synapse/synapse/handlers/sync.py

# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2018 New Vector Ltd
#
# 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.

import collections
import itertools
import logging

from six import iteritems, itervalues

from twisted.internet import defer

from synapse.api.constants import EventTypes, Membership
from synapse.push.clientformat import format_push_rules_for_user
from synapse.storage.roommember import MemberSummary
from synapse.types import RoomStreamToken
from synapse.util.async_helpers import concurrently_execute
from synapse.util.caches.expiringcache import ExpiringCache
from synapse.util.caches.lrucache import LruCache
from synapse.util.caches.response_cache import ResponseCache
from synapse.util.logcontext import LoggingContext
from synapse.util.metrics import Measure, measure_func
from synapse.visibility import filter_events_for_client

logger = logging.getLogger(__name__)

# Store the cache that tracks which lazy-loaded members have been sent to a given
# client for no more than 30 minutes.
LAZY_LOADED_MEMBERS_CACHE_MAX_AGE = 30 * 60 * 1000

# Remember the last 100 members we sent to a client for the purposes of
# avoiding redundantly sending the same lazy-loaded members to the client
LAZY_LOADED_MEMBERS_CACHE_MAX_SIZE = 100


SyncConfig = collections.namedtuple("SyncConfig", [
    "user",
    "filter_collection",
    "is_guest",
    "request_key",
    "device_id",
])


class TimelineBatch(collections.namedtuple("TimelineBatch", [
    "prev_batch",
    "events",
    "limited",
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if room needs to be part of the sync result.
        """
        return bool(self.events)
    __bool__ = __nonzero__  # python3


class JoinedSyncResult(collections.namedtuple("JoinedSyncResult", [
    "room_id",           # str
    "timeline",          # TimelineBatch
    "state",             # dict[(str, str), FrozenEvent]
    "ephemeral",
    "account_data",
    "unread_notifications",
    "summary",
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if room needs to be part of the sync result.
        """
        return bool(
            self.timeline
            or self.state
            or self.ephemeral
            or self.account_data
            # nb the notification count does not, er, count: if there's nothing
            # else in the result, we don't need to send it.
        )
    __bool__ = __nonzero__  # python3


class ArchivedSyncResult(collections.namedtuple("ArchivedSyncResult", [
    "room_id",            # str
    "timeline",           # TimelineBatch
    "state",              # dict[(str, str), FrozenEvent]
    "account_data",
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if room needs to be part of the sync result.
        """
        return bool(
            self.timeline
            or self.state
            or self.account_data
        )
    __bool__ = __nonzero__  # python3


class InvitedSyncResult(collections.namedtuple("InvitedSyncResult", [
    "room_id",   # str
    "invite",    # FrozenEvent: the invite event
])):
    __slots__ = []

    def __nonzero__(self):
        """Invited rooms should always be reported to the client"""
        return True
    __bool__ = __nonzero__  # python3


class GroupsSyncResult(collections.namedtuple("GroupsSyncResult", [
    "join",
    "invite",
    "leave",
])):
    __slots__ = []

    def __nonzero__(self):
        return bool(self.join or self.invite or self.leave)
    __bool__ = __nonzero__  # python3


class DeviceLists(collections.namedtuple("DeviceLists", [
    "changed",   # list of user_ids whose devices may have changed
    "left",      # list of user_ids whose devices we no longer track
])):
    __slots__ = []

    def __nonzero__(self):
        return bool(self.changed or self.left)
    __bool__ = __nonzero__  # python3


class SyncResult(collections.namedtuple("SyncResult", [
    "next_batch",  # Token for the next sync
    "presence",  # List of presence events for the user.
    "account_data",  # List of account_data events for the user.
    "joined",  # JoinedSyncResult for each joined room.
    "invited",  # InvitedSyncResult for each invited room.
    "archived",  # ArchivedSyncResult for each archived room.
    "to_device",  # List of direct messages for the device.
    "device_lists",  # List of user_ids whose devices have changed
    "device_one_time_keys_count",  # Dict of algorithm to count for one time keys
                                   # for this device
    "groups",
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if the notifier needs to wait for more events when polling for
        events.
        """
        return bool(
            self.presence or
            self.joined or
            self.invited or
            self.archived or
            self.account_data or
            self.to_device or
            self.device_lists or
            self.groups
        )
    __bool__ = __nonzero__  # python3


class SyncHandler(object):

    def __init__(self, hs):
        self.hs_config = hs.config
        self.store = hs.get_datastore()
        self.notifier = hs.get_notifier()
        self.presence_handler = hs.get_presence_handler()
        self.event_sources = hs.get_event_sources()
        self.clock = hs.get_clock()
        self.response_cache = ResponseCache(hs, "sync")
        self.state = hs.get_state_handler()
        self.auth = hs.get_auth()

        # ExpiringCache((User, Device)) -> LruCache(state_key => event_id)
        self.lazy_loaded_members_cache = ExpiringCache(
            "lazy_loaded_members_cache", self.clock,
            max_len=0, expiry_ms=LAZY_LOADED_MEMBERS_CACHE_MAX_AGE,
        )

    @defer.inlineCallbacks
    def wait_for_sync_for_user(self, sync_config, since_token=None, timeout=0,
                               full_state=False):
        """Get the sync for a client if we have new data for it now. Otherwise
        wait for new data to arrive on the server. If the timeout expires, then
        return an empty sync result.
        Returns:
            Deferred[SyncResult]
        """
        # If the user is not part of the mau group, then check that limits have
        # not been exceeded (if not part of the group by this point, almost certain
        # auth_blocking will occur)
        user_id = sync_config.user.to_string()
        yield self.auth.check_auth_blocking(user_id)

        res = yield self.response_cache.wrap(
            sync_config.request_key,
            self._wait_for_sync_for_user,
            sync_config, since_token, timeout, full_state,
        )
        defer.returnValue(res)

    @defer.inlineCallbacks
    def _wait_for_sync_for_user(self, sync_config, since_token, timeout,
                                full_state):
        context = LoggingContext.current_context()
        if context:
            if since_token is None:
                context.tag = "initial_sync"
            elif full_state:
                context.tag = "full_state_sync"
            else:
                context.tag = "incremental_sync"

        if timeout == 0 or since_token is None or full_state:
            # we are going to return immediately, so don't bother calling
            # notifier.wait_for_events.
            result = yield self.current_sync_for_user(
                sync_config, since_token, full_state=full_state,
            )
            defer.returnValue(result)
        else:
            def current_sync_callback(before_token, after_token):
                return self.current_sync_for_user(sync_config, since_token)

            result = yield self.notifier.wait_for_events(
                sync_config.user.to_string(), timeout, current_sync_callback,
                from_token=since_token,
            )
            defer.returnValue(result)

    def current_sync_for_user(self, sync_config, since_token=None,
                              full_state=False):
        """Get the sync for client needed to match what the server has now.
        Returns:
            A Deferred SyncResult.
        """
        return self.generate_sync_result(sync_config, since_token, full_state)

    @defer.inlineCallbacks
    def push_rules_for_user(self, user):
        user_id = user.to_string()
        rules = yield self.store.get_push_rules_for_user(user_id)
        rules = format_push_rules_for_user(user, rules)
        defer.returnValue(rules)

