Route gets mapped to parameters of different route

Question

When you execute Url.Action("Foo","Bar"), MVC will create a collection of route values from your inputs (In that case action=Foo, controller=Bar) and it will then look at your routes, trying to match one that matches based on its segments and default values.

Your XmlRpc route has no segments and no default values, and is the first one defined. This means it will always be the first match when generating urls using @Url.Action, @Html.ActionLink etc.

A quick way to prevent that route from being matched when generating urls would be adding a default controller parameter (using a controller name that you are sure you will never use). For example:

routes.Add("XmlRpc", new Route("XmlRpc", new RouteValueDictionary() { { "controller", "XmlRpc" } }, new MetaWeblogRouteHandler()));

Now when you execute Url.Action("Foo","Bar"), you will get the expected /Bar/Foo url, as "Bar" doesn´t match the default controller value in the route definition, "XmlRpc".

However that seems a bit hacky.

A better option would be creating your own RouteBase class. This willonly care for the url /XmlRpc, which will then be served using MetaWeblogRouteHandler and will be ignored when generating links using the Html and Url helpers:

public class XmlRpcRoute : RouteBase
{
    public override RouteData GetRouteData(HttpContextBase httpContext)
    {
        //The route will only be a match when requesting the url ~/XmlRpc, and in that case the MetaWeblogRouteHandler will handle the request
        if (httpContext.Request.AppRelativeCurrentExecutionFilePath.Equals("~/XmlRpc", StringComparison.CurrentCultureIgnoreCase))
            return new RouteData(this, new MetaWeblogRouteHandler());

        //If url is other than /XmlRpc, return null so MVC keeps looking at the other routes
        return null;
    }

    public override VirtualPathData GetVirtualPath(RequestContext requestContext, RouteValueDictionary values)
    {            
        //return null, so this route is skipped by MVC when generating outgoing Urls (as in @Url.Action and @Html.ActionLink)
        return null;
    }
}

public static void RegisterRoutes(RouteCollection routes)
{
    routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
    //Add the route using our custom XmlRpcRoute class
    routes.Add("XmlRpc", new XmlRpcRoute());

    ... your other routes ...
}

However, in the end you are creating a route just to run an IHttpHandler outside the MVC flow, for a single url. You are even struggling to keep that route from interferring with the rest of the MVC components, like when generating urls using helpers.

You could then just add directly a handler for that module in the web.config file, also adding an ignore rule for /XmlRpc in your MVC routes:

<configuration>
  ...
  <system.webServer>
    <handlers>
      <!-- Make sure to update the namespace "WebApplication1.Blog" to whatever your namespace is-->
      <add name="MetaWebLogHandler" verb="POST,GET" type="WebApplication1.Blog.MetaWeblogHandler" path="/XmlRpc" />
    </handlers>
  </system.webServer>
</configuration>

public static void RegisterRoutes(RouteCollection routes)
{
    routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
    //Make sure MVC ignores /XmlRpc, which will be directly handled by MetaWeblogHandler
    routes.IgnoreRoute("XmlRpc");

    ... your other routes ...         
}

Using either of these 3 approaches, this is what I get:

/Home/Index renders the Index view of the HomeController
/ renders the Index view of the BlogController
@Url.Action("Foo","Bar") generates the url /Bar/Foo
@Html.ActionLink("MyLink","Foo","Bar") renders the following html: <a href="/Bar/Foo">MyLink</a>
/XmlRcp renders the a view describing the MetaWeblogHandler and its available methods, where there is a single method available (blog.index, taking no parameters and returning a string)

In order for testing this, I have created a new empty MVC 5 application, adding the NuGet package xmlrpcnet-server.

I have created a HomeController and a BlogController, both with an index action, and I have created the following MetaWeblog classes:

public interface IMetaWeblog
{
    [XmlRpcMethod("blog.index")]
    string Index();        
}

public class MetaWeblogHandler : XmlRpcService, IMetaWeblog
{
    string IMetaWeblog.Index()
    {
        return "Hello World";
    }        
}

public class MetaWeblogRouteHandler : IRouteHandler
{
    public IHttpHandler GetHttpHandler(RequestContext requestContext)
    {
        return new MetaWeblogHandler();
    }
}