text: # -*- coding: utf-8 -*-
  # Copyright 2014-2016 OpenMarket Ltd
  # Copyright 2020 The Matrix.org Foundation C.I.C.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  """This module is responsible for keeping track of presence status of local
  and remote users.
  
  The methods that define policy are:
      - PresenceHandler._update_states
      - PresenceHandler._handle_timeouts
      - should_notify
  """
  import abc
  import logging
  from contextlib import contextmanager
  from typing import Dict, Iterable, List, Set, Tuple
  
  from prometheus_client import Counter
  from typing_extensions import ContextManager
  
  from twisted.internet import defer
  
  import synapse.metrics
  from synapse.api.constants import EventTypes, Membership, PresenceState
  from synapse.api.errors import SynapseError
  from synapse.logging.context import run_in_background
  from synapse.logging.utils import log_function
  from synapse.metrics import LaterGauge
  from synapse.metrics.background_process_metrics import run_as_background_process
  from synapse.storage.presence import UserPresenceState
  from synapse.types import JsonDict, UserID, get_domain_from_id
  from synapse.util.async_helpers import Linearizer
  from synapse.util.caches.descriptors import cached
  from synapse.util.metrics import Measure
  from synapse.util.wheel_timer import WheelTimer
  
  MYPY = False
  if MYPY:
      import synapse.server
  
  logger = logging.getLogger(__name__)
  
  
  notified_presence_counter = Counter("synapse_handler_presence_notified_presence", "")
  federation_presence_out_counter = Counter(
      "synapse_handler_presence_federation_presence_out", ""
  )
  presence_updates_counter = Counter("synapse_handler_presence_presence_updates", "")
  timers_fired_counter = Counter("synapse_handler_presence_timers_fired", "")
  federation_presence_counter = Counter(
      "synapse_handler_presence_federation_presence", ""
  )
  bump_active_time_counter = Counter("synapse_handler_presence_bump_active_time", "")
  
  get_updates_counter = Counter("synapse_handler_presence_get_updates", "", ["type"])
  
  notify_reason_counter = Counter(
      "synapse_handler_presence_notify_reason", "", ["reason"]
  )
  state_transition_counter = Counter(
      "synapse_handler_presence_state_transition", "", ["from", "to"]
  )
  
  
  # If a user was last active in the last LAST_ACTIVE_GRANULARITY, consider them
  # "currently_active"
  LAST_ACTIVE_GRANULARITY = 60 * 1000
  
  # How long to wait until a new /events or /sync request before assuming
  # the client has gone.
  SYNC_ONLINE_TIMEOUT = 30 * 1000
  
  # How long to wait before marking the user as idle. Compared against last active
  IDLE_TIMER = 5 * 60 * 1000
  
  # How often we expect remote servers to resend us presence.
  FEDERATION_TIMEOUT = 30 * 60 * 1000
  
  # How often to resend presence to remote servers
  FEDERATION_PING_INTERVAL = 25 * 60 * 1000
  
  # How long we will wait before assuming that the syncs from an external process
  # are dead.
  EXTERNAL_PROCESS_EXPIRY = 5 * 60 * 1000
  
  assert LAST_ACTIVE_GRANULARITY < IDLE_TIMER
  
  
  class BasePresenceHandler(abc.ABC):
      """Parts of the PresenceHandler that are shared between workers and master"""
  
      def __init__(self, hs: "synapse.server.HomeServer"):
          self.clock = hs.get_clock()
          self.store = hs.get_datastore()
  
          active_presence = self.store.take_presence_startup_info()
          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
      ) -> ContextManager[None]:
          """Returns a context manager that should surround any stream requests
          from the user.
  
          This allows us to keep track of who is currently streaming and who isn't
          without having to have timers outside of this module to avoid flickering
          when users disconnect/reconnect.
  
          Args:
              user_id: the user that is starting a sync
              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.
          """
  
      @abc.abstractmethod
      def get_currently_syncing_users_for_replication(self) -> Iterable[str]:
          """Get an iterable of syncing users on this worker, to send to the presence handler
  
          This is called when a replication connection is established. It should return
          a list of user ids, which are then sent as USER_SYNC commands to inform the
          process handling presence about those users.
  
          Returns:
              An iterable of user_id strings.
          """
  
      async def get_state(self, target_user: UserID) -> UserPresenceState:
          results = await self.get_states([target_user.to_string()])
          return results[0]
  
      async def get_states(
          self, target_user_ids: Iterable[str]
      ) -> List[UserPresenceState]:
          """Get the presence state for users."""
  
          updates_d = await self.current_state_for_users(target_user_ids)
          updates = list(updates_d.values())
  
          for user_id in set(target_user_ids) - {u.user_id for u in updates}:
              updates.append(UserPresenceState.default(user_id))
  
          return updates
  
      async def current_state_for_users(
          self, user_ids: Iterable[str]
      ) -> Dict[str, UserPresenceState]:
          """Get the current presence state for multiple users.
  
