Filters
, implements server-side includes.mod_ssl
, implements SSL encryption (https).mod_deflate
, implements compression/decompression on the fly.modcharsetlite
, transcodes between different character sets.modextfilter
, runs an external program as a filter.Apache also uses a number of filters internally to perform functions like chunking and byte-range handling.
Apache HTTP Server Version 2.4
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_includemod_sslmod_deflatemod_charset_litemod_ext_filterApache 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:
, 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,mod_filter
Filters can be used to process content originating from the client in addition to processing content originating on the server using the module.mod_reflector
accepts POST requests from clients, and reflects the content request body received within the POST request back in the response, passing through the output filter stack on the way back to the client.mod_reflector
This technique can be used as an alternative to a web service running within an application server stack, where an output filter provides the transformation required on the request body. For example, the module might be used to provide a general compression service, or an image transformation filter might be turned into an image transformation service.mod_deflate
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 , SetInputFilter, SetOutputFilter, AddInputFilter, AddOutputFilter, and RemoveInputFilter.RemoveOutputFilter
The Dynamic Way enables both static and flexible, dynamic configuration of output filters, as discussed in the page. Relevant directives are mod_filter, FilterChain, and FilterDeclare.FilterProvider
One further directive is still supported, but deprecated. Use dynamic configuration instead.AddOutputFilterByType
Filters
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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 i
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 prior information about what the o
Exposing Filters as an HTTP Service
Filters can be used to process content originating from the client in addition to processing content originating on the server using the mod_reflector module.
Using Filters
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).