Reading bit value goes into an infinity loop

When reading a bit type value, I encountered a bug that caused an infinite loop under certain conditions.

Steps to reproduce

using (var conn = new NpgsqlConnection(connnectionString))
{
    conn.Open();

    using (var cmd = conn.CreateCommand())
    {
        cmd.CommandText = @"SELECT 1::bit(100000);";

        using (var reader = cmd.ExecuteReader(CommandBehavior.SequentialAccess))
        {
            reader.Read();
            reader.GetValue(0); // infinite loop!!
        }
    }
}

The issue

BitStringHandler has the cause. In case a bit value cuts across a buffer boundary, the last byte will never read and result in an infinite loop. The buf.ReadBytesLeft property remains at 1 and the loop cannot be escaped.

https://github.com/npgsql/npgsql/blob/b1fd3f2add28dbcff554eb117c83189d91f8c183/src/Npgsql/TypeHandlers/BitStringHandler.cs#L58-L74

Above example is terrible, but our application is facing same problem. It reads 16-bit column values, and cuts across a buffer boundary depending on the data state.

If I set CommandBehavior to default, it works. but we use Dapper, and Dapper’s Query method internally sets CommandBehavior.SequentialAccess link.

Further technical details

Npgsql version: 4.1.2 PostgreSQL version: 9.6 Operating system: Windows 10

[YohDeadfall]

Would like, but without a rush. Am out of the city till tomorrow (:

[mintsoft]

@YohDeadfall Aha that makes sense, thanks!