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<TITLE>Filters - Apache HTTPD</TITLE>
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<H1 ALIGN="CENTER">Filters</H1>
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<strong>Related Modules</strong><br><br>
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<strong>Related Directives</strong><br><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
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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