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Apache HTTP Server Version 2.4

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Apache Module mod_brotli

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Description:Compress content via Brotli before it is delivered to the client
Status:Extension
Module Identifier:brotli_module
Source File:mod_brotli.c
Compatibility:Available in version 2.4.26 and later.

Summary

The mod_brotli module provides the BROTLI_COMPRESS 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. This module uses the Brotli library found at https://github.com/google/brotli.

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Sample Configurations

Compression and TLS

Some web applications are vulnerable to an information disclosure attack when a TLS connection carries compressed data. For more information, review the details of the "BREACH" family of attacks.

This is a simple configuration that compresses common text-based content types.

Compress only a few types

AddOutputFilterByType BROTLI_COMPRESS text/html text/plain text/xml text/css text/javascript application/javascript
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Enabling Compression

Compression and TLS

Some web applications are vulnerable to an information disclosure attack when a TLS connection carries compressed data. For more information, review the details of the "BREACH" family of attacks.

Output Compression

Compression is implemented by the BROTLI_COMPRESS filter. The following directive will enable compression for documents in the container where it is placed:

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

If you want to restrict the compression to particular MIME types in general, you may use the AddOutputFilterByType directive. Here is an example of enabling compression only for the html files of the Apache documentation:

<Directory "/your-server-root/manual">
    AddOutputFilterByType BROTLI_COMPRESS text/html
</Directory>

Note

The BROTLI_COMPRESS filter is always inserted after RESOURCE filters like PHP or SSI. It never touches internal subrequests.

Note

There is an environment variable no-brotli, set via SetEnv, which will disable brotli compression for a particular request, even if it is supported by the client.
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Dealing with proxy servers

The mod_brotli module sends a Vary: Accept-Encoding HTTP response header to alert proxies that a cached response should be sent only to clients that send the appropriate Accept-Encoding request header. This prevents compressed content from being sent to a client that will not understand it.

If you use some special exclusions dependent on, for example, the User-Agent header, you must manually configure an addition to the Vary header to alert proxies of the additional restrictions. For example, in a typical configuration where the addition of the BROTLI_COMPRESS filter depends on the User-Agent, you should add:

Header append Vary User-Agent

If your decision about compression depends on other information than request headers (e.g. HTTP version), you have to set the Vary header to the value *. This prevents compliant proxies from caching entirely.

Example

Header set Vary *
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Serving pre-compressed content

Since mod_brotli 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:

<IfModule mod_headers.c>
    # Serve brotli compressed CSS files if they exist
    # and the client accepts brotli.
    RewriteCond "%{HTTP:Accept-encoding}" "br"
    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}" "br"
    RewriteCond "%{REQUEST_FILENAME}\.br" "-s"
    RewriteRule "^(.*)\.js"               "$1\.js\.br" [QSA]


    # Serve correct content types, and prevent double compression.
    RewriteRule "\.css\.br$" "-" [T=text/css,E=no-brotli:1]
    RewriteRule "\.js\.br$"  "-" [T=text/javascript,E=no-brotli:1]


    <FilesMatch "(\.js\.br|\.css\.br)$">
      # Serve correct encoding type.
      Header append Content-Encoding br

      # Force proxies to cache brotli &
      # non-brotli css/js files separately.
      Header append Vary Accept-Encoding
    </FilesMatch>
</IfModule>
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BrotliAlterETag