a href="/en/filter.html" title="English"> en </a> | 25<a href="/es/filter.html" hreflang="es" rel="alternate" title="Espa�ol"> es </a> | 26<a href="/fr/filter.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a> | 27<a href="/ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 28<a href="/ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | 29<a href="/tr/filter.html" hreflang="tr" rel="alternate" title="T�rk�e"> tr </a></p> 30</div> 31 32 <p>This document describes the use of filters in Apache.</p> 33 </div> 34<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#intro">Filtering in Apache 2</a></li> 35<li><img alt="" src="/images/down.gif" /> <a href="#smart">Smart Filtering</a></li> 36<li><img alt="" src="/images/down.gif" /> <a href="#service">Exposing Filters as an HTTP Service</a></li> 37<li><img alt="" src="/images/down.gif" /> <a href="#using">Using Filters</a></li> 38</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> 39<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 40<div class="section"> 41<h2><a name="intro" id="intro">Filtering in Apache 2</a></h2> 42 43 <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><li><code class="module"><a href="/mod/mod_reflector.html">mod_reflector</a></code></li><li><code class="module"><a href="/mod/mod_buffer.html">mod_buffer</a></code></li><li><code class="module"><a href="/mod/mod_data.html">mod_data</a></code></li><li><code class="module"><a href="/mod/mod_ratelimit.html">mod_ratelimit</a></code></li><li><code class="module"><a href="/mod/mod_reqtimeout.html">mod_reqtimeout</a></code></li><li><code class="module"><a href="/mod/mod_request.html">mod_request</a></code></li><li><code class="module"><a href="/mod/mod_sed.html">mod_sed</a></code></li><li><code class="module"><a href="/mod/mod_substitute.html">mod_substitute</a></code></li><li><code class="module"><a href="/mod/mod_xml2enc.html">mod_xml2enc</a></code></li><li><code class="module"><a href="/mod/mod_proxy_html.html">mod_proxy_html</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_reflector.html#reflectorheader">ReflectorHeader</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> 44 45<p>The Filter Chain is available in Apache 2.0 and higher, 46and enables applications to process incoming and outgoing data 47in a highly flexible and configurable manner, regardless of 48where the data comes from. We can pre-process incoming data, 49and post-process outgoing data, at will. This is basically 50independent of the traditional request processing phases.</p> 51<p class="figure"> 52<img src="images/filter_arch.png" width="569" height="392" alt="Filters can be chained, in a Data Axis orthogonal to request processing" /> 53</p> 54<p>Some examples of filtering in the standard Apache distribution are:</p> 55<ul> 56<li><code class="module"><a href="/mod/mod_include.html">mod_include</a></code>, implements server-side includes.</li> 57<li><code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code>, implements SSL encryption (https).</li> 58<li><code class="module"><a href="/mod/mod_deflate.html">mod_deflate</a></code>, implements compression/decompression on the fly.</li> 59<li><code class="module"><a href="/mod/mod_charset_lite.html">mod_charset_lite</a></code>, transcodes between different character sets.</li> 60<li><code class="module"><a href="/mod/mod_ext_filter.html">mod_ext_filter</a></code>, runs an external program as a filter.</li> 61</ul> 62<p>Apache also uses a number of filters internally to perform 63functions like chunking and byte-range handling.</p> 64 65<p>A wider range of applications are implemented by third-party filter 66modules available from <a href="http://modules.apache.org/">modules.apache.org</a> and 67elsewhere. A few of these are:</p> 68 69<ul> 70<li>HTML and XML processing and rewriting</li> 71<li>XSLT transforms and XIncludes</li> 72<li>XML Namespace support</li> 73<li>File Upload handling and decoding of HTML Forms</li> 74<li>Image processing</li> 75<li>Protection of vulnerable applications such as PHP scripts</li> 76<li>Text search-and-replace editing</li> 77</ul> 78</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 79<div class="section"> 80<h2><a name="smart" id="smart">Smart Filtering</a></h2> 81 82<p class="figure"> 83<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" /> 84</p> 85<p><code class="module"><a href="/mod/mod_filter.html">mod_filter</a></code>, included in Apache 2.1 and later, 86enables the filter chain to be configured dynamically at run time. 87So for example you can set up a proxy to rewrite 88HTML with an HTML