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Domain Forwarding with IHttpHandler

, 9 Sep 2003
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Use HttpHandlers to forward the user to different webpages depending on the requested hostname (domainname).

Introduction

In this article I describe how to use a custom HttpHandler as a domain-forwarder.

Background

With the Hostheader feature in IIS you can map many hostnames to one IP-Address. For example your IIS Server has the IP-Address 195.243.118.165. You or your ISP has some A-Records for this IP-Address.

www.mydomain.com A 195.243.118.165
www.virtualdomain1.com A 195.243.118.165
www.virtualdomain2.com A 195.243.118.165

Now, you have configured a website in IIS which responds to all these domains. The following image show a sample IIS configuration.

All requests to www.mydomain.com, www.virtualdomain1.com and www.virtualdomain2.com target the same website. Often you have to do such configurations because the amount of public IP-addresses is limited.

At this point you want to provide the user a different webpage depending on the used domain name. This sample application will provide a simple solution for this problem.

Using the code

Create a class in your ASP.NET application which implements the IHttpHandler. You have to implement one method and one property:

  • public void ProcessRequest (HttpContext)
  • public void IsReusable

Here is the sample code:

public class DomainHandler : IHttpHandler
{
    /// Implementing IHttpHandler
    public void ProcessRequest(HttpContext context) 
    {
        // Extract the host name from the request url
        // an look up the redirect url in the Web.config
        String redir = ConfigurationSettings.AppSettings
                              [context.Request.Url.Host];
        if (redir != null)
        {
            // check for valid redirect url, preventing loops
            if (RedirectIsValid(redir, context.Request.Url))
            {
                // redirect the user to the url found in web.config
                context.Response.Redirect(redir, true);
            }
            else
            {
                // display an error.
                context.Response.Write("<h1><font 
                   color=red>Error invalid DomainHandler 
                   configuration</font></h1><br>
                   <b>Please check your Web.config 
                   file.</b>");
            }
        }
    }

    // prevents possible redirect loops
    // it is not allowed to have an redirect url targeting its self
    private bool RedirectIsValid(String redir, Uri currentUri)
    {
        String val1 = redir.ToLower();
        String url = currentUri.AbsoluteUri.ToLower();
        String host = currentUri.Host.ToLower();

        if (val1 == url) { return false; } 
        if (val1 == ( "http://" + host)) { return false; }
        if (val1 == ("http://" + host + "/")) { return false; }
        if (val1 == host) { return false; }
        if (val1 == (host + "/")) { return false; }

        return true;
    }

    /// Implementing IHttpHandler
    public bool IsReusable
    {
        get
        {
            return true;
        }
    }
}
//

Points of interest

I decided to store my URL mappings in the web.config file as key-value pairs in the appSettings Section. Additionally you must register the new HttpHandler in your web.config file.

Sample web.config file is provided here:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
<!--<span class="code-comment">
Use as keys your full qualified host names.
As Value you provide a absolute url, you want to redirect to.
--></span> 
<add key="localhost" value="http://localhost/DomainForward/target1.htm" />
<add key="www.virualdomain1.com" value="http://www.myDomain.com/domain1" />
<add key="www.virualdomain2.com" value="http://www.myDomain.com/domain2" />
</appSettings>

<system.web>

<compilation 
defaultLanguage="c#"
debug="true"
/>

<httpHandlers>
<add verb="*" path="Default.aspx" 
    type="DomainFilter.DomainHandler, DomainFilter" />
</httpHandlers> 

</system.web>

</configuration>

In the path attribute in the httpHandlers section you specify a really existing filename which matches your "IIS-Defaultpage-Configuration".

In my sample application for simplicity I used a subweb, the default in Visual Studio. In a real world example, you would install the application in the root-web.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Andi Fleischmann
Web Developer
Germany Germany
No Biography provided

Comments and Discussions

 
QuestionBind Domain to Application Pages PingroupMorteza M17-Nov-12 4:05 
QuestionBlank page Pinmemberthanks_in_advance12-Sep-12 23:57 
GeneralForwarding IP PinmemberOm Rudi29-Mar-09 6:38 
GeneralSmall improvement to RedirectIsValid PinmemberSameer Alibhai31-Jul-07 10:19 
GeneralDifference on IIS6 [modified] Pinmemberspdl200027-Oct-06 13:27 
I am trying to catch all requests on the first level of a web site, like:
 
domain.com/my.name
 
And then I can forward the user depending on his name.
It works great (with a couple of adjustments in VWD Express, once everything is running under a virtual directory:
 

 
localhost:3081/domainForward/my.name
 
****
 
But as soon I copy the code to an IIS6 server and it is running under the root, IIS is only doing what I want if the filename ends with "*.aspx"
All other pages will receive a 404 Error.
 
Does anybody know a setting in IIS 6 to catch all possible names...?
 
Thanks
 

P.S. I have a solution now, whereby I redirect 404 pages to default.aspx but these are lots of redirects....
 

 
-- modified at 19:55 Friday 27th October, 2006
GeneralMultiple URL Same Website Pinmembermukeshdas4-Oct-04 0:06 
GeneralRe: Multiple URL Same Website PinmemberAndi Fleischmann4-Oct-04 0:39 
GeneralRe: Multiple URL Same Website Pinmembermukeshdas5-Oct-04 20:00 
GeneralRe: Multiple URL Same Website PinmemberAndi Fleischmann5-Oct-04 22:46 
GeneralVB.NET Pinsussjtisdale25-Sep-04 12:10 
GeneralRe: VB.NET PinmemberDicke Berta30-Sep-04 4:34 
GeneralRe: VB.NET Pinmemberjtisdale30-Sep-04 10:21 
GeneralMapping .html/.htm to .aspx PinmemberNeal Stublen11-Sep-03 20:55 
GeneralRe: Mapping .html/.htm to .aspx PinmemberNeal Stublen11-Sep-03 21:28 
Questionwhats the point? PinmemberPhilip Fitzsimons11-Sep-03 2:52 
AnswerRe: whats the point? PinmemberAndi Fleischmann11-Sep-03 5:59 
Questionhow about server.execute ? PinmemberBecio17-Mar-03 23:00 
AnswerRe: how about server.execute ? PinmemberBlake Coverett10-Sep-03 12:13 
GeneralApp inside App PinmemberJ.M.Piulachs13-Mar-03 23:19 
GeneralRe: App inside App PinmemberDa Bert14-Mar-03 18:01 
GeneralWhat if no file name? (was &quot;App inside App&quot;) PinmemberRhy Mednick19-Sep-03 6:53 

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