          Returns:
              dict: `user_id` -> `UserPresenceState`
          """
          states = {
              user_id: self.user_to_current_state.get(user_id, None)
              for user_id in user_ids
          }
  
          missing = [user_id for user_id, state in states.items() if not state]
          if missing:
              # There are things not in our in memory cache. Lets pull them out of
              # the database.
              res = await self.store.get_presence_for_users(missing)
              states.update(res)
  
              missing = [user_id for user_id, state in states.items() if not state]
              if missing:
                  new = {
                      user_id: UserPresenceState.default(user_id) for user_id in missing
                  }
                  states.update(new)
                  self.user_to_current_state.update(new)
  
          return states
  
      @abc.abstractmethod
      async def set_state(
          self, target_user: UserID, state: JsonDict, ignore_status_msg: bool = False
      ) -> None:
          """Set the presence state of the user. """
  
      @abc.abstractmethod
      async def bump_presence_active_time(self, user: UserID):
          """We've seen the user do something that indicates they're interacting
          with the app.
          """
  
  
  class PresenceHandler(BasePresenceHandler):
      def __init__(self, hs: "synapse.server.HomeServer"):
          super().__init__(hs)
          self.hs = hs
          self.is_mine_id = hs.is_mine_id
          self.server_name = hs.hostname
          self.wheel_timer = WheelTimer()
          self.notifier = hs.get_notifier()
          self.federation = hs.get_federation_sender()
          self.state = hs.get_state_handler()
          self._presence_enabled = hs.config.use_presence
  
          federation_registry = hs.get_federation_registry()
  
          federation_registry.register_edu_handler("m.presence", self.incoming_presence)
  
          LaterGauge(
              "synapse_handlers_presence_user_to_current_state_size",
              "",
              [],
              lambda: len(self.user_to_current_state),
          )
  
          now = self.clock.time_msec()
          for state in self.user_to_current_state.values():
              self.wheel_timer.insert(
                  now=now, obj=state.user_id, then=state.last_active_ts + IDLE_TIMER
              )
              self.wheel_timer.insert(
                  now=now,
                  obj=state.user_id,
                  then=state.last_user_sync_ts + SYNC_ONLINE_TIMEOUT,
              )
              if self.is_mine_id(state.user_id):
                  self.wheel_timer.insert(
                      now=now,
                      obj=state.user_id,
                      then=state.last_federation_update_ts + FEDERATION_PING_INTERVAL,
                  )
              else:
                  self.wheel_timer.insert(
                      now=now,
                      obj=state.user_id,
                      then=state.last_federation_update_ts + FEDERATION_TIMEOUT,
                  )
  
          # Set of users who have presence in the `user_to_current_state` that
          # have not yet been persisted
          self.unpersisted_users_changes = set()  # type: Set[str]
  
          hs.get_reactor().addSystemEventTrigger(
              "before",
              "shutdown",
              run_as_background_process,
              "presence.on_shutdown",
              self._on_shutdown,
          )
  
          self._next_serial = 1
  
          # Keeps track of the number of *ongoing* syncs on this process. While
          # this is non zero a user will never go offline.
          self.user_to_num_current_syncs = {}  # type: Dict[str, int]
  
          # Keeps track of the number of *ongoing* syncs on other processes.
          # While any sync is ongoing on another process the user will never
          # go offline.
          # Each process has a unique identifier and an update frequency. If
          # no update is received from that process within the update period then
          # we assume that all the sync requests on that process have stopped.
          # Stored as a dict from process_id to set of user_id, and a dict of
          # process_id to millisecond timestamp last updated.
          self.external_process_to_current_syncs = {}  # type: Dict[int, Set[str]]
          self.external_process_last_updated_ms = {}  # type: Dict[int, int]
  
          self.external_sync_linearizer = Linearizer(name="external_sync_linearizer")
  
          # Start a LoopingCall in 30s that fires every 5s.
          # The initial delay is to allow disconnected clients a chance to
          # reconnect before we treat them as offline.
          def run_timeout_handler():
              return run_as_background_process(
                  "handle_presence_timeouts", self._handle_timeouts
              )
  
          self.clock.call_later(30, self.clock.looping_call, run_timeout_handler, 5000)
  
          def run_persister():
              return run_as_background_process(
                  "persist_presence_changes", self._persist_unpersisted_changes
              )
  
          self.clock.call_later(60, self.clock.looping_call, run_persister, 60 * 1000)
  
          LaterGauge(
              "synapse_handlers_presence_wheel_timer_size",
              "",
              [],
              lambda: len(self.wheel_timer),
          )
  
          # Used to handle sending of presence to newly joined users/servers
          if hs.config.use_presence:
              self.notifier.add_replication_callback(self.notify_new_event)
  
          # Presence is best effort and quickly heals itself, so lets just always
          # stream from the current state when we restart.
          self._event_pos = self.store.get_current_events_token()
          self._event_processing = False
  
      async def _on_shutdown(self):
          """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
          timers. This allows changes to persist across startup without having to
          persist every single change.
  