    @defer.inlineCallbacks
    def ephemeral_by_room(self, sync_result_builder, now_token, since_token=None):
        """Get the ephemeral events for each room the user is in
        Args:
            sync_result_builder(SyncResultBuilder)
            now_token (StreamToken): Where the server is currently up to.
            since_token (StreamToken): Where the server was when the client
                last synced.
        Returns:
            A tuple of the now StreamToken, updated to reflect the which typing
            events are included, and a dict mapping from room_id to a list of
            typing events for that room.
        """

        sync_config = sync_result_builder.sync_config

        with Measure(self.clock, "ephemeral_by_room"):
            typing_key = since_token.typing_key if since_token else "0"

            room_ids = sync_result_builder.joined_room_ids

            typing_source = self.event_sources.sources["typing"]
            typing, typing_key = yield typing_source.get_new_events(
                user=sync_config.user,
                from_key=typing_key,
                limit=sync_config.filter_collection.ephemeral_limit(),
                room_ids=room_ids,
                is_guest=sync_config.is_guest,
            )
            now_token = now_token.copy_and_replace("typing_key", typing_key)

            ephemeral_by_room = {}

            for event in typing:
                # we want to exclude the room_id from the event, but modifying the
                # result returned by the event source is poor form (it might cache
                # the object)
                room_id = event["room_id"]
                event_copy = {k: v for (k, v) in iteritems(event)
                              if k != "room_id"}
                ephemeral_by_room.setdefault(room_id, []).append(event_copy)

            receipt_key = since_token.receipt_key if since_token else "0"

            receipt_source = self.event_sources.sources["receipt"]
            receipts, receipt_key = yield receipt_source.get_new_events(
                user=sync_config.user,
                from_key=receipt_key,
                limit=sync_config.filter_collection.ephemeral_limit(),
                room_ids=room_ids,
                is_guest=sync_config.is_guest,
            )
            now_token = now_token.copy_and_replace("receipt_key", receipt_key)

            for event in receipts:
                room_id = event["room_id"]
                # exclude room id, as above
                event_copy = {k: v for (k, v) in iteritems(event)
                              if k != "room_id"}
                ephemeral_by_room.setdefault(room_id, []).append(event_copy)

        defer.returnValue((now_token, ephemeral_by_room))

    @defer.inlineCallbacks
    def _load_filtered_recents(self, room_id, sync_config, now_token,
                               since_token=None, recents=None, newly_joined_room=False):
        """
        Returns:
            a Deferred TimelineBatch
        """
        with Measure(self.clock, "load_filtered_recents"):
            timeline_limit = sync_config.filter_collection.timeline_limit()
            block_all_timeline = sync_config.filter_collection.blocks_all_room_timeline()

            if recents is None or newly_joined_room or timeline_limit < len(recents):
                limited = True
            else:
                limited = False

            if recents:
                recents = sync_config.filter_collection.filter_room_timeline(recents)

                # We check if there are any state events, if there are then we pass
                # all current state events to the filter_events function. This is to
                # ensure that we always include current state in the timeline
                current_state_ids = frozenset()
                if any(e.is_state() for e in recents):
                    current_state_ids = yield self.state.get_current_state_ids(room_id)
                    current_state_ids = frozenset(itervalues(current_state_ids))

                recents = yield filter_events_for_client(
                    self.store,
                    sync_config.user.to_string(),
                    recents,
                    always_include_ids=current_state_ids,
                )
            else:
                recents = []

            if not limited or block_all_timeline:
                defer.returnValue(TimelineBatch(
                    events=recents,
                    prev_batch=now_token,
                    limited=False
                ))

            filtering_factor = 2
            load_limit = max(timeline_limit * filtering_factor, 10)
            max_repeat = 5  # Only try a few times per room, otherwise
            room_key = now_token.room_key
            end_key = room_key

            since_key = None
            if since_token and not newly_joined_room:
                since_key = since_token.room_key

            while limited and len(recents) < timeline_limit and max_repeat:
                # If we have a since_key then we are trying to get any events
                # that have happened since `since_key` up to `end_key`, so we
                # can just use `get_room_events_stream_for_room`.
                # Otherwise, we want to return the last N events in the room
                # in toplogical ordering.
                if since_key:
                    events, end_key = yield self.store.get_room_events_stream_for_room(
                        room_id,
                        limit=load_limit + 1,
                        from_key=since_key,
                        to_key=end_key,
                    )
                else:
                    events, end_key = yield self.store.get_recent_events_for_room(
                        room_id,
                        limit=load_limit + 1,
                        end_token=end_key,
                    )
                loaded_recents = sync_config.filter_collection.filter_room_timeline(
                    events
                )

                # We check if there are any state events, if there are then we pass
                # all current state events to the filter_events function. This is to
                # ensure that we always include current state in the timeline
                current_state_ids = frozenset()
                if any(e.is_state() for e in loaded_recents):
                    current_state_ids = yield self.state.get_current_state_ids(room_id)
                    current_state_ids = frozenset(itervalues(current_state_ids))

                loaded_recents = yield filter_events_for_client(
                    self.store,
                    sync_config.user.to_string(),
                    loaded_recents,
                    always_include_ids=current_state_ids,
                )
                loaded_recents.extend(recents)
                recents = loaded_recents

                if len(events) <= load_limit:
                    limited = False
                    break
                max_repeat -= 1

            if len(recents) > timeline_limit:
                limited = True
                recents = recents[-timeline_limit:]
                room_key = recents[0].internal_metadata.before

            prev_batch_token = now_token.copy_and_replace(
                "room_key", room_key
            )

        defer.returnValue(TimelineBatch(
            events=recents,
            prev_batch=prev_batch_token,
            limited=limited or newly_joined_room
        ))

    @defer.inlineCallbacks
    def get_state_after_event(self, event, types=None, filtered_types=None):
        """
        Get the room state after the given event

        Args:
            event(synapse.events.EventBase): event of interest
            types(list[(str, str|None)]|None): List of (type, state_key) tuples
                which are used to filter the state fetched. If `state_key` is None,
                all events are returned of the given type.
                May be None, which matches any key.
            filtered_types(list[str]|None): Only apply filtering via `types` to this
                list of event types.  Other types of events are returned unfiltered.
                If None, `types` filtering is applied to all events.

        Returns:
            A Deferred map from ((type, state_key)->Event)
        """
        state_ids = yield self.store.get_state_ids_for_event(
            event.event_id, types, filtered_types=filtered_types,
        )
        if event.is_state():
            state_ids = state_ids.copy()
            state_ids[(event.type, event.state_key)] = event.event_id
        defer.returnValue(state_ids)

    @defer.inlineCallbacks
    def get_state_at(self, room_id, stream_position, types=None, filtered_types=None):
        """ Get the room state at a particular stream position

        Args:
            room_id(str): room for which to get state
            stream_position(StreamToken): point at which to get state
            types(list[(str, str|None)]|None): List of (type, state_key) tuples
                which are used to filter the state fetched. If `state_key` is None,
                all events are returned of the given type.
            filtered_types(list[str]|None): Only apply filtering via `types` to this
                list of event types.  Other types of events are returned unfiltered.
                If None, `types` filtering is applied to all events.

