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

Commits ffa2e4670 and 52a10224e 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
index 49eec3e83564978a871d9ec432a51de82caf7784..b288d346f92682e106957c4145310479fbb0da97 100644 (file)
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3654,6 +3654,13 @@ keep_going:                      /* We will come back to here until there is
                /* 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;