          If this does not run it simply means that some of the timers will fire
          earlier than they should when synapse is restarted. This affect of this
          is some spurious presence changes that will self-correct.
          """
          # If the DB pool has already terminated, don't try updating
          if not self.store.db.is_running():
              return
  
          logger.info(
              "Performing _on_shutdown. Persisting %d unpersisted changes",
              len(self.user_to_current_state),
          )
  
          if self.unpersisted_users_changes:
  
              await self.store.update_presence(
                  [
                      self.user_to_current_state[user_id]
                      for user_id in self.unpersisted_users_changes
                  ]
              )
          logger.info("Finished _on_shutdown")
  
      async def _persist_unpersisted_changes(self):
          """We periodically persist the unpersisted changes, as otherwise they
          may stack up and slow down shutdown times.
          """
          unpersisted = self.unpersisted_users_changes
          self.unpersisted_users_changes = set()
  
          if unpersisted:
              logger.info("Persisting %d unpersisted presence updates", len(unpersisted))
              await self.store.update_presence(
                  [self.user_to_current_state[user_id] for user_id in unpersisted]
              )
  
      async def _update_states(self, new_states):
          """Updates presence of users. Sets the appropriate timeouts. Pokes
          the notifier and federation if and only if the changed presence state
          should be sent to clients/servers.
          """
          now = self.clock.time_msec()
  
          with Measure(self.clock, "presence_update_states"):
  
              # NOTE: We purposefully don't await between now and when we've
              # calculated what we want to do with the new states, to avoid races.
  
              to_notify = {}  # Changes we want to notify everyone about
              to_federation_ping = {}  # These need sending keep-alives
  
              # Only bother handling the last presence change for each user
              new_states_dict = {}
              for new_state in new_states:
                  new_states_dict[new_state.user_id] = new_state
              new_state = new_states_dict.values()
  
              for new_state in new_states:
                  user_id = new_state.user_id
  
                  # Its fine to not hit the database here, as the only thing not in
                  # the current state cache are OFFLINE states, where the only field
                  # of interest is last_active which is safe enough to assume is 0
                  # here.
                  prev_state = self.user_to_current_state.get(
                      user_id, UserPresenceState.default(user_id)
                  )
  
                  new_state, should_notify, should_ping = handle_update(
                      prev_state,
                      new_state,
                      is_mine=self.is_mine_id(user_id),
                      wheel_timer=self.wheel_timer,
                      now=now,
                  )
  
                  self.user_to_current_state[user_id] = new_state
  
                  if should_notify:
                      to_notify[user_id] = new_state
                  elif should_ping:
                      to_federation_ping[user_id] = new_state
  
              # TODO: We should probably ensure there are no races hereafter
  
              presence_updates_counter.inc(len(new_states))
  
              if to_notify:
                  notified_presence_counter.inc(len(to_notify))
                  await self._persist_and_notify(list(to_notify.values()))
  
              self.unpersisted_users_changes |= {s.user_id for s in new_states}
              self.unpersisted_users_changes -= set(to_notify.keys())
  
              to_federation_ping = {
                  user_id: state
                  for user_id, state in to_federation_ping.items()
                  if user_id not in to_notify
              }
              if to_federation_ping:
                  federation_presence_out_counter.inc(len(to_federation_ping))
  
                  self._push_to_remotes(to_federation_ping.values())
  
      async def _handle_timeouts(self):
          """Checks the presence of users that have timed out and updates as
          appropriate.
          """
          logger.debug("Handling presence timeouts")
          now = self.clock.time_msec()
  
          # Fetch the list of users that *may* have timed out. Things may have
          # changed since the timeout was set, so we won't necessarily have to
          # take any action.
          users_to_check = set(self.wheel_timer.fetch(now))
  
          # Check whether the lists of syncing processes from an external
          # process have expired.
          expired_process_ids = [
              process_id
              for process_id, last_update in self.external_process_last_updated_ms.items()
              if now - last_update > EXTERNAL_PROCESS_EXPIRY
          ]
          for process_id in expired_process_ids:
              # For each expired process drop tracking info and check the users
              # that were syncing on that process to see if they need to be timed
              # out.
              users_to_check.update(
                  self.external_process_to_current_syncs.pop(process_id, ())
              )
              self.external_process_last_updated_ms.pop(process_id)
  
          states = [
              self.user_to_current_state.get(user_id, UserPresenceState.default(user_id))
              for user_id in users_to_check
          ]
  
          timers_fired_counter.inc(len(states))
  
          syncing_user_ids = {
              user_id
              for user_id, count in self.user_to_num_current_syncs.items()
              if count
          }
          for user_ids in self.external_process_to_current_syncs.values():
              syncing_user_ids.update(user_ids)
  
          changes = handle_timeouts(
              states,
              is_mine_fn=self.is_mine_id,
              syncing_user_ids=syncing_user_ids,
              now=now,
          )
  
          return await self._update_states(changes)
  
      async def bump_presence_active_time(self, user):
          """We've seen the user do something that indicates they're interacting
          with the app.
          """
          # If presence is disabled, no-op
          if not self.hs.config.use_presence:
              return
  
          user_id = user.to_string()
  
          bump_active_time_counter.inc()
  
          prev_state = await self.current_state_for_user(user_id)
  
          new_fields = {"last_active_ts": self.clock.time_msec()}
          if prev_state.state == PresenceState.UNAVAILABLE:
              new_fields["state"] = PresenceState.ONLINE
  
          await self._update_states([prev_state.copy_and_replace(**new_fields)])
  
      async def user_syncing(
          self, user_id: str, affect_presence: bool = True
      ) -> ContextManager[None]:
          """Returns a context manager that should surround any stream requests
          from the user.
  
          This allows us to keep track of who is currently streaming and who isn't
          without having to have timers outside of this module to avoid flickering
          when users disconnect/reconnect.
  
