Apache HTTP Server Version 2.2
This document describes the use of filters in Apache.
|Related Modules||Related Directives|
The Filter Chain is available in Apache 2.0 and higher, and enables applications to process incoming and outgoing data in a highly flexible and configurable manner, regardless of where the data comes from. We can pre-process incoming data, and post-process outgoing data, at will. This is basically independent of the traditional request processing phases.
Some examples of filtering in the standard Apache distribution are:
mod_include, implements server-side includes.
mod_ssl, implements SSL encryption (https).
mod_deflate, implements compression/decompression on the fly.
mod_charset_lite, transcodes between different character sets.
mod_ext_filter, runs an external program as a filter.
Apache also uses a number of filters internally to perform functions like chunking and byte-range handling.
A wider range of applications are implemented by third-party filter modules available from modules.apache.org and elsewhere. A few of these are:
mod_filter, included in Apache 2.1 and later,
enables the filter chain to be configured dynamically at run time.
So for example you can set up a proxy to rewrite
HTML with an HTML filter and JPEG images with a completely
separate filter, despite the proxy having no prior information
about what the origin server will send. This works by using a
filter harness, that dispatches to different providers according
to the actual contents at runtime. Any filter may be either
inserted directly in the chain and run unconditionally, or
used as a provider and inserted dynamically. For example,
There are two ways to use filtering: Simple and Dynamic. In general, you should use one or the other; mixing them can have unexpected consequences (although simple Input filtering can be mixed freely with either simple or dynamic Output filtering).
The Simple Way is the only way to configure input filters, and is
sufficient for output filters where you need a static filter chain.
Relevant directives are
One further directive
AddOutputFilterByType is still supported,
but may be problematic and is now deprecated. Use dynamic