Avoid picking already-bound TCP ports in kerberos and ldap test suites.

src/test/kerberos and src/test/ldap need to run a private authentication
server of the relevant type, for which they need a free TCP port.
They were just picking a random port number in 48K-64K, which works
except when something's already using the particular port.  Notably,
the probability of failure rises dramatically if one simply runs those
tests in a tight loop, because each test cycle leaves behind a bunch of
high ports that are transiently in TIME_WAIT state.

To fix, split out the code that PostgresNode.pm already had for
identifying a free TCP port number, so that it can be invoked to choose
a port for the KDC or LDAP server.  This isn't 100% bulletproof, since
conceivably something else on the machine could grab the port between
the time we check and the time we actually start the server.  But that's
a pretty short window, so in practice this should be good enough.

Back-patch to v11 where these test suites were added.

Patch by me, reviewed by Andrew Dunstan.

Discussion: https://postgr.es/m/3397.1564872168@sss.pgh.pa.us

1 files changed, 1 insertions, 1 deletions

diff --git a/src/test/ldap/t/001_auth.pl b/src/test/ldap/t/001_auth.pl
index 84a3300d964..47bc090f618 100644
--- a/src/test/ldap/t/001_auth.pl
+++ b/src/test/ldap/t/001_auth.pl
@@ -55,7 +55,7 @@ my $slapd_pidfile = "${TestLib::tmp_check}/slapd.pid";
 my $slapd_logfile = "${TestLib::tmp_check}/slapd.log";
 my $ldap_conf     = "${TestLib::tmp_check}/ldap.conf";
 my $ldap_server   = 'localhost';
-my $ldap_port     = int(rand() * 16384) + 49152;
+my $ldap_port     = get_free_port();
 my $ldaps_port    = $ldap_port + 1;
 my $ldap_url      = "ldap://$ldap_server:$ldap_port";
 my $ldaps_url     = "ldaps://$ldap_server:$ldaps_port";