          Args:
              user_id (str)
              affect_presence (bool): 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.
          """
          # Override if it should affect the user's presence, if presence is
          # disabled.
          if not self.hs.config.use_presence:
              affect_presence = False
  
          if affect_presence:
              curr_sync = self.user_to_num_current_syncs.get(user_id, 0)
              self.user_to_num_current_syncs[user_id] = curr_sync + 1
  
              prev_state = await self.current_state_for_user(user_id)
              if prev_state.state == PresenceState.OFFLINE:
                  # If they're currently offline then bring them online, otherwise
                  # just update the last sync times.
                  await self._update_states(
                      [
                          prev_state.copy_and_replace(
                              state=PresenceState.ONLINE,
                              last_active_ts=self.clock.time_msec(),
                              last_user_sync_ts=self.clock.time_msec(),
                          )
                      ]
                  )
              else:
                  await self._update_states(
                      [
                          prev_state.copy_and_replace(
                              last_user_sync_ts=self.clock.time_msec()
                          )
                      ]
                  )
  
          async def _end():
              try:
                  self.user_to_num_current_syncs[user_id] -= 1
  
                  prev_state = await self.current_state_for_user(user_id)
                  await self._update_states(
                      [
                          prev_state.copy_and_replace(
                              last_user_sync_ts=self.clock.time_msec()
                          )
                      ]
                  )
              except Exception:
                  logger.exception("Error updating presence after sync")
  
          @contextmanager
          def _user_syncing():
              try:
                  yield
              finally:
                  if affect_presence:
                      run_in_background(_end)
  
          return _user_syncing()
  
      def get_currently_syncing_users_for_replication(self) -> Iterable[str]:
          # since we are the process handling presence, there is nothing to do here.
          return []
  
      async def update_external_syncs_row(
          self, process_id, user_id, is_syncing, sync_time_msec
      ):
          """Update the syncing users for an external process as a delta.
  
          Args:
              process_id (str): An identifier for the process the users are
                  syncing against. This allows synapse to process updates
                  as user start and stop syncing against a given process.
              user_id (str): The user who has started or stopped syncing
              is_syncing (bool): Whether or not the user is now syncing
              sync_time_msec(int): Time in ms when the user was last syncing
          """
          with (await self.external_sync_linearizer.queue(process_id)):
              prev_state = await self.current_state_for_user(user_id)
  
              process_presence = self.external_process_to_current_syncs.setdefault(
                  process_id, set()
              )
  
              updates = []
              if is_syncing and user_id not in process_presence:
                  if prev_state.state == PresenceState.OFFLINE:
                      updates.append(
                          prev_state.copy_and_replace(
                              state=PresenceState.ONLINE,
                              last_active_ts=sync_time_msec,
                              last_user_sync_ts=sync_time_msec,
                          )
                      )
                  else:
                      updates.append(
                          prev_state.copy_and_replace(last_user_sync_ts=sync_time_msec)
                      )
                  process_presence.add(user_id)
              elif user_id in process_presence:
                  updates.append(
                      prev_state.copy_and_replace(last_user_sync_ts=sync_time_msec)
                  )
  
              if not is_syncing:
                  process_presence.discard(user_id)
  
              if updates:
                  await self._update_states(updates)
  
              self.external_process_last_updated_ms[process_id] = self.clock.time_msec()
  
      async def update_external_syncs_clear(self, process_id):
          """Marks all users that had been marked as syncing by a given process
          as offline.
  
          Used when the process has stopped/disappeared.
          """
          with (await self.external_sync_linearizer.queue(process_id)):
              process_presence = self.external_process_to_current_syncs.pop(
                  process_id, set()
              )
              prev_states = await self.current_state_for_users(process_presence)
              time_now_ms = self.clock.time_msec()
  
              await self._update_states(
                  [
                      prev_state.copy_and_replace(last_user_sync_ts=time_now_ms)
                      for prev_state in prev_states.values()
                  ]
              )
              self.external_process_last_updated_ms.pop(process_id, None)
  
      async def current_state_for_user(self, user_id):
          """Get the current presence state for a user.
          """
          res = await self.current_state_for_users([user_id])
          return res[user_id]
  
      async def _persist_and_notify(self, states):
          """Persist states in the database, poke the notifier and send to
          interested remote servers
          """
          stream_id, max_token = await self.store.update_presence(states)
  
          parties = await get_interested_parties(self.store, states)
          room_ids_to_states, users_to_states = parties
  
          self.notifier.on_new_event(
              "presence_key",
              stream_id,
              rooms=room_ids_to_states.keys(),
              users=[UserID.from_string(u) for u in users_to_states],
          )
  
          self._push_to_remotes(states)
  
      async def notify_for_states(self, state, stream_id):
          parties = await get_interested_parties(self.store, [state])
          room_ids_to_states, users_to_states = parties
  
          self.notifier.on_new_event(
              "presence_key",
              stream_id,
              rooms=room_ids_to_states.keys(),
              users=[UserID.from_string(u) for u in users_to_states],
          )
  
      def _push_to_remotes(self, states):
          """Sends state updates to remote servers.
  
