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<div id="preamble"><h1>Apache Module mod_deflate</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="/en/mod/mod_deflate.html" title="English"> en </a> |
<a href="/fr/mod/mod_deflate.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a> |
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<a href="/ko/mod/mod_deflate.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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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#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>
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 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="/images/down.gif" /> <a href="#deflatecompressionlevel">DeflateCompressionLevel</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
</ul><h3>See also</h3>
<ul class="seealso">
</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></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 class="section">
<h2><a name="enable" id="enable">Enabling Compression</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>
<h3><a name="output" id="output">Output Compression</a></h3>
<p>Compression is implemented by the <code>DEFLATE</code>
will enable compression for documents in the container where it
is placed:</p>
<pre class="prettyprint lang-config">
SetOutputFilter DEFLATE
SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip
</pre>
<p>If you want to restrict the compression to particular MIME types
in general, you may use the <code class="directive"><a href="/mod/mod_filter.html#addoutputfilterbytype">AddOutputFilterByType</a></code> directive. Here is an example of
enabling compression only for the html files of the Apache
documentation:</p>
<pre class="prettyprint lang-config">
<Directory "/your-server-root/manual">
</Directory>
</pre>
<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 a environment variable <code>force-gzip</code>,
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 outputfilter 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>
<pre class="prettyprint lang-config">
<Location /dav-area>
ProxyPass http://example.com/
SetOutputFilter INFLATE
</Location>
</pre>
<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>
<pre class="prettyprint lang-config">
<Location /dav-area>
SetInputFilter DEFLATE
</Location>
</pre>
<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
<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 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>
<pre class="prettyprint lang-config">
Header append Vary User-Agent
</pre>
<p>If your decision about compression depends on other information
<code>Vary</code> header to the value <code>*</code>. This prevents
compliant proxies from caching entirely.</p>
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">
Header set Vary *
</pre>
</div>
</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>
</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="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>
</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="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>
</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
<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">
DeflateFilterNote ratio
LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' deflate
CustomLog logs/deflate_log deflate
</pre>
</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 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>
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><pre class="prettyprint lang-config">
DeflateFilterNote Input instream
DeflateFilterNote Output outstream
DeflateFilterNote Ratio ratio
LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate
CustomLog logs/deflate_log deflate
</pre>
</div>
<h3>See also</h3>
<ul>
</ul>
</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>
</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="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>
</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>
</div>
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