        Returns:
            A Deferred map from ((type, state_key)->Event)
        """
        # FIXME this claims to get the state at a stream position, but
        # get_recent_events_for_room operates by topo ordering. This therefore
        # does not reliably give you the state at the given stream position.
        # (https://github.com/matrix-org/synapse/issues/3305)
        last_events, _ = yield self.store.get_recent_events_for_room(
            room_id, end_token=stream_position.room_key, limit=1,
        )

        if last_events:
            last_event = last_events[-1]
            state = yield self.get_state_after_event(
                last_event, types, filtered_types=filtered_types,
            )

        else:
            # no events in this room - so presumably no state
            state = {}
        defer.returnValue(state)

    @defer.inlineCallbacks
    def compute_summary(self, room_id, sync_config, batch, state, now_token):
        """ Works out a room summary block for this room, summarising the number
        of joined members in the room, and providing the 'hero' members if the
        room has no name so clients can consistently name rooms.  Also adds
        state events to 'state' if needed to describe the heroes.

        Args:
            room_id(str):
            sync_config(synapse.handlers.sync.SyncConfig):
            batch(synapse.handlers.sync.TimelineBatch): The timeline batch for
                the room that will be sent to the user.
            state(dict): dict of (type, state_key) -> Event as returned by
                compute_state_delta
            now_token(str): Token of the end of the current batch.

        Returns:
             A deferred dict describing the room summary
        """

        # FIXME: we could/should get this from room_stats when matthew/stats lands

        # FIXME: this promulgates https://github.com/matrix-org/synapse/issues/3305
        last_events, _ = yield self.store.get_recent_event_ids_for_room(
            room_id, end_token=now_token.room_key, limit=1,
        )

        if not last_events:
            defer.returnValue(None)
            return

        last_event = last_events[-1]
        state_ids = yield self.store.get_state_ids_for_event(
            last_event.event_id, [
                (EventTypes.Name, ''),
                (EventTypes.CanonicalAlias, ''),
            ]
        )

        # this is heavily cached, thus: fast.
        details = yield self.store.get_room_summary(room_id)

        name_id = state_ids.get((EventTypes.Name, ''))
        canonical_alias_id = state_ids.get((EventTypes.CanonicalAlias, ''))

        summary = {}
        empty_ms = MemberSummary([], 0)

        # TODO: only send these when they change.
        summary["m.joined_member_count"] = (
            details.get(Membership.JOIN, empty_ms).count
        )
        summary["m.invited_member_count"] = (
            details.get(Membership.INVITE, empty_ms).count
        )

        if name_id or canonical_alias_id:
            defer.returnValue(summary)

        joined_user_ids = [
            r[0] for r in details.get(Membership.JOIN, empty_ms).members
        ]
        invited_user_ids = [
            r[0] for r in details.get(Membership.INVITE, empty_ms).members
        ]
        gone_user_ids = (
            [r[0] for r in details.get(Membership.LEAVE, empty_ms).members] +
            [r[0] for r in details.get(Membership.BAN, empty_ms).members]
        )

        # FIXME: only build up a member_ids list for our heroes
        member_ids = {}
        for membership in (
            Membership.JOIN,
            Membership.INVITE,
            Membership.LEAVE,
            Membership.BAN
        ):
            for user_id, event_id in details.get(membership, empty_ms).members:
                member_ids[user_id] = event_id

        # FIXME: order by stream ordering rather than as returned by SQL
        me = sync_config.user.to_string()
        if (joined_user_ids or invited_user_ids):
            summary['m.heroes'] = sorted(
                [
                    user_id
                    for user_id in (joined_user_ids + invited_user_ids)
                    if user_id != me
                ]
            )[0:5]
        else:
            summary['m.heroes'] = sorted(
                [
                    user_id
                    for user_id in gone_user_ids
                    if user_id != me
                ]
            )[0:5]

        if not sync_config.filter_collection.lazy_load_members():
            defer.returnValue(summary)

        # ensure we send membership events for heroes if needed
        cache_key = (sync_config.user.to_string(), sync_config.device_id)
        cache = self.get_lazy_loaded_members_cache(cache_key)

        # track which members the client should already know about via LL:
        # Ones which are already in state...
        existing_members = set(
            user_id for (typ, user_id) in state.keys()
            if typ == EventTypes.Member
        )

        # ...or ones which are in the timeline...
        for ev in batch.events:
            if ev.type == EventTypes.Member:
                existing_members.add(ev.state_key)

        # ...and then ensure any missing ones get included in state.
        missing_hero_event_ids = [
            member_ids[hero_id]
            for hero_id in summary['m.heroes']
            if (
                cache.get(hero_id) != member_ids[hero_id] and
                hero_id not in existing_members
            )
        ]

        missing_hero_state = yield self.store.get_events(missing_hero_event_ids)
        missing_hero_state = missing_hero_state.values()

        for s in missing_hero_state:
            cache.set(s.state_key, s.event_id)
            state[(EventTypes.Member, s.state_key)] = s

        defer.returnValue(summary)

    def get_lazy_loaded_members_cache(self, cache_key):
        cache = self.lazy_loaded_members_cache.get(cache_key)
        if cache is None:
            logger.debug("creating LruCache for %r", cache_key)
            cache = LruCache(LAZY_LOADED_MEMBERS_CACHE_MAX_SIZE)
            self.lazy_loaded_members_cache[cache_key] = cache
        else:
            logger.debug("found LruCache for %r", cache_key)
        return cache

    @defer.inlineCallbacks
    def compute_state_delta(self, room_id, batch, sync_config, since_token, now_token,
                            full_state):
        """ Works out the difference in state between the start of the timeline
        and the previous sync.

        Args:
            room_id(str):
            batch(synapse.handlers.sync.TimelineBatch): The timeline batch for
                the room that will be sent to the user.
            sync_config(synapse.handlers.sync.SyncConfig):
            since_token(str|None): Token of the end of the previous batch. May
                be None.
            now_token(str): Token of the end of the current batch.
            full_state(bool): Whether to force returning the full state.

        Returns:
             A deferred dict of (type, state_key) -> Event
        """
        # TODO(mjark) Check if the state events were received by the server
        # after the previous sync, since we need to include those state
        # updates even if they occured logically before the previous event.
        # TODO(mjark) Check for new redactions in the state events.

        with Measure(self.clock, "compute_state_delta"):

            types = None
            filtered_types = None

            lazy_load_members = sync_config.filter_collection.lazy_load_members()
            include_redundant_members = (
                sync_config.filter_collection.include_redundant_members()
            )

            if lazy_load_members:
                # We only request state for the members needed to display the
                # timeline:

                types = [
                    (EventTypes.Member, state_key)
                    for state_key in set(
                        event.sender  # FIXME: we also care about invite targets etc.
                        for event in batch.events
                    )
                ]

                # only apply the filtering to room members
                filtered_types = [EventTypes.Member]

            timeline_state = {
                (event.type, event.state_key): event.event_id
                for event in batch.events if event.is_state()
            }

            if full_state:
                if batch:
                    current_state_ids = yield self.store.get_state_ids_for_event(
                        batch.events[-1].event_id, types=types,
                        filtered_types=filtered_types,
                    )

                    state_ids = yield self.store.get_state_ids_for_event(
                        batch.events[0].event_id, types=types,
                        filtered_types=filtered_types,
                    )

                else:
                    current_state_ids = yield self.get_state_at(
                        room_id, stream_position=now_token, types=types,
                        filtered_types=filtered_types,
                    )

                    state_ids = current_state_ids

                state_ids = _calculate_state(
                    timeline_contains=timeline_state,
                    timeline_start=state_ids,
                    previous={},
                    current=current_state_ids,
                    lazy_load_members=lazy_load_members,
                )
            elif batch.limited:
                state_at_timeline_start = yield self.store.get_state_ids_for_event(
                    batch.events[0].event_id, types=types,
                    filtered_types=filtered_types,
                )

