Filter

Introduction

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.

Levels

In EWF, there are two levels of filters.

WSF_FILTER

Typical examples of such filters are: logging, compression, routing (WSF_ROUTING_FILTER), ...

WSF_FILTER_HANDLER

Handler that can also play the role of a filter.

Typical examples of such filters are: authentication, ...

References

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