Improved request error handling.

src/Microsoft.AspNetCore.Server.HttpSys/AsyncAcceptContext.cs

@@ -6,6 +6,7 @@ using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.HttpSys.Internal;
 
 namespace Microsoft.AspNetCore.Server.HttpSys
@@ -80,6 +81,11 @@ namespace Microsoft.AspNetCore.Server.HttpSys
                                 complete = true;
                             }
                         }
+                        catch (Exception)
+                        {
+                            server.SendError(asyncResult._nativeRequestContext.RequestId, StatusCodes.Status400BadRequest);
+                            throw;
+                        }
                         finally
                         {
                             // The request has been handed to the user, which means this code can't reuse the blob.  Reset it here.

src/Microsoft.AspNetCore.Server.HttpSys/HttpSysListener.cs

@@ -316,7 +316,7 @@ namespace Microsoft.AspNetCore.Server.HttpSys
             return true;
         }
 
-        private unsafe void SendError(ulong requestId, int httpStatusCode, IList<string> authChallenges)
+        internal unsafe void SendError(ulong requestId, int httpStatusCode, IList<string> authChallenges = null)
         {
             HttpApiTypes.HTTP_RESPONSE_V2 httpResponse = new HttpApiTypes.HTTP_RESPONSE_V2();
             httpResponse.Response_V1.Version = new HttpApiTypes.HTTP_VERSION();

src/Microsoft.AspNetCore.Server.HttpSys/MessagePump.cs

@@ -168,7 +168,7 @@ namespace Microsoft.AspNetCore.Server.HttpSys
                     {
                         LogHelper.LogException(_logger, "ListenForNextRequestAsync", exception);
                     }
-                    return;
+                    continue;
                 }
                 try
                 {