Fixes: U4-5151 Backoffice controllers collide on name even if different namespace

src/Umbraco.Web/WebApi/NamespaceHttpControllerSelector.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Collections;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Web.Http;
+using System.Web.Http.Controllers;
+using System.Web.Http.Dispatcher;
+
+namespace Umbraco.Web.WebApi
+{
+    public class NamespaceHttpControllerSelector : DefaultHttpControllerSelector
+    {
+        private const string ControllerKey = "controller";
+        private readonly HttpConfiguration _configuration;
+        private readonly Lazy<IEnumerable<Type>> _duplicateControllerTypes;
+
+        public NamespaceHttpControllerSelector(HttpConfiguration configuration) : base(configuration)
+        {
+            _configuration = configuration;
+            _duplicateControllerTypes = new Lazy<IEnumerable<Type>>(GetDuplicateControllerTypes);
+        }
+
+        public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
+        {
+            var routeData = request.GetRouteData();
+            if (routeData == null || routeData.Route == null || routeData.Route.DataTokens["Namespaces"] == null) 
+                return base.SelectController(request);
+            
+            // Look up controller in route data
+            object controllerName;
+            routeData.Values.TryGetValue(ControllerKey, out controllerName);
+            var controllerNameAsString = controllerName as string;
+            if (controllerNameAsString == null) 
+                return base.SelectController(request);
+            
+            //get the currently cached default controllers - this will not contain duplicate controllers found so if
+            // this controller is found in the underlying cache we don't need to do anything
+            var map = base.GetControllerMapping();
+            if (map.ContainsKey(controllerNameAsString)) 
+                return base.SelectController(request);
+            
+            //the cache does not contain this controller because it's most likely a duplicate, 
+            // so we need to sort this out ourselves and we can only do that if the namespace token
+            // is formatted correctly.
+            var namespaces = routeData.Route.DataTokens["Namespaces"] as IEnumerable<string>;
+            if (namespaces == null)
+                return base.SelectController(request);
+
+            //see if this is in our cache
+            var found = _duplicateControllerTypes.Value
+                .Where(x => string.Equals(x.Name, controllerNameAsString + ControllerSuffix, StringComparison.OrdinalIgnoreCase))
+                .FirstOrDefault(x => namespaces.Contains(x.Namespace));
+
+            if (found == null)
+                return base.SelectController(request);
+
+            return new HttpControllerDescriptor(_configuration, controllerNameAsString, found);
+        }
+
+        private IEnumerable<Type> GetDuplicateControllerTypes()
+        {
+            var assembliesResolver = _configuration.Services.GetAssembliesResolver();
+            var controllersResolver = _configuration.Services.GetHttpControllerTypeResolver();
+            var controllerTypes = controllersResolver.GetControllerTypes(assembliesResolver);
+
+            //we have all controller types, so just store the ones with duplicate class names - we don't
+            // want to cache too much and the underlying selector caches everything else
+
+            var duplicates = controllerTypes.GroupBy(x => x.Name)
+                .Where(x => x.Count() > 1)
+                .SelectMany(x => x);
+
+            return duplicates;
+        }
+        
+    }
+}