Thread: ASCII Null control character validation

Hello, hackers!

I found in src/backend/utils/mb/wchar.c: pg_verify_mbstr_len() that it
reports ASCII Null character (\000) as invalid. As for me, it should
pass validation. However, ASCII Null character breaks a line and the
end of the line is missed, try:

INSERT INTO mytable VALUES (E'a\001b\000c and rest of line MIA');

Find patch attached. Am I wrong?

-- 
Alexey Chernyshov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Alexey Chernyshov <a.chernyshov@postgrespro.ru> writes:
> I found in src/backend/utils/mb/wchar.c: pg_verify_mbstr_len() that it
> reports ASCII Null character (\000) as invalid. As for me, it should
> pass validation.

This is intentional and we're not going to change it.  There is too
much code in the backend that relies on NUL-terminated strings ...

> However, ASCII Null character breaks a line and the
> end of the line is missed, try:
> INSERT INTO mytable VALUES (E'a\001b\000c and rest of line MIA');

... like that for instance.  See (many) past discussions of this issue.
        regards, tom lane

On 11/30/17 03:13, Alexey Chernyshov wrote:
> I found in src/backend/utils/mb/wchar.c: pg_verify_mbstr_len() that it
> reports ASCII Null character (\000) as invalid. As for me, it should
> pass validation. However, ASCII Null character breaks a line and the
> end of the line is missed, try:
> 
> INSERT INTO mytable VALUES (E'a\001b\000c and rest of line MIA');
> 
> Find patch attached. Am I wrong?

The main reason why you can't usefully have null characters in a string
literal is that the type input functions take a cstring as input, so no
string with a null character can possibly be input to a type.

So removing that check would just cause failure or confusion later.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services