# Filters

This document describes the use of filters in Apache.

# Filters

mod_deflate
mod_ext_filter
mod_include
AddInputFilter
AddOutputFilter
RemoveInputFilter
RemoveOutputFilter
ExtFilterDefine
ExtFilterOptions
SetInputFilter
SetOutputFilter

A filter is a process that is applied to data that is sent or received by the server. Data sent by clients to the server is processed by input filters while data sent by the server to the client is processed by output filters. Multiple filters can be applied to the data, and the order of the filters can be explicitly specified.

Filters are used internally by Apache to perform functions such as chunking and byte-range request handling. In addition, modules can provide filters that are selectable using run-time configuration directives. The set of filters that apply to data can be manipulated with the SetInputFilter, SetOutputFilter, AddInputFilter, AddOutputFilter, RemoveInputFilter, and RemoveOutputFilter directives.

The following user-selectable filters are currently provided with the Apache HTTP Server distribution.

INCLUDES
  Server-Side Includes processing by mod_include
DEFLATE
  Compress output before sending it to the client using mod_deflate

In addition, the module mod_ext_filter allows for external programs to be defined as filters.