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-<title>Filters - Apache HTTP Server</title>
+<title>Filters - Apache HTTP Server Version 2.5</title>
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-<p class="apache">Apache HTTP Server Version 2.1</p>
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+<p class="apache">Apache HTTP Server Version 2.5</p>
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-<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 2.1</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1>
+<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 2.5</a></div><div id="page-content"><div id="preamble"><h1>Filters</h1>
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-<p><span>Available Languages: </span><a href="./en/filter.html"> en </a> | <a href="./ja/filter.html"> ja </a> | <a href="./ko/filter.html"> ko </a></p>
+<p><span>Available Languages: </span><a href="./en/filter.html" title="English"> en </a> |
+<a href="./es/filter.html" hreflang="es" rel="alternate" title="Español"> es </a> |
+<a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
+<a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
+<a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
+<a href="./tr/filter.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
</div>
<p>This document describes the use of filters in Apache.</p>
</div>
+<div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#intro">Filtering in Apache 2</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#smart">Smart Filtering</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#service">Exposing Filters as an HTTP Service</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#using">Using Filters</a></li>
+</ul><h3>See also</h3><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
-<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>
+<h2><a name="intro" id="intro">Filtering in Apache 2</a></h2>
- <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>
+ <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><li><code class="module"><a href="./mod/mod_policy.html">mod_policy</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>
+
+<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><code class="module"><a href="./mod/mod_include.html">mod_include</a></code>, implements server-side includes.</li>
+<li><code class="module"><a href="./mod/mod_ssl.html">mod_ssl</a></code>, implements SSL encryption (https).</li>
+<li><code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code>, implements compression/decompression on the fly.</li>
+<li><code class="module"><a href="./mod/mod_charset_lite.html">mod_charset_lite</a></code>, transcodes between different character sets.</li>
+<li><code class="module"><a href="./mod/mod_ext_filter.html">mod_ext_filter</a></code>, 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 available from <a href="http://modules.apache.org/">modules.apache.org</a> and
+elsewhere. 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 alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="smart" id="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 later,
+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
+compressible 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 alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="service" id="service">Exposing Filters as an HTTP Service</a></h2>
+
+
+<p>Filters can be used to process content originating from the client in
+addition to processing content originating on the server using the
+<code class="module"><a href="./mod/mod_reflector.html">mod_reflector</a></code> module.</p>
+
+<p><code class="module"><a href="./mod/mod_reflector.html">mod_reflector</a></code> accepts POST requests from clients, and reflects
+the content request body received within the POST request back in the response,
+passing through the output filter stack on the way back to the client.</p>
+
+<p>This technique can be used as an alternative to a web service running within
+an application server stack, where an output filter provides the transformation
+required on the request body. For example, the <code class="module"><a href="./mod/mod_deflate.html">mod_deflate</a></code>
+module might be used to provide a general compression service, or an image
+transformation filter might be turned into an image transformation service.</p>
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="using" id="using">Using Filters</a></h2>
- <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>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
+sufficient 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>
+ <code class="directive"><a href="./mod/mod_mime.html#removeoutputfilter">RemoveOutputFilter</a></code>.</p>
- <p>The following user-selectable filters are currently provided
- with the Apache HTTP Server distribution.</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>, and
+ <code class="directive"><a href="./mod/mod_filter.html#filterprovider">FilterProvider</a></code>.</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>One further directive <code class="directive"><a href="./mod/mod_filter.html#addoutputfilterbytype">AddOutputFilterByType</a></code> is still supported,
+but deprecated. Use dynamic configuration instead.</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>
</div></div>
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-<p><span>Available Languages: </span><a href="./en/filter.html"> en </a> | <a href="./ja/filter.html"> ja </a> | <a href="./ko/filter.html"> ko </a></p>
-</div><div id="footer">
-<p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p>
-<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></div>
+<p><span>Available Languages: </span><a href="./en/filter.html" title="English"> en </a> |
+<a href="./es/filter.html" hreflang="es" rel="alternate" title="Español"> es </a> |
+<a href="./fr/filter.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
+<a href="./ja/filter.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
+<a href="./ko/filter.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
+<a href="./tr/filter.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
+</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. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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