Use event streams to calculate presence

Primarily this fixes a bug in the handling of remote users joining a
room where the server sent out the presence for all local users in the
room to all servers in the room.

We also change to using the state delta stream, rather than the
distributor, as it will make it easier to split processing out of the
master process (as well as being more flexible).

Finally, when sending presence states to newly joined servers we filter
out old presence states to reduce the number sent. Initially we filter
out states that are offline and have a last active more than a week ago,
though this can be changed down the line.

Fixes #3962

synapse/federation/send_queue.py

@@ -55,7 +55,12 @@ class FederationRemoteSendQueue(object):
         self.is_mine_id = hs.is_mine_id
 
         self.presence_map = {}  # Pending presence map user_id -> UserPresenceState
-        self.presence_changed = SortedDict()  # Stream position -> user_id
+        self.presence_changed = SortedDict()  # Stream position -> list[user_id]
+
+        # Stores the destinations we need to explicitly send presence to about a
+        # given user.
+        # Stream position -> (user_id, destinations)
+        self.presence_destinations = SortedDict()
 
         self.keyed_edu = {}  # (destination, key) -> EDU
         self.keyed_edu_changed = SortedDict()  # stream position -> (destination, key)
@@ -77,7 +82,7 @@ class FederationRemoteSendQueue(object):
 
         for queue_name in [
             "presence_map", "presence_changed", "keyed_edu", "keyed_edu_changed",
-            "edus", "device_messages", "pos_time",
+            "edus", "device_messages", "pos_time", "presence_destinations",
         ]:
             register(queue_name, getattr(self, queue_name))
 
@@ -121,6 +126,15 @@ class FederationRemoteSendQueue(object):
                 for user_id in uids
             )
 
+            keys = self.presence_destinations.keys()
+            i = self.presence_destinations.bisect_left(position_to_delete)
+            for key in keys[:i]:
+                del self.presence_destinations[key]
+
+            user_ids.update(
+                user_id for user_id, _ in self.presence_destinations.values()
+            )
+
             to_del = [
                 user_id for user_id in self.presence_map if user_id not in user_ids
             ]
@@ -209,6 +223,20 @@ class FederationRemoteSendQueue(object):
 
         self.notifier.on_new_replication_data()
 
+    def send_presence_to_destinations(self, states, destinations):
+        """As per FederationSender
+
+        Args:
+            states (list[UserPresenceState])
+            destinations (list[str])
+        """
+        for state in states:
+            pos = self._next_pos()
+            self.presence_map.update({state.user_id: state for state in states})
+            self.presence_destinations[pos] = (state.user_id, destinations)
+
+        self.notifier.on_new_replication_data()
+
     def send_device_messages(self, destination):
         """As per FederationSender"""
         pos = self._next_pos()
@@ -261,6 +289,16 @@ class FederationRemoteSendQueue(object):
                 state=self.presence_map[user_id],
             )))
 
+        # Fetch presence to send to destinations
+        i = self.presence_destinations.bisect_right(from_token)
+        j = self.presence_destinations.bisect_right(to_token) + 1
+
+        for pos, (user_id, dests) in self.presence_destinations.items()[i:j]:
+            rows.append((pos, PresenceDestinationsRow(
+                state=self.presence_map[user_id],
+                destinations=list(dests),
+            )))
+
         # Fetch changes keyed edus
         i = self.keyed_edu_changed.bisect_right(from_token)
         j = self.keyed_edu_changed.bisect_right(to_token) + 1
@@ -357,6 +395,29 @@ class PresenceRow(BaseFederationRow, namedtuple("PresenceRow", (
         buff.presence.append(self.state)
 
 
+class PresenceDestinationsRow(BaseFederationRow, namedtuple("PresenceDestinationsRow", (
+    "state",  # UserPresenceState
+    "destinations",  # list[str]
+))):
+    TypeId = "pd"
+
+    @staticmethod
+    def from_data(data):
+        return PresenceDestinationsRow(
+            state=UserPresenceState.from_dict(data["state"]),
+            destinations=data["dests"],
+        )
+
+    def to_data(self):
+        return {
+            "state": self.state.as_dict(),
+            "dests": self.destinations,
+        }
+
+    def add_to_buffer(self, buff):
+        buff.presence_destinations.append((self.state, self.destinations))
+
+
 class KeyedEduRow(BaseFederationRow, namedtuple("KeyedEduRow", (
     "key",  # tuple(str) - the edu key passed to send_edu
     "edu",  # Edu
@@ -428,6 +489,7 @@ TypeToRow = {
     Row.TypeId: Row
     for Row in (
         PresenceRow,
+        PresenceDestinationsRow,
         KeyedEduRow,
         EduRow,
         DeviceRow,
@@ -437,6 +499,7 @@ TypeToRow = {
 
 ParsedFederationStreamData = namedtuple("ParsedFederationStreamData", (
     "presence",  # list(UserPresenceState)
+    "presence_destinations",  # list of tuples of UserPresenceState and destinations
     "keyed_edus",  # dict of destination -> { key -> Edu }
     "edus",  # dict of destination -> [Edu]
     "device_destinations",  # set of destinations
@@ -458,6 +521,7 @@ def process_rows_for_federation(transaction_queue, rows):
 
     buff = ParsedFederationStreamData(
         presence=[],
+        presence_destinations=[],
         keyed_edus={},
         edus={},
         device_destinations=set(),
@@ -476,6 +540,11 @@ def process_rows_for_federation(transaction_queue, rows):
     if buff.presence:
         transaction_queue.send_presence(buff.presence)
 
+    for state, destinations in buff.presence_destinations:
+        transaction_queue.send_presence_to_destinations(
+            states=[state], destinations=destinations,
+        )
+
     for destination, edu_map in iteritems(buff.keyed_edus):
         for key, edu in edu_map.items():
             transaction_queue.send_edu(edu, key)