synapse/synapse/handlers/device.py

# -*- coding: utf-8 -*-
# Copyright 2016 OpenMarket Ltd
# Copyright 2019 New Vector Ltd
# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
from typing import Any, Dict, Optional

from six import iteritems, itervalues

from twisted.internet import defer

from synapse.api import errors
from synapse.api.constants import EventTypes
from synapse.api.errors import (
    FederationDeniedError,
    HttpResponseException,
    RequestSendFailed,
    SynapseError,
)
from synapse.logging.opentracing import log_kv, set_tag, trace
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.types import (
    RoomStreamToken,
    get_domain_from_id,
    get_verify_key_from_cross_signing_key,
)
from synapse.util import stringutils
from synapse.util.async_helpers import Linearizer
from synapse.util.caches.expiringcache import ExpiringCache
from synapse.util.metrics import measure_func
from synapse.util.retryutils import NotRetryingDestination

from ._base import BaseHandler

logger = logging.getLogger(__name__)

MAX_DEVICE_DISPLAY_NAME_LEN = 100


class DeviceWorkerHandler(BaseHandler):
    def __init__(self, hs):
        super(DeviceWorkerHandler, self).__init__(hs)

        self.hs = hs
        self.state = hs.get_state_handler()
        self.state_store = hs.get_storage().state
        self._auth_handler = hs.get_auth_handler()

    @trace
    @defer.inlineCallbacks
    def get_devices_by_user(self, user_id):
        """
        Retrieve the given user's devices

        Args:
            user_id (str):
        Returns:
            defer.Deferred: list[dict[str, X]]: info on each device
        """

        set_tag("user_id", user_id)
        device_map = yield self.store.get_devices_by_user(user_id)

        ips = yield self.store.get_last_client_ip_by_device(user_id, device_id=None)

        devices = list(device_map.values())
        for device in devices:
            _update_device_from_client_ips(device, ips)

        log_kv(device_map)
        return devices

    @trace
    @defer.inlineCallbacks
    def get_device(self, user_id, device_id):
        """ Retrieve the given device

        Args:
            user_id (str):
            device_id (str):

        Returns:
            defer.Deferred: dict[str, X]: info on the device
        Raises:
            errors.NotFoundError: if the device was not found
        """
        try:
            device = yield self.store.get_device(user_id, device_id)
        except errors.StoreError:
            raise errors.NotFoundError
        ips = yield self.store.get_last_client_ip_by_device(user_id, device_id)
        _update_device_from_client_ips(device, ips)

        set_tag("device", device)
        set_tag("ips", ips)

        return device

    @measure_func("device.get_user_ids_changed")
    @trace
    @defer.inlineCallbacks
    def get_user_ids_changed(self, user_id, from_token):
        """Get list of users that have had the devices updated, or have newly
        joined a room, that `user_id` may be interested in.

        Args:
            user_id (str)
            from_token (StreamToken)
        """

        set_tag("user_id", user_id)
        set_tag("from_token", from_token)
        now_room_key = yield self.store.get_room_events_max_id()

        room_ids = yield self.store.get_rooms_for_user(user_id)

        # First we check if any devices have changed for users that we share
        # rooms with.
        users_who_share_room = yield self.store.get_users_who_share_room_with_user(
            user_id
        )

        tracked_users = set(users_who_share_room)

        # Always tell the user about their own devices
        tracked_users.add(user_id)

        changed = yield self.store.get_users_whose_devices_changed(
            from_token.device_list_key, tracked_users
        )

        # Then work out if any users have since joined
        rooms_changed = self.store.get_rooms_that_changed(room_ids, from_token.room_key)

        member_events = yield self.store.get_membership_changes_for_user(
            user_id, from_token.room_key, now_room_key
        )
        rooms_changed.update(event.room_id for event in member_events)

        stream_ordering = RoomStreamToken.parse_stream_token(from_token.room_key).stream

        possibly_changed = set(changed)
        possibly_left = set()
        for room_id in rooms_changed:
            current_state_ids = yield self.store.get_current_state_ids(room_id)

            # The user may have left the room
            # TODO: Check if they actually did or if we were just invited.
            if room_id not in room_ids:
                for key, event_id in iteritems(current_state_ids):
                    etype, state_key = key
                    if etype != EventTypes.Member:
                        continue
                    possibly_left.add(state_key)
                continue

            # Fetch the current state at the time.
            try:
                event_ids = yield self.store.get_forward_extremeties_for_room(
                    room_id, stream_ordering=stream_ordering
                )
            except errors.StoreError:
                # we have purged the stream_ordering index since the stream
                # ordering: treat it the same as a new room
                event_ids = []

