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<?xml version="1.0"?>
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<modulesynopsis metafile="mod_brotli.xml.meta">
<name>mod_brotli</name>
<description>Compress content via Brotli before it is delivered to the
client</description>
<status>Extension</status>
<sourcefile>mod_brotli.c</sourcefile>
<identifier>brotli_module</identifier>
<summary>
<p>The <module>mod_brotli</module> module provides
the <code>BROTLI_COMPRESS</code> output filter that allows output from
your server to be compressed using the brotli compression format before being sent to the client over
the network.</p>
</summary>
<seealso><a href="../filter.html">Filters</a></seealso>
<section id="recommended"><title>Sample Configurations</title>
<note type="warning"><title>Compression and TLS</title>
<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>
</note>
<p>This is a simple configuration that compresses common text-based content types.</p>
<example><title>Compress only a few types</title>
<highlight language="config">
AddOutputFilterByType BROTLI_COMPRESS text/html text/plain text/xml text/css text/javascript application/javascript
</highlight>
</example>
</section>
<section id="enable"><title>Enabling Compression</title>
<note type="warning"><title>Compression and TLS</title>
<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>
</note>
<section id="output"><title>Output Compression</title>
<p>Compression is implemented by the <code>BROTLI_COMPRESS</code>
<a href="../filter.html">filter</a>. The following directive
will enable compression for documents in the container where it
is placed:</p>
<highlight language="config">
SetOutputFilter BROTLI_COMPRESS
SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-brotli
</highlight>
<p>If you want to restrict the compression to particular MIME types
in general, you may use the <directive module="mod_filter"
>AddOutputFilterByType</directive> directive. Here is an example of
enabling compression only for the html files of the Apache
documentation:</p>
<highlight language="config">
&lt;Directory "/your-server-root/manual"&gt;
AddOutputFilterByType BROTLI_COMPRESS text/html
&lt;/Directory&gt;
</highlight>
<note><title>Note</title>
The <code>BROTLI_COMPRESS</code> filter is always inserted after RESOURCE
filters like PHP or SSI. It never touches internal subrequests.
</note>
<note><title>Note</title>
There is an environment variable <code>no-brotli</code>,
set via <directive module="mod_env">SetEnv</directive>, which
will ignore the accept-encoding setting of your browser and will
send compressed output.
</note>
</section>
<section id="input"><title>Input Decompression</title>
<p>The <module>mod_brotli</module> module also provides a filter for
decompressing a brotli compressed request body . In order to activate
this feature you have to insert the <code>BROTLI_COMPRESS</code> filter into
the input filter chain using <directive module="core"
>SetInputFilter</directive> or <directive module="mod_mime"
>AddInputFilter</directive>, for example:</p>
<highlight language="config">
&lt;Location "/dav-area"&gt;
SetInputFilter BROTLI_COMPRESS
&lt;/Location&gt;
</highlight>
<p>Now if a request contains a <code>Content-Encoding:
brotli</code> header, the body will be automatically decompressed.
Few browsers have the ability to brotli request bodies. However,
some special applications actually do support request
compression, for instance some <a
href="http://www.webdav.org">WebDAV</a> clients.</p>
<note type="warning"><title>Note on Content-Length</title>
<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>
</note>
</section>
</section>
<section id="proxies"><title>Dealing with proxy servers</title>
<p>The <module>mod_brotli</module> 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>
<highlight language="config">
Header append Vary User-Agent
</highlight>
<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>
<example><title>Example</title>
<highlight language="config">
Header set Vary *
</highlight>
</example>
</section>
<section id="precompressed"><title>Serving pre-compressed
content</title>
<p>Since <module>mod_brotli</module> re-compresses content each
time a request is made, some performance benefit can be derived by
pre-compressing the content and telling mod_brotli to serve them
without re-compressing them. This may be accomplished using a
configuration like the following:</p>
<highlight language="config">
&lt;IfModule mod_headers.c&gt;