          Args:
              states (list(UserPresenceState))
          """
          self.federation.send_presence(states)
  
      async def incoming_presence(self, origin, content):
          """Called when we receive a `m.presence` EDU from a remote server.
          """
          if not self._presence_enabled:
              return
  
          now = self.clock.time_msec()
          updates = []
          for push in content.get("push", []):
              # A "push" contains a list of presence that we are probably interested
              # in.
              user_id = push.get("user_id", None)
              if not user_id:
                  logger.info(
                      "Got presence update from %r with no 'user_id': %r", origin, push
                  )
                  continue
  
              if get_domain_from_id(user_id) != origin:
                  logger.info(
                      "Got presence update from %r with bad 'user_id': %r",
                      origin,
                      user_id,
                  )
                  continue
  
              presence_state = push.get("presence", None)
              if not presence_state:
                  logger.info(
                      "Got presence update from %r with no 'presence_state': %r",
                      origin,
                      push,
                  )
                  continue
  
              new_fields = {"state": presence_state, "last_federation_update_ts": now}
  
              last_active_ago = push.get("last_active_ago", None)
              if last_active_ago is not None:
                  new_fields["last_active_ts"] = now - last_active_ago
  
              new_fields["status_msg"] = push.get("status_msg", None)
              new_fields["currently_active"] = push.get("currently_active", False)
  
              prev_state = await self.current_state_for_user(user_id)
              updates.append(prev_state.copy_and_replace(**new_fields))
  
          if updates:
              federation_presence_counter.inc(len(updates))
              await self._update_states(updates)
  
      async def set_state(self, target_user, state, ignore_status_msg=False):
          """Set the presence state of the user.
          """
          status_msg = state.get("status_msg", None)
          presence = state["presence"]
  
          valid_presence = (
              PresenceState.ONLINE,
              PresenceState.UNAVAILABLE,
              PresenceState.OFFLINE,
          )
          if presence not in valid_presence:
              raise SynapseError(400, "Invalid presence state")
  
          user_id = target_user.to_string()
  
          prev_state = await self.current_state_for_user(user_id)
  
          new_fields = {"state": presence}
  
          if not ignore_status_msg:
              msg = status_msg if presence != PresenceState.OFFLINE else None
              new_fields["status_msg"] = msg
  
          if presence == PresenceState.ONLINE:
              new_fields["last_active_ts"] = self.clock.time_msec()
  
          await self._update_states([prev_state.copy_and_replace(**new_fields)])
  
      async def is_visible(self, observed_user, observer_user):
          """Returns whether a user can see another user's presence.
          """
          observer_room_ids = await self.store.get_rooms_for_user(
              observer_user.to_string()
          )
          observed_room_ids = await self.store.get_rooms_for_user(
              observed_user.to_string()
          )
  
          if observer_room_ids & observed_room_ids:
              return True
  
          return False
  
      async def get_all_presence_updates(
          self, instance_name: str, last_id: int, current_id: int, limit: int
      ) -> Tuple[List[Tuple[int, list]], int, bool]:
          """
          Gets a list of presence update rows from between the given stream ids.
          Each row has:
          - stream_id(str)
          - user_id(str)
          - state(str)
          - last_active_ts(int)
          - last_federation_update_ts(int)
          - last_user_sync_ts(int)
          - status_msg(int)
          - currently_active(int)
  
          Args:
              instance_name: The writer we want to fetch updates from. Unused
                  here since there is only ever one writer.
              last_id: The token to fetch updates from. Exclusive.
              current_id: The token to fetch updates up to. Inclusive.
              limit: The requested limit for the number of rows to return. The
                  function may return more or fewer rows.
  
          Returns:
              A tuple consisting of: the updates, a token to use to fetch
              subsequent updates, and whether we returned fewer rows than exists
              between the requested tokens due to the limit.
  
              The token returned can be used in a subsequent call to this
              function to get further updatees.
  
              The updates are a list of 2-tuples of stream ID and the row data
          """
  
          # TODO(markjh): replicate the unpersisted changes.
          # This could use the in-memory stores for recent changes.
          rows = await self.store.get_all_presence_updates(
              instance_name, last_id, current_id, limit
          )
          return rows
  
      def notify_new_event(self):
          """Called when new events have happened. Handles users and servers
          joining rooms and require being sent presence.
          """
  
          if self._event_processing:
              return
  
          async def _process_presence():
              assert not self._event_processing
  
              self._event_processing = True
              try:
                  await self._unsafe_process()
              finally:
                  self._event_processing = False
  
          run_as_background_process("presence.notify_new_event", _process_presence)
  
      async def _unsafe_process(self):
          # Loop round handling deltas until we're up to date
          while True:
              with Measure(self.clock, "presence_delta"):
                  room_max_stream_ordering = self.store.get_room_max_stream_ordering()
                  if self._event_pos == room_max_stream_ordering:
                      return
  
                  logger.debug(
                      "Processing presence stats %s->%s",
                      self._event_pos,
                      room_max_stream_ordering,
                  )
                  max_pos, deltas = await self.store.get_current_state_deltas(
                      self._event_pos, room_max_stream_ordering
                  )
                  await self._handle_state_delta(deltas)
  
                  self._event_pos = max_pos
  
                  # Expose current event processing position to prometheus
                  synapse.metrics.event_processing_positions.labels("presence").set(
                      max_pos
                  )
  