            # special-case for an empty prev state: include all members
            # in the changed list
            if not event_ids:
                log_kv(
                    {"event": "encountered empty previous state", "room_id": room_id}
                )
                for key, event_id in iteritems(current_state_ids):
                    etype, state_key = key
                    if etype != EventTypes.Member:
                        continue
                    possibly_changed.add(state_key)
                continue

            current_member_id = current_state_ids.get((EventTypes.Member, user_id))
            if not current_member_id:
                continue

            # mapping from event_id -> state_dict
            prev_state_ids = yield self.state_store.get_state_ids_for_events(event_ids)

            # Check if we've joined the room? If so we just blindly add all the users to
            # the "possibly changed" users.
            for state_dict in itervalues(prev_state_ids):
                member_event = state_dict.get((EventTypes.Member, user_id), None)
                if not member_event or member_event != current_member_id:
                    for key, event_id in iteritems(current_state_ids):
                        etype, state_key = key
                        if etype != EventTypes.Member:
                            continue
                        possibly_changed.add(state_key)
                    break

            # If there has been any change in membership, include them in the
            # possibly changed list. We'll check if they are joined below,
            # and we're not toooo worried about spuriously adding users.
            for key, event_id in iteritems(current_state_ids):
                etype, state_key = key
                if etype != EventTypes.Member:
                    continue

                # check if this member has changed since any of the extremities
                # at the stream_ordering, and add them to the list if so.
                for state_dict in itervalues(prev_state_ids):
                    prev_event_id = state_dict.get(key, None)
                    if not prev_event_id or prev_event_id != event_id:
                        if state_key != user_id:
                            possibly_changed.add(state_key)
                        break

        if possibly_changed or possibly_left:
            # Take the intersection of the users whose devices may have changed
            # and those that actually still share a room with the user
            possibly_joined = possibly_changed & users_who_share_room
            possibly_left = (possibly_changed | possibly_left) - users_who_share_room
        else:
            possibly_joined = []
            possibly_left = []

        result = {"changed": list(possibly_joined), "left": list(possibly_left)}

        log_kv(result)

        return result

    @defer.inlineCallbacks
    def on_federation_query_user_devices(self, user_id):
        stream_id, devices = yield self.store.get_devices_with_keys_by_user(user_id)
        master_key = yield self.store.get_e2e_cross_signing_key(user_id, "master")
        self_signing_key = yield self.store.get_e2e_cross_signing_key(
            user_id, "self_signing"
        )

        return {
            "user_id": user_id,
            "stream_id": stream_id,
            "devices": devices,
            "master_key": master_key,
            "self_signing_key": self_signing_key,
        }


class DeviceHandler(DeviceWorkerHandler):
    def __init__(self, hs):
        super(DeviceHandler, self).__init__(hs)

        self.federation_sender = hs.get_federation_sender()

        self.device_list_updater = DeviceListUpdater(hs, self)

        federation_registry = hs.get_federation_registry()

        federation_registry.register_edu_handler(
            "m.device_list_update", self.device_list_updater.incoming_device_list_update
        )

        hs.get_distributor().observe("user_left_room", self.user_left_room)

    @defer.inlineCallbacks
    def check_device_registered(
        self, user_id, device_id, initial_device_display_name=None
    ):
        """
        If the given device has not been registered, register it with the
        supplied display name.

        If no device_id is supplied, we make one up.

        Args:
            user_id (str):  @user:id
            device_id (str | None): device id supplied by client
            initial_device_display_name (str | None): device display name from
                 client
        Returns:
            str: device id (generated if none was supplied)
        """
        if device_id is not None:
            new_device = yield self.store.store_device(
                user_id=user_id,
                device_id=device_id,
                initial_device_display_name=initial_device_display_name,
            )
            if new_device:
                yield self.notify_device_update(user_id, [device_id])
            return device_id

        # if the device id is not specified, we'll autogen one, but loop a few
        # times in case of a clash.
        attempts = 0
        while attempts < 5:
            device_id = stringutils.random_string(10).upper()
            new_device = yield self.store.store_device(
                user_id=user_id,
                device_id=device_id,
                initial_device_display_name=initial_device_display_name,
            )
            if new_device:
                yield self.notify_device_update(user_id, [device_id])
                return device_id
            attempts += 1

        raise errors.StoreError(500, "Couldn't generate a device ID.")

