Disable response buffering via the IHttpBufferingFeature (#379)

* Disable response buffering via the IHttpBufferingFeature
- To make sure SignalR works with servers and middleware
that do perform response buffering, disable it via the
IHttpBufferingFeature for SSE.
- Added test to verify buffering is disabled

src/Microsoft.AspNetCore.Sockets/Transports/ServerSentEventsTransport.cs

@@ -9,6 +9,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using System.Threading.Tasks.Channels;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Sockets.Internal.Formatters;
 using Microsoft.Extensions.Logging;
 
@@ -29,6 +30,11 @@ namespace Microsoft.AspNetCore.Sockets.Transports
         {
             context.Response.ContentType = "text/event-stream";
             context.Response.Headers["Cache-Control"] = "no-cache";
+
+            // Make sure we disable all response buffering for SSE
+            var bufferingFeature = context.Features.Get<IHttpBufferingFeature>();
+            bufferingFeature?.DisableResponseBuffering();
+
             context.Response.Headers["Content-Encoding"] = "identity";
 
             await context.Response.Body.FlushAsync();

test/Microsoft.AspNetCore.Sockets.Tests/ServerSentEventsTests.cs

@@ -1,12 +1,14 @@
 // 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.IO;
 using System.IO.Pipelines;
 using System.Text;
 using System.Threading.Tasks;
 using System.Threading.Tasks.Channels;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Sockets.Transports;
 using Microsoft.Extensions.Logging;
 using Xunit;
@@ -30,6 +32,22 @@ namespace Microsoft.AspNetCore.Sockets.Tests
             Assert.Equal("no-cache", context.Response.Headers["Cache-Control"]);
         }
 
+        [Fact]
+        public async Task SSETurnsResponseBufferingOff()
+        {
+            var channel = Channel.CreateUnbounded<Message>();
+            var context = new DefaultHttpContext();
+            var feature = new HttpBufferingFeature();
+            context.Features.Set<IHttpBufferingFeature>(feature);
+            var sse = new ServerSentEventsTransport(channel, new LoggerFactory());
+
+            Assert.True(channel.Out.TryComplete());
+
+            await sse.ProcessRequestAsync(context, context.RequestAborted);
+
+            Assert.True(feature.ResponseBufferingDisabled);
+        }
+
         [Theory]
         [InlineData("Hello World", "data: T\r\ndata: Hello World\r\n\r\n")]
         [InlineData("Hello\nWorld", "data: T\r\ndata: Hello\r\ndata: World\r\n\r\n")]
@@ -53,5 +71,22 @@ namespace Microsoft.AspNetCore.Sockets.Tests
 
             Assert.Equal(expected, Encoding.UTF8.GetString(ms.ToArray()));
         }
+
+        private class HttpBufferingFeature : IHttpBufferingFeature
+        {
+            public bool RequestBufferingDisabled { get; set; }
+
+            public bool ResponseBufferingDisabled { get; set; }
+
+            public void DisableRequestBuffering()
+            {
+                RequestBufferingDisabled = true;
+            }
+
+            public void DisableResponseBuffering()
+            {
+                ResponseBufferingDisabled = true;
+            }
+        }
     }
 }