source code bean

I was having a chat the other day with Danish Peter (yes, another one) about URL rewrites in ASP.NET. In a previous post I wrote about how to use friendly URLs in the Zend framework, in this post, which is based on our discussion, I will discuss how to do this in ASP.NET.

Friendly URLs are achieved by a technique called URL-rewrite. A friendly URL is a URL that is easy to read and understand. Let me give you an example (from a site my girlfriend loves) of what is NOT a friendly URL:

http://www.bebe.com/bebe-Jersey-Knit-Apron-Dress/dp/B001UX1NBQ?ie=UTF8&asinSearchPageIndex=13&pf_rd_r=1C6TS27BZZ1CAD6WY81S&navAsinList=B001UNM3XS%2CB001OPYKKQ%2CB001UNNQ52%2CB001RPD88I%
2CB001R4NHHQ%2CB0026BM39W%2CB001QOU6TY%2CB001UX1NNY%2CB001UAA4WI
%2CB0024QP6KM%2CB0026RRN4G%2CB0027DCI6W%2CB001UX3QL6%2CB001UX1NBQ
%2CB001VROPT8%2CB00265NBKS%2CB001RPM80C%2CB001UBWNTO%2CB001RPIC1G
%2CB001PA2NMW&node=675941011&pf_rd_s=search-results&field_browse=675941011&searchSize=20&navAsinListIndex=0&pf_rd_t=101&field_availability=0&id=bebe%20Jersey%20Knit%20Apron%20Dress&searchBinNameList=null&store=core&pf_rd_p=476815091&ref=search_results_14&searchNodeID=675941011&pf_rd_i=675941011&field_launch-date=-1y&searchRank=-custom-rank&searchPage=1&pf_rd_m=A2FMOXN01TSNYY

This might be an extreme example, but there are plenty of sites which are as bad. If the above URL was transformed into a friendly URL it might look something like:

http://www.bebe.com/Apparel/Dresses/Jersey-Knit-Apron-Dress.html

The second address is easier to read. URL rewrite techniques have been around for a long time and the first time I used it was back in the early Apache 1.3 days. Today good sites use friendly URLs and if you have not adopted it yet, you need to start using it.

There are several benefits from using a friendly url scheme, the most prominent are:

1. 1. The clear structure makes it easier for humans to read and understand the addres
2. 2. It is easier for search engines to understand what the address is and crawler the site. URL structure that goes more than three directories deep is not always read by a spider.
3. 3. If search engines understand the URL, it is also easier for them to help people finding what they want, giving better search results. Hence using keywords and proper titles makes life easier.

What options are there for ASP.NET?
There is no built in support for having friendly URLs in ASP.NET, but you could spend your time writing your own URL-rewrite module. Writing your own module is basically spending time reinventing the wheel. If you have the time, go ahead, but if not there are already several good ones out there (free and open source). One that I have found very useful is the URLRewriter.NET (http://urlrewriter.net/). URLRewriter.NET provides similar rewrite capabilities as the mod_rewrite does for Apache.

Using URLRewriter.NET
It is possible to use the URLRewriter.NET module without making any changes to the IIS configuration, this will however limit the functionallity the URLRewriter.NET rewriting capabilities. To use its full power, IIS should be configured to map all requests to the ASP.NET runtime (how to do this is covered in the manual). We will only be touching the surface of URLRewriter.NET so we will not have to do any modifications to the IIS configuration.

To add URLRewriter.NET to your project start out by opening Visual Studio or Visual Web Developer. Open your project and then right click the project in the solution explorer and click on Add Reference, go browse and find the folder you downloaded and unzipped. You will find the binary (.dll) file in “Loation”\urlrewriternet20rc1b6\UrlRewriterV2\bin\Release.

Before we can use the module we need to make some changes to the web.config. Add the following in the configSections:

This will allow the URL writer to read the rewrite rules we will define later. Now we need to add this module to the httpModules section:

By adding the rewriter as a httpModule we allow it to intercept web requests and route the requests to the actual aspx file serving the page. Now we need to define the rewrite rules:

The rewrite rules are defined using regular expressions. Regular expressions are very powerful and is something every programmer should know. The syntax might be hard to remember but there are several great tools to help build advanced regular expressions, for example the RegexDesigner.NET (http://www.sellsbrothers.com/tools/#regexd) that Chris Sells has created.

The above rewrite rules are simple. The first rewrite rule will rewrite URLs like

sourcecodebean.com/2009/04/01/1.shtml

to

sourcecodebean.com/Default.aspx?Year=2009&Month=04&Date=01&Id=1

And the second rewrite rule will match requests starting with ~/Article/ so it will rewrite URLs like

sourcecodebean.com/Article/1.shtml

to

sourcecodebean.com/Articles.aspx?ID=1

Finishing up
By now you hopefully have a functioning site that uses friendly URLs. One of the common problems you might run into is broken links. To avoid this you should make sure that you reference all your pages from the root level (~) and that all your links has the runat=server tag.

Thanks for your input Peter! You can check out his Danish Peter blog over at Magic Mouse.