      async def _handle_state_delta(self, deltas):
          """Process current state deltas to find new joins that need to be
          handled.
          """
          for delta in deltas:
              typ = delta["type"]
              state_key = delta["state_key"]
              room_id = delta["room_id"]
              event_id = delta["event_id"]
              prev_event_id = delta["prev_event_id"]
  
              logger.debug("Handling: %r %r, %s", typ, state_key, event_id)
  
              if typ != EventTypes.Member:
                  continue
  
              if event_id is None:
                  # state has been deleted, so this is not a join. We only care about
                  # joins.
                  continue
  
              event = await self.store.get_event(event_id, allow_none=True)
              if not event or event.content.get("membership") != Membership.JOIN:
                  # We only care about joins
                  continue
  
              if prev_event_id:
                  prev_event = await self.store.get_event(prev_event_id, allow_none=True)
                  if (
                      prev_event
                      and prev_event.content.get("membership") == Membership.JOIN
                  ):
                      # Ignore changes to join events.
                      continue
  
              await self._on_user_joined_room(room_id, state_key)
  
      async def _on_user_joined_room(self, room_id, user_id):
          """Called when we detect a user joining the room via the current state
          delta stream.
  
          Args:
              room_id (str)
              user_id (str)
  
          Returns:
              Deferred
          """
  
          if self.is_mine_id(user_id):
              # If this is a local user then we need to send their presence
              # out to hosts in the room (who don't already have it)
  
              # TODO: We should be able to filter the hosts down to those that
              # haven't previously seen the user
  
              state = await self.current_state_for_user(user_id)
              hosts = await self.state.get_current_hosts_in_room(room_id)
  
              # Filter out ourselves.
              hosts = {host for host in hosts if host != self.server_name}
  
              self.federation.send_presence_to_destinations(
                  states=[state], destinations=hosts
              )
          else:
              # A remote user has joined the room, so we need to:
              #   1. Check if this is a new server in the room
              #   2. If so send any presence they don't already have for
              #      local users in the room.
  
              # TODO: We should be able to filter the users down to those that
              # the server hasn't previously seen
  
              # TODO: Check that this is actually a new server joining the
              # room.
  
              user_ids = await self.state.get_current_users_in_room(room_id)
              user_ids = list(filter(self.is_mine_id, user_ids))
  
              states_d = await self.current_state_for_users(user_ids)
  
              # Filter out old presence, i.e. offline presence states where
              # the user hasn't been active for a week. We can change this
              # depending on what we want the UX to be, but at the least we
              # should filter out offline presence where the state is just the
              # default state.
              now = self.clock.time_msec()
              states = [
                  state
                  for state in states_d.values()
                  if state.state != PresenceState.OFFLINE
                  or now - state.last_active_ts < 7 * 24 * 60 * 60 * 1000
                  or state.status_msg is not None
              ]
  
              if states:
                  self.federation.send_presence_to_destinations(
                      states=states, destinations=[get_domain_from_id(user_id)]
                  )
  
  
  def should_notify(old_state, new_state):
      """Decides if a presence state change should be sent to interested parties.
      """
      if old_state == new_state:
          return False
  
      if old_state.status_msg != new_state.status_msg:
          notify_reason_counter.labels("status_msg_change").inc()
          return True
  
      if old_state.state != new_state.state:
          notify_reason_counter.labels("state_change").inc()
          state_transition_counter.labels(old_state.state, new_state.state).inc()
          return True
  
      if old_state.state == PresenceState.ONLINE:
          if new_state.currently_active != old_state.currently_active:
              notify_reason_counter.labels("current_active_change").inc()
              return True
  
          if (
              new_state.last_active_ts - old_state.last_active_ts
              > LAST_ACTIVE_GRANULARITY
          ):
              # Only notify about last active bumps if we're not currently acive
              if not new_state.currently_active:
                  notify_reason_counter.labels("last_active_change_online").inc()
                  return True
  
      elif new_state.last_active_ts - old_state.last_active_ts > LAST_ACTIVE_GRANULARITY:
          # Always notify for a transition where last active gets bumped.
          notify_reason_counter.labels("last_active_change_not_online").inc()
          return True
  
      return False
  
  
  def format_user_presence_state(state, now, include_user_id=True):
      """Convert UserPresenceState to a format that can be sent down to clients
      and to other servers.
  
      The "user_id" is optional so that this function can be used to format presence
      updates for client /sync responses and for federation /send requests.
      """
      content = {"presence": state.state}
      if include_user_id:
          content["user_id"] = state.user_id
      if state.last_active_ts:
          content["last_active_ago"] = now - state.last_active_ts
      if state.status_msg and state.state != PresenceState.OFFLINE:
          content["status_msg"] = state.status_msg
      if state.state == PresenceState.ONLINE:
          content["currently_active"] = state.currently_active
  
      return content
  
  
  class PresenceEventSource(object):
      def __init__(self, hs):
          # We can't call get_presence_handler here because there's a cycle:
          #
          #   Presence -> Notifier -> PresenceEventSource -> Presence
          #
          self.get_presence_handler = hs.get_presence_handler
          self.clock = hs.get_clock()
          self.store = hs.get_datastore()
          self.state = hs.get_state_handler()
  
