Fix flaky SignalR test: RequestTimeoutDisabledWhenConnected (#59819)

Author: BrennanConroy

src/SignalR/common/Http.Connections/test/HttpConnectionDispatcherTests.cs

@@ -3525,7 +3525,7 @@ public async Task RequestTimeoutDisabledWhenConnected(HttpTransportType transpor
                     app.UseRouting();
                     app.UseEndpoints(endpoints =>
                     {
-                        endpoints.MapConnectionHandler<TestConnectionHandler>("/foo");
+                        endpoints.MapConnectionHandler<EchoConnectionHandler>("/foo");
                     });
                 })
                 .UseUrls("http://127.0.0.1:0");
@@ -3550,6 +3550,10 @@ public async Task RequestTimeoutDisabledWhenConnected(HttpTransportType transpor
 
             await connection.StartAsync();
 
+            // Easy way to make sure everything is set is to send and receive data over the connection
+            await connection.Transport.Output.WriteAsync(new byte[2]);
+            await connection.Transport.Input.ReadAsync();
+
             var negotiateResponse = NegotiateProtocol.ParseResponse(stream.ToArray());
 
             Assert.True(manager.TryGetConnection(negotiateResponse.ConnectionToken, out var context));
@@ -3898,6 +3902,34 @@ public override async Task OnConnectedAsync(ConnectionContext connection)
     }
 }
 
+public class EchoConnectionHandler : ConnectionHandler
+{
+    public override async Task OnConnectedAsync(ConnectionContext connection)
+    {
+        while (true)
+        {
+            var result = await connection.Transport.Input.ReadAsync();
+            var buffer = result.Buffer;
+
+            try
+            {
+                if (!buffer.IsEmpty)
+                {
+                    await connection.Transport.Output.WriteAsync(buffer.ToArray());
+                }
+                else if (result.IsCompleted)
+                {
+                    break;
+                }
+            }
+            finally
+            {
+                connection.Transport.Input.AdvanceTo(result.Buffer.End);
+            }
+        }
+    }
+}
+
 public class ServiceProviderConnectionHandler : ConnectionHandler
 {
     public override async Task OnConnectedAsync(ConnectionContext connection)