filter and JPEG images with a completely 89separate filter, despite the proxy having no prior information 90about what the origin server will send. This works by using a 91filter harness, that dispatches to different providers according 92to the actual contents at runtime. Any filter may be either 93inserted directly in the chain and run unconditionally, or 94used as a provider and inserted dynamically. For example,</p> 95<ul> 96<li>an HTML processing filter will only run if the content is 97text/html or application/xhtml+xml</li> 98<li>A compression filter will only run if the input is a 99compressible type and not already compressed</li> 100<li>A charset conversion filter will be inserted if a text 101document is not already in the desired charset</li> 102</ul> 103</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 104<div class="section"> 105<h2><a name="service" id="service">Exposing Filters as an HTTP Service</a></h2> 106 107 108<p>Filters can be used to process content originating from the client in 109addition to processing content originating on the server using the 110<code class="module"><a href="/mod/mod_reflector.html">mod_reflector</a></code> module.</p> 111 112<p><code class="module"><a href="/mod/mod_reflector.html">mod_reflector</a></code> accepts POST requests from clients, and reflects 113the content request body received within the POST request back in the response, 114passing through the output filter stack on the way back to the client.</p> 115 116<p>This technique can be used as an alternative to a web service running within 117an application server stack, where an output filter provides the transformation 118required on the request body. For example, the <code class="module"><a href="/mod/mod_deflate.html">mod_deflate</a></code> 119module might be used to provide a general compression service, or an image 120transformation filter might be turned into an image transformation service.</p> 121 122</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 123<div class="section"> 124<h2><a name="using" id="using">Using Filters</a></h2> 125 126<p>There are two ways to use filtering: Simple and Dynamic. 127In general, you should use one or the other; mixing them can 128have unexpected consequences (although simple Input filtering 129can be mixed freely with either simple or dynamic Output filtering).</p> 130<p>The Simple Way is the only way to configure input filters, and is 131sufficient for output filters where you need a static filter chain. 132Relevant directives are 133 <code class="directive"><a href="/mod/core.html#setinputfilter">SetInputFilter</a></code>, 134 <code class="directive"><a href="/mod/core.html#setoutputfilter">SetOutputFilter</a></code>, 135 <code class="directive"><a href="/mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>, 136 <code class="directive"><a href="/mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>, 137 <code class="directive"><a href="/mod/mod_mime.html#removeinputfilter">RemoveInputFilter</a></code>, and 138 <code class="directive"><a href="/mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code>.</p> 139 140<p>The Dynamic Way enables both static and flexible, dynamic configuration 141of output filters, as discussed in the <code class="module"><a href="/mod/mod_filter.html">mod_filter</a></code> page. 142Relevant directives are 143 <code class="directive"><a href="/mod/mod_filter.html#filterchain">FilterChain</a></code>, 144 <code class="directive"><a href="/mod/mod_filter.html#filterdeclare">FilterDeclare</a></code>, and 145 <code class="directive"><a href="/mod/mod_filter.html#filterprovider">FilterProvider</a></code>.</p> 146 147<p>One further directive <code class="directive"><a href="/mod/mod_filter.html#addoutputfilterbytype">AddOutputFilterByType</a></code> is still supported, 148but deprecated. Use dynamic configuration instead.</p> 149 150 </div></div> 151<div class="bottomlang"> 152<p><span>Available Languages: </span><a href="/en/filter.html" title="English"> en </a> | 153<a href="/es/filter.html" hreflang="es" rel="alternate" title="Espa�ol"> es </a> | 154<a href="/fr/filter.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a> | 155<a href="/ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 156<a href="/ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | 157<a href="/tr/filter.html" hreflang="tr" rel="alternate" title="T�rk�e"> tr </a></p> 158</div><div class="top"><a href="#page-header"><img src="/images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. 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