Ignore closed connection in Cancel. Fixes #820

Author: bgrainger

docs/content/tutorials/migrating-from-connector-net.md

@@ -262,3 +262,4 @@ The following bugs in Connector/NET are fixed by switching to MySqlConnector. (~
 * [#101252](https://bugs.mysql.com/bug.php?id=101252): Can't query `CHAR(36)` column containing `NULL`
 * [#101253](https://bugs.mysql.com/bug.php?id=101253): Default value for `MySqlParameter.Value` changed from null to `0`
 * [#101302](https://bugs.mysql.com/bug.php?id=101302): Stored Procedure `BOOL` parameter can only be mapped to `MySqlDbType.Byte`
+* [#101507](https://bugs.mysql.com/bug.php?id=101507): `MySqlCommand.Cancel` throws `NullReferenceException` for a closed connection

src/MySqlConnector/MySqlConnection.cs

@@ -687,29 +687,28 @@ internal ServerSession Session
 
 		internal void Cancel(ICancellableCommand command)
 		{
-			var session = Session;
-			if (!session.TryStartCancel(command))
+			if (m_session is null || State != ConnectionState.Open || !m_session.TryStartCancel(command))
 				return;
 
 			try
 			{
 				// open a dedicated connection to the server to kill the active query
 				var csb = new MySqlConnectionStringBuilder(m_connectionString);
 				csb.Pooling = false;
-				if (m_session!.IPAddress is not null)
+				if (m_session.IPAddress is not null)
 					csb.Server = m_session.IPAddress.ToString();
 				csb.ConnectionTimeout = 3u;
 
 				using var connection = new MySqlConnection(csb.ConnectionString);
 				connection.Open();
 				using var killCommand = new MySqlCommand("KILL QUERY {0}".FormatInvariant(command.Connection!.ServerThread), connection);
-				session.DoCancel(command, killCommand);
+				m_session.DoCancel(command, killCommand);
 			}
 			catch (MySqlException ex)
 			{
 				// cancelling the query failed; setting the state back to 'Querying' will allow another call to 'Cancel' to try again
 				Log.Warn(ex, "Session{0} cancelling command {1} failed", m_session!.Id, command.CommandId);
-				session.AbortCancel(command);
+				m_session.AbortCancel(command);
 			}
 		}
 

tests/SideBySide/CommandTests.cs

@@ -283,6 +283,26 @@ public void CancelEmptyCommandIsNoop()
 			cmd.Cancel();
 		}
 
+		[SkippableFact(Baseline = "https://bugs.mysql.com/bug.php?id=101507")]
+		public void CancelCommandForClosedConnectionIsNoop()
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			connection.Open();
+			using var cmd = connection.CreateCommand();
+			connection.Close();
+			cmd.Cancel();
+		}
+
+		[SkippableFact(Baseline = "https://bugs.mysql.com/bug.php?id=101507")]
+		public void CancelCommandForDisposedConnectionIsNoop()
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			connection.Open();
+			using var cmd = connection.CreateCommand();
+			connection.Dispose();
+			cmd.Cancel();
+		}
+
 		[Fact]
 		public void CommandsAreIndependent()
 		{