Diagnose incompatible OpenLDAP versions during build and test.

With OpenLDAP versions 2.4.24 through 2.4.31, inclusive, PostgreSQL
backends can crash at exit.  Raise a warning during "configure" based on
the compile-time OpenLDAP version number, and test the crash scenario in
the dblink test suite.  Back-patch to 9.0 (all supported versions).

contrib/dblink/Makefile

@@ -7,7 +7,9 @@ SHLIB_LINK = $(libpq)
 
 DATA_built = dblink.sql 
 DATA = uninstall_dblink.sql 
-REGRESS = dblink
+REGRESS = paths dblink
+REGRESS_OPTS = --dbname=$(CONTRIB_TESTDB) --dlpath=$(top_builddir)/src/test/regress
+EXTRA_CLEAN = sql/paths.sql expected/paths.out
 
 
 # the db name is hard-coded in the tests

contrib/dblink/expected/.gitignore

@@ -0,0 +1 @@
+/paths.out

contrib/dblink/expected/dblink.out

@@ -115,6 +115,29 @@ SELECT *
 FROM dblink('SELECT * FROM foo') AS t(a int, b text, c text[])
 WHERE t.a > 7;
 ERROR:  connection not available
+-- The first-level connection's backend will crash on exit given OpenLDAP
+-- [2.4.24, 2.4.31].  We won't see evidence of any crash until the victim
+-- process terminates and the postmaster responds.  If process termination
+-- entails writing a core dump, that can take awhile.  Wait for the process to
+-- vanish.  At that point, the postmaster has called waitpid() on the crashed
+-- process, and it will accept no new connections until it has reinitialized
+-- the cluster.  (We can't exploit pg_stat_activity, because the crash happens
+-- after the backend updates shared memory to reflect its impending exit.)
+DO $pl$
+BEGIN
+	PERFORM wait_pid(crash_pid)
+	FROM dblink('dbname=contrib_regression', $$
+		SELECT pg_backend_pid() FROM dblink(
+			'service=test_ldap dbname=contrib_regression',
+			-- This string concatenation is a hack to shoehorn a
+			-- set_pgservicefile call into the SQL statement.
+			'SELECT 1' || set_pgservicefile('pg_service.conf')
+		) t(c int)
+	$$) AS t(crash_pid int);
+EXCEPTION WHEN sqlclient_unable_to_establish_sqlconnection THEN
+	-- Expect "syntax error in service file" in a non-LDAP build.
+END
+$pl$;
 -- create a persistent connection
 SELECT dblink_connect('dbname=contrib_regression');
  dblink_connect 

contrib/dblink/input/paths.source

@@ -0,0 +1,14 @@
+-- Initialization that requires path substitution.
+
+CREATE FUNCTION putenv(text)
+   RETURNS void
+   AS '@libdir@/regress@DLSUFFIX@', 'regress_putenv'
+   LANGUAGE C STRICT;
+
+CREATE FUNCTION wait_pid(int)
+   RETURNS void
+   AS '@libdir@/regress@DLSUFFIX@'
+   LANGUAGE C STRICT;
+
+CREATE FUNCTION set_pgservicefile(text) RETURNS void LANGUAGE SQL
+    AS $$SELECT putenv('PGSERVICEFILE=@abs_srcdir@/' || $1)$$;

contrib/dblink/output/paths.source

@@ -0,0 +1,11 @@
+-- Initialization that requires path substitution.
+CREATE FUNCTION putenv(text)
+   RETURNS void
+   AS '@libdir@/regress@DLSUFFIX@', 'regress_putenv'
+   LANGUAGE C STRICT;
+CREATE FUNCTION wait_pid(int)
+   RETURNS void
+   AS '@libdir@/regress@DLSUFFIX@'
+   LANGUAGE C STRICT;
+CREATE FUNCTION set_pgservicefile(text) RETURNS void LANGUAGE SQL
+    AS $$SELECT putenv('PGSERVICEFILE=@abs_srcdir@/' || $1)$$;

contrib/dblink/pg_service.conf

@@ -0,0 +1,7 @@
+# pg_service.conf for minimally exercising libpq use of LDAP.
+
+# Having failed to reach an LDAP server, libpq essentially ignores the
+# "service=test_ldap" in its connection string.  Contact the "discard"
+# service; the test works whether or not it answers.
+[test_ldap]
+ldap://127.0.0.1:9/base?attribute?one?filter

contrib/dblink/sql/.gitignore

@@ -0,0 +1 @@
+/paths.sql

contrib/dblink/sql/dblink.sql

@@ -78,6 +78,30 @@ SELECT *
 FROM dblink('SELECT * FROM foo') AS t(a int, b text, c text[])
 WHERE t.a > 7;
 
+-- The first-level connection's backend will crash on exit given OpenLDAP
+-- [2.4.24, 2.4.31].  We won't see evidence of any crash until the victim
+-- process terminates and the postmaster responds.  If process termination
+-- entails writing a core dump, that can take awhile.  Wait for the process to
+-- vanish.  At that point, the postmaster has called waitpid() on the crashed
+-- process, and it will accept no new connections until it has reinitialized
+-- the cluster.  (We can't exploit pg_stat_activity, because the crash happens
+-- after the backend updates shared memory to reflect its impending exit.)
+DO $pl$
+BEGIN
+	PERFORM wait_pid(crash_pid)
+	FROM dblink('dbname=contrib_regression', $$
+		SELECT pg_backend_pid() FROM dblink(
+			'service=test_ldap dbname=contrib_regression',
+			-- This string concatenation is a hack to shoehorn a
+			-- set_pgservicefile call into the SQL statement.
+			'SELECT 1' || set_pgservicefile('pg_service.conf')
+		) t(c int)
+	$$) AS t(crash_pid int);
+EXCEPTION WHEN sqlclient_unable_to_establish_sqlconnection THEN
+	-- Expect "syntax error in service file" in a non-LDAP build.
+END
+$pl$;
+
 -- create a persistent connection
 SELECT dblink_connect('dbname=contrib_regression');