synapse-product/synapse/handlers/sync.py

# -*- coding: utf-8 -*-
# Copyright 2015 - 2016 OpenMarket 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.

from ._base import BaseHandler

from synapse.streams.config import PaginationConfig
from synapse.api.constants import Membership, EventTypes
from synapse.util import unwrapFirstError

from twisted.internet import defer

import collections
import logging

logger = logging.getLogger(__name__)


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


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)


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


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
        )


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


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.
])):
    __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
        )


class SyncHandler(BaseHandler):

    def __init__(self, hs):
        super(SyncHandler, self).__init__(hs)
        self.event_sources = hs.get_event_sources()
        self.clock = hs.get_clock()

    @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:
            A Deferred SyncResult.
        """

        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.
        """
        if since_token is None or full_state:
            return self.full_state_sync(sync_config, since_token)
        else:
            return self.incremental_sync_with_gap(sync_config, since_token)

    def last_read_event_id_for_room_and_user(self, room_id, user_id, ephemeral_by_room):
        if room_id not in ephemeral_by_room:
            return None
        for e in ephemeral_by_room[room_id]:
            if e['type'] != 'm.receipt':
                continue
            for receipt_event_id, val in e['content'].items():
                if 'm.read' in val:
                    if user_id in val['m.read']:
                        return receipt_event_id
        return None

    @defer.inlineCallbacks
    def full_state_sync(self, sync_config, timeline_since_token):
        """Get a sync for a client which is starting without any state.

        If a 'message_since_token' is given, only timeline events which have
        happened since that token will be returned.

        Returns:
            A Deferred SyncResult.
        """
        now_token = yield self.event_sources.get_current_token()

        now_token, ephemeral_by_room = yield self.ephemeral_by_room(
            sync_config, now_token
        )

        presence_stream = self.event_sources.sources["presence"]
        # TODO (mjark): This looks wrong, shouldn't we be getting the presence
        # UP to the present rather than after the present?
        pagination_config = PaginationConfig(from_token=now_token)
        presence, _ = yield presence_stream.get_pagination_rows(
            user=sync_config.user,
            pagination_config=pagination_config.get_source_config("presence"),
            key=None
        )

        membership_list = (Membership.INVITE, Membership.JOIN)
        if sync_config.filter_collection.include_leave:
            membership_list += (Membership.LEAVE, Membership.BAN)

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

        account_data, account_data_by_room = (
            yield self.store.get_account_data_for_user(
                sync_config.user.to_string()
            )
        )

        tags_by_room = yield self.store.get_tags_for_user(
            sync_config.user.to_string()
        )

        joined = []
        invited = []
        archived = []
        deferreds = []
        for event in room_list:
            if event.membership == Membership.JOIN:
                room_sync_deferred = self.full_state_sync_for_joined_room(
                    room_id=event.room_id,
                    sync_config=sync_config,
                    now_token=now_token,
                    timeline_since_token=timeline_since_token,
                    ephemeral_by_room=ephemeral_by_room,
                    tags_by_room=tags_by_room,
                    account_data_by_room=account_data_by_room,
                )
                room_sync_deferred.addCallback(joined.append)
                deferreds.append(room_sync_deferred)
            elif event.membership == Membership.INVITE:
                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):
                leave_token = now_token.copy_and_replace(
                    "room_key", "s%d" % (event.stream_ordering,)
                )
                room_sync_deferred = self.full_state_sync_for_archived_room(
                    sync_config=sync_config,
                    room_id=event.room_id,
                    leave_event_id=event.event_id,
                    leave_token=leave_token,
                    timeline_since_token=timeline_since_token,
                    tags_by_room=tags_by_room,
                    account_data_by_room=account_data_by_room,
                )
                room_sync_deferred.addCallback(archived.append)
                deferreds.append(room_sync_deferred)

        yield defer.gatherResults(
            deferreds, consumeErrors=True
        ).addErrback(unwrapFirstError)

        account_data_for_user = sync_config.filter_collection.filter_account_data(
            self.account_data_for_user(account_data)
        )

        presence = sync_config.filter_collection.filter_presence(
            presence
        )

        defer.returnValue(SyncResult(
            presence=presence,
            account_data=account_data_for_user,
            joined=joined,
            invited=invited,
            archived=archived,
            next_batch=now_token,
        ))

