--- a/grpc_request_buffering.t
+++ b/grpc_request_buffering.t
@@ -23,7 +23,7 @@ use Test::Nginx::HTTP2;
 select STDERR; $| = 1;
 select STDOUT; $| = 1;
 
-my $t = Test::Nginx->new()->has(qw/http http_v2 grpc mirror/);
+my $t = Test::Nginx->new()->has(qw/http http_v2 grpc mirror proxy/);
 
 $t->write_file_expand('nginx.conf', <<'EOF');
 
@@ -39,6 +39,7 @@ http {
 
     server {
         listen       127.0.0.1:8080 http2;
+        listen       127.0.0.1:8082;
         server_name  localhost;
 
         location /mirror { }
@@ -48,12 +49,22 @@ http {
             add_header X-Body $request_body;
             mirror /mirror;
         }
+
+        location /proxy {
+            proxy_pass http://127.0.0.1:8082/mirror;
+            proxy_intercept_errors on;
+            error_page 404 = @fallback;
+        }
+
+        location @fallback {
+            grpc_pass 127.0.0.1:8081;
+        }
     }
 }
 
 EOF
 
-$t->try_run('no grpc')->plan(9);
+$t->try_run('no grpc')->plan(12);
 
 ###############################################################################
 
@@ -77,6 +88,28 @@ is($frame->{flags}, 1, 'request - DATA f
 ($frame) = grep { $_->{type} eq "HEADERS" } @$frames;
 is($frame->{headers}{'x-body'}, 'Hello', 'request body in memory');
 
+# expect body cleanup is disabled with preserve_output (ticket #1565).
+# after request body first bytes were proxied on behalf of initial window size,
+# send response header from upstream, this leads to body cleanup code path
+
+$frames = $f->{http_start}('/proxy');
+is(eval(join '+', map { $_->{length} } grep { $_->{type} eq "DATA" } @$frames),
+	65535, 'preserve_output - first body bytes');
+
+TODO: {
+local $TODO = 'not yet' unless $t->has_version('1.15.1');
+
+$frames = $f->{http_end}();
+is(eval(join '+', map { $_->{length} } grep { $_->{type} eq "DATA" } @$frames),
+	465, 'preserve_output - last body bytes');
+
+like(`grep -F '[crit]' ${\($t->testdir())}/error.log`, qr/^$/s, 'no crits');
+
+}
+
+$t->todo_alerts() if $t->read_file('nginx.conf') =~ /sendfile on/
+	and !$t->has_version('1.15.1');
+
 ###############################################################################
 
 sub grpc {
@@ -94,12 +127,13 @@ sub grpc {
 	$f->{http_start} = sub {
 		($uri, my %extra) = @_;
 		$s = Test::Nginx::HTTP2->new() if !defined $s;
-		$s->new_stream({ body => 'Hello', headers => [
+		my ($body) = $uri eq '/proxy' ? 'Hello' x 13200 : 'Hello';
+		$s->new_stream({ body => $body, headers => [
 			{ name => ':method', value => 'POST', mode => 0 },
 			{ name => ':scheme', value => 'http', mode => 0 },
 			{ name => ':path', value => $uri },
 			{ name => ':authority', value => 'localhost' },
-			{ name => 'content-length', value => '5' }]});
+			{ name => 'content-length', value => length($body) }]});
 
 		if (!$extra{reuse}) {
 			eval {
@@ -124,7 +158,9 @@ sub grpc {
 				pure => 1, preface => "") or return;
 		}
 
-		my $frames = $c->read(all => [{ fin => 1 }]);
+		my $frames = $uri eq '/proxy'
+			? $c->read(all => [{ length => 65535 }])
+			: $c->read(all => [{ fin => 1 }]);
 
 		if (!$extra{reuse}) {
 			$c->h2_settings(0);
@@ -140,6 +176,15 @@ sub grpc {
 			{ name => ':status', value => '200', mode => 0 },
 			{ name => 'content-type', value => 'application/grpc' },
 		]}, $sid);
+
+		# reopen window for request body after response HEADERS is sent
+
+		if ($uri eq '/proxy') {
+			$c->h2_window(2**16, $sid);
+			$c->h2_window(2**16);
+			return $c->read(all => [{ sid => $sid, fin => 1 }]);
+		}
+
 		$c->h2_body('Hello world', { body_more => 1 });
 		$c->new_stream({ headers => [
 			{ name => 'grpc-status', value => '0', mode => 2 },