`MySqlConnection.Dispose` hangs if an exception occurs calling a stored function

[smfeest]

If an error occurs while calling a MySQL function through a command with a return value parameter, then any attempt to dispose the underlying connection results in the application hanging indefinitely.

Below is a minimal test case for reproducing the issue.

1. Create a new database containing a function that always fails:

CREATE DATABASE functiontest;
CREATE USER functiontest@localhost;
GRANT ALL PRIVILEGES ON `functiontest`.* TO 'functiontest'@'localhost';

DELIMITER $$
CREATE FUNCTION FAILING_FUNCTION()
RETURNS INT
BEGIN
    DECLARE v1 INT;
    SELECT c1 FROM table_that_does_not_exist INTO v1;
    RETURN v1;
END$$
DELIMITER ;

2. Create a basic console application that attempts to call the function:

using System;
using System.Data;
using System.Data.Common;
using MySql.Data.MySqlClient;

namespace mysqlbug
{
    class Program
    {
        static void Main(string[] args)
        {
            var connection = new MySqlConnection("Server=localhost;Uid=functiontest;Database=functiontest;");

            try
            {
                connection.Open();

                using (var command = connection.CreateCommand())
                {
                    command.CommandType = CommandType.StoredProcedure;
                    command.CommandText = "FAILING_FUNCTION";

                    var returnParameter = command.CreateParameter();
                    returnParameter.DbType = DbType.Int32;
                    returnParameter.Direction = ParameterDirection.ReturnValue;
                    command.Parameters.Add(returnParameter);

                    command.ExecuteNonQuery();
                }
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception: {0}", e);
            }
            finally
            {
                Console.WriteLine("BeforeDispose");
                connection.Dispose();
                Console.WriteLine("AfterDispose");
            }
        }
    }
}

3. Run the application. It always hangs on connection.Dispose().

Similarly, if you wrap the command in a transaction:

// ...
connection.Open();

using (var transaction = connection.BeginTransaction())
using (var command = connection.CreateCommand())
{
    // ...

The following exception occurs when the transaction is disposed:

Exception: MySql.Data.MySqlClient.MySqlException: There is already an open DataReader associated with this Connection which must be closed first.
   at MySql.Data.Serialization.MySqlSession.StartQuerying(MySqlCommand command)
   at MySql.Data.MySqlClient.CommandExecutors.TextCommandExecutor.<ExecuteReaderAsync>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MySql.Data.MySqlClient.CommandExecutors.TextCommandExecutor.<ExecuteNonQueryAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteNonQuery()
   at MySql.Data.MySqlClient.MySqlTransaction.Dispose(Boolean disposing)
   at mysqlbug.Program.Main(String[] args) in /Users/sfeest/Personal/git/mysqlbug/Program.cs:line 30

[smfeest]

Based on the exception shown when disposing the transaction, I wonder whether the cause might be that the reader created here is not being disposed when an exception is thrown executing the command:

https://github.com/mysql-net/MySqlConnector/blob/master/src/MySqlConnector/MySqlClient/CommandExecutors/StoredProcedureCommandExecutor.cs#L78

[bgrainger]

Thanks for the detailed and comprehensive bug report! I can reproduce this problem.

[smfeest]

Thank you so much @bgrainger (both for the fix, and for this great library!)

[bgrainger]

Fixed in 0.24.0.