Best way to implement a 404 in ASP.NET

Question

I'm trying to determine the best way to implement a 404 page in a standard ASP.NET web application. I currently catch 404 errors in the Application_Error event in the Global.asax file and redirect to a friendly 404.aspx page. The problem is that the request sees a 302 redirect followed by a 404 page missing. Is there a way to bypass the redirect and respond with an immediate 404 containing the friendly error message?

Does a web crawler such as Googlebot care if the request for a non existing page returns a 302 followed by a 404?

Answer 1

Handle this in your Global.asax's OnError event:

protected void Application_Error(object sender, EventArgs e){
  // An error has occured on a .Net page.
  var serverError = Server.GetLastError() as HttpException;

  if (serverError != null){
    if (serverError.GetHttpCode() == 404){
      Server.ClearError();
      Server.Transfer("/Errors/404.aspx");
    }
  }
}

In you error page, you should ensure that you're setting the status code correctly:

// If you're running under IIS 7 in Integrated mode set use this line to override
// IIS errors:
Response.TrySkipIisCustomErrors = true;

// Set status code and message; you could also use the HttpStatusCode enum:
// System.Net.HttpStatusCode.NotFound
Response.StatusCode = 404;
Response.StatusDescription = "Page not found";

You can also handle the various other error codes in here quite nicely.

Google will generally follow the 302, and then honour the 404 status code - so you need to make sure that you return that on your error page.