Filters are OO (just like the streams and wrappers). We use a bucket-brigade (similar concept to Apache2 filters) Brigade is a doubly-linked list that contains a number of data buckets chained together. No need to maintain/realloc a monolithic buffer. meta-buckets can contain information about EOF conditions. Useful structure since the data and EOF events may occur on separate invocations of %fread()%. For filters that simply pass through data, buckets can be passed on to next filter without the overhead of %memcpy()%/%malloc()% - just re-link filter into the next brigade. Separate stacks for reading and writing.