Subject: [PATCH v1] BackgroundPsql: Fix potential for lost errors on windows

From: Andres Freund <[email-masked]>
Date: Thu, 13 Feb 2025 10:09:49 -0500

Author:
Reviewed-by:
Discussion: https://postgr.es/m/
Backpatch:
---
 .../perl/PostgreSQL/Test/BackgroundPsql.pm    | 55 +++++++++++++++----
 1 file changed, 43 insertions(+), 12 deletions(-)

diff --git a/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm b/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm
index dbfd82e4fac..7e76845307d 100644
--- a/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm
+++ b/src/test/perl/PostgreSQL/Test/BackgroundPsql.pm
@@ -89,7 +89,8 @@ sub new
 		'stdin' => '',
 		'stdout' => '',
 		'stderr' => '',
-		'query_timer_restart' => undef
+		'query_timer_restart' => undef,
+		'query_cnt' => 1,
 	};
 	my $run;
 
@@ -219,27 +220,57 @@ sub query
 	my ($self, $query) = @_;
 	my $ret;
 	my $output;
+	my $query_cnt = $self->{query_cnt}++;
+
 	local $Test::Builder::Level = $Test::Builder::Level + 1;
 
-	note "issuing query via background psql: $query";
+	note "issuing query $query_cnt via background psql: $query";
 
 	$self->{timeout}->start() if (defined($self->{query_timer_restart}));
 
 	# Feed the query to psql's stdin, followed by \n (so psql processes the
 	# line), by a ; (so that psql issues the query, if it doesn't include a ;
-	# itself), and a separator echoed with \echo, that we can wait on.
-	my $banner = "background_psql: QUERY_SEPARATOR";
-	$self->{stdin} .= "$query\n;\n\\echo $banner\n";
-
-	pump_until($self->{run}, $self->{timeout}, \$self->{stdout}, qr/$banner/);
+	# itself), and a separator echoed both with \echo and \warn, that we can
+	# wait on.
+	#
+	# To avoid somehow confusing the separator from separately issued queries,
+	# and to make it easier to debug, we include a per-psql query counter in
+	# the separator.
+	#
+	# We need both \echo (printing to stdout) and \warn (printing to stderr),
+	# because on windows we can get data on stdout before seeing data on
+	# stderr (or vice versa), even if psql printed them in the opposite
+	# order. We therefore wait on both.
+	#
+	# We need to match for the newline, because we try to remove it below, and
+	# it's possible to consume just the input *without* the newline. In
+	# interactive psql we emit \r\n, so we need to allow for that. Also need
+	# to be careful that we don't e.g. match the echoed \echo command, rather
+	# than its output.
+	my $banner = "background_psql: QUERY_SEPARATOR $query_cnt";
+	my $banner_match = qr/(^|\n)$banner\r?\n/;
+	$self->{stdin} .= "$query\n;\n\\echo $banner\n\\warn $banner\n";
+	pump_until(
+		$self->{run}, $self->{timeout},
+		\$self->{stdout}, qr/$banner_match/);
+	pump_until(
+		$self->{run}, $self->{timeout},
+		\$self->{stderr}, qr/$banner_match/);
 
 	die "psql query timed out" if $self->{timeout}->is_expired;
+
+	note "query returned:\n",
+	  explain {
+		stdout => $self->{stdout},
+		stderr => $self->{stderr},
+	  };
+
+	# Remove banner from stdout and stderr, our caller doesn't care.  The
+	# first newline is optional, as there would not be one if consuming an
+	# empty query result.
 	$output = $self->{stdout};
-
-	# Remove banner again, our caller doesn't care.  The first newline is
-	# optional, as there would not be one if consuming an empty query
-	# result.
-	$output =~ s/\n?$banner\n$//s;
+	$output =~ s/$banner_match//;
+	$self->{stderr} =~ s/$banner_match//;
 
 	# clear out output for the next query
 	$self->{stdout} = '';
-- 
2.48.1.76.g4e746b1a31.dirty

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