Subtleties with using Url.RouteUrl to get fully-qualified URLs

At some point I missed the Url.RouteUrl overload that took a protocol and returned an absolute URL based on the current context. It is quite handy when you are sending URLs out into the world (e.g., RSS feed link). I ended up using the less-handy overload that took an explicit host (same as the current, in this case) and passing it in. When someone pointed out the simpler overload, I did the obvious and deleted the host from the call. That didn’t quite work.

For those looking for a way to get a fully-qualified URL through the route system, the less-than-obvious answer is to call the overload for Url.RouteUrl that gets a URL with a different protocol (Url.RouteUrl(string, object, string)), passing in Request.Url.Scheme for the current protocol.

Url.RouteUrl("Default", new { action = "Index", controller = "Department", id = 1 }, Request.Url.Scheme);
// https://www.currentdomain.com/department/index/1

Say you want to send someone to a different subdomain in your app while using the same routes. There’s an overload for that: Url.RouteUrl(string, RouteValueDictionary, string, string). Combined with the above example, here’s how these all play out if you are currently handling a www.currentdomain.com request and your route table includes the fallback default ({controller}/{action}/{id}).

Url.RouteUrl("Default", new { action = "Index", controller = "Department", id = 1 });
// /department/index/1
Url.RouteUrl("Default", new { action = "Index", controller = "Department", id = 1 }, Request.Url.Scheme);
// https://www.currentdomain.com/department/index/1
Url.RouteUrl("Default", new RouteValueDictionary(new { action = "Index", controller = "Department", id = 1 }), "http", "sub.currentdomain.com");
// https://sub.currentdomain.com/department/index/1

Now if you switch between the two fully-qualified calls, you may try just deleting or adding the hostName parameter, respectively. One direction is a compile error, and one direction is a runtime oddity resulting in a hideous URL.

Url.RouteUrl("Default", new { action = "Index", controller = "Department", id = 1 }, "http", "sub.currentdomain.com");
// Compile error (expects a RouteValueDictionary)
Url.RouteUrl("Default", new RouteValueDictionary(new { action = "Index", controller = "Department", id = 1 }), "http", "sub.currentdomain.com");
// Eye-bleeding and incorrect route as it "serializes" the RouteValueDictionary.
// In my case, I ended up with something like this:
// https://www.currentdomain.com/current/route/1/?Count=3&Keys=System.Collections.Generic.Dictionary%602%2BKeyCollection%5BSystem.String%2CSystem.Object%5D&Values=System.Collections.Generic.Dictionary%602%2BValueCollection%5BSystem.String%2CSystem.Object%5D

On a side note, if your development environment uses localhost with a port and you use some web.config app setting for that URL change between development and production (“localhost:12345” vs “www.currentdomain.com”). You will want your host setting to be without the port. Url.RouteUrl will hiccup on your development environment if the port is part of the host name (it’s no longer just the host at that point).

Url.RouteUrl("Default", new RouteValueDictionary(new { action = "Index", controller = "Department", id = 1 }), "http", ConfigurationManager.AppSettings["hostwithport"]);
// https://localhost:12345:12345/department/index/1