Implementing an IIS Application Filter Using .NET HttpModules and Response Filtering

n this article, I will concentrate on the critical differences in the processing model implemented by HttpHandlers versus that implemented by HttpModules. I'll be presenting specific coding samples as necessary in order in order to illustrate various points, but I won't be presenting a comprehensive sample of my own implementation.  A wealth of information and code samples are available to demonstrate how to establish an HttpModule to participate in your application’s web requests and I’ll present these links toward the end of the article. In the meantime, It's my hope that this article will complement the existing samples and documentation and assist you with the development of your own IIS Application filtering solution.

If you’ve worked with ISAPI filters under IIS4, the HttpModule processing model is probably nothing new to you. However ISAPI filtering under IIS4 was relatively out-of-bounds for VB developers and therefore the fundamental processing model may be less than intuitive to many VB developers.

HttpHandler—the Target for your Request
The HttpHandler model is relatively easy to understand. An HttpHandler is the target of a web request. In fact, a WebForm (.aspx) page derives from System.Web.UI.Page which implements the HttpHandler interface. Check it out in the object browser.