pgpool: Delimit query-cache key to prevent collisions

Delimit query-cache key to prevent collisions

I have reviewed the patch you provided.
It has also passed all regression tests.

encode_key() constructs the cache key using md5(user || query || database) without delimiters.
This allows different sessions to produce identical keys
(e.g., "admin" + "Q" + "testdb" and "adm" + "Q" + "intestdb"),
leading to data leakage between users/databases.

Changes:
Explicit Delimiters: Insert NUL bytes between the user, query, and database fields in the buffer.
Hash Full Range: Updated the hash function to process the entire byte range (including NUL separators)
instead of stopping at the first NUL byte.

Reported-by: Emond Papegaaij <emond(dot)papegaaij(at)gmail(dot)com>
Reported-by: Claude code
Author: Taiki Koshino <koshino(at)sraoss(dot)co(dot)jp>
Discussion: https://www.postgresql.org/message-id/TY4PR01MB17374DD1C2B89248B8714F84394C22%40TY4PR01MB17374.jpnprd01.prod.outlook.com
Backpatch-through: v4.3

Branch
------
V4_7_STABLE

Details
-------
https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=f070a1181716f817099582201cdc0db18cb34fee

Modified Files
--------------
src/query_cache/pool_memqcache.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)