1062 warning returns invalid UTF8 message

[est]

1. Minimal reproduce step (Required)

select version();
5.7.25-TiDB-v5.1.0
create table t1 (id binary(20) unique);
INSERT IGNORE INTO t1  VALUES (X'0e6b4234fd0b08d4c4ec656529d94df02b37c472');
INSERT IGNORE INTO t1  VALUES (X'0e6b4234fd0b08d4c4ec656529d94df02b37c472');
show warnings;

Protocol returning Warning 1062 with following message:

• On MySQL (8.0.15-6):
  "Duplicate entry '\\x0EkB4\\xFD\\x0B\\x08\\xD4\\xC4\\xECee)\\xD9M\\xF0+7\\xC4r' for key 'idx_id'"

• On TiDB (5.7.25-TiDB-v5.1.0):
  "Duplicate entry '\x0ekB4\x0b\x08ee)M+7r' for key 'idx_id'"

The above output were Python (mycli+PyMySQL) string objects I grabbed through debugging, other clients would see gibberish.

2. What did you expect to see? (Required)

The TiDB should return properly escaped, valid UTF-8 string message

3. What did you see instead (Required)

The TiDB returns a message containing invalid UTF-8 bytes which cause client library decoding errors

4. What is your TiDB version? (Required)

5.7.25-TiDB-v5.1.0

[Defined2014]

When length of insert row less than length of column, the result also not same as MySQL, we also should fix it.

mysql> INSERT IGNORE INTO t1  VALUES (X'0e6b4234fd0b08');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT IGNORE INTO t1  VALUES (X'0e6b4234fd0b08');
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+----------------------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                                            |
+---------+------+----------------------------------------------------------------------------------------------------+
| Warning | 1062 | Duplicate entry '\x0EkB4\xFD\x0B\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\' for key 't1.id' |
+---------+------+----------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)