Update filter documentation page. (1ece4907) · Commits · CYBER - Cyber Security / TS 103 523 MSP / TLMSP / TLMSP Apache Httpd

docs/manual/filter.html.en

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		<?xml version="1.0" encoding="ISO-8859-1"?>
		<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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		-->
		<title>Filters - Apache HTTP Server</title>
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		<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 2.3</p>
		<img alt="" src="./images/feather.gif" /></div>
		<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
		<img src="./images/feather.gif" alt="" /></div>
		<div class="up"><a href="./"><img src="./images/left.gif" alt="<-" title="<-" /></a></div>
		<div id="path">
		<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="./">Version 2.3</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1>
		<div class="toplang">
		@@ -27,46 +27,99 @@

		<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 id="quickview"><ul id="toc"><li><img src="./images/down.gif" alt="" /> <a href="#intro">Filtering in Apache 2</a></li>
		<li><img src="./images/down.gif" alt="" /> <a href="#smart">Smart Filtering</a></li>
		<li><img src="./images/down.gif" alt="" /> <a href="#using">Using Filters</a></li>
		</ul></div>
		<div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div>
		<div class="section">
		<h2><a name="filters" id="filters">Filters</a></h2>
		<h2><a id="intro" name="intro">Filtering in Apache 2</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>
		<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>

		<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>The Filter Chain is available in Apache 2.0 and higher,
		and enables applications to process incoming and outgoing data
		in a highly flexible and configurable manner, regardless of
		where the data comes from. We can pre-process incoming data,
		and post-process outgoing data, at will. This is basically
		independent of the traditional request processing phases.</p>
		<p class="figure">
		<img src="images/filter_arch.png" width="569" height="392" alt="Filters can be chained, in a Data Axis orthogonal to request processing" />
		</p>
		<p>Some examples of filtering in the standard Apache distribution are:</p>
		<ul>
		<li>mod_includes, implements server-side includes.</li>
		<li>mod_ssl, implements SSL encryption (https).</li>
		<li>mod_deflate, implements compression/decompression on the fly.</li>
		<li>mod_charset_lite, transcodes between different character sets.</li>
		<li>mod_ext_filter, runs an external program as a filter.</li>
		</ul>
		<p>Apache also uses a number of filters internally, to perform
		functions like chunking and byte-range handling.</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
		<p>A wider range of applications are implemented by third-party
		filter modules. A few of these are:</p>
		<ul>
		<li>HTML and XML processing and rewriting</li>
		<li>XSLT transforms and XIncludes</li>
		<li>XML Namespace support</li>
		<li>File Upload handling and decoding of HTML Forms</li>
		<li>Image processing</li>
		<li>Protection of vulnerable applications such as PHP scripts</li>
		<li>Text search-and-replace editing</li>
		</ul>
		</div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div>
		<div class="section">
		<h2><a id="smart" name="smart">Smart Filtering</a></h2>

		<p class="figure">
		<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" />
		</p>
		<p><code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code>, included in Apache 2.1 and up,
		enables the filter chain to be configured dynamically at run time.
		So for example you can set up a proxy to rewrite
		HTML with an HTML filter and JPEG images with a completely
		separate filter, despite the proxy having no prior information
		about what the origin server will send. This works by using a
		filter harness, that dispatches to different providers according
		to the actual contents at runtime. Any filter may be either
		inserted directly in the chain and run unconditionally, or
		used as a provider and inserted dynamically. For example,</p>
		<ul>
		<li>an HTML processing filter will only run if the content is
		text/html or application/xhtml+xml</li>
		<li>A compression filter will only run if the input is a
		compressable type and not already compressed</li>
		<li>A charset conversion filter will be inserted if a text
		document is not already in the desired charset</li>
		</ul>
		</div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div>
		<div class="section">
		<h2><a id="using" name="using">Using Filters</a></h2>

		<p>There are two ways to use filtering: Simple and Dynamic.
		In general, you should use one or the other: mixing them can
		have unexpected consequences (although simple Input filtering
		can be mixed freely with either simple or dynamic Output filtering!</p>
		<p>The Simple Way is the only way to configure input filters, and is
		suficient for output filters where you need a static filter chain.
		Relevant directives are
		<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>
		<code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code>.</p>

		<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>
		<p>The Dynamic Way enables both static and flexible, dynamic configuration
		of output filters, as discussed in the <code class="module"><a href="./mod/mod_filter.html">mod_filter</a></code> page.
		Relevant directives are
		<code class="directive"><a href="./mod/mod_filter.html#filterchain">FilterChain</a></code>,
		<code class="directive"><a href="./mod/mod_filter.html#filterdeclare">FilterDeclare</a></code>,
		<code class="directive"><a href="./mod/mod_filter.html#filterprovider">FilterProvider</a></code>.</p>
		<p>One further directive AddOutputFilterByType is still supported,
		but may be problematic and is now deprecated. Use dynamic configuration
		instead.</p>
		</div></div>
		<div class="bottomlang">
		<p><span>Available Languages: </span><a href="./en/filter.html" title="English"> en </a> \|

docs/manual/filter.xml

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		@@ -28,15 +28,21 @@
		<p>This document describes the use of filters in Apache.</p>
		</summary>