    @defer.inlineCallbacks
    def full_state_sync_for_joined_room(self, room_id, sync_config,
                                        now_token, timeline_since_token,
                                        ephemeral_by_room, tags_by_room,
                                        account_data_by_room):
        """Sync a room for a client which is starting without any state
        Returns:
            A Deferred JoinedSyncResult.
        """

        batch = yield self.load_filtered_recents(
            room_id, sync_config, now_token, since_token=timeline_since_token
        )

        room_sync = yield self.incremental_sync_with_gap_for_room(
            room_id, sync_config,
            now_token=now_token,
            since_token=timeline_since_token,
            ephemeral_by_room=ephemeral_by_room,
            tags_by_room=tags_by_room,
            account_data_by_room=account_data_by_room,
            all_ephemeral_by_room=ephemeral_by_room,
            batch=batch,
            full_state=True,
        )

        defer.returnValue(room_sync)

    def account_data_for_user(self, account_data):
        account_data_events = []

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

        return account_data_events

    def account_data_for_room(self, room_id, tags_by_room, account_data_by_room):
        account_data_events = []
        tags = tags_by_room.get(room_id)
        if tags is not None:
            account_data_events.append({
                "type": "m.tag",
                "content": {"tags": tags},
            })

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

        return account_data_events

    @defer.inlineCallbacks
    def ephemeral_by_room(self, sync_config, now_token, since_token=None):
        """Get the ephemeral events for each room the user is in
        Args:
            sync_config (SyncConfig): The flags, filters and user for the sync.
            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.
        """

        typing_key = since_token.typing_key if since_token else "0"

        rooms = yield self.store.get_rooms_for_user(sync_config.user.to_string())
        room_ids = [room.room_id for room in rooms]

        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 event.iteritems()
                          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 event.iteritems()
                          if k != "room_id"}
            ephemeral_by_room.setdefault(room_id, []).append(event_copy)

        defer.returnValue((now_token, ephemeral_by_room))

    def full_state_sync_for_archived_room(self, room_id, sync_config,
                                          leave_event_id, leave_token,
                                          timeline_since_token, tags_by_room,
                                          account_data_by_room):
        """Sync a room for a client which is starting without any state
        Returns:
            A Deferred ArchivedSyncResult.
        """

        return self.incremental_sync_for_archived_room(
            sync_config, room_id, leave_event_id, timeline_since_token, tags_by_room,
            account_data_by_room, full_state=True, leave_token=leave_token,
        )

    @defer.inlineCallbacks
    def incremental_sync_with_gap(self, sync_config, since_token):
        """ Get the incremental delta needed to bring the client up to
        date with the server.
        Returns:
            A Deferred SyncResult.
        """
        now_token = yield self.event_sources.get_current_token()

        rooms = yield self.store.get_rooms_for_user(sync_config.user.to_string())
        room_ids = [room.room_id for room in rooms]

        presence_source = self.event_sources.sources["presence"]
        presence, presence_key = yield presence_source.get_new_events(
            user=sync_config.user,
            from_key=since_token.presence_key,
            limit=sync_config.filter_collection.presence_limit(),
            room_ids=room_ids,
            is_guest=sync_config.is_guest,
        )
        now_token = now_token.copy_and_replace("presence_key", presence_key)

        # We now fetch all ephemeral events for this room in order to get
        # this users current read receipt. This could almost certainly be
        # optimised.
        _, all_ephemeral_by_room = yield self.ephemeral_by_room(
            sync_config, now_token
        )

        now_token, ephemeral_by_room = yield self.ephemeral_by_room(
            sync_config, now_token, since_token
        )

        rm_handler = self.hs.get_handlers().room_member_handler
        app_service = yield self.store.get_app_service_by_user_id(
            sync_config.user.to_string()
        )
        if app_service:
            rooms = yield self.store.get_app_service_rooms(app_service)
            joined_room_ids = set(r.room_id for r in rooms)
        else:
            joined_room_ids = yield rm_handler.get_joined_rooms_for_user(
                sync_config.user
            )

        user_id = sync_config.user.to_string()

        timeline_limit = sync_config.filter_collection.timeline_limit()

        tags_by_room = yield self.store.get_updated_tags(
            user_id,
            since_token.account_data_key,
        )

        account_data, account_data_by_room = (
            yield self.store.get_updated_account_data_for_user(
                user_id,
                since_token.account_data_key,
            )
        )

