Port SqlClient fixes for NP Flush and for NP/TCP native error codes to 2.0.0 branch

src/System.Data.SqlClient/src/System/Data/SqlClient/SNI/SNINpHandle.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.ComponentModel;
 using System.IO;
 using System.IO.Pipes;
 using System.Net.Security;
@@ -141,6 +142,9 @@ public override void Dispose()
                     _pipeStream.Dispose();
                     _pipeStream = null;
                 }
+
+                //Release any references held by _stream.
+                _stream = null;
             }
         }
 
@@ -157,7 +161,8 @@ public override uint Receive(out SNIPacket packet, int timeout)
 
                     if (packet.Length == 0)
                     {
-                        return ReportErrorAndReleasePacket(packet, 0, SNICommon.ConnTerminatedError, string.Empty);
+                        var e = new Win32Exception();
+                        return ReportErrorAndReleasePacket(packet, (uint)e.NativeErrorCode, 0, e.Message);
                     }
                 }
                 catch (ObjectDisposedException ode)

src/System.Data.SqlClient/src/System/Data/SqlClient/SNI/SNITcpHandle.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Diagnostics;
 using System.IO;
 using System.Net;
@@ -440,7 +441,8 @@ public override uint Receive(out SNIPacket packet, int timeoutInMilliseconds)
 
                     if (packet.Length == 0)
                     {
-                        return ReportErrorAndReleasePacket(packet, 0, SNICommon.ConnTerminatedError, string.Empty);
+                        var e = new Win32Exception();
+                        return ReportErrorAndReleasePacket(packet, (uint)e.NativeErrorCode, 0, e.Message);
                     }
 
                     return TdsEnums.SNI_SUCCESS;

src/System.Data.SqlClient/src/System/Data/SqlClient/SNI/SslOverTdsStream.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.IO;
+using System.IO.Pipes;
 
 namespace System.Data.SqlClient.SNI
 {
@@ -160,7 +161,12 @@ public override void SetLength(long value)
         /// </summary>
         public override void Flush()
         {
-            _stream.Flush();
+            // Can sometimes get Pipe broken errors from flushing a PipeStream.
+            // PipeStream.Flush() also doesn't do anything, anyway.
+            if (!(_stream is PipeStream))
+            {
+                _stream.Flush();
+            }
         }
 
         /// <summary>

src/System.Data.SqlClient/tests/ManualTests/SQL/LocalDBTest/LocalDBTest.cs

@@ -29,6 +29,15 @@ public static void LocalDBMarsTest()
             OpenConnection(builder.ConnectionString);
         }
 
+        [ConditionalFact(nameof(IsLocalDBEnvironmentSet))]
+        public static void InvalidDBTest()
+        {
+            using (var connection = new SqlConnection(@"Data Source=(localdb)\MSSQLLOCALDB;Database=DOES_NOT_EXIST;Pooling=false;"))
+            {
+                DataTestUtility.AssertThrowsWrapper<SqlException>(() => connection.Open());
+            }
+        }
+
         private static void OpenConnection(string connString)
         {
             using (SqlConnection connection = new SqlConnection(connString))