Enable SSL library detection via PQsslAttribute()

Currently, libpq client code must have a connection handle
before it can query the "library" SSL attribute.  This poses
problems if the client needs to know what SSL library is in
use before constructing a connection string.

Allow PQsslAttribute(NULL, "library") to return the library
in use -- currently, just "OpenSSL" or NULL. The new behavior
is announced with the LIBPQ_HAS_SSL_LIBRARY_DETECTION feature
macro, allowing clients to differentiate between a libpq that
was compiled without SSL support and a libpq that's just too
old to tell.

Author: Jacob Champion <pchampion@vmware.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/4c8b76ef434a96627170a31c3acd33cbfd6e41f1.camel@vmware.com

1 files changed, 20 insertions, 0 deletions

diff --git a/src/interfaces/libpq/t/002_api.pl b/src/interfaces/libpq/t/002_api.pl
new file mode 100644
index 0000000000..7c6c5788a0
--- /dev/null
+++ b/src/interfaces/libpq/t/002_api.pl
@@ -0,0 +1,20 @@
+# Copyright (c) 2022, PostgreSQL Global Development Group
+use strict;
+use warnings;
+
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Test PQsslAttribute(NULL, "library")
+my ($out, $err) = run_command(['testclient', '--ssl']);
+
+if ($ENV{with_ssl} eq 'openssl')
+{
+	is($out, 'OpenSSL', 'PQsslAttribute(NULL, "library") returns "OpenSSL"');
+}
+else
+{
+	is($err, 'SSL is not enabled', 'PQsslAttribute(NULL, "library") returns NULL');
+}
+
+done_testing();