pg_basebackup: Generate valid temporary slot names under PQbackendPID()

pgbouncer can cause PQbackendPID() to return negative values due to it
filling be_pid with random bytes (even these days pid_max can only be
set up to 2^22 on 64b machines on Linux, for example, so this cannot
happen with normal PID numbers).  When this happens, pg_basebackup may
generate a temporary slot name that may not be accepted by the parser,
leading to spurious failures, like:
pg_basebackup: error: could not send replication command
ERROR:  replication slot name "pg_basebackup_-1201966863" contains
invalid character

This commit fixes that problem by formatting the result from
PQbackendPID() as an unsigned integer when creating the temporary
replication slot name, so as the invalid character is gone and the
command can be parsed.

Author: Jelte Fennema
Reviewed-by: Daniel Gustafsson, Nishant Sharma
Discussion: https://postgr.es/m/CAGECzQQOGvYfp8ziF4fWQ_o8s2K7ppaoWBQnTmdakn3s-4Z=5g@mail.gmail.com
Backpatch-through: 11

diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index af2575a58b1ff4926921f06040780e6b1fbeef59..401d1a415f6f9e74a451a7a200712fc36b85b1e7 100644 (file)
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -612,7 +612,8 @@ StartLogStreamer(char *startpos, uint32 timeline, char *sysidentifier)
     * Create replication slot if requested
     */
    if (temp_replication_slot && !replication_slot)
-       replication_slot = psprintf("pg_basebackup_%d", (int) PQbackendPID(param->bgconn));
+       replication_slot = psprintf("pg_basebackup_%u",
+                                   (unsigned int) PQbackendPID(param->bgconn));
    if (temp_replication_slot || create_slot)
    {
        if (!CreateReplicationSlot(param->bgconn, replication_slot, NULL,