From b081c35a8b6d3bb44d0f4d8f003a924923ec5f48 Mon Sep 17 00:00:00 2001
From: Fujii Masao <fujii@postgresql.org>
Date: Fri, 28 Nov 2025 10:50:02 +0900
Subject: [PATCH v4 3/4] Add test for pg_recvlogical reconnection behavior.

This commit adds a test to verify that data already received and flushed by
pg_recvlogical is not streamed again even after the connection is lost,
reestablished, and logical replication is restarted.

Author: Mircea Cadariu <cadariu.mircea@gmail.com>
Co-authored-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/CAHGQGwFeTymZQ7RLvMU6WuDGar8bUQCazg=VOfA-9GeBkg-FzA@mail.gmail.com
---
 src/bin/pg_basebackup/t/030_pg_recvlogical.pl | 94 +++++++++++++++++++
 1 file changed, 94 insertions(+)

diff --git a/src/bin/pg_basebackup/t/030_pg_recvlogical.pl b/src/bin/pg_basebackup/t/030_pg_recvlogical.pl
index e4ef44c4d4f..063ad96b9be 100644
--- a/src/bin/pg_basebackup/t/030_pg_recvlogical.pl
+++ b/src/bin/pg_basebackup/t/030_pg_recvlogical.pl
@@ -6,6 +6,7 @@ use warnings FATAL => 'all';
 use PostgreSQL::Test::Utils;
 use PostgreSQL::Test::Cluster;
 use Test::More;
+use Config;
 
 program_help_ok('pg_recvlogical');
 program_version_ok('pg_recvlogical');
@@ -151,4 +152,97 @@ my $result = $node->safe_psql('postgres',
 );
 is($result, 't', "failover is enabled for the new slot");
 
+# Test that when pg_recvlogical reconnects, it does not write duplicate
+# records to the output file
+my $outfile = $node->basedir . '/reconnect.out';
+
+$node->command_ok(
+	[
+		'pg_recvlogical',
+		'--slot' => 'reconnect_test',
+		'--dbname' => $node->connstr('postgres'),
+		'--create-slot',
+	],
+	'slot created for reconnection test');
+
+# Insert the first record for this test
+$node->safe_psql('postgres', 'INSERT INTO test_table VALUES (1)');
+
+my @pg_recvlogical_cmd = (
+	'pg_recvlogical',
+	'--slot' => 'reconnect_test',
+	'--dbname' => $node->connstr('postgres'),
+	'--start',
+	'--file' => $outfile,
+	'--fsync-interval' => '1',
+	'--status-interval' => '100',
+	'--verbose');
+
+# On Windows, specify --endpos so pg_recvlogical can terminate, since
+# signals cannot be used. Use the current LSN plus 32MB as endpos, which
+# would be sufficient to cover the WAL generated by the test INSERTs.
+if ($Config{osname} eq 'MSWin32')
+{
+	$nextlsn = $node->safe_psql('postgres',
+		"SELECT pg_current_wal_insert_lsn() + pg_size_bytes('32MB')");
+	chomp($nextlsn);
+	push(@pg_recvlogical_cmd, '--endpos' => $nextlsn);
+}
+
+my ($stdout, $stderr);
+my $recv = IPC::Run::start(
+	[@pg_recvlogical_cmd],
+	'>' => \$stdout,
+	'2>' => \$stderr);
+
+# Wait for pg_recvlogical to receive and write the first INSERT
+my $first_ins = wait_for_file($outfile, qr/INSERT/);
+
+# Terminate the walsender to force pg_recvlogical to reconnect
+my $backend_pid = $node->safe_psql('postgres',
+	"SELECT active_pid FROM pg_replication_slots WHERE slot_name = 'reconnect_test'"
+);
+$node->safe_psql('postgres', "SELECT pg_terminate_backend($backend_pid)");
+
+# Wait for pg_recvlogical to reconnect
+$node->poll_query_until('postgres',
+	"SELECT active_pid IS NOT NULL AND active_pid != $backend_pid FROM pg_replication_slots WHERE slot_name = 'reconnect_test'"
+) or die "Timed out while waiting for pg_recvlogical to reconnect";
+
+# Insert the second record for this test
+$node->safe_psql('postgres', 'INSERT INTO test_table VALUES (2)');
+
+# Wait for pg_recvlogical to receive and write the second INSERT
+wait_for_file($outfile, qr/INSERT/, $first_ins);
+
+# Terminate pg_recvlogical by generating WAL until the current position
+# reaches the specified --endpos on Windows, or by sending a TERM signal
+# on other platforms.
+if ($Config{osname} eq 'MSWin32')
+{
+	$node->poll_query_until('postgres',
+		"SELECT pg_switch_wal() >= '$nextlsn' FROM pg_logical_emit_message(false, 'test', 'test')"
+	) or die "Timed out while waiting for pg_recvlogical to end";
+}
+else
+{
+	$recv->signal('TERM');
+}
+
+$recv->finish();
+
+my $outfiledata = slurp_file("$outfile");
+my $count = (() = $outfiledata =~ /INSERT/g);
+cmp_ok($count, '==', 2,
+	'pg_recvlogical has received and written two INSERTs');
+
+$node->command_ok(
+	[
+		'pg_recvlogical',
+		'--slot' => 'reconnect_test',
+		'--dbname' => $node->connstr('postgres'),
+		'--drop-slot'
+	],
+	'reconnect_test slot dropped');
+
 done_testing();
-- 
2.51.2