How to simulate Server.Transfer in ASP.NET MVC?

In ASP.NET MVC you can return a redirect ActionResult quite easily:

 return RedirectToAction("Index");

 or

 return RedirectToRoute(new { controller = "home", version = Math.Random() * 10 });

This will actually give an HTTP redirect, which is normally fine. However, when using Google Analytics this causes big issues because the original referrer is lost, so Google doesn't know where you came from. This loses useful information such as any search engine terms.

As a side note, this method has the advantage of removing any parameters that may have come from campaigns but still allows me to capture them server side. Leaving them in the query string leads to people bookmarking or twitter or blog a link that they shouldn't. I've seen this several times where people have twittered links to our site containing campaign IDs.

Anyway, I am writing a 'gateway' controller for all incoming visits to the site which I may redirect to different places or alternative versions.

For now I care more about Google for now (than accidental bookmarking), and I want to be able to send someone who visits / to the page that they would get if they went to /home/7, which is version 7 of a homepage.

Like I said before if I do this I lose the ability for google to analyse the referrer:

 return RedirectToAction(new { controller = "home", version = 7 });

What I really want is a

 return ServerTransferAction(new { controller = "home", version = 7 });

which will get me that view without a client side redirect. I don't think such a thing exists, though.

Currently the best thing I can come up with is to duplicate the whole controller logic for HomeController.Index(..) in my GatewayController.Index Action. This means I had to move 'Views/Home' into 'Shared' so it was accessible. There must be a better way.

How about a TransferResult class? (based on Stans answer)

/// <summary>
/// Transfers execution to the supplied url.
/// </summary>
public class TransferResult : ActionResult
{
    public string Url { get; private set; }

    public TransferResult(string url)
    {
        this.Url = url;
    }

    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
            throw new ArgumentNullException("context");

        var httpContext = HttpContext.Current;

        // MVC 3 running on IIS 7+
        if (HttpRuntime.UsingIntegratedPipeline)
        {
            httpContext.Server.TransferRequest(this.Url, true);
        }
        else
        {
            // Pre MVC 3
            httpContext.RewritePath(this.Url, false);

            IHttpHandler httpHandler = new MvcHttpHandler();
            httpHandler.ProcessRequest(httpContext);
        }
    }
}

Updated: Now works with MVC3 (using code from Simon's post). It should (haven't been able to test it) also work in MVC2 by looking at whether or not it's running within the integrated pipeline of IIS7+.

For full transparency; In our production environment we've never use the TransferResult directly. We use a TransferToRouteResult which in turn calls executes the TransferResult. Here's what's actually running on my production servers.

public class TransferToRouteResult : ActionResult
{
    public string RouteName { get;set; }
    public RouteValueDictionary RouteValues { get; set; }

    public TransferToRouteResult(RouteValueDictionary routeValues)
        : this(null, routeValues)
    {
    }

    public TransferToRouteResult(string routeName, RouteValueDictionary routeValues)
    {
        this.RouteName = routeName ?? string.Empty;
        this.RouteValues = routeValues ?? new RouteValueDictionary();
    }

    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
            throw new ArgumentNullException("context");

        var urlHelper = new UrlHelper(context.RequestContext);
        var url = urlHelper.RouteUrl(this.RouteName, this.RouteValues);

        var actualResult = new TransferResult(url);
        actualResult.ExecuteResult(context);
    }
}

And if you're using T4MVC (if not... do!) this extension might come in handy.

public static class ControllerExtensions
{
    public static TransferToRouteResult TransferToAction(this Controller controller, ActionResult result)
    {
        return new TransferToRouteResult(result.GetRouteValueDictionary());
    }
}

Using this little gem you can do

// in an action method
TransferToAction(MVC.Error.Index());