Yes, we use DeiveParameters to get metadata for procedure parameters.
Thank you for the clue, I tried MySqlConnection.GetSchema("Parameters"), but it throws an exception:
System.ArgumentException : Value was either too large or too small for an Int32.Couldn't store <4294967295> in CHARACTER_MAXIMUM_LENGTH Column. Expected type is Int32.
It looks like column types are wrong. According to the reader.GetSchemaTable(), this column is mapped to Int64.

Originally posted by @dxmi in #1125 (comment)