Fix FlushAsync when a ConnectionAdapter is configured (#1957)

* Also remove async void everywhere

src/Microsoft.AspNetCore.Server.Kestrel.Core/Adapter/Internal/RawStream.cs

@@ -75,17 +75,13 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Adapter.Internal
 
         public override async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken token)
         {
-            ArraySegment<byte> segment;
+            var output = _output.Alloc();
+
             if (buffer != null)
             {
-                segment = new ArraySegment<byte>(buffer, offset, count);
+                output.Write(new ArraySegment<byte>(buffer, offset, count));
             }
-            else
+
-            {
-                segment = default(ArraySegment<byte>);
-            }
-            var output = _output.Alloc();
-            output.Write(segment);
             await output.FlushAsync(token);
         }
 

src/Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv/Internal/ListenerSecondary.cs

@@ -81,10 +81,10 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.Internal
         private static void ConnectCallback(UvConnectRequest connect, int status, UvException error, TaskCompletionSource<int> tcs)
         {
             var listener = (ListenerSecondary)tcs.Task.AsyncState;
-            listener.ConnectedCallback(connect, status, error, tcs);
+            _ = listener.ConnectedCallback(connect, status, error, tcs);
         }
 
-        private async void ConnectedCallback(UvConnectRequest connect, int status, UvException error, TaskCompletionSource<int> tcs)
+        private async Task ConnectedCallback(UvConnectRequest connect, int status, UvException error, TaskCompletionSource<int> tcs)
         {
             connect.Dispose();
             if (error != null)

src/Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets/SocketConnection.cs

@@ -38,7 +38,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets
             _remoteEndPoint = (IPEndPoint)_socket.RemoteEndPoint;
         }
 
-        public async void Start(IConnectionHandler connectionHandler)
+        public async Task StartAsync(IConnectionHandler connectionHandler)
         {
             try
             {

src/Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets/SocketTransport.cs

@@ -105,7 +105,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets
                     acceptSocket.NoDelay = _endPointInformation.NoDelay;
 
                     var connection = new SocketConnection(acceptSocket, this);
-                    connection.Start(_handler);
+                    _ = connection.StartAsync(_handler);
                 }
             }
             catch (Exception)

test/Microsoft.AspNetCore.Server.Kestrel.FunctionalTests/ConnectionAdapterTests.cs

@@ -7,6 +7,7 @@ using System.Net;
 using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Server.Kestrel.Core;
 using Microsoft.AspNetCore.Server.Kestrel.Core.Adapter.Internal;
 using Microsoft.AspNetCore.Testing;
@@ -172,6 +173,39 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
             }
         }
 
+        [Fact]
+        public async Task CanFlushAsyncWithConnectionAdapter()
+        {
+            var listenOptions = new ListenOptions(new IPEndPoint(IPAddress.Loopback, 0))
+            {
+                ConnectionAdapters = { new PassThroughConnectionAdapter() }
+            };
+
+            var serviceContext = new TestServiceContext();
+
+            using (var server = new TestServer(async context =>
+            {
+                await context.Response.WriteAsync("Hello ");
+                await context.Response.Body.FlushAsync();
+                await context.Response.WriteAsync("World!");
+            }, serviceContext, listenOptions))
+            {
+                using (var connection = server.CreateConnection())
+                {
+                    await connection.Send(
+                        "GET / HTTP/1.0",
+                        "",
+                        "");
+                    await connection.ReceiveEnd(
+                        "HTTP/1.1 200 OK",
+                        "Connection: close",
+                        $"Date: {serviceContext.DateHeaderValue}",
+                        "",
+                        "Hello World!");
+                }
+            }
+        }
+
         private class RewritingConnectionAdapter : IConnectionAdapter
         {
             private RewritingStream _rewritingStream;