        # Get a list of membership change events that have happened.
        rooms_changed = yield self.store.get_room_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 = []
        archived = []
        invited = []
        for room_id, events in mem_change_events_by_room_id.items():
            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
            if room_id in joined_room_ids or has_join:
                old_state = yield self.get_state_at(room_id, since_token)
                old_mem_ev = old_state.get((EventTypes.Member, user_id), None)
                if not old_mem_ev or old_mem_ev.membership != Membership.JOIN:
                        newly_joined_rooms.append(room_id)

                if room_id in joined_room_ids:
                    continue

            if not non_joins:
                continue

            # Only bother if we're still currently invited
            should_invite = non_joins[-1].membership == Membership.INVITE
            if should_invite:
                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]
                room_sync = yield self.incremental_sync_for_archived_room(
                    sync_config, room_id, leave_event.event_id, since_token,
                    tags_by_room, account_data_by_room,
                    full_state=room_id in newly_joined_rooms
                )
                if room_sync:
                    archived.append(room_sync)

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

        joined = []
        # 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 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)

                newly_joined_room = room_id in newly_joined_rooms
                full_state = newly_joined_room

                batch = yield self.load_filtered_recents(
                    room_id, sync_config, prev_batch_token,
                    since_token=since_token,
                    recents=events,
                    newly_joined_room=newly_joined_room,
                )
            else:
                batch = TimelineBatch(
                    events=[],
                    prev_batch=since_token,
                    limited=False,
                )
                full_state = False

            room_sync = yield self.incremental_sync_with_gap_for_room(
                room_id=room_id,
                sync_config=sync_config,
                since_token=since_token,
                now_token=now_token,
                ephemeral_by_room=ephemeral_by_room,
                tags_by_room=tags_by_room,
                account_data_by_room=account_data_by_room,
                all_ephemeral_by_room=all_ephemeral_by_room,
                batch=batch,
                full_state=full_state,
            )
            if room_sync:
                joined.append(room_sync)

        account_data_for_user = sync_config.filter_collection.filter_account_data(
            self.account_data_for_user(account_data)
        )

        presence = sync_config.filter_collection.filter_presence(
            presence
        )

        defer.returnValue(SyncResult(
            presence=presence,
            account_data=account_data_for_user,
            joined=joined,
            invited=invited,
            archived=archived,
            next_batch=now_token,
        ))

    @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
        """
        filtering_factor = 2
        timeline_limit = sync_config.filter_collection.timeline_limit()
        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

        limited = recents is None or newly_joined_room or timeline_limit < len(recents)

        if recents is not None:
            recents = sync_config.filter_collection.filter_room_timeline(recents)
            recents = yield self._filter_events_for_client(
                sync_config.user.to_string(),
                recents,
                is_peeking=sync_config.is_guest,
            )
        else:
            recents = []

        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:
            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,
            )
            loaded_recents = sync_config.filter_collection.filter_room_timeline(events)
            loaded_recents = yield self._filter_events_for_client(
                sync_config.user.to_string(),
                loaded_recents,
                is_peeking=sync_config.is_guest,
            )
            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 incremental_sync_with_gap_for_room(self, room_id, sync_config,
                                           since_token, now_token,
                                           ephemeral_by_room, tags_by_room,
                                           account_data_by_room,
                                           all_ephemeral_by_room,
                                           batch, full_state=False):
        if full_state:
            state = yield self.get_state_at(room_id, now_token)

        elif batch.limited:
            current_state = yield self.get_state_at(room_id, now_token)

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

            state = yield self.compute_state_delta(
                since_token=since_token,
                previous_state=state_at_previous_sync,
                current_state=current_state,
            )
        else:
            state = {
                (event.type, event.state_key): event
                for event in batch.events if event.is_state()
            }

        just_joined = yield self.check_joined_room(sync_config, state)
        if just_joined:
            state = yield self.get_state_at(room_id, now_token)

        notifs = yield self.unread_notifs_for_room_id(
            room_id, sync_config, all_ephemeral_by_room
        )

        unread_notifications = {}
        if notifs is not None:
            unread_notifications["notification_count"] = len(notifs)
            unread_notifications["highlight_count"] = len([
                1 for notif in notifs if _action_has_highlight(notif["actions"])
            ])

