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<title>Filters - Apache HTTPD</title>
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<h1 align="CENTER">Filters</h1>
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<td valign="top"><strong>Related Modules</strong><br />
<br />
<a href="mod/mod_ext_filter.html">mod_ext_filter</a><br />
<a href="mod/mod_include.html">mod_include</a><br />
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<td valign="top"><strong>Related Directives</strong><br />
<br />
<a
href="mod/mod_mime.html#addinputfilter">AddInputFilter</a><br />
<a
href="mod/mod_mime.html#addoutputfilter">AddOutputFilter</a><br />
<a
href="mod/mod_ext_filter.html#extfilterdefine">ExtFilterDefine</a><br />
<a
href="mod/mod_ext_filter.html#extfilteroptions">ExtFilterOptions</a><br />
<a
href="mod/core.html#setinputfilter">SetInputFilter</a><br />
<a
href="mod/core.html#setoutputfilter">SetOutputFilter</a><br />
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<p>A <em>filter</em> is a process which 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>Filters are used internally by Apache to perform functions
such as chunking and byte-range request handling. In addition,
modules can provide filters which are selectable using run-time
configuration directives. The set of filters which apply to
data can be manipulated with the <code>SetInputFilter</code>
and <code>SetOutputFilter</code> directives.</p>
<p>The only configurable filter currently included with the
Apache distribution is the <code>INCLUDES</code> filter which
is provided by <a href="mod/mod_include.html">mod_include</a>
to process output for Server Side Includes. There is also an
experimental module called <a
href="mod/mod_ext_filter.html">mod_ext_filter</a> which allows
for external programs to be defined as filters.</p>
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