Routing to controller with a required, non-empty Guid parameter

Question

I would like to map http://localhost/Guid-goes-here to ResellerController and fire Index action of that controller only when Guid-goes-here is not the empty Guid.

My routing table looks like this:

public static void RegisterRoutes(RouteCollection routes)
{
    routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

    routes.MapRoute(
        "Reseller",
        "{id}",
        new { controller = "Reseller", action = "Index", id = Guid.Empty }  
        // We can mark parameters as UrlParameter.Optional, but how to make it required?
    );

    routes.MapRoute(
        "Default", // Route name
        "{controller}/{action}/{id}", // URL with parameters
        new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
    );

}

The action on the ResellerController looks like this:

public ActionResult Index(Guid id)
{
    // do some stuff with non-empty guid here
}

Once the application has started, navigating to http://localhost routes me to the ResellerController with the empty Guid as the argument to the Index action's id parameter.

Answer 1

public static void RegisterRoutes(RouteCollection routes)
{
    routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

    routes.MapRoute(
        "Reseller",
        "{id}",
        new { controller = "Reseller", action = "Index", id = UrlParameter.Optional },
        new { id = @"^(\{{0,1}([0-9a-fA-F]){8}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){12}\}{0,1})$" }
    );

    routes.MapRoute(
        "Default", // Route name
        "{controller}/{action}/{id}", // URL with parameters
        new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
    );
}

or if you want a more robust constraint than some cryptic regex:

public class GuidConstraint : IRouteConstraint
{
    public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
    {
        var value = values[parameterName] as string;
        Guid guid;
        if (!string.IsNullOrEmpty(value) && Guid.TryParse(value, out guid))
        {
            return true;
        }
        return false;
    }
}

and then:

routes.MapRoute(
    "Reseller",
    "{id}",
    new { controller = "Reseller", action = "Index", id = UrlParameter.Optional },
    new { id = new GuidConstraint() }
);