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- Copyright 2002-2005 The Apache Software Foundation or its licensors, as
- applicable.
-
- Licensed under the Apache License, Version 2.0 (the "License");
- you may not use this file except in compliance with the License.
- You may obtain a copy of the License at
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
</summary>
<seealso><a href="../filter.html">Filters</a></seealso>
+<section id="supportedencodings"><title>Supported Encodings</title>
+ <p>The <code>gzip</code> encoding is the only one supported to ensure complete compatibility
+ with old browser implementations. The <code>deflate</code> encoding is not supported,
+ please check the <a href="http://www.gzip.org/zlib/zlib_faq.html#faq38">zlib's documentation</a>
+ for a complete explanation.
+ </p>
+</section>
+
<section id="recommended"><title>Sample Configurations</title>
- <p>This is a simple sample configuration for the impatient.</p>
+ <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>
- AddOutputFilterByType DEFLATE text/html text/plain text/xml
- </example>
-
- <p>The following configuration, while resulting in more compressed content,
- is also much more complicated. Do not use this unless you fully understand
- all the configuration details.</p>
-
- <example><title>Compress everything except images</title>
- <Location /><br />
- <indent>
- # Insert filter<br />
- SetOutputFilter DEFLATE<br />
- <br />
- # Netscape 4.x has some problems...<br />
- BrowserMatch ^Mozilla/4 gzip-only-text/html<br />
- <br />
- # Netscape 4.06-4.08 have some more problems<br />
- BrowserMatch ^Mozilla/4\.0[678] no-gzip<br />
- <br />
- # MSIE masquerades as Netscape, but it is fine<br />
- # BrowserMatch \bMSIE !no-gzip !gzip-only-text/html<br />
- <br />
- # NOTE: Due to a bug in mod_setenvif up to Apache 2.0.48<br />
- # the above regex won't work. You can use the following<br />
- # workaround to get the desired effect:<br />
- BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html<br />
- <br />
- # Don't compress images<br />
- SetEnvIfNoCase Request_URI \<br />
- <indent>
- \.(?:gif|jpe?g|png)$ no-gzip dont-vary<br />
- </indent>
- <br />
- # Make sure proxies don't deliver the wrong content<br />
- Header append Vary User-Agent env=!dont-vary<br />
- </indent>
- </Location>
+ <highlight language="config">
+ AddOutputFilterByType DEFLATE 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>DEFLATE</code>
will enable compression for documents in the container where it
is placed:</p>
- <example>
- SetOutputFilter DEFLATE
- </example>
+ <highlight language="config">
+SetOutputFilter DEFLATE
+SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip
+ </highlight>
- <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 <directive module="core"
+ 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>
- <example>
- <Directory "/your-server-root/manual"><br />
- <indent>
- AddOutputFilterByType DEFLATE text/html<br />
- </indent>
- </Directory>
- </example>
-
- <p>For browsers that have problems even with compression of all file
- types, use the <directive module="mod_setenvif"
- >BrowserMatch</directive> 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>
-
- <example>
- BrowserMatch ^Mozilla/4 gzip-only-text/html<br />
- BrowserMatch ^Mozilla/4\.0[678] no-gzip<br />
- BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
- </example>
-
- <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 <directive module="mod_setenvif">BrowserMatch</directive>
- 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>
+ <highlight language="config">
+<Directory "/your-server-root/manual">
+ AddOutputFilterByType DEFLATE text/html
+</Directory>
+ </highlight>
<note><title>Note</title>
The <code>DEFLATE</code> filter is always inserted after RESOURCE
filters like PHP or SSI. It never touches internal subrequests.
