ONLamp: Writing Filters for Apache 2.0
August 28, 2001
"Filters work because the Apache developers consider Web pages as chunks of information. In general, we don't care what those chunks look like or how they are stored on the server. In Apache filter terminology, each chunk is stored in a bucket, and lists of buckets form brigades. Lists of brigades can then create a Web document. Filters operate on one brigade at a time, and are called upon repeatedly until the entire document has been processed. This allows the server to stream information to the client."
"... Before a filter can be enabled for a given request, it must be registered with the server. This is done using the ap_register_output_filter function. This function is invoked with three arguments: the filter name, the filter function pointer and the filter type ..."