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<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>
<p class="apache">Apache HTTP Server Version 2.2</p>
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<div class="retired"><h4>Please note</h4>
<p> This document refers to a legacy release (<strong>2.2</strong>) of Apache httpd. The active release (<strong>2.4</strong>) is documented <a href="http://httpd.apache.org/docs/current">here</a>. If you have not already upgraded, please follow <a href="http://httpd.apache.org/docs/current/upgrading.html">this link</a> for more information.</p>
<p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_deflate.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_deflate</h1>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Compress content before it is delivered to the
client</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>deflate_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_deflate.c</td></tr></table>
<h3>Summary</h3>
<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module provides
the <code>DEFLATE</code> output filter that allows output from
your server to be compressed before being sent to the client over
the network.</p>
</div>
<div id="quickview"><h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#recommended">Sample Configurations</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#enable">Enabling Compression</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#proxies">Dealing with proxy servers</a></li>
</ul><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#deflatebuffersize">DeflateBufferSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatecompressionlevel">DeflateCompressionLevel</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatefilternote">DeflateFilterNote</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflateinflatelimitrequestbody">DeflateInflateLimitRequestBody</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflateinflateratioburst">DeflateInflateRatioBurst</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflateinflateratiolimit">DeflateInflateRatioLimit</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatememlevel">DeflateMemLevel</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatewindowsize">DeflateWindowSize</a></li>
</ul>
<h3>See also</h3>
<ul class="seealso">
<li><a href="../filter.html">Filters</a></li>
</ul><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="recommended" id="recommended">Sample Configurations</a></h2>
<div class="warning"><h3>Compression and TLS</h3>
<p>Some web applications are vulnerable to an information disclosure
attack when a TLS connection carries deflate compressed data. For more
information, review the details of the "BREACH" family of attacks.</p>
</div>
<p>This is a simple configuration that compresses common text-based content types.</p>
<div class="example"><h3>Compress only a few types</h3><pre class="prettyprint lang-config">AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/javascript</pre>
</div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="enable" id="enable">Enabling Compression</a></h2>
<h3><a name="output" id="output">Output Compression</a></h3>
<p>Compression is implemented by the <code>DEFLATE</code>
<a href="../filter.html">filter</a>. The following directive
will enable compression for documents in the container where it
is placed:</p>
<div class="example"><p><code>
SetOutputFilter DEFLATE
</code></p></div>
<p>Some popular browsers cannot handle compression of all content
so you may want to set the <code>gzip-only-text/html</code> note to
<code>1</code> to only allow html files to be compressed (see
below). If you set this to <em>anything but <code>1</code></em> it
will be ignored.</p>
<p>If you want to restrict the compression to particular MIME types
in general, you may use the <code class="directive"><a href="../mod/core.html#addoutputfilterbytype">AddOutputFilterByType</a></code> directive. Here is an example of
enabling compression only for the html files of the Apache
documentation:</p>
<div class="example"><p><code>
<Directory "/your-server-root/manual"><br />
<span class="indent">
AddOutputFilterByType DEFLATE text/html<br />
</span>
</Directory>
</code></p></div>
<p>For browsers that have problems even with compression of all file
types, use the <code class="directive"><a href="../mod/mod_setenvif.html#browsermatch">BrowserMatch</a></code> directive to set the <code>no-gzip</code>
note for that particular browser so that no compression will be
performed. You may combine <code>no-gzip</code> with <code>gzip-only-text/html</code> to get the best results. In that case
the former overrides the latter. Take a look at the following
excerpt from the <a href="#recommended">configuration example</a>
defined in the section above:</p>
<div class="example"><p><code>
BrowserMatch ^Mozilla/4 gzip-only-text/html<br />
BrowserMatch ^Mozilla/4\.0[678] no-gzip<br />
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
</code></p></div>
<p>At first we probe for a <code>User-Agent</code> string that
indicates a Netscape Navigator version of 4.x. These versions
cannot handle compression of types other than
<code>text/html</code>. The versions 4.06, 4.07 and 4.08 also
have problems with decompressing html files. Thus, we completely
turn off the deflate filter for them.</p>
<p>The third <code class="directive"><a href="../mod/mod_setenvif.html#browsermatch">BrowserMatch</a></code>
directive fixes the guessed identity of the user agent, because
the Microsoft Internet Explorer identifies itself also as "Mozilla/4"
but is actually able to handle requested compression. Therefore we
match against the additional string "MSIE" (<code>\b</code> means
"word boundary") in the <code>User-Agent</code> Header and turn off
the restrictions defined before.</p>
<div class="note"><h3>Note</h3>
The <code>DEFLATE</code> filter is always inserted after RESOURCE
filters like PHP or SSI. It never touches internal subrequests.
