Fix session leak with user variables. Fixes #305

Moving 'CreateQueryPayload' earlier in the function keeps the internal state as 'Connected' (rather than 'Querying') so the session is correctly returned to the pool after the exception is handled.

The 'Querying' state is now only used when an outgoing connection to the MySQL server is initiated.

Author: bgrainger

src/MySqlConnector/MySqlClient/CommandExecutors/TextCommandExecutor.cs

@@ -51,19 +51,11 @@ public virtual async Task<DbDataReader> ExecuteReaderAsync(string commandText, M
 			CommandBehavior behavior, IOBehavior ioBehavior, CancellationToken cancellationToken)
 		{
 			cancellationToken.ThrowIfCancellationRequested();
+			var payload = CreateQueryPayload(commandText, parameterCollection);
 			using (m_command.RegisterCancel(cancellationToken))
 			{
 				m_command.Connection.Session.StartQuerying(m_command);
 				m_command.LastInsertedId = -1;
-				var statementPreparerOptions = StatementPreparerOptions.None;
-				if (m_command.Connection.AllowUserVariables || m_command.CommandType == CommandType.StoredProcedure)
-					statementPreparerOptions |= StatementPreparerOptions.AllowUserVariables;
-				if (m_command.Connection.OldGuids)
-					statementPreparerOptions |= StatementPreparerOptions.OldGuids;
-				if (m_command.CommandType == CommandType.StoredProcedure)
-					statementPreparerOptions |= StatementPreparerOptions.AllowOutputParameters;
-				var preparer = new MySqlStatementPreparer(commandText, parameterCollection, statementPreparerOptions);
-				var payload = new PayloadData(preparer.ParseAndBindParameters());
 				try
 				{
 					await m_command.Connection.Session.SendAsync(payload, ioBehavior, CancellationToken.None).ConfigureAwait(false);
@@ -83,6 +75,19 @@ public virtual async Task<DbDataReader> ExecuteReaderAsync(string commandText, M
 			}
 		}
 
+		private PayloadData CreateQueryPayload(string commandText, MySqlParameterCollection parameterCollection)
+		{
+			var statementPreparerOptions = StatementPreparerOptions.None;
+			if (m_command.Connection.AllowUserVariables || m_command.CommandType == CommandType.StoredProcedure)
+				statementPreparerOptions |= StatementPreparerOptions.AllowUserVariables;
+			if (m_command.Connection.OldGuids)
+				statementPreparerOptions |= StatementPreparerOptions.OldGuids;
+			if (m_command.CommandType == CommandType.StoredProcedure)
+				statementPreparerOptions |= StatementPreparerOptions.AllowOutputParameters;
+			var preparer = new MySqlStatementPreparer(commandText, parameterCollection, statementPreparerOptions);
+			return new PayloadData(preparer.ParseAndBindParameters());
+		}
+
 		readonly MySqlCommand m_command;
 	}
 }