new file mode 100644
--- /dev/null
+++ b/h2_priority.t
@@ -0,0 +1,446 @@
+#!/usr/bin/perl
+
+# (C) Sergey Kandaurov
+# (C) Nginx, Inc.
+
+# Tests for HTTP/2 protocol with priority.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+
+BEGIN { use FindBin; chdir($FindBin::Bin); }
+
+use lib 'lib';
+use Test::Nginx;
+use Test::Nginx::HTTP2 qw/ :DEFAULT :frame /;
+
+###############################################################################
+
+select STDERR; $| = 1;
+select STDOUT; $| = 1;
+
+my $t = Test::Nginx->new()->has(qw/http http_v2/)->plan(20)
+	->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+daemon off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    server {
+        listen       127.0.0.1:8080 http2;
+        server_name  localhost;
+    }
+}
+
+EOF
+
+$t->run();
+
+# file size is slightly beyond initial window size: 2**16 + 80 bytes
+
+$t->write_file('t1.html',
+	join('', map { sprintf "X%04dXXX", $_ } (1 .. 8202)));
+
+$t->write_file('t2.html', 'SEE-THIS');
+
+###############################################################################
+
+# stream muliplexing + PRIORITY frames
+
+my $sess = new_session();
+my $sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+my $sid2 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_priority($sess, 0, $sid);
+h2_priority($sess, 255, $sid2);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+my $frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 }
+]);
+
+my @data = grep { $_->{type} eq "DATA" } @$frames;
+is(join(' ', map { $_->{sid} } @data), "$sid2 $sid", 'weight - PRIORITY 1');
+
+# and vice versa
+
+$sess = new_session();
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_priority($sess, 255, $sid);
+h2_priority($sess, 0, $sid2);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 }
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+is(join(' ', map { $_->{sid} } @data), "$sid $sid2", 'weight - PRIORITY 2');
+
+# stream muliplexing + HEADERS PRIORITY flag
+
+$sess = new_session();
+$sid = new_stream($sess, { path => '/t1.html', prio => 0 });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html', prio => 255 });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 }
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+my $sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid2 $sid", 'weight - HEADERS PRIORITY 1');
+
+# and vice versa
+
+$sess = new_session();
+$sid = new_stream($sess, { path => '/t1.html', prio => 255 });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html', prio => 0 });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 }
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+$sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid $sid2", 'weight - HEADERS PRIORITY 2');
+
+# 5.3.1.  Stream Dependencies
+
+# PRIORITY frame
+
+$sess = new_session();
+
+h2_priority($sess, 16, 3, 0);
+h2_priority($sess, 16, 1, 3);
+
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 },
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+$sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid2 $sid", 'dependency - PRIORITY 1');
+
+# and vice versa
+
+$sess = new_session();
+
+h2_priority($sess, 16, 1, 0);
+h2_priority($sess, 16, 3, 1);
+
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 },
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+$sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid $sid2", 'dependency - PRIORITY 2');
+
+# PRIORITY - self dependency
+
+# 5.3.1.  Stream Dependencies
+#   A stream cannot depend on itself.  An endpoint MUST treat this as a
+#   stream error of type PROTOCOL_ERROR.
+
+$sess = new_session();
+$sid = new_stream($sess);
+h2_read($sess, all => [{ sid => $sid, fin => 1 }]);
+
+h2_priority($sess, 0, $sid, $sid);
+$frames = h2_read($sess, all => [{ type => 'RST_STREAM' }]);
+
+my ($frame) = grep { $_->{type} eq "RST_STREAM" } @$frames;
+is($frame->{sid}, $sid, 'dependency - PRIORITY self - RST_STREAM');
+is($frame->{code}, 1, 'dependency - PRIORITY self - PROTOCOL_ERROR');
+
+# HEADERS PRIORITY flag, reprioritize prior PRIORITY frame records
+
+$sess = new_session();
+
+h2_priority($sess, 16, 1, 0);
+h2_priority($sess, 16, 3, 0);
+
+$sid = new_stream($sess, { path => '/t1.html', dep => 3 });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 },
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+$sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid2 $sid", 'dependency - HEADERS PRIORITY 1');
+
+# and vice versa
+
+$sess = new_session();
+
+h2_priority($sess, 16, 1, 0);
+h2_priority($sess, 16, 3, 0);
+
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html', dep => 1 });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+h2_window($sess, 2**17, $sid);
+h2_window($sess, 2**17, $sid2);
