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Using HttpModules with URL Re-writing to Handle Fake Directory Requests

, 30 Oct 2014 CPOL
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Explains how to use HttpModule in conjunction with IIS to handle requests to fake directories

Introduction

When using HttpModules to re-write URLs, accessing a directory will not work. For example, a request to http://somewebsite/fakedirectory/ will not work unless the fakedirectory actually exists with some default index file in it. This occurs because when a request comes into IIS it first ascertains that the directory and file actually exist before ever instantiating the HttpModule in your ASP.NET application.

httpmoduledirectoryhandle/pic1.png

Solution

Solving this is actually fairly easy. The first thing to do is to load IIS and change the 404 errors to a URL destination and point it to your site.

Screenshot - pic2.png

This will tell IIS to automatically redirect any unknown request (e.g. to a directory that does not exist) to your application. When you do this your application will receive a request like the following: http://somewebsite/default.aspx?404;http://somewebsite/fakedirectory/

Using the Code

Because this is in a standard form, the HttpModule can parse this easily, extract the real website that the user wanted and then perform the standard rewrite.

internal static String GetRequestedURL(String originalRequest)
{
    // Determine the page the user is requesting.
    String url = originalRequest;
 
    // Check for an error URL which IIS will throw when a non-existing 
    // directory is requested and custom errors are thrown back to this site
    if (url.Contains(";") && url.Contains("404"))
    {
        // Split the URL on the semi-colon. Error requests look like:
        // errorpage.aspx?404;http://originalrequest OR
        // errorpage.aspx?404;http://originalrequest:80
        String[] splitUrl = url.Split(';');
 
        // Set the URL to the original request to allow processing of it.
        if (splitUrl.Length >= 1)
        {
            url = splitUrl[1];
 
            // Remove the first http://
            url = url.Replace("http://", "");
 
            // Get only the application path and beyond of the string. This 
            // may be / if it's in the root folder.
            int index = url.IndexOf(
                System.Web.HttpContext.Current.Request.ApplicationPath);
            if (index >= 0)
            {
                url = url.Substring(index);
            }
        }
    }
 
    return url;
}

The GetRequestURL function will take a RawURL parameter and then check if it is a 404 error. If it is, it will parse out the original request and return it. If it is not a 404 error then it will return the untouched RawURL.

Concluding Remarks

While this is a fairly simple answer, I have been looking everywhere for a solution and nobody seems to have an easy answer. Even using the HttpHandler will not solve the problem because there's no extension on the requests for a directory. This is the best solution I have found and it works every time without having to do any extensive changes.

History

  • April 03, 2007 - Created
  • April 11, 2007 - Modified to take into account root applications

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Terrence Sheflin
Team Leader
Canada Canada
I am a Lead Software Architect (UI/UX), focusing mainly on developing with JavaScript, C#, ASP.NET WebApi and MVC.

Comments and Discussions

 
Questionhave you consider to post this as a tip? PinprotectorNelek8-Nov-14 14:25 
QuestionMy vote of 5! PinprofessionalVolynsky Alex4-Nov-14 9:43 

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