                # for now, we disable LL for gappy syncs - see
                # https://github.com/vector-im/riot-web/issues/7211#issuecomment-419976346
                # N.B. this slows down incr syncs as we are now processing way
                # more state in the server than if we were LLing.
                #
                # We still have to filter timeline_start to LL entries (above) in order
                # for _calculate_state's LL logic to work, as we have to include LL
                # members for timeline senders in case they weren't loaded in the initial
                # sync.  We do this by (counterintuitively) by filtering timeline_start
                # members to just be ones which were timeline senders, which then ensures
                # all of the rest get included in the state block (if we need to know
                # about them).
                types = None
                filtered_types = None

                state_at_previous_sync = yield self.get_state_at(
                    room_id, stream_position=since_token, types=types,
                    filtered_types=filtered_types,
                )

                current_state_ids = yield self.store.get_state_ids_for_event(
                    batch.events[-1].event_id, types=types,
                    filtered_types=filtered_types,
                )

                state_ids = _calculate_state(
                    timeline_contains=timeline_state,
                    timeline_start=state_at_timeline_start,
                    previous=state_at_previous_sync,
                    current=current_state_ids,
                    # we have to include LL members in case LL initial sync missed them
                    lazy_load_members=lazy_load_members,
                )
            else:
                state_ids = {}
                if lazy_load_members:
                    if types:
                        # We're returning an incremental sync, with no
                        # "gap" since the previous sync, so normally there would be
                        # no state to return.
                        # But we're lazy-loading, so the client might need some more
                        # member events to understand the events in this timeline.
                        # So we fish out all the member events corresponding to the
                        # timeline here, and then dedupe any redundant ones below.

                        state_ids = yield self.store.get_state_ids_for_event(
                            batch.events[0].event_id, types=types,
                            filtered_types=None,  # we only want members!
                        )

            if lazy_load_members and not include_redundant_members:
                cache_key = (sync_config.user.to_string(), sync_config.device_id)
                cache = self.get_lazy_loaded_members_cache(cache_key)

                # if it's a new sync sequence, then assume the client has had
                # amnesia and doesn't want any recent lazy-loaded members
                # de-duplicated.
                if since_token is None:
                    logger.debug("clearing LruCache for %r", cache_key)
                    cache.clear()
                else:
                    # only send members which aren't in our LruCache (either
                    # because they're new to this client or have been pushed out
                    # of the cache)
                    logger.debug("filtering state from %r...", state_ids)
                    state_ids = {
                        t: event_id
                        for t, event_id in iteritems(state_ids)
                        if cache.get(t[1]) != event_id
                    }
                    logger.debug("...to %r", state_ids)

                # add any member IDs we are about to send into our LruCache
                for t, event_id in itertools.chain(
                    state_ids.items(),
                    timeline_state.items(),
                ):
                    if t[0] == EventTypes.Member:
                        cache.set(t[1], event_id)

        state = {}
        if state_ids:
            state = yield self.store.get_events(list(state_ids.values()))

        defer.returnValue({
            (e.type, e.state_key): e
            for e in sync_config.filter_collection.filter_room_state(list(state.values()))
        })

    @defer.inlineCallbacks
    def unread_notifs_for_room_id(self, room_id, sync_config):
        with Measure(self.clock, "unread_notifs_for_room_id"):
            last_unread_event_id = yield self.store.get_last_receipt_event_id_for_user(
                user_id=sync_config.user.to_string(),
                room_id=room_id,
                receipt_type="m.read"
            )

            notifs = []
            if last_unread_event_id:
                notifs = yield self.store.get_unread_event_push_actions_by_room_for_user(
                    room_id, sync_config.user.to_string(), last_unread_event_id
                )
                defer.returnValue(notifs)

        # There is no new information in this period, so your notification
        # count is whatever it was last time.
        defer.returnValue(None)

    @defer.inlineCallbacks
    def generate_sync_result(self, sync_config, since_token=None, full_state=False):
        """Generates a sync result.

        Args:
            sync_config (SyncConfig)
            since_token (StreamToken)
            full_state (bool)

        Returns:
            Deferred(SyncResult)
        """
        logger.info("Calculating sync response for %r", sync_config.user)

        # NB: The now_token gets changed by some of the generate_sync_* methods,
        # this is due to some of the underlying streams not supporting the ability
        # to query up to a given point.
        # Always use the `now_token` in `SyncResultBuilder`
        now_token = yield self.event_sources.get_current_token()

        user_id = sync_config.user.to_string()
        app_service = self.store.get_app_service_by_user_id(user_id)
        if app_service:
            # We no longer support AS users using /sync directly.
            # See https://github.com/matrix-org/matrix-doc/issues/1144
            raise NotImplementedError()
        else:
            joined_room_ids = yield self.get_rooms_for_user_at(
                user_id, now_token.room_stream_id,
            )

        sync_result_builder = SyncResultBuilder(
            sync_config, full_state,
            since_token=since_token,
            now_token=now_token,
            joined_room_ids=joined_room_ids,
        )

        account_data_by_room = yield self._generate_sync_entry_for_account_data(
            sync_result_builder
        )

        res = yield self._generate_sync_entry_for_rooms(
            sync_result_builder, account_data_by_room
        )
        newly_joined_rooms, newly_joined_users, _, _ = res
        _, _, newly_left_rooms, newly_left_users = res

        block_all_presence_data = (
            since_token is None and
            sync_config.filter_collection.blocks_all_presence()
        )
        if self.hs_config.use_presence and not block_all_presence_data:
            yield self._generate_sync_entry_for_presence(
                sync_result_builder, newly_joined_rooms, newly_joined_users
            )

        yield self._generate_sync_entry_for_to_device(sync_result_builder)

        device_lists = yield self._generate_sync_entry_for_device_list(
            sync_result_builder,
            newly_joined_rooms=newly_joined_rooms,
            newly_joined_users=newly_joined_users,
            newly_left_rooms=newly_left_rooms,
            newly_left_users=newly_left_users,
        )

        device_id = sync_config.device_id
        one_time_key_counts = {}
        if device_id:
            one_time_key_counts = yield self.store.count_e2e_one_time_keys(
                user_id, device_id
            )

        yield self._generate_sync_entry_for_groups(sync_result_builder)

        defer.returnValue(SyncResult(
            presence=sync_result_builder.presence,
            account_data=sync_result_builder.account_data,
            joined=sync_result_builder.joined,
            invited=sync_result_builder.invited,
            archived=sync_result_builder.archived,
            to_device=sync_result_builder.to_device,
            device_lists=device_lists,
            groups=sync_result_builder.groups,
            device_one_time_keys_count=one_time_key_counts,
            next_batch=sync_result_builder.now_token,
        ))