# Serve brotli compressed CSS files if they exist
# and the client accepts brotli.
RewriteCond "%{HTTP:Accept-encoding}" "brotli"
RewriteCond "%{REQUEST_FILENAME}\.br" "-s"
RewriteRule "^(.*)\.css" "$1\.css\.br" [QSA]
# Serve brotli compressed JS files if they exist
# and the client accepts brotli.
RewriteCond "%{HTTP:Accept-encoding}" "brotli"
RewriteCond "%{REQUEST_FILENAME}\.br" "-s"
RewriteRule "^(.*)\.js" "$1\.js\.br" [QSA]
# Serve correct content types, and prevent mod_brotli double brotli.
RewriteRule "\.css\.gz$" "-" [T=text/css,E=no-brotli:1]
RewriteRule "\.js\.gz$" "-" [T=text/javascript,E=no-brotli:1]
&lt;FilesMatch "(\.js\.gz|\.css\.gz)$"&gt;
# Serve correct encoding type.
Header append Content-Encoding brotli
# Force proxies to cache brotli &amp;
# non-brotli css/js files separately.
Header append Vary Accept-Encoding
&lt;/FilesMatch&gt;
&lt;/IfModule&gt;
</highlight>
</section>
<directivesynopsis>
<name>BrotliFilterNote</name>
<description>Places the compression ratio in a note for logging</description>
<syntax>BrotliFilterNote [<var>type</var>] <var>notename</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>BrotliFilterNote</directive> 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>
<example><title>Example</title>
<highlight language="config">
BrotliFilterNote ratio
LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' brotli
CustomLog "logs/brotli_log" brotli
</highlight>
</example>
<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>
<example><title>Accurate Logging</title>
<highlight language="config">
BrotliFilterNote Input instream
BrotliFilterNote Output outstream
BrotliFilterNote Ratio ratio
LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' brotli
CustomLog "logs/brotli_log" brotli
</highlight>
</example>
</usage>
<seealso><module>mod_log_config</module></seealso>
</directivesynopsis>
<directivesynopsis>
<name>BrotliCompressionQuality</name>
<description>Compression quality</description>
<syntax>BrotliCompressionQuality <var>value</var></syntax>
<default>BrotliCompressionQuality 5</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>BrotliCompressionQuality</directive> directive specifies
the compression quality performed (a value between 0 and 11). Higher
quality values result in better compression but also slower compression
as well.
</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>BrotliCompressionWindow</name>
<description>Brotli sliding compression window size</description>
<syntax>BrotliCompressionWindow <var>value</var></syntax>
<default>BrotliCompressionWindow 18</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>BrotliCompressionWindow</directive> directive specifies the
brotli sliding compression window size (a value between 10 and 24). Generally, the
higher the window size, the higher can the compression ratio be expected
but requires more memory.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>BrotliCompressionMaxInputBlock</name>
<description>Maximum input block size</description>
<syntax>BrotliCompressionMaxInputBlock <var>value</var></syntax>
<default>BrotliCompressionMaxInputBlock 0</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>BrotliCompressionMaxInputBlock</directive> directive specifies
the maximum input block size between 16 and 24, with the caveat that
larger block sizes require more memory.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>BrotliAlterETag</name>
<description>How the outgoing ETag header should be modified during compression</description>
<syntax>BrotliAlterETag AddSuffix|NoChange|Remove</syntax>
<default>BrotliAlterETag AddSuffix</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>BrotliAlterETag</directive> directive specifies
how the ETag hader should be altered when a response is compressed.</p>
<dl>
<dt>AddSuffix</dt>
<dd><p>Append the compression method onto the end of the ETag, causing
compressed and uncompressed representations to have unique ETags.
This has been the default since 2.4.0, but prevents serving
"HTTP Not Modified" (304) responses to conditional requests for
compressed content.</p></dd>
<dt>NoChange</dt>
<dd><p>Don't change the ETag on a compressed response. This was the default
prior to 2.4.0, but does not satisfy the HTTP/1.1 property that all
representations of the same resource have unique ETags. </p></dd>
<dt>Remove</dt>
<dd><p>Remove the ETag header from compressed responses. This prevents
some conditional requests from being possible, but avoids the
shortcomings of the preceding options. </p></dd>
</dl>
</usage>
</directivesynopsis>
</modulesynopsis>