Create a new shared package, Microsoft.AspNet.SpaServices, to hold MapSpaFallbackRoute (and other common infrastructure yet to be added)

Microsoft.AspNet.SpaServices/SpaRouteConstraint.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.AspNet.Http;
+using Microsoft.AspNet.Routing;
+
+namespace Microsoft.AspNet.SpaServices 
+{
+    internal class SpaRouteConstraint : IRouteConstraint
+    {
+        private readonly string clientRouteTokenName;
+    
+        public SpaRouteConstraint(string clientRouteTokenName) {
+            if (string.IsNullOrEmpty(clientRouteTokenName)) {
+                throw new ArgumentException("Value cannot be null or empty", "clientRouteTokenName");
+            }
+            
+            this.clientRouteTokenName = clientRouteTokenName;
+        }
+        
+        public bool Match(HttpContext httpContext, IRouter route, string routeKey, IDictionary<string, object> values, RouteDirection routeDirection)
+        {
+            var clientRouteValue = (values[this.clientRouteTokenName] as string) ?? string.Empty;
+            return !HasDotInLastSegment(clientRouteValue);
+        }
+    
+        private bool HasDotInLastSegment(string uri)
+        {
+            var lastSegmentStartPos = uri.LastIndexOf('/');
+            return uri.IndexOf('.', lastSegmentStartPos + 1) >= 0;
+        }
+    }
+}