The basic idea of a filter is to pre-process incoming data and post-process outgoing data. Filters are part of a filter chain, thus following the chain of responsability design pattern.
Each filter decides to call the next filter or not.
In EWF, there are two levels of filters.
Typical examples of such filters are: logging, compression, routing (WSF_ROUTING_FILTER), ...
Handler that can also play the role of a filter.
Typical examples of such filters are: authentication, ...
Filters (also called middelwares) in other environments: * in Python: http://www.wsgi.org/en/latest/libraries.html * in Node.js: http://expressjs.com/guide.html#middleware * in Apache: http://httpd.apache.org/docs/2.2/en/filter.html