Thread: BUG #18510: jsonpath does not support trailing backslash at the end of the query

The following bug has been logged on the website:

Bug reference:      18510
Logged by:          Lex Vorona
Email address:      voronaam@gmail.com
PostgreSQL version: 16.3
Operating system:   Linux (Ubuntu)
Description:

Note that JSONPATH documentation states [1]:

>  to write a backslash itself, you must write \\

It works for a backslash as long as it is not the last character in the
input string.

Simplest way to reproduce:

psql (16.3 (Ubuntu 16.3-1.pgdg22.04+1))

postgres=# select '$.field ? (@ like_regex "a\\b")'::jsonpath; -- works
            jsonpath             
---------------------------------
 $."field"?(@ like_regex "a\\b")
(1 row)


postgres=# select '$.field ? (@ like_regex "a\\")'::jsonpath; -- does not
work
ERROR:  invalid regular expression: invalid escape \ sequence
LINE 1: select '$.field ? (@ like_regex "a\\")'::jsonpath;
               ^

Also reproducible with functions like jsonb_path_exists(...) which
automatically cast parameters to jsonpath.


1:
https://www.postgresql.org/docs/current/datatype-json.html#DATATYPE-JSONPATH

On 2024-Jun-14, David G. Johnston wrote:

> It is working just fine.  It sees both the regex and the backslash
> character and then helpfully tells you that the regex you wrote is
> bogus since the backslash you wrote isn't escaping anything.

Not really connected to this bug, but I think we should get rid of the
error that says that the end backslashes are useless.  If that error
wasn't there, we would be one step closer to being able to mark the
operator for LIKE as leakproof.  Right now, if you mark that operator as
leakproof and use it in a security barrier view, attackers can leak
entire strings by testing with that operator for each character one at a
time.

=# select * from secret where data like substring(data, 1, 7) escape 'r';
ERROR:  LIKE pattern must not end with escape character

Here I verify that the character number 7 is an 'r'.

So this one error is the sole reason we have to mark the LIKE operator
as leaky, which is sad.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Just treat us the way you want to be treated + some extra allowance
 for ignorance."                                    (Michael Brusser)