		<section id="filters">
		<title>Filters</title>
		<section id="intro">
		<title>Filtering in Apache 2</title>
		<related>
		<modulelist>
		<module>mod_filter</module>
		<module>mod_deflate</module>
		<module>mod_ext_filter</module>
		<module>mod_include</module>
		<module>mod_charset_lite</module>
		</modulelist>
		<directivelist>
		<directive module="mod_filter">FilterChain</directive>
		<directive module="mod_filter">FilterDeclare</directive>
		<directive module="mod_filter">FilterProtocol</directive>
		<directive module="mod_filter">FilterProvider</directive>
		<directive module="mod_mime">AddInputFilter</directive>
		<directive module="mod_mime">AddOutputFilter</directive>
		<directive module="mod_mime">RemoveInputFilter</directive>
		@@ -48,39 +54,90 @@
		</directivelist>
		</related>

		<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>The Filter Chain is available in Apache 2.0 and higher,
		and enables applications to process incoming and outgoing data
		in a highly flexible and configurable manner, regardless of
		where the data comes from. We can pre-process incoming data,
		and post-process outgoing data, at will. This is basically
		independent of the traditional request processing phases.</p>
		<p class="figure">
		<img src="images/filter_arch.png" width="569" height="392" alt=
		"Filters can be chained, in a Data Axis orthogonal to request processing"
		/>
		</p>
		<p>Some examples of filtering in the standard Apache distribution are:</p>
		<ul>
		<li>mod_includes, implements server-side includes.</li>
		<li>mod_ssl, implements SSL encryption (https).</li>
		<li>mod_deflate, implements compression/decompression on the fly.</li>
		<li>mod_charset_lite, transcodes between different character sets.</li>
		<li>mod_ext_filter, runs an external program as a filter.</li>
		</ul>
		<p>Apache also uses a number of filters internally, to perform
		functions like chunking and byte-range handling.</p>

		<p>A wider range of applications are implemented by third-party
		filter modules. A few of these are:</p>
		<ul>
		<li>HTML and XML processing and rewriting</li>
		<li>XSLT transforms and XIncludes</li>
		<li>XML Namespace support</li>
		<li>File Upload handling and decoding of HTML Forms</li>
		<li>Image processing</li>
		<li>Protection of vulnerable applications such as PHP scripts</li>
		<li>Text search-and-replace editing</li>
		</ul>
		</section>
		<section id="smart">
		<title>Smart Filtering</title>
		<p class="figure">
		<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"/>
		</p>
		<p><module>mod_filter</module>, included in Apache 2.1 and up,
		enables the filter chain to be configured dynamically at run time.
		So for example you can set up a proxy to rewrite
		HTML with an HTML filter and JPEG images with a completely
		separate filter, despite the proxy having no prior information
		about what the origin server will send. This works by using a
		filter harness, that dispatches to different providers according
		to the actual contents at runtime. Any filter may be either
		inserted directly in the chain and run unconditionally, or
		used as a provider and inserted dynamically. For example,</p>
		<ul>
		<li>an HTML processing filter will only run if the content is
		text/html or application/xhtml+xml</li>
		<li>A compression filter will only run if the input is a
		compressable type and not already compressed</li>
		<li>A charset conversion filter will be inserted if a text
		document is not already in the desired charset</li>
		</ul>
		</section>

		<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
		<section id="using">
		<title>Using Filters</title>
		<p>There are two ways to use filtering: Simple and Dynamic.
		In general, you should use one or the other: mixing them can
		have unexpected consequences (although simple Input filtering
		can be mixed freely with either simple or dynamic Output filtering!</p>
		<p>The Simple Way is the only way to configure input filters, and is
		suficient for output filters where you need a static filter chain.
		Relevant directives are
		<directive module="core">SetInputFilter</directive>,
		<directive module="core">SetOutputFilter</directive>,
		<directive module="mod_mime">AddInputFilter</directive>,
		<directive module="mod_mime">AddOutputFilter</directive>,
		<directive module="mod_mime">RemoveInputFilter</directive>, and
		<directive module="mod_mime">RemoveOutputFilter</directive>
		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 <module>mod_include</module></dd>
		<dt>DEFLATE</dt>
		<dd>Compress output before sending it to the client using
		<module>mod_deflate</module>
		</dd>
		</dl>
		<directive module="mod_mime">RemoveOutputFilter</directive>.</p>

		<p>In addition, the module <module>mod_ext_filter</module> allows
		for external programs to be defined as filters.</p>
		<p>The Dynamic Way enables both static and flexible, dynamic configuration
		of output filters, as discussed in the <module>mod_filter</module> page.
		Relevant directives are
		<directive module="mod_filter">FilterChain</directive>,
		<directive module="mod_filter">FilterDeclare</directive>,
		<directive module="mod_filter">FilterProvider</directive>.</p>
		<p>One further directive AddOutputFilterByType is still supported,
		but may be problematic and is now deprecated. Use dynamic configuration
		instead.</p>
		</section>
		</manualpage>

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