      @log_function
      async def get_new_events(
          self,
          user,
          from_key,
          room_ids=None,
          include_offline=True,
          explicit_room_id=None,
          **kwargs
      ):
          # The process for getting presence events are:
          #  1. Get the rooms the user is in.
          #  2. Get the list of user in the rooms.
          #  3. Get the list of users that are in the user's presence list.
          #  4. If there is a from_key set, cross reference the list of users
          #     with the `presence_stream_cache` to see which ones we actually
          #     need to check.
          #  5. Load current state for the users.
          #
          # We don't try and limit the presence updates by the current token, as
          # sending down the rare duplicate is not a concern.
  
          with Measure(self.clock, "presence.get_new_events"):
              if from_key is not None:
                  from_key = int(from_key)
  
              max_token = self.store.get_current_presence_token()
              if from_key == max_token:
                  # This is necessary as due to the way stream ID generators work
                  # we may get updates that have a stream ID greater than the max
                  # token (e.g. max_token is N but stream generator may return
                  # results for N+2, due to N+1 not having finished being
                  # persisted yet).
                  #
                  # This is usually fine, as it just means that we may send down
                  # some presence updates multiple times. However, we need to be
                  # careful that the sync stream either actually does make some
                  # progress or doesn't return, otherwise clients will end up
                  # tight looping calling /sync due to it immediately returning
                  # the same token repeatedly.
                  #
                  # Hence this guard where we just return nothing so that the sync
                  # doesn't return. C.f. #5503.
                  return [], max_token
  
              presence = self.get_presence_handler()
              stream_change_cache = self.store.presence_stream_cache
  
              users_interested_in = await self._get_interested_in(user, explicit_room_id)
  
              user_ids_changed = set()
              changed = None
              if from_key:
                  changed = stream_change_cache.get_all_entities_changed(from_key)
  
              if changed is not None and len(changed) < 500:
                  # For small deltas, its quicker to get all changes and then
                  # work out if we share a room or they're in our presence list
                  get_updates_counter.labels("stream").inc()
                  for other_user_id in changed:
                      if other_user_id in users_interested_in:
                          user_ids_changed.add(other_user_id)
              else:
                  # Too many possible updates. Find all users we can see and check
                  # if any of them have changed.
                  get_updates_counter.labels("full").inc()
  
                  if from_key:
                      user_ids_changed = stream_change_cache.get_entities_changed(
                          users_interested_in, from_key
                      )
                  else:
                      user_ids_changed = users_interested_in
  
              updates = await presence.current_state_for_users(user_ids_changed)
  
          if include_offline:
              return (list(updates.values()), max_token)
          else:
              return (
                  [s for s in updates.values() if s.state != PresenceState.OFFLINE],
                  max_token,
              )
  
      def get_current_key(self):
          return self.store.get_current_presence_token()
  
      async def get_pagination_rows(self, user, pagination_config, key):
          return await self.get_new_events(user, from_key=None, include_offline=False)
  
      @cached(num_args=2, cache_context=True)
      async def _get_interested_in(self, user, explicit_room_id, cache_context):
          """Returns the set of users that the given user should see presence
          updates for
          """
          user_id = user.to_string()
          users_interested_in = set()
          users_interested_in.add(user_id)  # So that we receive our own presence
  
          users_who_share_room = await self.store.get_users_who_share_room_with_user(
              user_id, on_invalidate=cache_context.invalidate
          )
          users_interested_in.update(users_who_share_room)
  
          if explicit_room_id:
              user_ids = await self.store.get_users_in_room(
                  explicit_room_id, on_invalidate=cache_context.invalidate
              )
              users_interested_in.update(user_ids)
  
          return users_interested_in
  
  
  def handle_timeouts(user_states, is_mine_fn, syncing_user_ids, now):
      """Checks the presence of users that have timed out and updates as
      appropriate.
  
      Args:
          user_states(list): List of UserPresenceState's to check.
          is_mine_fn (fn): Function that returns if a user_id is ours
          syncing_user_ids (set): Set of user_ids with active syncs.
          now (int): Current time in ms.
  
      Returns:
          List of UserPresenceState updates
      """
      changes = {}  # Actual changes we need to notify people about
  
      for state in user_states:
          is_mine = is_mine_fn(state.user_id)
  
          new_state = handle_timeout(state, is_mine, syncing_user_ids, now)
          if new_state:
              changes[state.user_id] = new_state
  
      return list(changes.values())
  
  
  def handle_timeout(state, is_mine, syncing_user_ids, now):
      """Checks the presence of the user to see if any of the timers have elapsed
  
      Args:
          state (UserPresenceState)
          is_mine (bool): Whether the user is ours
          syncing_user_ids (set): Set of user_ids with active syncs.
          now (int): Current time in ms.
  