</note>
<note><title>Note</title>
- There is a environment variable <code>force-gzip</code>,
- set via <directive module="core">SetEnv</directive>, which
+ There is an environment variable <code>force-gzip</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>
<p>The <module>mod_deflate</module> 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 <directive module="core"
+ the output filter chain using <directive module="core"
>SetOutputFilter</directive> or <directive module="mod_mime"
>AddOutputFilter</directive>, for example:</p>
- <example>
- <Location /dav-area><br />
- <indent>
- ProxyPass http://example.com/<br />
- SetOutputFilter INFLATE<br />
- </indent>
- </Location>
- </example>
+ <highlight language="config">
+<Location "/dav-area">
+ ProxyPass "http://example.com/"
+ SetOutputFilter INFLATE
+</Location>
+ </highlight>
<p>This Example will uncompress gzip'ed output from example.com, so other
filters can do further processing with it.
</p>
-
+
</section>
<section id="input"><title>Input Decompression</title>
<p>The <module>mod_deflate</module> module also provides a filter for
>SetInputFilter</directive> or <directive module="mod_mime"
>AddInputFilter</directive>, for example:</p>
- <example>
- <Location /dav-area><br />
- <indent>
- SetInputFilter DEFLATE<br />
- </indent>
- </Location>
- </example>
-
+ <highlight language="config">
+<Location "/dav-area">
+ SetInputFilter DEFLATE
+</Location>
+ </highlight>
+
<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,
not understand it.</p>
<p>If you use some special exclusions dependent
- on, for example, the <code>User-Agent</code> header, you must
+ 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>
- <example>
+ <highlight language="config">
Header append Vary User-Agent
- </example>
-
+ </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_deflate</module> re-compresses content each
+ time a request is made, some performance benefit can be derived by
+ pre-compressing the content and telling mod_deflate to serve them
+ without re-compressing them. This may be accomplished using a
+ configuration like the following:</p>
+
+ <highlight language="config">
+<IfModule mod_headers.c>
+ # Serve gzip compressed CSS files if they exist
+ # and the client accepts gzip.
+ RewriteCond "%{HTTP:Accept-encoding}" "gzip"
+ RewriteCond "%{REQUEST_FILENAME}\.gz" "-s"
+ RewriteRule "^(.*)\.css" "$1\.css\.gz" [QSA]
+
+ # Serve gzip compressed JS files if they exist
+ # and the client accepts gzip.
+ RewriteCond "%{HTTP:Accept-encoding}" "gzip"
+ RewriteCond "%{REQUEST_FILENAME}\.gz" "-s"
+ RewriteRule "^(.*)\.js" "$1\.js\.gz" [QSA]
+
+
+ # Serve correct content types, and prevent mod_deflate double gzip.
+ RewriteRule "\.css\.gz$" "-" [T=text/css,E=no-gzip:1]
+ RewriteRule "\.js\.gz$" "-" [T=text/javascript,E=no-gzip:1]
+
+
+ <FilesMatch "(\.js\.gz|\.css\.gz)$">
+ # Serve correct encoding type.
+ Header append Content-Encoding gzip
+
+ # Force proxies to cache gzipped &
+ # non-gzipped css/js files separately.
+ Header append Vary Accept-Encoding
+ </FilesMatch>
+</IfModule>
+ </highlight>
+
+</section>
+
<directivesynopsis>
<name>DeflateFilterNote</name>
<description>Places the compression ratio in a note for logging</description>
<syntax>DeflateFilterNote [<var>type</var>] <var>notename</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
-<compatibility><var>type</var> is available since Apache 2.0.45</compatibility>
<usage>
<p>The <directive>DeflateFilterNote</directive> directive
>access log</a>.</p>
<example><title>Example</title>
- DeflateFilterNote ratio<br />
- <br />
- LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' deflate<br />
- CustomLog logs/deflate_log deflate
+ <highlight language="config">
+ DeflateFilterNote ratio
+
+ LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' deflate
+ CustomLog "logs/deflate_log" deflate
+ </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 note for logging. <var>type</var> can be one of:</p>
+ left as a note for logging. <var>type</var> can be one of:</p>
<dl>
<dt><code>Input</code></dt>
<p>Thus you may log it this way:</p>
<example><title>Accurate Logging</title>
- 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
+ <highlight language="config">
+DeflateFilterNote Input instream
+DeflateFilterNote Output outstream
+DeflateFilterNote Ratio ratio
+
+LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate
+CustomLog "logs/deflate_log" deflate
+</highlight>
</example>
</usage>
<seealso><module>mod_log_config</module></seealso>
<usage>
<p>The <directive>DeflateBufferSize</directive> directive specifies
the size in bytes of the fragments that zlib should compress at one
- time.</p>
+ time. If the compressed response size is bigger than the one specified
+ by this directive then httpd will switch to chunked encoding
+ (HTTP header <code>Transfer-Encoding</code> set to <code>Chunked</code>), with the
+ side effect of not setting any <code>Content-Length</code> HTTP header. This is particularly
+ important when httpd works behind reverse caching proxies or when httpd is configured with
+ <module>mod_cache</module> and <module>mod_cache_disk</module> because
+ HTTP responses without any <code>Content-Length</code> header might not be cached.
