[#MDEV-27177] OLD_MODE Ignored during initial hand shake for utf8

In the config file I have

old_mode=''

Which is correctly parsed and used

SELECT @@OLD_MODE, @@GLOBAL.OLD_MODE;

+------------+-------------------+

| @@OLD_MODE | @@GLOBAL.OLD_MODE |

+------------+-------------------+

|            |                   |

+------------+-------------------+

Correctly a query like that is interpreted correctly as

SELECT @@character_set_client, @@character_set_connection, @@collation_connection;

+------------------------+----------------------------+------------------------+

| @@character_set_client | @@character_set_connection | @@collation_connection |

+------------------------+----------------------------+------------------------+

| latin1                 | latin1                     | latin1_bin             |

+------------------------+----------------------------+------------------------+

SET character_set_client = 'utf8';

SET character_set_connection = 'utf8';

SET collation_connection = 'utf8_general_ci';

SELECT @@character_set_client, @@character_set_connection, @@collation_connection;

+------------------------+----------------------------+------------------------+

| @@character_set_client | @@character_set_connection | @@collation_connection |

+------------------------+----------------------------+------------------------+

| utf8mb4                | utf8mb4                    | utf8mb4_general_ci     |

+------------------------+----------------------------+------------------------+

The problem arise when a client is connecting and issue during the handshake a command to
Charset: utf8 COLLATE utf8_general_ci (33)

(For example a default-character-set=utf8 in the my.cnf file)

now

SELECT @@character_set_client, @@character_set_connection, @@collation_connection;

+------------------------+----------------------------+------------------------+

| @@character_set_client | @@character_set_connection | @@collation_connection |

+------------------------+----------------------------+------------------------+

| utf8mb3                | utf8mb3                    | utf8mb3_general_ci     |

+------------------------+----------------------------+------------------------+

status;

--------------

mysql  Ver 15.1 Distrib 10.6.5-MariaDB, for Linux (x86_64) using  EditLine wrapper

Connection id:          28

/* omissis */

Server version:         10.6.5-MariaDB-debug Source distribution

Protocol version:       10

Server characterset:    utf8mb4

Db     characterset:    utf8mb4

Client characterset:    utf8mb3

Conn.  characterset:    utf8mb3

I will now check in the source code more info about that

[MDEV-27177] OLD_MODE Ignored during initial hand shake for utf8 Created: 2021-12-06 Updated: 2023-03-03
Status:	Confirmed
Project:	MariaDB Server
Component/s:	Character Sets
Affects Version/s:	10.6.5, 10.6, 10.7
Fix Version/s:	10.6