Remove unnecessary state machines in DefautHubDispatcher (#2167)

* Remove unnecessary state machines in DefautHubDispatcher
- Remove state machines for async tail calls
- Added fast path for auth check when there are no policies

src/Microsoft.AspNetCore.SignalR.Core/Internal/DefaultHubDispatcher.cs

@@ -73,7 +73,7 @@ namespace Microsoft.AspNetCore.SignalR.Internal
             }
         }
 
-        public override async Task DispatchMessageAsync(HubConnectionContext connection, HubMessage hubMessage)
+        public override Task DispatchMessageAsync(HubConnectionContext connection, HubMessage hubMessage)
         {
             // Messages are dispatched sequentially and will stop other messages from being processed until they complete.
             // Streaming methods will run sequentially until they start streaming, then they will fire-and-forget allowing other messages to run.
@@ -81,18 +81,15 @@ namespace Microsoft.AspNetCore.SignalR.Internal
             switch (hubMessage)
             {
                 case InvocationBindingFailureMessage bindingFailureMessage:
-                    await ProcessBindingFailure(connection, bindingFailureMessage);
-                    break;
+                    return ProcessBindingFailure(connection, bindingFailureMessage);
 
                 case InvocationMessage invocationMessage:
                     Log.ReceivedHubInvocation(_logger, invocationMessage);
-                    await ProcessInvocation(connection, invocationMessage, isStreamedInvocation: false);
-                    break;
+                    return ProcessInvocation(connection, invocationMessage, isStreamedInvocation: false);
 
                 case StreamInvocationMessage streamInvocationMessage:
                     Log.ReceivedStreamHubInvocation(_logger, streamInvocationMessage);
-                    await ProcessInvocation(connection, streamInvocationMessage, isStreamedInvocation: true);
-                    break;
+                    return ProcessInvocation(connection, streamInvocationMessage, isStreamedInvocation: true);
 
                 case CancelInvocationMessage cancelInvocationMessage:
                     // Check if there is an associated active stream and cancel it if it exists.
@@ -118,6 +115,8 @@ namespace Microsoft.AspNetCore.SignalR.Internal
                     Log.UnsupportedMessageReceived(_logger, hubMessage.GetType().FullName);
                     throw new NotSupportedException($"Received unsupported message: {hubMessage}");
             }
+
+            return Task.CompletedTask;
         }
 
         private Task ProcessBindingFailure(HubConnectionContext connection, InvocationBindingFailureMessage bindingFailureMessage)
@@ -142,19 +141,19 @@ namespace Microsoft.AspNetCore.SignalR.Internal
             return descriptor.ParameterTypes;
         }
 
-        private async Task ProcessInvocation(HubConnectionContext connection,
+        private Task ProcessInvocation(HubConnectionContext connection,
             HubMethodInvocationMessage hubMethodInvocationMessage, bool isStreamedInvocation)
         {
             if (!_methods.TryGetValue(hubMethodInvocationMessage.Target, out var descriptor))
             {
                 // Send an error to the client. Then let the normal completion process occur
                 Log.UnknownHubMethod(_logger, hubMethodInvocationMessage.Target);
-                await connection.WriteAsync(CompletionMessage.WithError(
-                    hubMethodInvocationMessage.InvocationId, $"Unknown hub method '{hubMethodInvocationMessage.Target}'"));
+                return connection.WriteAsync(CompletionMessage.WithError(
+                    hubMethodInvocationMessage.InvocationId, $"Unknown hub method '{hubMethodInvocationMessage.Target}'")).AsTask();
             }
             else
             {
-                await Invoke(descriptor, connection, hubMethodInvocationMessage, isStreamedInvocation);
+                return Invoke(descriptor, connection, hubMethodInvocationMessage, isStreamedInvocation);
             }
         }
 
@@ -323,14 +322,19 @@ namespace Microsoft.AspNetCore.SignalR.Internal
             hub.Groups = _hubContext.Groups;
         }
 
-        private async Task<bool> IsHubMethodAuthorized(IServiceProvider provider, ClaimsPrincipal principal, IList<IAuthorizeData> policies)
+        private Task<bool> IsHubMethodAuthorized(IServiceProvider provider, ClaimsPrincipal principal, IList<IAuthorizeData> policies)
         {
             // If there are no policies we don't need to run auth
             if (!policies.Any())
             {
-                return true;
+                return TaskCache.True;
             }
 
+            return IsHubMethodAuthorizedSlow(provider, principal, policies);
+        }
+
+        private static async Task<bool> IsHubMethodAuthorizedSlow(IServiceProvider provider, ClaimsPrincipal principal, IList<IAuthorizeData> policies)
+        {
             var authService = provider.GetRequiredService<IAuthorizationService>();
             var policyProvider = provider.GetRequiredService<IAuthorizationPolicyProvider>();
 

src/Microsoft.AspNetCore.SignalR.Core/Internal/TaskCache.cs

@@ -0,0 +1,13 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.SignalR.Internal
+{
+    internal static class TaskCache
+    {
+        public static readonly Task<bool> True = Task.FromResult(true);
+        public static readonly Task<bool> False = Task.FromResult(false);
+    }
+}