ISAPI Vs Everything!

I was just reading up on the MSDN website about authoring ISAPI filters... mainly because I want to write my own IIS version of Apache's "mod_Rewrite" and because the commercial, pre-written versions are like $99 per server

Anyway, on the MSDN website, it states that ISAPI is faster than ASP and CGI, so if ISAPI is faster than ASP and can do everything it can... why arn't we using it instead?

Especilly seeming as ISAPI is lower on in the process of the HTTP Request/Response stage, so naturally it would be faster

I know ISAPI is mostly done in C++.... and I know quite a bit of C++ already, so in theory, wouldn't it be better for me to write my next IIS-only web-application in C++/ISAPI?

Yes, and no.

Yes it may be faster, I'm not so sure as I've not written anything in ISAPI. But what are the legacy implications of building a web app in this way? When you move on to something else and aren't there any more, you will probably have had to do some extensive documentation, and even then, it would require a reasonably low level programmer to maintain it, whereas with more 'classic' web languages it can be worked on by a web programmer (which are a lot easier to find).

Also, I wouldn't be surprisedi if ISAPI will offer the opportunity to take more control over the security features of the web server - are you knowledgeable enough about security issues when programming ISAPI so as not to leave yourself open?

.NET nowadays runs compiled web pages, anyway - using the new Common Language Runtime. This is faster than uncompiled scripting and you can easily add in dll components using the same languages you've used in your web page. I'd consider that myself, but as I said before, I've no experience with ISAPI - those are just my imediate thoughts.