public RedirectHandler(Handler target, HttpStatusCode code)
        {
            Target = target;
            Code = code;

            if (!IsRedirectStatus (code))
                throw new InvalidOperationException ();
        }
 public Uri RegisterHandler(Handler handler)
 {
     var path = string.Format ("/{0}/{1}/", handler.GetType (), ++nextId);
     handlers.Add (path, handler);
     return new Uri (uri, path);
 }