Fix PQport to never return NULL unless the connection is NULL.

tglsfdc · tglsfdc · commit bfa9b25c94fe · 2025-07-17T12:46:57.000-04:00
This is the documented behavior, and it worked that way before v10. However, addition of the connhost[] array created cases where conn->connhost[conn->whichhost].port is NULL. The rest of libpq is careful to substitute DEF_PGPORT[_STR] for a null or empty port string, but we failed to do so here, leading to possibly returning NULL. As of v18 that causes psql's \conninfo command to segfault. Older psql versions avoid that, but it's pretty likely that other clients have trouble with this, so we'd better back-patch the fix. In stable branches, just revert to our historical behavior of returning an empty string when there was no user-given port specification. However, it seems substantially more useful and indeed more correct to hand back DEF_PGPORT_STR in such cases, so let's make v18 and master do that. Author: Daniele Varrazzo <daniele.varrazzo@gmail.com> Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/CA+mi_8YTS8WPZPO0PAb2aaGLwHuQ0DEQRF0ZMnvWss4y9FwDYQ@mail.gmail.com Backpatch-through: 13
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
@@ -7528,10 +7528,12 @@ PQport(const PGconn *conn)
 	if (!conn)
 		return NULL;
 
-	if (conn->connhost != NULL)
+	if (conn->connhost != NULL &&
+		conn->connhost[conn->whichhost].port != NULL &&
+		conn->connhost[conn->whichhost].port[0] != '\0')
 		return conn->connhost[conn->whichhost].port;
 
-	return "";
+	return DEF_PGPORT_STR;
 }
 
 /*
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
@@ -357,7 +357,8 @@ typedef struct pg_conn_host
 	pg_conn_host_type type;		/* type of host address */
 	char	   *host;			/* host name or socket path */
 	char	   *hostaddr;		/* host numeric IP address */
-	char	   *port;			/* port number (always provided) */
+	char	   *port;			/* port number (if NULL or empty, use
+								 * DEF_PGPORT[_STR]) */
 	char	   *password;		/* password for this host, read from the
 								 * password file; NULL if not sought or not
 								 * found in password file. */