+ </p>
</usage>
</directivesynopsis>
<default>Zlib's default</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
-<compatibility>This directive is available since Apache 2.0.45</compatibility>
<usage>
<p>The <directive>DeflateCompressionLevel</directive> directive specifies
- what level of compression should be used, the higher the value,
+ 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>
</usage>
</directivesynopsis>
+<directivesynopsis>
+<name>DeflateAlterETag</name>
+<description>How the outgoing ETag header should be modified during compression</description>
+<syntax>DeflateAlterETag AddSuffix|NoChange|Remove</syntax>
+<default>DeflateAlterETag AddSuffix</default>
+<contextlist><context>server config</context><context>virtual host</context>
+</contextlist>
-</modulesynopsis>
+<usage>
+ <p>The <directive>DeflateAlterETag</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>
+
+<directivesynopsis>
+<name>DeflateInflateLimitRequestBody</name>
+<description>Maximum size of inflated request bodies</description>
+<syntax>DeflateInflateLimitRequestBody<var>value</var></syntax>
+<default>None, but LimitRequestBody applies after deflation</default>
+<contextlist><context>server config</context><context>virtual host</context>
+<context>directory</context><context>.htaccess</context></contextlist>
+<override>All</override>
+<compatibility>2.4.10 and later</compatibility>
+
+<usage>
+ <p>The <directive>DeflateInflateLimitRequestBody</directive> directive
+ specifies the maximum size of an inflated request body. If it is unset,
+ <directive module="core">LimitRequestBody</directive> is applied to the
+ inflated body.</p>
+</usage>
+</directivesynopsis>
+
+<directivesynopsis>
+<name>DeflateInflateRatioLimit</name>
+<description>Maximum inflation ratio for request bodies</description>
+<syntax>DeflateInflateRatioLimit <var>value</var></syntax>
+<default>200</default>
+<contextlist><context>server config</context><context>virtual host</context>
+<context>directory</context><context>.htaccess</context></contextlist>
+<override>All</override>
+<compatibility>2.4.10 and later</compatibility>
+<usage>
+ <p>The <directive>DeflateInflateRatioLimit</directive> 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
+ <directive>DeflateInflateRatioBurst</directive> times, the request
+ will be terminated.</p>
+</usage>
+</directivesynopsis>
+
+<directivesynopsis>
+<name>DeflateInflateRatioBurst</name>
+<description>Maximum number of times the inflation ratio for request bodies
+ can be crossed</description>
+<syntax>DeflateInflateRatioBurst <var>value</var></syntax>
+<default>3</default>
+<contextlist><context>server config</context><context>virtual host</context>
+<context>directory</context><context>.htaccess</context></contextlist>
+<override>All</override>
+<compatibility>2.4.10 and later</compatibility>
+
+<usage>
+ <p>The <directive>DeflateInflateRatioBurst</directive> directive
+ specifies the maximum number of times the
+ <directive>DeflateInflateRatioLimit</directive> can be crossed before
+ terminating the request.</p>
+</usage>
+</directivesynopsis>
+
+</modulesynopsis>
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