    @measure_func("_generate_sync_entry_for_groups")
    @defer.inlineCallbacks
    def _generate_sync_entry_for_groups(self, sync_result_builder):
        user_id = sync_result_builder.sync_config.user.to_string()
        since_token = sync_result_builder.since_token
        now_token = sync_result_builder.now_token

        if since_token and since_token.groups_key:
            results = yield self.store.get_groups_changes_for_user(
                user_id, since_token.groups_key, now_token.groups_key,
            )
        else:
            results = yield self.store.get_all_groups_for_user(
                user_id, now_token.groups_key,
            )

        invited = {}
        joined = {}
        left = {}
        for result in results:
            membership = result["membership"]
            group_id = result["group_id"]
            gtype = result["type"]
            content = result["content"]

            if membership == "join":
                if gtype == "membership":
                    # TODO: Add profile
                    content.pop("membership", None)
                    joined[group_id] = content["content"]
                else:
                    joined.setdefault(group_id, {})[gtype] = content
            elif membership == "invite":
                if gtype == "membership":
                    content.pop("membership", None)
                    invited[group_id] = content["content"]
            else:
                if gtype == "membership":
                    left[group_id] = content["content"]

        sync_result_builder.groups = GroupsSyncResult(
            join=joined,
            invite=invited,
            leave=left,
        )

    @measure_func("_generate_sync_entry_for_device_list")
    @defer.inlineCallbacks
    def _generate_sync_entry_for_device_list(self, sync_result_builder,
                                             newly_joined_rooms, newly_joined_users,
                                             newly_left_rooms, newly_left_users):
        user_id = sync_result_builder.sync_config.user.to_string()
        since_token = sync_result_builder.since_token

        if since_token and since_token.device_list_key:
            changed = yield self.store.get_user_whose_devices_changed(
                since_token.device_list_key
            )

            # TODO: Be more clever than this, i.e. remove users who we already
            # share a room with?
            for room_id in newly_joined_rooms:
                joined_users = yield self.state.get_current_user_in_room(room_id)
                newly_joined_users.update(joined_users)

            for room_id in newly_left_rooms:
                left_users = yield self.state.get_current_user_in_room(room_id)
                newly_left_users.update(left_users)

            # TODO: Check that these users are actually new, i.e. either they
            # weren't in the previous sync *or* they left and rejoined.
            changed.update(newly_joined_users)

            if not changed and not newly_left_users:
                defer.returnValue(DeviceLists(
                    changed=[],
                    left=newly_left_users,
                ))

            users_who_share_room = yield self.store.get_users_who_share_room_with_user(
                user_id
            )

            defer.returnValue(DeviceLists(
                changed=users_who_share_room & changed,
                left=set(newly_left_users) - users_who_share_room,
            ))
        else:
            defer.returnValue(DeviceLists(
                changed=[],
                left=[],
            ))

    @defer.inlineCallbacks
    def _generate_sync_entry_for_to_device(self, sync_result_builder):
        """Generates the portion of the sync response. Populates
        `sync_result_builder` with the result.

        Args:
            sync_result_builder(SyncResultBuilder)

        Returns:
            Deferred(dict): A dictionary containing the per room account data.
        """
        user_id = sync_result_builder.sync_config.user.to_string()
        device_id = sync_result_builder.sync_config.device_id
        now_token = sync_result_builder.now_token
        since_stream_id = 0
        if sync_result_builder.since_token is not None:
            since_stream_id = int(sync_result_builder.since_token.to_device_key)

        if since_stream_id != int(now_token.to_device_key):
            # We only delete messages when a new message comes in, but that's
            # fine so long as we delete them at some point.

            deleted = yield self.store.delete_messages_for_device(
                user_id, device_id, since_stream_id
            )
            logger.debug("Deleted %d to-device messages up to %d",
                         deleted, since_stream_id)

            messages, stream_id = yield self.store.get_new_messages_for_device(
                user_id, device_id, since_stream_id, now_token.to_device_key
            )

            logger.debug(
                "Returning %d to-device messages between %d and %d (current token: %d)",
                len(messages), since_stream_id, stream_id, now_token.to_device_key
            )
            sync_result_builder.now_token = now_token.copy_and_replace(
                "to_device_key", stream_id
            )
            sync_result_builder.to_device = messages
        else:
            sync_result_builder.to_device = []

    @defer.inlineCallbacks
    def _generate_sync_entry_for_account_data(self, sync_result_builder):
        """Generates the account data portion of the sync response. Populates
        `sync_result_builder` with the result.

        Args:
            sync_result_builder(SyncResultBuilder)

        Returns:
            Deferred(dict): A dictionary containing the per room account data.
        """
        sync_config = sync_result_builder.sync_config
        user_id = sync_result_builder.sync_config.user.to_string()
        since_token = sync_result_builder.since_token

        if since_token and not sync_result_builder.full_state:
            account_data, account_data_by_room = (
                yield self.store.get_updated_account_data_for_user(
                    user_id,
                    since_token.account_data_key,
                )
            )

            push_rules_changed = yield self.store.have_push_rules_changed_for_user(
                user_id, int(since_token.push_rules_key)
            )

            if push_rules_changed:
                account_data["m.push_rules"] = yield self.push_rules_for_user(
                    sync_config.user
                )
        else:
            account_data, account_data_by_room = (
                yield self.store.get_account_data_for_user(
                    sync_config.user.to_string()
                )
            )

            account_data['m.push_rules'] = yield self.push_rules_for_user(
                sync_config.user
            )

        account_data_for_user = sync_config.filter_collection.filter_account_data([
            {"type": account_data_type, "content": content}
            for account_data_type, content in account_data.items()
        ])

        sync_result_builder.account_data = account_data_for_user

        defer.returnValue(account_data_by_room)

    @defer.inlineCallbacks
    def _generate_sync_entry_for_presence(self, sync_result_builder, newly_joined_rooms,
                                          newly_joined_users):
        """Generates the presence portion of the sync response. Populates the
        `sync_result_builder` with the result.

        Args:
            sync_result_builder(SyncResultBuilder)
            newly_joined_rooms(list): List of rooms that the user has joined
                since the last sync (or empty if an initial sync)
            newly_joined_users(list): List of users that have joined rooms
                since the last sync (or empty if an initial sync)
        """
        now_token = sync_result_builder.now_token
        sync_config = sync_result_builder.sync_config
        user = sync_result_builder.sync_config.user

        presence_source = self.event_sources.sources["presence"]

        since_token = sync_result_builder.since_token
        if since_token and not sync_result_builder.full_state:
            presence_key = since_token.presence_key
            include_offline = True
        else:
            presence_key = None
            include_offline = False

        presence, presence_key = yield presence_source.get_new_events(
            user=user,
            from_key=presence_key,
            is_guest=sync_config.is_guest,
            include_offline=include_offline,
        )
        sync_result_builder.now_token = now_token.copy_and_replace(
            "presence_key", presence_key
        )

        extra_users_ids = set(newly_joined_users)
        for room_id in newly_joined_rooms:
            users = yield self.state.get_current_user_in_room(room_id)
            extra_users_ids.update(users)
        extra_users_ids.discard(user.to_string())

        if extra_users_ids:
            states = yield self.presence_handler.get_states(
                extra_users_ids,
            )
            presence.extend(states)

            # Deduplicate the presence entries so that there's at most one per user
            presence = list({p.user_id: p for p in presence}.values())

        presence = sync_config.filter_collection.filter_presence(
            presence
        )

        sync_result_builder.presence = presence

    @defer.inlineCallbacks
    def _generate_sync_entry_for_rooms(self, sync_result_builder, account_data_by_room):
        """Generates the rooms portion of the sync response. Populates the
        `sync_result_builder` with the result.

