3 files changed, 40 insertions, 19 deletions

diff --git a/man5/opentracker.conf.5 b/man5/opentracker.conf.5
index 9a836ae..2250fe5 100644
--- a/man5/opentracker.conf.5
+++ b/man5/opentracker.conf.5
@@ -90,7 +90,9 @@ technically sits in a range IANA assigns on request.
 
 A cluster of its own is better served by an address out of 239.192.0.0/14,
 which RFC 2365 sets aside for private use. Packets carry a ttl of 1 either
-way and never leave the local link.
+way and never leave the local link. Must be a valid mulitcast address from
+.Pa 224.0.0.0/4
+.
 .Pp
 .It livesync.cluster.node_ip Ar ip_address
 Specifies one trusted IP address for sync between trackers running in a cluster. Can be added more than once.
diff --git a/src/ot_config.c b/src/ot_config.c
index 4064d1b..36f50a6 100644
--- a/src/ot_config.c
+++ b/src/ot_config.c
@@ -382,7 +382,7 @@ static int parse_configfile(char *config_filename) {
 #ifdef WANT_SYNC_LIVE
       case CONFIG_LIVESYNC_CLUSTER_GROUP:
         if (!ip_parse(p, tmpip) || livesync_set_group(tmpip) == -1)
-          goto parse_error;
+          exerr("livesync.cluster.group wants a multicast address, out of 224.0.0.0/4.");
         break;
       case CONFIG_LIVESYNC_CLUSTER_NODE_IP:
         if (!scan_ip6_net(p, &tmpnet))
diff --git a/tests/integration/test_livesync.py b/tests/integration/test_livesync.py
index 52e871f..f4cb2db 100644
--- a/tests/integration/test_livesync.py
+++ b/tests/integration/test_livesync.py
@@ -10,7 +10,7 @@ import struct
 import subprocess
 import unittest
 
-from harness import TRACKER, TrackerTestCase
+from harness import TRACKER, Tracker, TrackerTestCase
 
 # enum { OT_SYNC_PEER4, OT_SYNC_PEER6 } in src/ot_livesync.c
 SYNC_PEER4 = 0
@@ -168,6 +168,13 @@ class LiveSyncUnconfigured(TrackerTestCase):
 
 # RFC 2365 sets 239.192.0.0/14 aside for exactly this kind of use
 OWN_GROUP = "239.192.0.7"
+# A group nothing in this suite ever joins. Deliberately not the default one:
+# other trackers here do join that, on ports the harness picks at random, and
+# a socket bound to the wildcard address shares a port's multicast traffic
+# with anything else on the host that has joined the group it is addressed
+# to. Two clusters sharing a host and a port is pathological in the field but
+# routine in a test suite.
+UNJOINED_GROUP = "239.192.0.99"
 
 
 @unittest.skipUnless(has_livesync(), "this build has no WANT_SYNC_LIVE")
@@ -182,27 +189,39 @@ class LiveSyncGroup(TrackerTestCase):
                                    group=OWN_GROUP)
         self.assertTrue(self.tracker.wait_until(lambda: self.tracker.torrent_count() == 1))
 
-    def test_the_default_group_is_left_alone(self):
-        """A cluster that picked its own group should not hear the one every
-        other opentracker is on."""
+    def test_another_group_is_left_alone(self):
+        """A cluster that picked its own group hears nothing from the others."""
         info_hash = self.hash_for("not-our-group")
-        self.tracker.livesync_send(packet(SYNC_PEER4, [(info_hash, peer4("10.1.3.2", 6881, FLAG_SEEDING))]))
+        self.tracker.livesync_send(packet(SYNC_PEER4, [(info_hash, peer4("10.1.3.2", 6881, FLAG_SEEDING))]),
+                                   group=UNJOINED_GROUP)
         self.assertFalse(self.tracker.wait_until(lambda: self.tracker.torrent_count() != 0, timeout=1))
 
 
 @unittest.skipUnless(has_livesync(), "this build has no WANT_SYNC_LIVE")
-class LiveSyncGroupRefused(TrackerTestCase):
-    """A unicast address is not a group. The line is refused like any other
-    bad config line, which leaves the default standing."""
+class LiveSyncGroupRefused(unittest.TestCase):
+    """A cluster that asked for a group of its own must not quietly end up on
+    the one every other opentracker is on, so a line that does not name a
+    group stops the tracker rather than falling back."""
 
-    config = ("livesync.cluster.group 10.0.0.1\n"
-              "livesync.cluster.listen 127.0.0.1:{livesync_port}\n"
-              "livesync.cluster.node_ip 127.0.0.1\n")
+    def start_with(self, group):
+        return Tracker("livesync.cluster.group %s\n"
+                       "livesync.cluster.listen 127.0.0.1:{livesync_port}\n"
+                       "livesync.cluster.node_ip 127.0.0.1\n" % group)
 
-    def test_the_line_is_refused(self):
-        self.assertIn("Parse error", self.tracker.output())
+    def test_a_unicast_address_stops_the_tracker(self):
+        with self.assertRaises(AssertionError) as caught:
+            self.start_with("10.0.0.1")
+        self.assertIn("multicast address", str(caught.exception))
 
-    def test_and_the_default_group_still_works(self):
-        info_hash = self.hash_for("fallback-group")
-        self.tracker.livesync_send(packet(SYNC_PEER4, [(info_hash, peer4("10.1.3.3", 6881, FLAG_SEEDING))]))
-        self.assertTrue(self.tracker.wait_until(lambda: self.tracker.torrent_count() == 1))
+    def test_so_does_something_that_is_not_an_address(self):
+        with self.assertRaises(AssertionError) as caught:
+            self.start_with("not-an-address")
+        self.assertIn("multicast address", str(caught.exception))
+
+    def test_a_group_at_either_end_of_the_range_is_taken(self):
+        for group in ("224.0.0.1", "239.255.255.255"):
+            tracker = self.start_with(group)
+            try:
+                self.assertEqual(tracker.torrent_count(), 0)
+            finally:
+                tracker.stop()