How to redirect with HttpContext - asp.net

Question

My questions are:
So I need to create a custom class / HttpHandler and throw this code in it? Or can I place this somewhere else like in the global.asax?
How do I check for the Host (so check for www.mydomain.com) incoming so I know when to redirect?
Code:
if ("comes from certain domain")
{
context.Response.Status = "301 Moved Permanently";
context.Response.AddHeader("Location", "http://www.testdomain.com/Some.aspx");
}

Answer 1

Paste this into a new .cs file in your App_Code folder:
using System;
using System.Web;
public class TestModule : IHttpModule
{
public void Init(HttpApplication context) {
context.BeginRequest += new EventHandler(context_BeginRequest);
}
void context_BeginRequest(object sender, EventArgs e) {
HttpApplication app = (HttpApplication)sender;
if (app.Request.Url.Host == "example.com") {
app.Response.Status = "301 Moved Permanently";
app.Response.AddHeader("Location", "http://www.testdomain.com/Some.aspx");
}
}
public void Dispose() {
}
}
Then add this to your web.config in system.web:
<httpModules>
<add type="TestModule" name="TestModule" />
</httpModules>

Answer 2

You should be able to place it in the Global.asax, in the Application_BeginRequest event.
protected void Application_BeginRequest(Object sender, EventArgs e)
{
HttpContext context = HttpContext.Current;
string host = context.Request.Url.Host;
if (host == "www.mydomain.com")
{
context.Response.Status = "301 Moved Permanently";
context.Response.AddHeader("Location",
"http://www.testdomain.com/Some.aspx");
}
}

Answer 3

I avoid putting anything unnecessary in global.asax as it tends to get cluttered. Instead, create an HttpModule, add an event handler
public void Init(System.Web.HttpApplication app)
{
app.BeginRequest += new System.EventHandler(Rewrite_BeginRequest);
}
and, in the beginRequest method,
public void Rewrite_BeginRequest(object sender, System.EventArgs args)
{
HttpApplication app = (HttpApplication)sender;
/// all request properties now available through app.Context.Request object
}