Expose DefaultConnectionContext POCO (#2421)

- Made TransportConnecton derive from ConnectionContext
- Less objects, less opinions about what the ConnectionContext is. This diverges from what we do with HttpContext but it seems better overall.
- Made DefaultConnectionContext
 - Usable for unit testing
 - Usable for benchmarking

src/Connections.Abstractions/ConnectionItems.cs

@@ -3,11 +3,12 @@
 
 using System;
 using System.Collections;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 
-namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal
+namespace Microsoft.AspNetCore.Connections
 {
-    internal class ConnectionItems : IDictionary<object, object>
+    public class ConnectionItems : IDictionary<object, object>
     {
         public ConnectionItems()
             : this(new Dictionary<object, object>())
@@ -115,4 +116,4 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal
             return Items.GetEnumerator();
         }
     }
-}
+}

src/Connections.Abstractions/DefaultConnectionContext.cs

@@ -1,55 +1,64 @@
-using System.Collections.Generic;
+// 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;
+using System.Collections.Generic;
 using System.IO.Pipelines;
+using System.Security.Claims;
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http.Features;
+using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Connections.Features;
 
 namespace Microsoft.AspNetCore.Connections
 {
-    public class DefaultConnectionContext : ConnectionContext
+    public class DefaultConnectionContext : ConnectionContext,
+                                            IConnectionIdFeature,
+                                            IConnectionItemsFeature,
+                                            IConnectionTransportFeature,
+                                            IApplicationTransportFeature,
+                                            IConnectionUserFeature
     {
-        private FeatureReferences<FeatureInterfaces> _features;
+        public DefaultConnectionContext() :
-
+            this(Guid.NewGuid().ToString())
-        public DefaultConnectionContext(IFeatureCollection features)
         {
-            _features = new FeatureReferences<FeatureInterfaces>(features);
         }
 
-        private IConnectionIdFeature ConnectionIdFeature =>
+        /// <summary>
-            _features.Fetch(ref _features.Cache.ConnectionId, _ => null);
+        /// Creates the DefaultConnectionContext without Pipes to avoid upfront allocations.
-
+        /// The caller is expected to set the <see cref="Transport"/> and <see cref="Application"/> pipes manually.
-        private IConnectionTransportFeature ConnectionTransportFeature =>
+        /// </summary>
-            _features.Fetch(ref _features.Cache.ConnectionTransport, _ => null);
+        /// <param name="id"></param>
-
+        public DefaultConnectionContext(string id)
-        private IConnectionItemsFeature ConnectionItemsFeature =>
-            _features.Fetch(ref _features.Cache.ConnectionItems, _ => null);
-
-        public override string ConnectionId
         {
-            get => ConnectionIdFeature.ConnectionId;
+            ConnectionId = id;
-            set => ConnectionIdFeature.ConnectionId = value;
+
+            Features = new FeatureCollection();
+            Features.Set<IConnectionUserFeature>(this);
+            Features.Set<IConnectionItemsFeature>(this);
+            Features.Set<IConnectionIdFeature>(this);
+            Features.Set<IConnectionTransportFeature>(this);
+            Features.Set<IApplicationTransportFeature>(this);
         }
 
-        public override IFeatureCollection Features => _features.Collection;
+        public DefaultConnectionContext(string id, IDuplexPipe transport, IDuplexPipe application)
-
+            : this(id)
-        public override IDuplexPipe Transport
         {
-            get => ConnectionTransportFeature.Transport;
+            Transport = transport;
-            set => ConnectionTransportFeature.Transport = value;
+            Application = application;
         }
 
-        public override IDictionary<object, object> Items
+        public override string ConnectionId { get; set; }
-        {
-            get => ConnectionItemsFeature.Items;
-            set => ConnectionItemsFeature.Items = value;
-        }
 
-        struct FeatureInterfaces
+        public override IFeatureCollection Features { get; }
-        {
-            public IConnectionIdFeature ConnectionId;
 
-            public IConnectionTransportFeature ConnectionTransport;
+        public ClaimsPrincipal User { get; set; }
 
-            public IConnectionItemsFeature ConnectionItems;
+        public override IDictionary<object, object> Items { get; set; } = new ConnectionItems();
-        }
+
+        public IDuplexPipe Application { get; set; }
+
+        public override IDuplexPipe Transport { get; set; }
     }
 }

src/Kestrel.Core/Internal/ConnectionListener.cs

@@ -46,7 +46,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
 
             // REVIEW: This task should be tracked by the server for graceful shutdown
             // Today it's handled specifically for http but not for aribitrary middleware
-            _ = Execute(new DefaultConnectionContext(connection));
+            _ = Execute(connection);
         }
 
         private async Task Execute(ConnectionContext connectionContext)

src/Kestrel.Transport.Abstractions/Internal/TransportConnection.cs

@@ -3,10 +3,12 @@ using System.Collections.Generic;
 using System.IO.Pipelines;
 using System.Net;
 using System.Threading;
+using Microsoft.AspNetCore.Connections;
+using Microsoft.AspNetCore.Http.Features;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal
 {
-    public abstract partial class TransportConnection
+    public abstract partial class TransportConnection : ConnectionContext
     {
         private IDictionary<object, object> _items;
 
@@ -26,16 +28,18 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal
         public IPAddress LocalAddress { get; set; }
         public int LocalPort { get; set; }
 
-        public string ConnectionId { get; set; }
+        public override string ConnectionId { get; set; }
+
+        public override IFeatureCollection Features => this;
 
         public virtual MemoryPool<byte> MemoryPool { get; }
         public virtual PipeScheduler InputWriterScheduler { get; }
         public virtual PipeScheduler OutputReaderScheduler { get; }
 
-        public IDuplexPipe Transport { get; set; }
+        public override IDuplexPipe Transport { get; set; }
         public IDuplexPipe Application { get; set; }
 
-        public IDictionary<object, object> Items
+        public override IDictionary<object, object> Items
         {
             get
             {