+h2_window($sess, 2**17);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 },
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+$sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid $sid2", 'dependency - HEADERS PRIORITY 2');
+
+# HEADERS - self dependency
+
+$sess = new_session();
+$sid = new_stream($sess, { dep => 1 });
+$frames = h2_read($sess, all => [{ type => 'RST_STREAM' }]);
+
+($frame) = grep { $_->{type} eq "RST_STREAM" } @$frames;
+is($frame->{sid}, $sid, 'dependency - HEADERS self - RST_STREAM');
+is($frame->{code}, 1, 'dependency - HEADERS self - PROTOCOL_ERROR');
+
+# PRIORITY frame, weighted dependencies
+
+$sess = new_session();
+
+h2_priority($sess, 16, 5, 0);
+h2_priority($sess, 255, 1, 5);
+h2_priority($sess, 0, 3, 5);
+
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+my $sid3 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid3, fin => 0x4 }]);
+
+h2_window($sess, 2**16, 1);
+h2_window($sess, 2**16, 3);
+h2_window($sess, 2**16, 5);
+h2_window($sess, 2**16);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 },
+	{ sid => $sid3, fin => 1 },
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+$sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid3 $sid $sid2", 'weighted dependency - PRIORITY 1');
+
+# and vice versa
+
+$sess = new_session();
+
+h2_priority($sess, 16, 5, 0);
+h2_priority($sess, 0, 1, 5);
+h2_priority($sess, 255, 3, 5);
+
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid2, fin => 0x4 }]);
+
+$sid3 = new_stream($sess, { path => '/t2.html' });
+h2_read($sess, all => [{ sid => $sid3, fin => 0x4 }]);
+
+h2_window($sess, 2**16, 1);
+h2_window($sess, 2**16, 3);
+h2_window($sess, 2**16, 5);
+h2_window($sess, 2**16);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid2, fin => 1 },
+	{ sid => $sid3, fin => 1 },
+]);
+
+@data = grep { $_->{type} eq "DATA" } @$frames;
+$sids = join ' ', map { $_->{sid} } @data;
+is($sids, "$sid3 $sid2 $sid", 'weighted dependency - PRIORITY 2');
+
+# PRIORITY - reprioritization with circular dependency - after [3] removed
+# initial dependency tree:
+# 1 <- [3] <- 5
+
+$sess = new_session();
+
+h2_window($sess, 2**18);
+
+h2_priority($sess, 16, 1, 0);
+h2_priority($sess, 16, 3, 1);
+h2_priority($sess, 16, 5, 3);
+
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid2, length => 2**16 - 1 }]);
+
+$sid3 = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid3, length => 2**16 - 1 }]);
+
+h2_window($sess, 2**16, $sid2);
+
+$frames = h2_read($sess, all => [{ sid => $sid2, fin => 1 }]);
+$sids = join ' ', map { $_->{sid} } grep { $_->{type} eq "DATA" } @$frames;
+is($sids, $sid2, 'removed dependency');
+
+for (1 .. 40) {
+	h2_read($sess, all => [{ sid => new_stream($sess), fin => 1 }]);
+}
+
+# make circular dependency
+# 1 <- 5 -- current dependency tree before reprioritization
+# 5 <- 1
+# 1 <- 5
+
+h2_priority($sess, 16, 1, 5);
+h2_priority($sess, 16, 5, 1);
+
+h2_window($sess, 2**16, $sid);
+h2_window($sess, 2**16, $sid3);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid, fin => 1 },
+	{ sid => $sid3, fin => 1 },
+]);
+
+($frame) = grep { $_->{type} eq "DATA" && $_->{sid} == $sid } @$frames;
+is($frame->{length}, 81, 'removed dependency - first stream');
+
+($frame) = grep { $_->{type} eq "DATA" && $_->{sid} == $sid3 } @$frames;
+is($frame->{length}, 81, 'removed dependency - last stream');
+
+# PRIORITY - reprioritization with circular dependency - exclusive [5]
+# 1 <- [5] <- 3
+
+$sess = new_session();
+
+h2_window($sess, 2**18);
+
+h2_priority($sess, 16, 1, 0);
+h2_priority($sess, 16, 3, 1);
+h2_priority($sess, 16, 5, 1, excl => 1);
+
+$sid = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid, length => 2**16 - 1 }]);
+
+$sid2 = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid2, length => 2**16 - 1 }]);
+
+$sid3 = new_stream($sess, { path => '/t1.html' });
+h2_read($sess, all => [{ sid => $sid3, length => 2**16 - 1 }]);
+
+h2_window($sess, 2**16, $sid);
+
+$frames = h2_read($sess, all => [{ sid => $sid, fin => 1 }]);
+$sids = join ' ', map { $_->{sid} } grep { $_->{type} eq "DATA" } @$frames;
+is($sids, $sid, 'exclusive dependency - parent removed');
+
+# make circular dependency
+# 5 <- 3 -- current dependency tree before reprioritization
+# 3 <- 5
+
+h2_priority($sess, 16, 5, 3);
+
+h2_window($sess, 2**16, $sid2);
+h2_window($sess, 2**16, $sid3);
+
+$frames = h2_read($sess, all => [
+	{ sid => $sid2, fin => 1 },
+	{ sid => $sid3, fin => 1 },
+]);
+
+($frame) = grep { $_->{type} eq "DATA" && $_->{sid} == $sid2 } @$frames;
+is($frame->{length}, 81, 'exclusive dependency - first stream');
+
+($frame) = grep { $_->{type} eq "DATA" && $_->{sid} == $sid3 } @$frames;
+is($frame->{length}, 81, 'exclusive dependency - last stream');
+
+###############################################################################