Track presence state per-device and amalgamate to a user state.

Tracks presence on an individual per-device basis and combines the
per-device state into a per-user state. This should help in situations
where a user has two devices with conflicting status (e.g. one is
syncing with unavailable and one is syncing with online).

The tie-breaking is done by priority:

    BUSY > ONLINE > UNAVAILABLE > OFFLINE

changelog.d/16066.bugfix

@@ -0,0 +1,2 @@
+Fix a long-standing bug where multi-device accounts could cause high load due to presence.
+

synapse/api/presence.py

@@ -20,6 +20,16 @@
 from synapse.types import JsonDict
 
 
+@attr.s(slots=True, auto_attribs=True)
+class UserDevicePresenceState:
+    user_id: str
+    device_id: Optional[str]
+    state: str
+    last_active_ts: int
+    last_user_sync_ts: int
+    status_msg: Optional[str]
+
+
 @attr.s(slots=True, frozen=True, auto_attribs=True)
 class UserPresenceState:
     """Represents the current presence state of the user.

synapse/handlers/events.py

@@ -67,6 +67,7 @@ async def get_stream(
 
         context = await presence_handler.user_syncing(
             requester.user.to_string(),
+            requester.device_id,
             affect_presence=affect_presence,
             presence_state=PresenceState.ONLINE,
         )

synapse/handlers/presence.py

@@ -49,7 +49,7 @@
 import synapse.metrics
 from synapse.api.constants import EduTypes, EventTypes, Membership, PresenceState
 from synapse.api.errors import SynapseError
-from synapse.api.presence import UserPresenceState
+from synapse.api.presence import UserDevicePresenceState, UserPresenceState
 from synapse.appservice import ApplicationService
 from synapse.events.presence_router import PresenceRouter
 from synapse.logging.context import run_in_background
@@ -150,11 +150,16 @@ def __init__(self, hs: "HomeServer"):
         self._busy_presence_enabled = hs.config.experimental.msc3026_enabled
 
         active_presence = self.store.take_presence_startup_info()
+        # The combine status across all user devices.
         self.user_to_current_state = {state.user_id: state for state in active_presence}
 
     @abc.abstractmethod
     async def user_syncing(
-        self, user_id: str, affect_presence: bool, presence_state: str
+        self,
+        user_id: str,
+        device_id: Optional[str],
+        affect_presence: bool,
+        presence_state: str,
     ) -> ContextManager[None]:
         """Returns a context manager that should surround any stream requests
         from the user.
@@ -241,6 +246,7 @@ async def current_state_for_user(self, user_id: str) -> UserPresenceState:
     async def set_state(
         self,
         target_user: UserID,
+        device_id: Optional[str],
         state: JsonDict,
         ignore_status_msg: bool = False,
         force_notify: bool = False,
@@ -368,7 +374,9 @@ async def send_full_presence_to_users(self, user_ids: StrCollection) -> None:
         # We set force_notify=True here so that this presence update is guaranteed to
         # increment the presence stream ID (which resending the current user's presence
         # otherwise would not do).
-        await self.set_state(UserID.from_string(user_id), state, force_notify=True)
+        await self.set_state(
+            UserID.from_string(user_id), None, state, force_notify=True
+        )
 
     async def is_visible(self, observed_user: UserID, observer_user: UserID) -> bool:
         raise NotImplementedError(
@@ -472,7 +480,11 @@ def send_stop_syncing(self) -> None:
                 self.send_user_sync(user_id, False, last_sync_ms)
 
     async def user_syncing(
-        self, user_id: str, affect_presence: bool, presence_state: str
+        self,
+        user_id: str,
+        device_id: Optional[str],
+        affect_presence: bool,
+        presence_state: str,
     ) -> ContextManager[None]:
         """Record that a user is syncing.
 
@@ -490,7 +502,10 @@ async def user_syncing(
             # what the spec wants: see comment in the BasePresenceHandler version
             # of this function.
             await self.set_state(
-                UserID.from_string(user_id), {"presence": presence_state}, True
+                UserID.from_string(user_id),
+                device_id,
+                {"presence": presence_state},
+                True,
             )
 
         curr_sync = self._user_to_num_current_syncs.get(user_id, 0)
@@ -586,6 +601,7 @@ def get_currently_syncing_users_for_replication(self) -> Iterable[str]:
     async def set_state(
         self,
         target_user: UserID,
+        device_id: Optional[str],
         state: JsonDict,
         ignore_status_msg: bool = False,
         force_notify: bool = False,
@@ -623,6 +639,7 @@ async def set_state(
         await self._set_state_client(
             instance_name=self._presence_writer_instance,
             user_id=user_id,
+            device_id=device_id,
             state=state,
             ignore_status_msg=ignore_status_msg,
             force_notify=force_notify,
@@ -755,6 +772,11 @@ def run_persister() -> Awaitable[None]:
         self._event_pos = self.store.get_room_max_stream_ordering()
         self._event_processing = False
 
