[5.1] Cherry-pick of #3270 - Handle null socket

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SNI/SNITcpHandle.cs

@@ -765,17 +765,29 @@ public override uint Send(SNIPacket packet)
         }
 
         /// <summary>
-        /// Receive a packet synchronously
+        /// Receives a packet synchronously.
         /// </summary>
-        /// <param name="packet">SNI packet</param>
-        /// <param name="timeoutInMilliseconds">Timeout in Milliseconds</param>
-        /// <returns>SNI error code</returns>
+        /// <param name="packet">The received SNI packet.</param>
+        /// <param name="timeoutInMilliseconds">
+        /// Timeout in milliseconds:
+        /// - If greater than 0, sets the socket's receive timeout to the specified value.
+        /// - If equal to -1, represents an infinite timeout (socket timeout is set to 0).
+        /// - If less than -1 or equal to 0, results in a timeout error.
+        /// </param>
+        /// <returns>SNI error code indicating the result of the operation.</returns>
         public override uint Receive(out SNIPacket packet, int timeoutInMilliseconds)
         {
             SNIPacket errorPacket;
             lock (this)
             {
                 packet = null;
+
+                if (_socket == null)
+                {
+                    SqlClientEventSource.Log.TrySNITraceEvent(nameof(SNITCPHandle), EventType.ERR, "Connection Id {0}, Socket is null.", args0: _connectionId);
+                    return ReportTcpSNIError(0, SNICommon.ConnOpenFailedError, Strings.SNI_ERROR_10);
+                }
+
                 try
                 {
                     if (timeoutInMilliseconds > 0)
@@ -784,8 +796,7 @@ public override uint Receive(out SNIPacket packet, int timeoutInMilliseconds)
                     }
                     else if (timeoutInMilliseconds == -1)
                     {
-                        // SqlClient internally represents infinite timeout by -1, and for TcpClient this is translated to a timeout of 0
-                        _socket.ReceiveTimeout = 0;
+                        _socket.ReceiveTimeout = Timeout.Infinite;
                     }
                     else
                     {
@@ -840,7 +851,9 @@ public override uint Receive(out SNIPacket packet, int timeoutInMilliseconds)
                 }
                 finally
                 {
-                    _socket.ReceiveTimeout = 0;
+                    // Reset the socket timeout to Timeout.Infinite after the receive operation is done
+                    // to avoid blocking the thread in case of a timeout error.
+                    _socket.ReceiveTimeout = Timeout.Infinite;
                 }
             }
         }

src/Microsoft.Data.SqlClient/netcore/src/Resources/Strings.resx

@@ -927,6 +927,9 @@
   <data name="SNI_ERROR_9" xml:space="preserve">
     <value>Associating port with I/O completion mechanism failed</value>
   </data>
+  <data name="SNI_ERROR_10" xml:space="preserve">
+    <value>Socket is null</value>
+  </data>
   <data name="SNI_ERROR_11" xml:space="preserve">
     <value>Timeout error</value>
   </data>
@@ -1944,4 +1947,4 @@
   <data name="SNI_PN11" xml:space="preserve">
     <value>SQL Network Interfaces</value>
   </data>
-</root>
+</root>

src/Microsoft.Data.SqlClient/netfx/src/Resources/Strings.resx

@@ -3805,7 +3805,7 @@
     <value>Associating port with I/O completion mechanism failed</value>
   </data>
   <data name="SNI_ERROR_10" xml:space="preserve">
-    <value />
+    <value>Socket is null</value>
   </data>
   <data name="SNI_ERROR_11" xml:space="preserve">
     <value>Timeout error</value>