Unexpected Connection Lost

[bajinsheng]

Bug Report

1. Minimal reproduce step (Required)

SELECT CAST(REVERSE(-1502572527) AS DATE); -- ERROR 2013 (HY000): Lost connection to MySQL server during query

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

No error.

3. What did you see instead (Required)

ERROR 2013 (HY000): Lost connection to MySQL server during query

4. What is your TiDB version? (Required)

| Release Version: v6.2.0-alpha-159-ge0527ba27
Edition: Community
Git Commit Hash: e0527ba
Git Branch: master
UTC Build Time: 2022-06-21 11:55:54
GoVersion: go1.18.3
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
Store: unistore |

[seiya-annie]

i tried in mysql8.3 , no error reported.

mysql> SELECT (NOT ('s' OR CAST(REVERSE(-1502572527) AS DATE)));
+---------------------------------------------------+
| (NOT ('s' OR CAST(REVERSE(-1502572527) AS DATE))) |
+---------------------------------------------------+
|                                              NULL |
+---------------------------------------------------+
1 row in set, 2 warnings (0.03 sec)

[seiya-annie]

and checked in log, seems this statement is not sent to tidb server. no log found for this.

[bb7133]

There are two issues for this bug, the minimal reproduction SQL is:

tidb> SELECT CAST("1111111111-" AS DATE);
ERROR 2013 (HY000): Lost connection to MySQL server during query

1: It is about the details of CAST implementation from strings to datetime, when 1111111111- is parsed, splited, the code goes to:

https://github.com/pingcap/tidb/blob/5c9ad77ae1f172b4474664d7f83c5661b1ad2939/types/time.go/#L1067-L1070

Finally and I can see that an EOF error is returned by fmt.Sscanf.

2: The EOF error is not handled correctly, so there's no log or error returned to the client.