+        # The per-device presence state, maps user to devices to per-device presence state.
+        self.user_to_device_to_current_state: Dict[
+            str, Dict[Optional[str], UserDevicePresenceState]
+        ] = {}
+
     async def _on_shutdown(self) -> None:
         """Gets called when shutting down. This lets us persist any updates that
         we haven't yet persisted, e.g. updates that only changes some internal
@@ -973,6 +995,7 @@ async def bump_presence_active_time(self, user: UserID) -> None:
     async def user_syncing(
         self,
         user_id: str,
+        device_id: Optional[str],
         affect_presence: bool = True,
         presence_state: str = PresenceState.ONLINE,
     ) -> ContextManager[None]:
@@ -985,6 +1008,7 @@ async def user_syncing(
 
         Args:
             user_id
+            device_id
             affect_presence: If false this function will be a no-op.
                 Useful for streams that are not associated with an actual
                 client that is being used by a user.
@@ -1010,7 +1034,10 @@ async def user_syncing(
                 # updated always, which is not what the spec calls for, but synapse has done
                 # this for... forever, I think.
                 await self.set_state(
-                    UserID.from_string(user_id), {"presence": presence_state}, True
+                    UserID.from_string(user_id),
+                    device_id,
+                    {"presence": presence_state},
+                    True,
                 )
                 # Retrieve the new state for the logic below. This should come from the
                 # in-memory cache.
@@ -1213,6 +1240,7 @@ async def incoming_presence(self, origin: str, content: JsonDict) -> None:
     async def set_state(
         self,
         target_user: UserID,
+        device_id: Optional[str],
         state: JsonDict,
         ignore_status_msg: bool = False,
         force_notify: bool = False,
@@ -1221,6 +1249,7 @@ async def set_state(
 
         Args:
             target_user: The ID of the user to set the presence state of.
+            device_id: The optional device ID.
             state: The presence state as a JSON dictionary.
             ignore_status_msg: True to ignore the "status_msg" field of the `state` dict.
                 If False, the user's current status will be updated.
@@ -1249,6 +1278,41 @@ async def set_state(
 
         prev_state = await self.current_state_for_user(user_id)
 
+        # Always update the device specific information.
+        device_state = self.user_to_device_to_current_state.setdefault(
+            user_id, {}
+        ).setdefault(
+            device_id,
+            UserDevicePresenceState(
+                user_id,
+                device_id,
+                presence,
+                last_active_ts=self.clock.time_msec(),
+                last_user_sync_ts=self.clock.time_msec(),
+                status_msg=None,
+            ),
+        )
+        device_state.state = presence
+        if presence:
+            device_state.status_msg = status_msg
+        device_state.last_active_ts = self.clock.time_msec()
+        device_state.last_user_sync_ts = self.clock.time_msec()
+
+        # Based on (all) the user's devices calculate the new presence state.
+        presence_by_priority = {
+            PresenceState.BUSY: 4,
+            PresenceState.ONLINE: 3,
+            PresenceState.UNAVAILABLE: 2,
+            PresenceState.OFFLINE: 1,
+        }
+        for device_state in self.user_to_device_to_current_state[user_id].values():
+            if (
+                presence_by_priority[device_state.state]
+                > presence_by_priority[presence]
+            ):
+                presence = device_state.state
+
+        # The newly updated status as an amalgamation of all the device statuses.
         new_fields = {"state": presence}
 
         if not ignore_status_msg:
@@ -1962,6 +2026,7 @@ def handle_update(
     # If the users are ours then we want to set up a bunch of timers
     # to time things out.
     if is_mine:
+        # TODO Maybe don't do this if currently active?
         if new_state.state == PresenceState.ONLINE:
             # Idle timer
             wheel_timer.insert(

synapse/replication/http/presence.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import logging
-from typing import TYPE_CHECKING, Tuple
+from typing import TYPE_CHECKING, Optional, Tuple
 
 from twisted.web.server import Request
 
@@ -95,11 +95,13 @@ def __init__(self, hs: "HomeServer"):
     @staticmethod
     async def _serialize_payload(  # type: ignore[override]
         user_id: str,
+        device_id: Optional[str],
         state: JsonDict,
         ignore_status_msg: bool = False,
         force_notify: bool = False,
     ) -> JsonDict:
         return {
+            "device_id": device_id,
             "state": state,
             "ignore_status_msg": ignore_status_msg,
             "force_notify": force_notify,
@@ -110,6 +112,7 @@ async def _handle_request(  # type: ignore[override]
     ) -> Tuple[int, JsonDict]:
         await self._presence_handler.set_state(
             UserID.from_string(user_id),
+            content["device_id"],
             content["state"],
             content["ignore_status_msg"],
             content["force_notify"],

synapse/rest/client/presence.py

@@ -97,7 +97,7 @@ async def on_PUT(
             raise SynapseError(400, "Unable to parse state")
 
         if self._use_presence:
-            await self.presence_handler.set_state(user, state)
+            await self.presence_handler.set_state(user, requester.device_id, state)
 
         return 200, {}
 

synapse/rest/client/sync.py

@@ -205,6 +205,7 @@ async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
 
         context = await self.presence_handler.user_syncing(
             user.to_string(),
+            requester.device_id,
             affect_presence=affect_presence,
             presence_state=set_presence,
         )