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This document describes the use of filters in Apache.

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Filtering in Apache 2

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.

Filters can be chained, in a Data Axis orthogonal to request processing

Some examples of filtering in the standard Apache distribution are:

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:


Smart Filtering

Smart filtering applies different filter providers according to the state of request processing

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 complete