        Args:
            sync_result_builder(SyncResultBuilder)
            account_data_by_room(dict): Dictionary of per room account data

        Returns:
            Deferred(tuple): Returns a 4-tuple of
            `(newly_joined_rooms, newly_joined_users, newly_left_rooms, newly_left_users)`
        """
        user_id = sync_result_builder.sync_config.user.to_string()
        block_all_room_ephemeral = (
            sync_result_builder.since_token is None and
            sync_result_builder.sync_config.filter_collection.blocks_all_room_ephemeral()
        )

        if block_all_room_ephemeral:
            ephemeral_by_room = {}
        else:
            now_token, ephemeral_by_room = yield self.ephemeral_by_room(
                sync_result_builder,
                now_token=sync_result_builder.now_token,
                since_token=sync_result_builder.since_token,
            )
            sync_result_builder.now_token = now_token

        # We check up front if anything has changed, if it hasn't then there is
        # no point in going futher.
        since_token = sync_result_builder.since_token
        if not sync_result_builder.full_state:
            if since_token and not ephemeral_by_room and not account_data_by_room:
                have_changed = yield self._have_rooms_changed(sync_result_builder)
                if not have_changed:
                    tags_by_room = yield self.store.get_updated_tags(
                        user_id,
                        since_token.account_data_key,
                    )
                    if not tags_by_room:
                        logger.debug("no-oping sync")
                        defer.returnValue(([], [], [], []))

        ignored_account_data = yield self.store.get_global_account_data_by_type_for_user(
            "m.ignored_user_list", user_id=user_id,
        )

        if ignored_account_data:
            ignored_users = ignored_account_data.get("ignored_users", {}).keys()
        else:
            ignored_users = frozenset()

        if since_token:
            res = yield self._get_rooms_changed(sync_result_builder, ignored_users)
            room_entries, invited, newly_joined_rooms, newly_left_rooms = res

            tags_by_room = yield self.store.get_updated_tags(
                user_id, since_token.account_data_key,
            )
        else:
            res = yield self._get_all_rooms(sync_result_builder, ignored_users)
            room_entries, invited, newly_joined_rooms = res
            newly_left_rooms = []

            tags_by_room = yield self.store.get_tags_for_user(user_id)

        def handle_room_entries(room_entry):
            return self._generate_room_entry(
                sync_result_builder,
                ignored_users,
                room_entry,
                ephemeral=ephemeral_by_room.get(room_entry.room_id, []),
                tags=tags_by_room.get(room_entry.room_id),
                account_data=account_data_by_room.get(room_entry.room_id, {}),
                always_include=sync_result_builder.full_state,
            )

        yield concurrently_execute(handle_room_entries, room_entries, 10)

        sync_result_builder.invited.extend(invited)

        # Now we want to get any newly joined users
        newly_joined_users = set()
        newly_left_users = set()
        if since_token:
            for joined_sync in sync_result_builder.joined:
                it = itertools.chain(
                    joined_sync.timeline.events, itervalues(joined_sync.state)
                )
                for event in it:
                    if event.type == EventTypes.Member:
                        if event.membership == Membership.JOIN:
                            newly_joined_users.add(event.state_key)
                        else:
                            prev_content = event.unsigned.get("prev_content", {})
                            prev_membership = prev_content.get("membership", None)
                            if prev_membership == Membership.JOIN:
                                newly_left_users.add(event.state_key)

        newly_left_users -= newly_joined_users

        defer.returnValue((
            newly_joined_rooms,
            newly_joined_users,
            newly_left_rooms,
            newly_left_users,
        ))

    @defer.inlineCallbacks
    def _have_rooms_changed(self, sync_result_builder):
        """Returns whether there may be any new events that should be sent down
        the sync. Returns True if there are.
        """
        user_id = sync_result_builder.sync_config.user.to_string()
        since_token = sync_result_builder.since_token
        now_token = sync_result_builder.now_token

        assert since_token

        # Get a list of membership change events that have happened.
        rooms_changed = yield self.store.get_membership_changes_for_user(
            user_id, since_token.room_key, now_token.room_key
        )

        if rooms_changed:
            defer.returnValue(True)

        stream_id = RoomStreamToken.parse_stream_token(since_token.room_key).stream
        for room_id in sync_result_builder.joined_room_ids:
            if self.store.has_room_changed_since(room_id, stream_id):
                defer.returnValue(True)
        defer.returnValue(False)

    @defer.inlineCallbacks
    def _get_rooms_changed(self, sync_result_builder, ignored_users):
        """Gets the the changes that have happened since the last sync.

        Args:
            sync_result_builder(SyncResultBuilder)
            ignored_users(set(str)): Set of users ignored by user.

        Returns:
            Deferred(tuple): Returns a tuple of the form:
            `(room_entries, invited_rooms, newly_joined_rooms, newly_left_rooms)`

            where:
                room_entries is a list [RoomSyncResultBuilder]
                invited_rooms is a list [InvitedSyncResult]
                newly_joined rooms is a list[str] of room ids
                newly_left_rooms is a list[str] of room ids
        """
        user_id = sync_result_builder.sync_config.user.to_string()
        since_token = sync_result_builder.since_token
        now_token = sync_result_builder.now_token
        sync_config = sync_result_builder.sync_config

        assert since_token

        # Get a list of membership change events that have happened.
        rooms_changed = yield self.store.get_membership_changes_for_user(
            user_id, since_token.room_key, now_token.room_key
        )

        mem_change_events_by_room_id = {}
        for event in rooms_changed:
            mem_change_events_by_room_id.setdefault(event.room_id, []).append(event)

        newly_joined_rooms = []
        newly_left_rooms = []
        room_entries = []
        invited = []
        for room_id, events in iteritems(mem_change_events_by_room_id):
            non_joins = [e for e in events if e.membership != Membership.JOIN]
            has_join = len(non_joins) != len(events)

            # We want to figure out if we joined the room at some point since
            # the last sync (even if we have since left). This is to make sure
            # we do send down the room, and with full state, where necessary

            old_state_ids = None
            if room_id in sync_result_builder.joined_room_ids and non_joins:
                # Always include if the user (re)joined the room, especially
                # important so that device list changes are calculated correctly.
                # If there are non join member events, but we are still in the room,
                # then the user must have left and joined
                newly_joined_rooms.append(room_id)

                # User is in the room so we don't need to do the invite/leave checks
                continue

            if room_id in sync_result_builder.joined_room_ids or has_join:
                old_state_ids = yield self.get_state_at(room_id, since_token)
                old_mem_ev_id = old_state_ids.get((EventTypes.Member, user_id), None)
                old_mem_ev = None
                if old_mem_ev_id:
                    old_mem_ev = yield self.store.get_event(
                        old_mem_ev_id, allow_none=True
                    )
                if not old_mem_ev or old_mem_ev.membership != Membership.JOIN:
                    newly_joined_rooms.append(room_id)

