PQconninfo() doesn't return anything for host=/socket/directory

Hi,

Programs that use PQconninfo() to build a new connection string, like in
my case pg_basebackup --write-recovery-conf, fail to do anything for
non-default socket directories leading to the newly built connection
string being unusable for connecting.
The reason for that is the following tidbit from
fe-connect.c:connectOptions2()

/*
* Allow unix socket specification in the host name
*/
if (conn->pghost && is_absolute_path(conn->pghost))
{
if (conn->pgunixsocket)
free(conn->pgunixsocket);
conn->pgunixsocket = conn->pghost;
conn->pghost = NULL;
}

This strikes me as unfortunate. Note that PQhost() does the right
thing...

I've attached a hack that fixes this, but I pretty much dislike the
direction it's going. Maybe the better fix is to simply not unset pghost
above and make connectDBStart() more intelligent?

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services