Filters

Filtering in Apache 2

Related Modules	Related Directives
mod_filter mod_deflate mod_ext_filter mod_include mod_charset_lite mod_reflector mod_buffer mod_data mod_ratelimit mod_reqtimeout mod_request mod_sed mod_substitute mod_xml2enc mod_proxy_html	FilterChain FilterDeclare FilterProtocol FilterProvider AddInputFilter AddOutputFilter RemoveInputFilter RemoveOutputFilter ReflectorHeader ExtFilterDefine ExtFilterOptions SetInputFilter SetOutputFilter

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. A few of these are:

• HTML and XML processing and rewriting
• XSLT transforms and XIncludes
• XML Namespace support
• File Upload handling and decoding of HTML Forms
• Image processing
• Protection of vulnerable applications such as PHP scripts
• Text search-and-replace editing

Smart Filtering

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 pri