            # If user is in the room then we don't need to do the invite/leave checks
            if room_id in sync_result_builder.joined_room_ids:
                continue

            if not non_joins:
                continue

            # Check if we have left the room. This can either be because we were
            # joined before *or* that we since joined and then left.
            if events[-1].membership != Membership.JOIN:
                if has_join:
                    newly_left_rooms.append(room_id)
                else:
                    if not old_state_ids:
                        old_state_ids = yield self.get_state_at(room_id, since_token)
                        old_mem_ev_id = old_state_ids.get(
                            (EventTypes.Member, user_id),
                            None,
                        )
                        old_mem_ev = None
                        if old_mem_ev_id:
                            old_mem_ev = yield self.store.get_event(
                                old_mem_ev_id, allow_none=True
                            )
                    if old_mem_ev and old_mem_ev.membership == Membership.JOIN:
                        newly_left_rooms.append(room_id)

            # Only bother if we're still currently invited
            should_invite = non_joins[-1].membership == Membership.INVITE
            if should_invite:
                if event.sender not in ignored_users:
                    room_sync = InvitedSyncResult(room_id, invite=non_joins[-1])
                    if room_sync:
                        invited.append(room_sync)

            # Always include leave/ban events. Just take the last one.
            # TODO: How do we handle ban -> leave in same batch?
            leave_events = [
                e for e in non_joins
                if e.membership in (Membership.LEAVE, Membership.BAN)
            ]

            if leave_events:
                leave_event = leave_events[-1]
                leave_stream_token = yield self.store.get_stream_token_for_event(
                    leave_event.event_id
                )
                leave_token = since_token.copy_and_replace(
                    "room_key", leave_stream_token
                )

                if since_token and since_token.is_after(leave_token):
                    continue

                room_entries.append(RoomSyncResultBuilder(
                    room_id=room_id,
                    rtype="archived",
                    events=None,
                    newly_joined=room_id in newly_joined_rooms,
                    full_state=False,
                    since_token=since_token,
                    upto_token=leave_token,
                ))

        timeline_limit = sync_config.filter_collection.timeline_limit()

        # Get all events for rooms we're currently joined to.
        room_to_events = yield self.store.get_room_events_stream_for_rooms(
            room_ids=sync_result_builder.joined_room_ids,
            from_key=since_token.room_key,
            to_key=now_token.room_key,
            limit=timeline_limit + 1,
        )

        # We loop through all room ids, even if there are no new events, in case
        # there are non room events taht we need to notify about.
        for room_id in sync_result_builder.joined_room_ids:
            room_entry = room_to_events.get(room_id, None)

            if room_entry:
                events, start_key = room_entry

                prev_batch_token = now_token.copy_and_replace("room_key", start_key)

                room_entries.append(RoomSyncResultBuilder(
                    room_id=room_id,
                    rtype="joined",
                    events=events,
                    newly_joined=room_id in newly_joined_rooms,
                    full_state=False,
                    since_token=None if room_id in newly_joined_rooms else since_token,
                    upto_token=prev_batch_token,
                ))
            else:
                room_entries.append(RoomSyncResultBuilder(
                    room_id=room_id,
                    rtype="joined",
                    events=[],
                    newly_joined=room_id in newly_joined_rooms,
                    full_state=False,
                    since_token=since_token,
                    upto_token=since_token,
                ))

        defer.returnValue((room_entries, invited, newly_joined_rooms, newly_left_rooms))

    @defer.inlineCallbacks
    def _get_all_rooms(self, sync_result_builder, ignored_users):
        """Returns entries for all rooms for the user.

        Args:
            sync_result_builder(SyncResultBuilder)
            ignored_users(set(str)): Set of users ignored by user.

        Returns:
            Deferred(tuple): Returns a tuple of the form:
            `([RoomSyncResultBuilder], [InvitedSyncResult], [])`
        """

        user_id = sync_result_builder.sync_config.user.to_string()
        since_token = sync_result_builder.since_token
        now_token = sync_result_builder.now_token
        sync_config = sync_result_builder.sync_config

        membership_list = (
            Membership.INVITE, Membership.JOIN, Membership.LEAVE, Membership.BAN
        )

        room_list = yield self.store.get_rooms_for_user_where_membership_is(
            user_id=user_id,
            membership_list=membership_list
        )

        room_entries = []
        invited = []

        for event in room_list:
            if event.membership == Membership.JOIN:
                room_entries.append(RoomSyncResultBuilder(
                    room_id=event.room_id,
                    rtype="joined",
                    events=None,
                    newly_joined=False,
                    full_state=True,
                    since_token=since_token,
                    upto_token=now_token,
                ))
            elif event.membership == Membership.INVITE:
                if event.sender in ignored_users:
                    continue
                invite = yield self.store.get_event(event.event_id)
                invited.append(InvitedSyncResult(
                    room_id=event.room_id,
                    invite=invite,
                ))
            elif event.membership in (Membership.LEAVE, Membership.BAN):
                # Always send down rooms we were banned or kicked from.
                if not sync_config.filter_collection.include_leave:
                    if event.membership == Membership.LEAVE:
                        if user_id == event.sender:
                            continue

                leave_token = now_token.copy_and_replace(
                    "room_key", "s%d" % (event.stream_ordering,)
                )
                room_entries.append(RoomSyncResultBuilder(
                    room_id=event.room_id,
                    rtype="archived",
                    events=None,
                    newly_joined=False,
                    full_state=True,
                    since_token=since_token,
                    upto_token=leave_token,
                ))

        defer.returnValue((room_entries, invited, []))

    @defer.inlineCallbacks
    def _generate_room_entry(self, sync_result_builder, ignored_users,
                             room_builder, ephemeral, tags, account_data,
                             always_include=False):
        """Populates the `joined` and `archived` section of `sync_result_builder`
        based on the `room_builder`.

        Args:
            sync_result_builder(SyncResultBuilder)
            ignored_users(set(str)): Set of users ignored by user.
            room_builder(RoomSyncResultBuilder)
            ephemeral(list): List of new ephemeral events for room
            tags(list): List of *all* tags for room, or None if there has been
                no change.
            account_data(list): List of new account data for room
            always_include(bool): Always include this room in the sync response,
                even if empty.
        """
        newly_joined = room_builder.newly_joined
        full_state = (
            room_builder.full_state
            or newly_joined
            or sync_result_builder.full_state
        )
        events = room_builder.events

        # We want to shortcut out as early as possible.
        if not (always_include or account_data or ephemeral or full_state):
            if events == [] and tags is None:
                return

        now_token = sync_result_builder.now_token
        sync_config = sync_result_builder.sync_config

        room_id = room_builder.room_id
        since_token = room_builder.since_token
        upto_token = room_builder.upto_token

        batch = yield self._load_filtered_recents(
            room_id, sync_config,
            now_token=upto_token,
            since_token=since_token,
            recents=events,
            newly_joined_room=newly_joined,
        )

        # When we join the room (or the client requests full_state), we should
        # send down any existing tags. Usually the user won't have tags in a
        # newly joined room, unless either a) they've joined before or b) the
        # tag was added by synapse e.g. for server notice rooms.
        if full_state:
            user_id = sync_result_builder.sync_config.user.to_string()
            tags = yield self.store.get_tags_for_room(user_id, room_id)

