URL Rewriting in ASP.NET – ISAPI Rewrite vs. UrlRewritingNet

Seeing your web site rank well in the major search engines (Google, Yahoo, MSN) is something that every web developer strives for. Making sure your web site’s pages are search engine friendly is a huge part of that effort. With ASP.NET, pages typically end in the .aspx extension. While this isn’t bad for SEO, most ASP.NET pages are also dynamic. So having a dynamic page that is rendered based on a bunch of query string variables doesn’t get you anywhere with SEO, especially if you use a lot of them. So for a while now, we’ve used ISAPI Rewrite to rewrite your dynamic pages into something that is a lot more user friendly. This ISAPI extension isn’t free though. It costs $99 to purchase a license. Not that bad, right?

Well recently, I discovered an Open Source solution called UrlRewritingNet. It was originally developed in 2006 for the 2.0 framework, however the developers claim it will work all the way up to the 3.5 framework. I’m not sure how much further development is being done though, as the last release was in August of 2006. It is Open Source, so theoretically you can download the source and make modifications yoruself if you need to.

UrlRewritingNet integrates directly into your ASP.NET web application as a HttpModule. With each incoming request, this module is called to see if the URL requested is a rewritten URL. This isn’t too different from ISAPI Rewrite except that the rewrite for ISAPI Rewrite is handled higher up the stack by IIS itself and not the web application. Using one solution over the other shouldn’t be much different from a performance standpoint, but tests would need run to prove it. That’s a task for another time however.

The one drawback, for me anyway, was that I did see that UrlRewritingNet requires all of the rewrites to be defined in the Web.config file. I’m not a huge fan of that. Web.config gets cluttered up enough as it is, so the more rewrites you need the bigger this file is going to get. With ISAPI Rewrite, all of the rewrites are stored in a separate file called httpd.ini, much like rewrites in Apache. On the plus side, it looks like you can extend UrlRewritingNet by developing your own rewrite rule providers. So if you need some functionality that isn’t provided, you can hook what you need up yourself.

UrlRewritingNet looks pretty promising and I hope I have some time to check it out and see if it is a good substitute for ISAPI Rewrite.

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