JSON function overflow error based on LONGTEXT field

Hi, I'm GSoC 2022 contributor, I'm working on the MCOL-785.
Now I have a problem: The JSON Function result is truncated when the function is called based on LONGTEXT field.

Take the JSON_ARRAY as an example:

MariaDB root@(none):test> create table t1(t TEXT, l LONGTEXT) engine=columnstore;

Query OK, 0 rows affected

Time: 0.147s

MariaDB root@(none):test> insert into t1 values('key1', 'key1');

Query OK, 1 row affected

Time: 0.179s

MariaDB root@(none):test> select json_array(t), json_array(l) from t1;

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

| json_array(t) | json_array(l) |

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

| ["key1"]      | ["key         |

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

1 row in set

Time: 0.097s

MariaDB root@(none):test>

After debugging, I found that such difference is caused by overflow error.

bool Item_func_json_array::fix_length_and_dec(THD *thd)

{

  ulonglong char_length= 2;

...

  for (n_arg=0 ; n_arg < arg_count ; n_arg++)

    char_length+= args[n_arg]->max_char_length() + 4;

...

}

First, the return type of args[n_arg]- >max_char_length() is uint32, the max value of uint32 is 4,294,967,295.
When called based on LONGTEXT, the result of args[n_arg]- >max_char_length() is 4,294,967,295(Maximum value of LONGTEXT). So args[n_arg]->max_char_length()+4 will be 3 due to overflow. And there is no overflow when calling based on TEXT.

I will make a patch to this issue. I would be very grateful if you can handle it soon.

same issues exist in JSON_OBJECT, JSON_ARRAY_APPEND(INSERT), JSON_INSERT(REPLACE|SET)

• My JSON_ARRAY implementation: func_json_array.cpp
• Pull Request: has been submitted and passed CI)