            # If there aren't any tags, don't send the empty tags list down
            # sync
            if not tags:
                tags = None

        account_data_events = []
        if tags is not None:
            account_data_events.append({
                "type": "m.tag",
                "content": {"tags": tags},
            })

        for account_data_type, content in account_data.items():
            account_data_events.append({
                "type": account_data_type,
                "content": content,
            })

        account_data = sync_config.filter_collection.filter_room_account_data(
            account_data_events
        )

        ephemeral = sync_config.filter_collection.filter_room_ephemeral(ephemeral)

        if not (always_include or batch or account_data or ephemeral or full_state):
            return

        state = yield self.compute_state_delta(
            room_id, batch, sync_config, since_token, now_token,
            full_state=full_state
        )

        summary = {}

        # we include a summary in room responses when we're lazy loading
        # members (as the client otherwise doesn't have enough info to form
        # the name itself).
        if (
            sync_config.filter_collection.lazy_load_members() and
            (
                # we recalulate the summary:
                #   if there are membership changes in the timeline, or
                #   if membership has changed during a gappy sync, or
                #   if this is an initial sync.
                any(ev.type == EventTypes.Member for ev in batch.events) or
                (
                    # XXX: this may include false positives in the form of LL
                    # members which have snuck into state
                    batch.limited and
                    any(t == EventTypes.Member for (t, k) in state)
                ) or
                since_token is None
            )
        ):
            summary = yield self.compute_summary(
                room_id, sync_config, batch, state, now_token
            )

        if room_builder.rtype == "joined":
            unread_notifications = {}
            room_sync = JoinedSyncResult(
                room_id=room_id,
                timeline=batch,
                state=state,
                ephemeral=ephemeral,
                account_data=account_data_events,
                unread_notifications=unread_notifications,
                summary=summary,
            )

            if room_sync or always_include:
                notifs = yield self.unread_notifs_for_room_id(
                    room_id, sync_config
                )

                if notifs is not None:
                    unread_notifications["notification_count"] = notifs["notify_count"]
                    unread_notifications["highlight_count"] = notifs["highlight_count"]

                sync_result_builder.joined.append(room_sync)

            if batch.limited:
                user_id = sync_result_builder.sync_config.user.to_string()
                logger.info(
                    "Incremental gappy sync of room %s for user %s with %d state events" % (
                        room_id,
                        user_id,
                        len(state),
                    )
                )
        elif room_builder.rtype == "archived":
            room_sync = ArchivedSyncResult(
                room_id=room_id,
                timeline=batch,
                state=state,
                account_data=account_data,
            )
            if room_sync or always_include:
                sync_result_builder.archived.append(room_sync)
        else:
            raise Exception("Unrecognized rtype: %r", room_builder.rtype)

    @defer.inlineCallbacks
    def get_rooms_for_user_at(self, user_id, stream_ordering):
        """Get set of joined rooms for a user at the given stream ordering.

        The stream ordering *must* be recent, otherwise this may throw an
        exception if older than a month. (This function is called with the
        current token, which should be perfectly fine).

        Args:
            user_id (str)
            stream_ordering (int)

        ReturnValue:
            Deferred[frozenset[str]]: Set of room_ids the user is in at given
            stream_ordering.
        """
        joined_rooms = yield self.store.get_rooms_for_user_with_stream_ordering(
            user_id,
        )

        joined_room_ids = set()

        # We need to check that the stream ordering of the join for each room
        # is before the stream_ordering asked for. This might not be the case
        # if the user joins a room between us getting the current token and
        # calling `get_rooms_for_user_with_stream_ordering`.
        # If the membership's stream ordering is after the given stream
        # ordering, we need to go and work out if the user was in the room
        # before.
        for room_id, membership_stream_ordering in joined_rooms:
            if membership_stream_ordering <= stream_ordering:
                joined_room_ids.add(room_id)
                continue

            logger.info("User joined room after current token: %s", room_id)

            extrems = yield self.store.get_forward_extremeties_for_room(
                room_id, stream_ordering,
            )
            users_in_room = yield self.state.get_current_user_in_room(
                room_id, extrems,
            )
            if user_id in users_in_room:
                joined_room_ids.add(room_id)

        joined_room_ids = frozenset(joined_room_ids)
        defer.returnValue(joined_room_ids)


def _action_has_highlight(actions):
    for action in actions:
        try:
            if action.get("set_tweak", None) == "highlight":
                return action.get("value", True)
        except AttributeError:
            pass

    return False


def _calculate_state(
    timeline_contains, timeline_start, previous, current, lazy_load_members,
):
    """Works out what state to include in a sync response.

    Args:
        timeline_contains (dict): state in the timeline
        timeline_start (dict): state at the start of the timeline
        previous (dict): state at the end of the previous sync (or empty dict
            if this is an initial sync)
        current (dict): state at the end of the timeline
        lazy_load_members (bool): whether to return members from timeline_start
            or not.  assumes that timeline_start has already been filtered to
            include only the members the client needs to know about.

    Returns:
        dict
    """
    event_id_to_key = {
        e: key
        for key, e in itertools.chain(
            iteritems(timeline_contains),
            iteritems(previous),
            iteritems(timeline_start),
            iteritems(current),
        )
    }

    c_ids = set(e for e in itervalues(current))
    ts_ids = set(e for e in itervalues(timeline_start))
    p_ids = set(e for e in itervalues(previous))
    tc_ids = set(e for e in itervalues(timeline_contains))

    # If we are lazyloading room members, we explicitly add the membership events
    # for the senders in the timeline into the state block returned by /sync,
    # as we may not have sent them to the client before.  We find these membership
    # events by filtering them out of timeline_start, which has already been filtered
    # to only include membership events for the senders in the timeline.
    # In practice, we can do this by removing them from the p_ids list,
    # which is the list of relevant state we know we have already sent to the client.
    # see https://github.com/matrix-org/synapse/pull/2970
    #            /files/efcdacad7d1b7f52f879179701c7e0d9b763511f#r204732809

    if lazy_load_members:
        p_ids.difference_update(
            e for t, e in iteritems(timeline_start)
            if t[0] == EventTypes.Member
        )

    state_ids = ((c_ids | ts_ids) - p_ids) - tc_ids

    return {
        event_id_to_key[e]: e for e in state_ids
    }


class SyncResultBuilder(object):
    "Used to help build up a new SyncResult for a user"
    def __init__(self, sync_config, full_state, since_token, now_token,
                 joined_room_ids):
        """
        Args:
            sync_config(SyncConfig)
            full_state(bool): The full_state flag as specified by user
            since_token(StreamToken): The token supplied by user, or None.
            now_token(StreamToken): The token to sync up to.
        """
        self.sync_config = sync_config
        self.full_state = full_state
        self.since_token = since_token
        self.now_token = now_token
        self.joined_room_ids = joined_room_ids

        self.presence = []
        self.account_data = []
        self.joined = []
        self.invited = []
        self.archived = []
        self.device = []
        self.groups = None
        self.to_device = []


class RoomSyncResultBuilder(object):
    """Stores information needed to create either a `JoinedSyncResult` or
    `ArchivedSyncResult`.
    """
    def __init__(self, room_id, rtype, events, newly_joined, full_state,
                 since_token, upto_token):
        """
        Args:
            room_id(str)
            rtype(str): One of `"joined"` or `"archived"`
            events(list): List of events to include in the room, (more events
                may be added when generating result).
            newly_joined(bool): If the user has newly joined the room
            full_state(bool): Whether the full state should be sent in result
            since_token(StreamToken): Earliest point to return events from, or None
            upto_token(StreamToken): Latest point to return events from.
        """
        self.room_id = room_id
        self.rtype = rtype
        self.events = events
        self.newly_joined = newly_joined
        self.full_state = full_state
        self.since_token = since_token
        self.upto_token = upto_token