      Returns:
          A UserPresenceState update or None if no update.
      """
      if state.state == PresenceState.OFFLINE:
          # No timeouts are associated with offline states.
          return None
  
      changed = False
      user_id = state.user_id
  
      if is_mine:
          if state.state == PresenceState.ONLINE:
              if now - state.last_active_ts > IDLE_TIMER:
                  # Currently online, but last activity ages ago so auto
                  # idle
                  state = state.copy_and_replace(state=PresenceState.UNAVAILABLE)
                  changed = True
              elif now - state.last_active_ts > LAST_ACTIVE_GRANULARITY:
                  # So that we send down a notification that we've
                  # stopped updating.
                  changed = True
  
          if now - state.last_federation_update_ts > FEDERATION_PING_INTERVAL:
              # Need to send ping to other servers to ensure they don't
              # timeout and set us to offline
              changed = True
  
          # If there are have been no sync for a while (and none ongoing),
          # set presence to offline
          if user_id not in syncing_user_ids:
              # If the user has done something recently but hasn't synced,
              # don't set them as offline.
              sync_or_active = max(state.last_user_sync_ts, state.last_active_ts)
              if now - sync_or_active > SYNC_ONLINE_TIMEOUT:
                  state = state.copy_and_replace(
                      state=PresenceState.OFFLINE, status_msg=None
                  )
                  changed = True
      else:
          # We expect to be poked occasionally by the other side.
          # This is to protect against forgetful/buggy servers, so that
          # no one gets stuck online forever.
          if now - state.last_federation_update_ts > FEDERATION_TIMEOUT:
              # The other side seems to have disappeared.
              state = state.copy_and_replace(state=PresenceState.OFFLINE, status_msg=None)
              changed = True
  
      return state if changed else None
  
  
  def handle_update(prev_state, new_state, is_mine, wheel_timer, now):
      """Given a presence update:
          1. Add any appropriate timers.
          2. Check if we should notify anyone.
  
      Args:
          prev_state (UserPresenceState)
          new_state (UserPresenceState)
          is_mine (bool): Whether the user is ours
          wheel_timer (WheelTimer)
          now (int): Time now in ms
  
      Returns:
          3-tuple: `(new_state, persist_and_notify, federation_ping)` where:
              - new_state: is the state to actually persist
              - persist_and_notify (bool): whether to persist and notify people
              - federation_ping (bool): whether we should send a ping over federation
      """
      user_id = new_state.user_id
  
      persist_and_notify = False
      federation_ping = False
  
      # If the users are ours then we want to set up a bunch of timers
      # to time things out.
      if is_mine:
          if new_state.state == PresenceState.ONLINE:
              # Idle timer
              wheel_timer.insert(
                  now=now, obj=user_id, then=new_state.last_active_ts + IDLE_TIMER
              )
  
              active = now - new_state.last_active_ts < LAST_ACTIVE_GRANULARITY
              new_state = new_state.copy_and_replace(currently_active=active)
  
              if active:
                  wheel_timer.insert(
                      now=now,
                      obj=user_id,
                      then=new_state.last_active_ts + LAST_ACTIVE_GRANULARITY,
                  )
  
          if new_state.state != PresenceState.OFFLINE:
              # User has stopped syncing
              wheel_timer.insert(
                  now=now,
                  obj=user_id,
                  then=new_state.last_user_sync_ts + SYNC_ONLINE_TIMEOUT,
              )
  
              last_federate = new_state.last_federation_update_ts
              if now - last_federate > FEDERATION_PING_INTERVAL:
                  # Been a while since we've poked remote servers
                  new_state = new_state.copy_and_replace(last_federation_update_ts=now)
                  federation_ping = True
  
      else:
          wheel_timer.insert(
              now=now,
              obj=user_id,
              then=new_state.last_federation_update_ts + FEDERATION_TIMEOUT,
          )
  
      # Check whether the change was something worth notifying about
      if should_notify(prev_state, new_state):
          new_state = new_state.copy_and_replace(last_federation_update_ts=now)
          persist_and_notify = True
  
      return new_state, persist_and_notify, federation_ping
  
  
  @defer.inlineCallbacks
  def get_interested_parties(store, states):
      """Given a list of states return which entities (rooms, users)
      are interested in the given states.
  
      Args:
          states (list(UserPresenceState))
  
      Returns:
          2-tuple: `(room_ids_to_states, users_to_states)`,
          with each item being a dict of `entity_name` -> `[UserPresenceState]`
      """
      room_ids_to_states = {}  # type: Dict[str, List[UserPresenceState]]
      users_to_states = {}  # type: Dict[str, List[UserPresenceState]]
      for state in states:
          room_ids = yield store.get_rooms_for_user(state.user_id)
          for room_id in room_ids:
              room_ids_to_states.setdefault(room_id, []).append(state)
  
          # Always notify self
          users_to_states.setdefault(state.user_id, []).append(state)
  
      return room_ids_to_states, users_to_states
  
  
  @defer.inlineCallbacks
  def get_interested_remotes(store, states, state_handler):
      """Given a list of presence states figure out which remote servers
      should be sent which.
  
      All the presence states should be for local users only.
  
      Args:
          store (DataStore)
          states (list(UserPresenceState))
  
      Returns:
          Deferred list of ([destinations], [UserPresenceState]), where for
          each row the list of UserPresenceState should be sent to each
          destination
      """
      hosts_and_states = []
  
      # First we look up the rooms each user is in (as well as any explicit
      # subscriptions), then for each distinct room we look up the remote
      # hosts in those rooms.
      room_ids_to_states, users_to_states = yield get_interested_parties(store, states)
  
      for room_id, states in room_ids_to_states.items():
          hosts = yield state_handler.get_current_hosts_in_room(room_id)
          hosts_and_states.append((hosts, states))
  
      for user_id, states in users_to_states.items():
          host = get_domain_from_id(user_id)
          hosts_and_states.append(([host], states))
  
      return hosts_and_states
  