1<?xml version="1.0" encoding="UTF-8"?> 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<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" /> 5<!-- 6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7 This file is generated from xml source: DO NOT EDIT 8 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 9 --> 10<title>Filters - Apache HTTP Server Version 2.4</title> 11<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> 12<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> 13<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" /> 14<script src="./style/scripts/prettify.min.js" type="text/javascript"> 15</script> 16 17<link href="./images/favicon.ico" rel="shortcut icon" /></head> 18<body id="manual-page"><div id="page-header"> 19<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> 20<p class="apache">Apache HTTP Server Version 2.4</p> 21<img alt="" src="./images/feather.png" /></div> 22<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div> 23<div id="path"> 24<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> 25<div class="toplang"> 26<p><span>Available Languages: </span><a href="./en/filter.html" title="English"> en </a> | 27<a href="./es/filter.html" hreflang="es" rel="alternate" title="Español"> es </a> | 28<a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | 29<a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 30<a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | 31<a href="./tr/filter.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> 32</div> 33 34 <p>This document describes the use of filters in Apache.</p> 35 </div> 36<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#intro">Filtering in Apache 2</a></li> 37<li><img alt="" src="./images/down.gif" /> <a href="#smart">Smart Filtering</a></li> 38<li><img alt="" src="./images/down.gif" /> <a href="#service">Exposing Filters as an HTTP Service</a></li> 39<li><img alt="" src="./images/down.gif" /> <a href="#using">Using Filters</a></li> 40</ul><h3>See also</h3><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> 41<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> 42<div class="section"> 43<h2><a name="intro" id="intro">Filtering in Apache 2</a></h2> 44 45 <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> 46 47<p>The Filter Chain is available in Apache 2.0 and higher, 48and enables applications to process incoming and outgoing data 49in a highly flexible and configurable manner, regardless of 50where the data comes from. We can pre-process incoming data, 51and post-process outgoing data, at will. This is basically 52independent of the traditional request processing phases.</p> 53<p class="figure"> 54<img src="images/filter_arch.png" width="569" height="392" alt="Filters can be chained, in a Data Axis orthogonal to request processing" /> 55</p> 56<p>Some examples of filtering in the standard Apache distribution are:</p> 57<ul> 58<li><code class="module"><a href="./mod/mod_include.html">mod_include</a></code>, implements server-side includes.</li> 59<li><code class="module"><a href="./mod/mod_ssl.html">mod_ssl</a></code>, implements SSL encryption (https).</li> 60<li><code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code>, implements compression/decompression on the fly.</li> 61<li><code class="module"><a href="./mod/mod_charset_lite.html">mod_charset_lite</a></code>, transcodes between different character sets.</li> 62<li><code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code>, runs an external program as a filter.</li> 63</ul> 64<p>Apache also uses a number of filters internally to perform 65functions like chunking and byte-range handling.</p> 66 67<p>A wider range of applications are implemented by third-party filter 68modules. A few of these are:</p> 69 70<ul> 71<li>HTML and XML processing and rewriting</li> 72<li>XSLT transforms and XIncludes</li> 73<li>XML Namespace support</li> 74<li>File Upload handling and decoding of HTML Forms</li> 75<li>Image processing</li> 76<li>Protection of vulnerable applications such as PHP scripts</li> 77<li>Text search-and-replace editing</li> 78</ul> 79</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> 80<div class="section"> 81<h2><a name="smart" id="smart">Smart Filtering</a></h2> 82 83<p class="figure"> 84<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" /> 85</p> 86<p><code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code>, included in Apache 2.1 and later, 87enables the filter chain to be configured dynamically at run time. 88So for example you can set up a proxy to rewrite 89HTML with an HTML filter and JPEG images with a completely 90separate filter, despite the proxy having no prior information 91about what the origin server will send. This works by using a 92filter harness, that dispatches to different providers according 93to the actual contents at runtime. Any filter may be either 94inserted directly in the chain and run unconditionally, or 95used as a provider and inserted dynamically. For example,</p> 96<ul> 97<li>an HTML processing filter will only run if the content is 98text/html or application/xhtml+xml</li> 99<li>A compression filter will only run if the input is a 100compressible type and not already compressed</li> 101<li>A charset conversion filter will be inserted if a text 102document is not already in the desired charset</li> 103</ul> 104</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> 105<div class="section"> 106<h2><a name="service" id="service">Exposing Filters as an HTTP Service</a></h2> 107 108 109<p>Filters can be used to process content originating from the client in 110addition to processing content originating on the server using the 111<code class="module"><a href="./mod/mod_reflector.html">mod_reflector</a></code> module.</p> 112 113<p><code class="module"><a href="./mod/mod_reflector.html">mod_reflector</a></code> accepts POST requests from clients, and reflects 114the content request body received within the POST request back in the response, 115passing through the output filter stack on the way back to the client.</p> 116 117<p>This technique can be used as an alternative to a web service running within 118an application server stack, where an output filter provides the transformation 119required on the request body. For example, the <code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code> 120module might be used to provide a general compression service, or an image 121transformation filter might be turned into an image transformation service.</p> 122 123</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> 124<div class="section"> 125<h2><a name="using" id="using">Using Filters</a></h2> 126 127<p>There are two ways to use filtering: Simple and Dynamic. 128In general, you should use one or the other; mixing them can 129have unexpected consequences (although simple Input filtering 130can be mixed freely with either simple or dynamic Output filtering).</p> 131<p>The Simple Way is the only way to configure input filters, and is 132sufficient for output filters where you need a static filter chain. 133Relevant directives are 134 <code class="directive"><a href="./mod/core.html#setinputfilter">SetInputFilter</a></code>, 135 <code class="directive"><a href="./mod/core.html#setoutputfilter">SetOutputFilter</a></code>, 136 <code class="directive"><a href="./mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>, 137 <code class="directive"><a href="./mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>, 138 <code class="directive"><a href="./mod/mod_mime.html#removeinputfilter">RemoveInputFilter</a></code>, and 139 <code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code>.</p> 140 141<p>The Dynamic Way enables both static and flexible, dynamic configuration 142of output filters, as discussed in the <code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code> page. 143Relevant directives are 144 <code class="directive"><a href="./mod/mod_filter.html#filterchain">FilterChain</a></code>, 145 <code class="directive"><a href="./mod/mod_filter.html#filterdeclare">FilterDeclare</a></code>, and 146 <code class="directive"><a href="./mod/mod_filter.html#filterprovider">FilterProvider</a></code>.</p> 147 148<p>One further directive <code class="directive"><a href="./mod/mod_filter.html#addoutputfilterbytype">AddOutputFilterByType</a></code> is still supported, 149but deprecated. Use dynamic configuration instead.</p> 150 151 </div></div> 152<div class="bottomlang"> 153<p><span>Available Languages: </span><a href="./en/filter.html" title="English"> en </a> | 154<a href="./es/filter.html" hreflang="es" rel="alternate" title="Español"> es </a> | 155<a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | 156<a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 157<a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | 158<a href="./tr/filter.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> 159</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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