</div>
<div class="note"><h3>Note</h3>
There is an environment variable <code>force-gzip</code>,
set via <code class="directive"><a href="../mod/mod_env.html#setenv">SetEnv</a></code>, which
will ignore the accept-encoding setting of your browser and will
send compressed output.
</div>
<h3><a name="inflate" id="inflate">Output Decompression</a></h3>
<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module also provides a filter for
inflating/uncompressing a gzip compressed response body. In order to activate
this feature you have to insert the <code>INFLATE</code> filter into
the output filter chain using <code class="directive"><a href="../mod/core.html#setoutputfilter">SetOutputFilter</a></code> or <code class="directive"><a href="../mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>, for example:</p>
<div class="example"><p><code>
<Location /dav-area><br />
<span class="indent">
ProxyPass http://example.com/<br />
SetOutputFilter INFLATE<br />
</span>
</Location>
</code></p></div>
<p>This Example will uncompress gzip'ed output from example.com, so other
filters can do further processing with it.
</p>
<h3><a name="input" id="input">Input Decompression</a></h3>
<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module also provides a filter for
decompressing a gzip compressed request body . In order to activate
this feature you have to insert the <code>DEFLATE</code> filter into
the input filter chain using <code class="directive"><a href="../mod/core.html#setinputfilter">SetInputFilter</a></code> or <code class="directive"><a href="../mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>, for example:</p>
<div class="example"><p><code>
<Location /dav-area><br />
<span class="indent">
SetInputFilter DEFLATE<br />
</span>
</Location>
</code></p></div>
<p>Now if a request contains a <code>Content-Encoding:
gzip</code> header, the body will be automatically decompressed.
Few browsers have the ability to gzip request bodies. However,
some special applications actually do support request
compression, for instance some <a href="http://www.webdav.org">WebDAV</a> clients.</p>
<div class="warning"><h3>Note on Content-Length</h3>
<p>If you evaluate the request body yourself, <em>don't trust
the <code>Content-Length</code> header!</em>
The Content-Length header reflects the length of the
incoming data from the client and <em>not</em> the byte count of
the decompressed data stream.</p>
</div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="proxies" id="proxies">Dealing with proxy servers</a></h2>
<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module sends a <code>Vary:
Accept-Encoding</code> HTTP response header to alert proxies that
a cached response should be sent only to clients that send the
appropriate <code>Accept-Encoding</code> request header. This
prevents compressed content from being sent to a client that will
not understand it.</p>
<p>If you use some special exclusions dependent
on, for example, the <code>User-Agent</code> header, you must
manually configure an addition to the <code>Vary</code> header
to alert proxies of the additional restrictions. For example,
in a typical configuration where the addition of the <code>DEFLATE</code>
filter depends on the <code>User-Agent</code>, you should add:</p>
<div class="example"><p><code>
Header append Vary User-Agent
</code></p></div>
<p>If your decision about compression depends on other information
than request headers (<em>e.g.</em> HTTP version), you have to set the
<code>Vary</code> header to the value <code>*</code>. This prevents
compliant proxies from caching entirely.</p>
<div class="example"><h3>Example</h3><p><code>
Header set Vary *
</code></p></div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateBufferSize" id="DeflateBufferSize">DeflateBufferSize</a> <a name="deflatebuffersize" id="deflatebuffersize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Fragment size to be compressed at one time by zlib</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateBufferSize <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateBufferSize 8096</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
<p>The <code class="directive">DeflateBufferSize</code> directive specifies
the size in bytes of the fragments that zlib should compress at one
time.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateCompressionLevel" id="DeflateCompressionLevel">DeflateCompressionLevel</a> <a name="deflatecompressionlevel" id="deflatecompressionlevel">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>How much compression do we apply to the output</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateCompressionLevel <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>Zlib's default</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>This directive is available since Apache 2.0.45</td></tr>
</table>
<p>The <code class="directive">DeflateCompressionLevel</code> directive specifies
what level of compression should be used, the higher the value,
the better the compression, but the more CPU time is required to
achieve this.</p>
<p>The value must between 1 (less compression) and 9 (more compression).</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateFilterNote" id="DeflateFilterNote">DeflateFilterNote</a> <a name="deflatefilternote" id="deflatefilternote">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Places the compression ratio in a note for logging</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateFilterNote [<var>type</var>] <var>notename</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td><var>type</var> is available since Apache 2.0.45</td></tr>