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

        account_data = self.account_data_for_room(
            room_id, tags_by_room, account_data_by_room
        )

        account_data = sync_config.filter_collection.filter_room_account_data(
            account_data
        )

        ephemeral = sync_config.filter_collection.filter_room_ephemeral(
            ephemeral_by_room.get(room_id, [])
        )

        room_sync = JoinedSyncResult(
            room_id=room_id,
            timeline=batch,
            state=state,
            ephemeral=ephemeral,
            account_data=account_data,
            unread_notifications=unread_notifications,
        )

        logger.debug("Room sync: %r", room_sync)

        defer.returnValue(room_sync)

    @defer.inlineCallbacks
    def incremental_sync_for_archived_room(self, sync_config, room_id, leave_event_id,
                                           since_token, tags_by_room,
                                           account_data_by_room, full_state,
                                           leave_token=None):
        """ Get the incremental delta needed to bring the client up to date for
        the archived room.
        Returns:
            A Deferred ArchivedSyncResult
        """

        if not leave_token:
            stream_token = yield self.store.get_stream_token_for_event(
                leave_event_id
            )

            leave_token = since_token.copy_and_replace("room_key", stream_token)

        if since_token and since_token.is_after(leave_token):
            defer.returnValue(None)

        batch = yield self.load_filtered_recents(
            room_id, sync_config, leave_token, since_token,
        )

        logger.debug("Recents %r", batch)

        state_events_at_leave = yield self.store.get_state_for_event(
            leave_event_id
        )

        if not full_state:
            state_at_previous_sync = yield self.get_state_at(
                room_id, stream_position=since_token
            )

            state_events_delta = yield self.compute_state_delta(
                since_token=since_token,
                previous_state=state_at_previous_sync,
                current_state=state_events_at_leave,
            )
        else:
            state_events_delta = state_events_at_leave

        state_events_delta = {
            (e.type, e.state_key): e
            for e in sync_config.filter_collection.filter_room_state(
                state_events_delta.values()
            )
        }

        account_data = self.account_data_for_room(
            room_id, tags_by_room, account_data_by_room
        )

        account_data = sync_config.filter_collection.filter_room_account_data(
            account_data
        )

        room_sync = ArchivedSyncResult(
            room_id=room_id,
            timeline=batch,
            state=state_events_delta,
            account_data=account_data,
        )

        logger.debug("Room sync: %r", room_sync)

        defer.returnValue(room_sync)

    @defer.inlineCallbacks
    def get_state_after_event(self, event):
        """
        Get the room state after the given event

        :param synapse.events.EventBase event: event of interest
        :return: A Deferred map from ((type, state_key)->Event)
        """
        state = yield self.store.get_state_for_event(event.event_id)
        if event.is_state():
            state = state.copy()
            state[(event.type, event.state_key)] = event
        defer.returnValue(state)

    @defer.inlineCallbacks
    def get_state_at(self, room_id, stream_position):
        """ Get the room state at a particular stream position
        :param str room_id: room for which to get state
        :param StreamToken stream_position: point at which to get state
        :returns: A Deferred map from ((type, state_key)->Event)
        """
        last_events, token = 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)

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

    def compute_state_delta(self, since_token, previous_state, current_state):
        """ Works out the differnce in state between the current state and the
        state the client got when it last performed a sync.

        :param str since_token: the point we are comparing against
        :param dict[(str,str), synapse.events.FrozenEvent] previous_state: the
            state to compare to
        :param dict[(str,str), synapse.events.FrozenEvent] current_state: the
            new state

        :returns A new event dictionary
        """
        # 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.

        state_delta = {}
        for key, event in current_state.iteritems():
            if (key not in previous_state or
                    previous_state[key].event_id != event.event_id):
                state_delta[key] = event
        return state_delta

    def check_joined_room(self, sync_config, state_delta):
        """
        Check if the user has just joined the given room (so should
        be given the full state)

        :param sync_config:
        :param dict[(str,str), synapse.events.FrozenEvent] state_delta: the
           difference in state since the last sync

        :returns A deferred Tuple (state_delta, limited)
        """
        join_event = state_delta.get((
            EventTypes.Member, sync_config.user.to_string()), None)
        if join_event is not None:
            if join_event.content["membership"] == Membership.JOIN:
                return True
        return False

    @defer.inlineCallbacks
    def unread_notifs_for_room_id(self, room_id, sync_config, ephemeral_by_room):
        last_unread_event_id = self.last_read_event_id_for_room_and_user(
            room_id, sync_config.user.to_string(), ephemeral_by_room
        )

        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)


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