Clear conn->errorMessage at successful completion of PQconnectdb().

tglsfdc · tglsfdc · commit 896a0c44f93b · 2021-09-13T16:53:11.000-04:00
Commits ffa2e46 and 52a1022 caused libpq's connection-establishment functions to usually leave a nonempty string in the connection's errorMessage buffer, even after a successful connection. While that was intentional on my part, more sober reflection says that it wasn't a great idea: the string would be a bit confusing. Also this broke at least one application that checked for connection success by examining the errorMessage, instead of using PQstatus() as documented. Let's clear the buffer at success exit, restoring the pre-v14 behavior. Discussion: https://postgr.es/m/4170264.1620321747@sss.pgh.pa.us
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
@@ -3658,6 +3658,13 @@ PQconnectPoll(PGconn *conn)
 				/* We can release the address list now. */
 				release_conn_addrinfo(conn);
 
+				/*
+				 * Contents of conn->errorMessage are no longer interesting
+				 * (and it seems some clients expect it to be empty after a
+				 * successful connection).
+				 */
+				resetPQExpBuffer(&conn->errorMessage);
+
 				/* We are open for business! */
 				conn->status = CONNECTION_OK;
 				return PGRES_POLLING_OK;
