Fix an off-by-one bug in presence event stream pagination; this might be responsible for any number of bug reports

synapse/handlers/presence.py

@@ -838,7 +838,7 @@ class PresenceEventSource(object):
         updates = []
         # TODO(paul): use a DeferredList ? How to limit concurrency.
         for observed_user in cachemap.keys():
-            if not (to_key < cachemap[observed_user].serial < from_key):
+            if not (to_key < cachemap[observed_user].serial <= from_key):
                 continue
 
             if (yield self.is_visible(observer_user, observed_user)):

tests/handlers/test_presence.py

@@ -29,6 +29,7 @@ from synapse.server import HomeServer
 from synapse.api.constants import PresenceState
 from synapse.api.errors import SynapseError
 from synapse.handlers.presence import PresenceHandler, UserPresenceCache
+from synapse.streams.config import SourcePaginationConfig
 
 
 OFFLINE = PresenceState.OFFLINE
@@ -676,6 +677,21 @@ class PresencePushTestCase(unittest.TestCase):
             msg="Presence event should be visible to self-reflection"
         )
 
+        config = SourcePaginationConfig(from_key=1, to_key=0)
+        (chunk, _) = yield self.event_source.get_pagination_rows(
+            self.u_apple, config, None
+        )
+        self.assertEquals(chunk,
+            [
+                {"type": "m.presence",
+                 "content": {
+                     "user_id": "@apple:test",
+                     "presence": ONLINE,
+                     "last_active_ago": 0,
+                }},
+            ]
+        )
+
         # Banana sees it because of presence subscription
         (events, _) = yield self.event_source.get_new_events_for_user(
             self.u_banana, 0, None