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<modulesynopsis metafile="mod_deflate.xml.meta">

<name>mod_deflate</name>

<description>Compress content before it is delivered to the

client</description>

<status>Extension</status>

<sourcefile>mod_deflate.c</sourcefile>

<identifier>deflate_module</identifier>

<summary>

<p>The <module>mod_deflate</module> 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>

</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 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>

<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 DEFLATE

SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip

</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 DEFLATE text/html

&lt;/Directory&gt;

</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 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>

</section>

<section id="inflate"><title>Output Decompression</title>

<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 output filter chain using <directive module="core"

>SetOutputFilter</directive> or <directive module="mod_mime"

>AddOutputFilter</directive>, for example:</p>

<highlight language="config">

&lt;Location "/dav-area"&gt;

ProxyPass http://example.com/

SetOutputFilter INFLATE

&lt;/Location&gt;

</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

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 <directive module="core"

>SetInputFilter</directive> or <directive module="mod_mime"

>AddInputFilter</directive>, for example:</p>

<highlight language="config">

&lt;Location "/dav-area"&gt;

SetInputFilter DEFLATE

&lt;/Location&gt;

</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,

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_deflate</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_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">

&lt;IfModule mod_headers.c&gt;

# 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]

&lt;FilesMatch "(\.js\.gz|\.css\.gz)$"&gt;

# Serve correct encoding type.

Header append Content-Encoding gzip

# Force proxies to cache gzipped &amp;

# non-gzipped css/js files separately.

Header append Vary Accept-Encoding

&lt;/FilesMatch&gt;

&lt;/IfModule&gt;

</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>

<usage>

<p>The <directive>DeflateFilterNote</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">

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 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">

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>

</directivesynopsis>

<directivesynopsis>

<name>DeflateBufferSize</name>

<description>Fragment size to be compressed at one time by zlib</description>

<syntax>DeflateBufferSize <var>value</var></syntax>

<default>DeflateBufferSize 8096</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>DeflateBufferSize</directive> directive specifies

the size in bytes of the fragments that zlib should compress at one

time.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>DeflateWindowSize</name>

<description>Zlib compression window size</description>

<syntax>DeflateWindowSize <var>value</var></syntax>

<default>DeflateWindowSize 15</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>DeflateWindowSize</directive> 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>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>DeflateMemLevel</name>

<description>How much memory should be used by zlib for compression</description>

<syntax>DeflateMemLevel <var>value</var></syntax>

<default>DeflateMemLevel 9</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>DeflateMemLevel</directive> directive specifies

how much memory should be used by zlib for compression

(a value between 1 and 9).</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>DeflateCompressionLevel</name>

<description>How much compression do we apply to the output</description>

<syntax>DeflateCompressionLevel <var>value</var></syntax>

<default>Zlib's default</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>DeflateCompressionLevel</directive> 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>

</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>

<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>

<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>

<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>

<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>