Refactor routine to find single log content pattern in TAP tests

The same routine to check if a specific pattern can be found in the
server logs was copied over four different test scripts.  This refactors
the whole to use a single routine located in PostgreSQL::Test::Cluster,
named log_contains, to grab the contents of the server logs and check
for a specific pattern.

On HEAD, the code previously used assumed that slurp_file() could not
handle an undefined offset, setting it to zero, but slurp_file() does
do an extra fseek() before retrieving the log contents only if an offset
is defined.  In two places, the test was retrieving the full log
contents with slurp_file() after calling substr() to apply an offset,
ignoring that slurp_file() would be able to handle that.

Backpatch all the way down to ease the introduction of new tests that
could rely on the new routine.

Author: Vignesh C
Reviewed-by: Andrew Dunstan, Dagfinn Ilmari Mannsåker, Michael Paquier
Discussion: https://postgr.es/m/CALDaNm0YSiLpjCmajwLfidQrFOrLNKPQir7s__PeVvh9U3uoTQ@mail.gmail.com
Backpatch-through: 11

src/test/perl/PostgresNode.pm

@@ -2470,6 +2470,21 @@ sub log_check
 
 =pod
 
+=item $node->log_contains(pattern, offset)
+
+Find pattern in logfile of node after offset byte.
+
+=cut
+
+sub log_contains
+{
+	my ($self, $pattern, $offset) = @_;
+
+	return TestLib::slurp_file($self->logfile, $offset) =~ m/$pattern/;
+}
+
+=pod
+
 =item $node->run_log(...)
 
 Runs a shell command like TestLib::run_log, but with connection parameters set

src/test/recovery/t/019_replslot_limit.pl

@@ -168,8 +168,7 @@ $node_primary->wait_for_catchup($node_standby, 'replay', $start_lsn);
 
 $node_standby->stop;
 
-ok( !find_in_log(
+ok( !$node_standby->log_contains(
-		$node_standby,
 		"requested WAL segment [0-9A-F]+ has already been removed"),
 	'check that required WAL segments are still available');
 
@@ -191,8 +190,7 @@ $node_primary->safe_psql('postgres', "CHECKPOINT;");
 my $invalidated = 0;
 for (my $i = 0; $i < 10000; $i++)
 {
-	if (find_in_log(
+	if ($node_primary->log_contains(
-			$node_primary,
 			"invalidating slot \"rep1\" because its restart_lsn [0-9A-F/]+ exceeds max_slot_wal_keep_size",
 			$logstart))
 	{
@@ -215,7 +213,7 @@ is($result, "rep1|f|t|lost|",
 my $checkpoint_ended = 0;
 for (my $i = 0; $i < 10000; $i++)
 {
-	if (find_in_log($node_primary, "checkpoint complete: ", $logstart))
+	if ($node_primary->log_contains("checkpoint complete: ", $logstart))
 	{
 		$checkpoint_ended = 1;
 		last;
@@ -245,8 +243,7 @@ $node_standby->start;
 my $failed = 0;
 for (my $i = 0; $i < 10000; $i++)
 {
-	if (find_in_log(
+	if ($node_standby->log_contains(
-			$node_standby,
 			"requested WAL segment [0-9A-F]+ has already been removed",
 			$logstart))
 	{
@@ -351,8 +348,7 @@ advance_wal($node_primary3, 2);
 my $max_attempts = $TestLib::timeout_default;
 while ($max_attempts-- >= 0)
 {
-	if (find_in_log(
+	if ($node_primary3->log_contains(
-			$node_primary3,
 			"terminating process $senderpid to release replication slot \"rep3\"",
 			$logstart))
 	{
@@ -374,8 +370,7 @@ $node_primary3->poll_query_until('postgres',
 $max_attempts = $TestLib::timeout_default;
 while ($max_attempts-- >= 0)
 {
-	if (find_in_log(
+	if ($node_primary3->log_contains(
-			$node_primary3,
 			'invalidating slot "rep3" because its restart_lsn', $logstart))
 	{
 		ok(1, "slot invalidation logged");
@@ -412,17 +407,3 @@ sub get_log_size
 
 	return (stat $node->logfile)[7];
 }
-
-# find $pat in logfile of $node after $off-th byte
-sub find_in_log
-{
-	my ($node, $pat, $off) = @_;
-
-	$off = 0 unless defined $off;
-	my $log = TestLib::slurp_file($node->logfile);
-	return 0 if (length($log) <= $off);
-
-	$log = substr($log, $off);
-
-	return $log =~ m/$pat/;
-}

src/test/recovery/t/033_replay_tsp_drops.pl

@@ -132,21 +132,11 @@ while ($max_attempts-- >= 0)
 {
 	last
 	  if (
-		find_in_log(
+		$node_standby->log_contains(
-			$node_standby, qr!WARNING: ( [A-Z0-9]+:)? creating missing directory: pg_tblspc/!,
+			qr!WARNING: ( [A-Z0-9]+:)? creating missing directory: pg_tblspc/!,
 			$logstart));
 	usleep(100_000);
 }
 ok($max_attempts > 0, "invalid directory creation is detected");
 
 done_testing();
-
-# find $pat in logfile of $node after $off-th byte
-sub find_in_log
-{
-	my ($node, $pat, $off) = @_;
-
-	my $log = PostgreSQL::Test::Utils::slurp_file($node->logfile, $off);
-
-	return $log =~ m/$pat/;
-}