json_array with base64 is not same with MySQL

[xiekeyi98]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

select json_array(b'0', b'1', b'10');

2. What did you expect to see?

In MySQL

mysql> select version();
+-------------------------+
| version()               |
+-------------------------+
| 5.7.25-0ubuntu0.18.04.2 |
+-------------------------+
1 row in set (0.00 sec)

mysql> select json_array(b'0', b'1', b'10');
+--------------------------------------------------------------------+
| json_array(b'0', b'1', b'10')                                      |
+--------------------------------------------------------------------+
| ["base64:type16:AA==", "base64:type16:AQ==", "base64:type16:Ag=="] |
+--------------------------------------------------------------------+
1 row in set (0.00 sec)

3. What did you see instead?

In TIDB

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v3.0.0-beta-321-gc6a757b24
Git Commit Hash: c6a757b2435965a72ada9d61ea8b7a367bd89b5f
Git Branch: master
UTC Build Time: 2019-04-02 02:38:04
GoVersion: go version go1.12.1 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false
1 row in set (0.01 sec)

mysql> select json_array(b'0', b'1', b'10');
+--------------------------------+
| json_array(b'0', b'1', b'10')  |
+--------------------------------+
| ["\u0000", "\u0001", "\u0002"] |
+--------------------------------+
1 row in set (0.00 sec)

[wjhuang2016]

base64:type16:AA==

type16 here is special in MySQL to distinguish binary literal from other opaque types.
Since we didn't introduce these types from MySQL, we can only hard code it to 16 presently.
Besides, in MySQL 8.0.15, its type is 15.

[kodeine]

So how exactly we decode base64:type16:AA==?

[ghost]

Confirming this issue still exists:

mysql> select json_array(b'0', b'1', b'10');
+--------------------------------+
| json_array(b'0', b'1', b'10')  |
+--------------------------------+
| ["\u0000", "\u0001", "\u0002"] |
+--------------------------------+
1 row in set (0.00 sec)

mysql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-870-g2a8b96845
Edition: Community
Git Commit Hash: 2a8b968453520e4fcf9d6ff46c9f23b4ad23feee
Git Branch: master
UTC Build Time: 2020-07-31 08:45:35
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)