</table>
<p>The <code class="directive">DeflateFilterNote</code> directive
specifies that a note about compression ratios should be attached
to the request. The name of the note is the value specified for
the directive. You can use that note for statistical purposes by
adding the value to your <a href="../logs.html#accesslog">access log</a>.</p>
<div class="example"><h3>Example</h3><p><code>
DeflateFilterNote ratio<br />
<br />
LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' deflate<br />
CustomLog logs/deflate_log deflate
</code></p></div>
<p>If you want to extract more accurate values from your logs, you
can use the <var>type</var> argument to specify the type of data
left as a note for logging. <var>type</var> can be one of:</p>
<dl>
<dt><code>Input</code></dt>
<dd>Store the byte count of the filter's input stream in the note.</dd>
<dt><code>Output</code></dt>
<dd>Store the byte count of the filter's output stream in the note.</dd>
<dt><code>Ratio</code></dt>
<dd>Store the compression ratio (<code>output/input * 100</code>)
in the note. This is the default, if the <var>type</var> argument
is omitted.</dd>
</dl>
<p>Thus you may log it this way:</p>
<div class="example"><h3>Accurate Logging</h3><p><code>
DeflateFilterNote Input instream<br />
DeflateFilterNote Output outstream<br />
DeflateFilterNote Ratio ratio<br />
<br />
LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate<br />
CustomLog logs/deflate_log deflate
</code></p></div>
<h3>See also</h3>
<ul>
<li><code class="module"><a href="../mod/mod_log_config.html">mod_log_config</a></code></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateInflateLimitRequestBody" id="DeflateInflateLimitRequestBody">DeflateInflateLimitRequestBody</a> <a name="deflateinflatelimitrequestbody" id="deflateinflatelimitrequestbody">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum size of inflated request bodies</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateInflateLimitRequestBody<var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>None, but LimitRequestBody applies after deflation</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>2.2.28 and later</td></tr>
</table>
<p>The <code class="directive">DeflateInflateLimitRequestBody</code> directive
specifies the maximum size of an inflated request body. If it is unset,
<code class="directive"><a href="../mod/core.html#limitrequestbody">LimitRequestBody</a></code> is applied to the
inflated body.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateInflateRatioBurst" id="DeflateInflateRatioBurst">DeflateInflateRatioBurst</a> <a name="deflateinflateratioburst" id="deflateinflateratioburst">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of times the inflation ratio for request bodies
can be crossed</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateInflateRatioBurst <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>3</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>2.2.28 and later</td></tr>
</table>
<p>The <code class="directive">DeflateInflateRatioBurst</code> directive
specifies the maximum number of times the
<code class="directive">DeflateInflateRatioLimit</code> can be crossed before
terminating the request.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateInflateRatioLimit" id="DeflateInflateRatioLimit">DeflateInflateRatioLimit</a> <a name="deflateinflateratiolimit" id="deflateinflateratiolimit">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum inflation ratio for request bodies</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateInflateRatioLimit <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>200</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>2.2.28 and later</td></tr>
</table>
<p>The <code class="directive">DeflateInflateRatioLimit</code> directive
specifies the maximum ratio of deflated to inflated size of an
inflated request body. This ratio is checked as the body is
streamed in, and if crossed more than
<code class="directive">DeflateInflateRatioBurst</code> times, the request
will be terminated.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateMemLevel" id="DeflateMemLevel">DeflateMemLevel</a> <a name="deflatememlevel" id="deflatememlevel">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>How much memory should be used by zlib for compression</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateMemLevel <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateMemLevel 9</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
<p>The <code class="directive">DeflateMemLevel</code> directive specifies
how much memory should be used by zlib for compression
(a value between 1 and 9).</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateWindowSize" id="DeflateWindowSize">DeflateWindowSize</a> <a name="deflatewindowsize" id="deflatewindowsize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Zlib compression window size</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateWindowSize <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateWindowSize 15</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
<p>The <code class="directive">DeflateWindowSize</code> directive specifies the
zlib compression window size (a value between 1 and 15). Generally, the
higher the window size, the higher can the compression ratio be expected.</p>
</div>
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