ASP.NET is a powerful platform for building Web applications, that provides a tremendous amount of flexibility and power for building just about any kind of Web application. Most people are familiar only with the high level frameworks like WebForms and WebServices which sit at the very top level of the ASP.NET hierarchy. This article looks at how Web requests flow through the ASP.NET framework from a very low level perspective, from Web Server, through ISAPI all the way up the request handler and your code. See what happens behind the scenes and stop thinking of ASP.NET as a black box.
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I've been sitting on this article for a couple of years now and finally got around to putting it out. The main reason has been that there are still a few open issues that I have not been able to trace completely in the transition from the ISAPI code into the ASP.NET pipeline. How exactly the interfacing works between the ISAPI layer and ASP.NET ISAPIRuntime classes is not exactly clear. It appears that the ISAPI extension directly calls into the runtime instances to instantiate requests.
If anybody finds any additional information, or reference material please leave a note here, so I can update the article if possible. It'd be great to complete the cycle and fill in the small missing blanks. I looked online over the years and asked at Microsoft, but it appears the Microsofties are not keen on sharing this information. Understandable as the implementation may change in the future, but it's still interesting to know how the plumbing works deep down in the bowels of IIS and the Worker Process.
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