MySQL Bugs: #103390: Can't read CHAR(36) column if MySqlCommand is prepared

Bug #103390	Can't read CHAR(36) column if MySqlCommand is prepared
Submitted:	20 Apr 2021 19:19	Modified:	7 Sep 2021 19:29
Reporter:	Bradley Grainger (OCA)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / NET	Severity:	S2 (Serious)
Version:	8.0.24, 8.0.25	OS:	Windows (10)
Assigned to:		CPU Architecture:	Other (x64)

Description:
This bug was introduced in 8.0.22 but may have been obscured by bug #101252 (that occurs in a similar situation); it was also less visible in that release because IgnorePrepare defaulted to true. It's still present in 8.0.24.

When querying a CHAR(36) column, reading a non-NULL value will fail if the MySqlCommand is prepared.

How to repeat:
Create a table and insert a GUID value:

drop table if exists prepared_command_test;
create table prepared_command_test(value char(36));
insert into prepared_command_test(value) values ('3e22b63e-8077-43ab-8cee-17aa1db80861');

Query that table with the following C# code:

using var connection = new MySqlConnection("...");
connection.Open();
using var cmd = connection.CreateCommand();
cmd.CommandText = "select value from prepared_command_test";
cmd.Prepare(); // works fine if this line is commented out
using var reader = cmd.ExecuteReader();
while (reader.Read()) // <-- throws here
	Console.WriteLine(reader.GetGuid(0));

The program throws an exception:

Unhandled Exception: System.ArgumentOutOfRangeException: Non-negative number required.
Parameter name: count
   at System.Text.UTF8Encoding.GetString(Byte[] bytes, Int32 index, Int32 count)
   at MySql.Data.MySqlClient.NativeDriver.ReadColumnValue(Int32 index, MySqlField field, IMySqlValue valObject)
   at MySql.Data.MySqlClient.ResultSet.ReadColumnData(Boolean outputParms)
   at MySql.Data.MySqlClient.ResultSet.NextRow(CommandBehavior behavior)
   at MySql.Data.MySqlClient.MySqlDataReader.Read()
   at Test.Program.Main(String[] args)

Hello Bradley,

Thank you for the report and test case.
Verified as described.

regards,
Umesh

Posted by developer:
 
Fixed as of the upcoming MySQL Connector/NET 8.0.27 release, and here's the proposed changelog entry from the documentation team:

When querying a CHAR(36) column, reading a non-NULL value could emit an
error if MySqlCommand is prepared.

Thank you for the bug report.