Simple custom URL rewriting in ASP.NET 1.1

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This post describes how you can create a simple url rewriting engine in ASP.NET in order to create custom urls for your webpage..
I’ve used the great tutorial on 15 seconds, Rewrite.NET - a URL Rewriting engine for .NET written by Robert Chartier and modified some minor parts.
Instead of fetching the urls from inside the web.config file, I’ve used a simple xml document to store my customs paths.
I have also found a method for preventing the postback issue and will describe on how to change the file extensions in your urls.

We will start off by creating a xml file and calling it MyUrls.xml. I chosed to move the content from the web.config file because I whish to be able to easily change the urls from a web interface that's not causing the project to reboot which will happen when you re-save the web.config file.

<?xml version="1.0" encoding="utf-8" ?>
<urls>
<url custom="/project/Start.aspx" real="/Project/index.aspx?id=123" />
<url custom="/Project/Custom.aspx" real="/Project/index.aspx?id=456" />
</urls>

We now create a new class called RewriteClass.cs and add it somewhere in our project.

using System;
using System.Xml;

namespace UrlRewriting
{

public class RewriteClass : System.Web.IHttpModule
{
public RewriteClass()
{
}

public void Init(System.Web.HttpApplication Appl)
{
Appl.BeginRequest +=new EventHandler(Appl_BeginRequest);
}

private void Appl_BeginRequest(object sender, EventArgs e)
{
//cast the sender to an HttpApplication object
System.Web.HttpApplication

Appl=(System.Web.HttpApplication)sender;

XmlDocument xDoc = new XmlDocument();
xDoc.Load(System.Web.HttpContext.Current.Server.MapPath("MyUrls.xml"));

XmlNodeList xnl = xDoc.SelectNodes("//urls/url");
for(int i=0; i<xnl.Count;i++)
{
//see if we have a match
string custom = xnl.Item(i).Attributes[0].Value;
string real = xnl.Item(i).Attributes[1].Value;
if(Appl.Request.Path.ToLower() == custom.ToLower())
{
SendToNewUrl(real,Appl);
break;
}
}
}
public void SendToNewUrl(string url, System.Web.HttpApplication Appl)
{
Appl.Context.RewritePath(url);
}
public void Dispose()
{
}
}
}

Now we’re almost finished. We have to add this code inside the web.config <system.web> [code goes here] </sytem.web>.

<httpModules>
<add name="RewriteClass" type="Project.RewriteClass, Project" />
</httpModules>

All done! Now for the postback issue. Go to /Project/Start.aspx and look at the form-tag in the page source code. Here’s what you will see:

<form name="Form1" method="post" action="index.aspx?id=123" id="Form1">

If we do a postback to this page, the real url will show. We can easily prevent this with a JavaScript code that we will register inside index.aspx.cs. Add this code of line inside Page_Load:

RegisterStartupScript("PostBackFix","<script type=\"text/javascript\">document.forms[0].action='';</script>");

This will prevent the real url from showing when postbacking unless user doesn’t have JavaScript enabled. The small amount of people how doesn’t have JavaScript enabled wont be harmed according to me.

Custom file extensions
If you wants to use another file extension instead of .aspx, let’s say .html, all you have to do is to map the .html extension to the aspnet_isapi.dll file.
Open up the properties for your webpage inside IIS and click on Configuration. If you can’t find .html in the Mappings list, click Add. Now browse your way to the aspnet_isapi.dll file stored here C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322[or your version]\apnet_isapi.dll.
Click Ok and move over to the Extension field and add .html. Check Limit to: and add GET,POST,HEAD. Now uncheck Check that file exists and click Ok. Finished!
You can now go back to MyUrls.xml file and modify Start.aspx to Start.html.

This of course can be a problem if your application is stored at a web hotel. But if you ask nicely, maybe they’ll help you out. My hotel did :)

References:

• http://www.15seconds.com/issue/030522.htm
• http://www.developerfusion.co.uk/show/4643/3/