    @trace
    @defer.inlineCallbacks
    def delete_device(self, user_id, device_id):
        """ Delete the given device

        Args:
            user_id (str):
            device_id (str):

        Returns:
            defer.Deferred:
        """

        try:
            yield self.store.delete_device(user_id, device_id)
        except errors.StoreError as e:
            if e.code == 404:
                # no match
                set_tag("error", True)
                log_kv(
                    {"reason": "User doesn't have device id.", "device_id": device_id}
                )
                pass
            else:
                raise

        yield defer.ensureDeferred(
            self._auth_handler.delete_access_tokens_for_user(
                user_id, device_id=device_id
            )
        )

        yield self.store.delete_e2e_keys_by_device(user_id=user_id, device_id=device_id)

        yield self.notify_device_update(user_id, [device_id])

    @trace
    @defer.inlineCallbacks
    def delete_all_devices_for_user(self, user_id, except_device_id=None):
        """Delete all of the user's devices

        Args:
            user_id (str):
            except_device_id (str|None): optional device id which should not
                be deleted

        Returns:
            defer.Deferred:
        """
        device_map = yield self.store.get_devices_by_user(user_id)
        device_ids = list(device_map)
        if except_device_id is not None:
            device_ids = [d for d in device_ids if d != except_device_id]
        yield self.delete_devices(user_id, device_ids)

    @defer.inlineCallbacks
    def delete_devices(self, user_id, device_ids):
        """ Delete several devices

        Args:
            user_id (str):
            device_ids (List[str]): The list of device IDs to delete

        Returns:
            defer.Deferred:
        """

        try:
            yield self.store.delete_devices(user_id, device_ids)
        except errors.StoreError as e:
            if e.code == 404:
                # no match
                set_tag("error", True)
                set_tag("reason", "User doesn't have that device id.")
                pass
            else:
                raise

        # Delete access tokens and e2e keys for each device. Not optimised as it is not
        # considered as part of a critical path.
        for device_id in device_ids:
            yield defer.ensureDeferred(
                self._auth_handler.delete_access_tokens_for_user(
                    user_id, device_id=device_id
                )
            )
            yield self.store.delete_e2e_keys_by_device(
                user_id=user_id, device_id=device_id
            )

        yield self.notify_device_update(user_id, device_ids)

    @defer.inlineCallbacks
    def update_device(self, user_id, device_id, content):
        """ Update the given device

        Args:
            user_id (str):
            device_id (str):
            content (dict): body of update request

        Returns:
            defer.Deferred:
        """

        # Reject a new displayname which is too long.
        new_display_name = content.get("display_name")
        if new_display_name and len(new_display_name) > MAX_DEVICE_DISPLAY_NAME_LEN:
            raise SynapseError(
                400,
                "Device display name is too long (max %i)"
                % (MAX_DEVICE_DISPLAY_NAME_LEN,),
            )

        try:
            yield self.store.update_device(
                user_id, device_id, new_display_name=new_display_name
            )
            yield self.notify_device_update(user_id, [device_id])
        except errors.StoreError as e:
            if e.code == 404:
                raise errors.NotFoundError()
            else:
                raise

    @trace
    @measure_func("notify_device_update")
    @defer.inlineCallbacks
    def notify_device_update(self, user_id, device_ids):
        """Notify that a user's device(s) has changed. Pokes the notifier, and
        remote servers if the user is local.
        """
        users_who_share_room = yield self.store.get_users_who_share_room_with_user(
            user_id
        )

        hosts = set()
        if self.hs.is_mine_id(user_id):
            hosts.update(get_domain_from_id(u) for u in users_who_share_room)
            hosts.discard(self.server_name)

        set_tag("target_hosts", hosts)

        position = yield self.store.add_device_change_to_streams(
            user_id, device_ids, list(hosts)
        )

        for device_id in device_ids:
            logger.debug(
                "Notifying about update %r/%r, ID: %r", user_id, device_id, position
            )

        room_ids = yield self.store.get_rooms_for_user(user_id)

        # specify the user ID too since the user should always get their own device list
        # updates, even if they aren't in any rooms.
        yield self.notifier.on_new_event(
            "device_list_key", position, users=[user_id], rooms=room_ids
        )

        if hosts:
            logger.info(
                "Sending device list update notif for %r to: %r", user_id, hosts
            )
            for host in hosts:
                self.federation_sender.send_device_messages(host)
                log_kv({"message": "sent device update to host", "host": host})

    @defer.inlineCallbacks
    def notify_user_signature_update(self, from_user_id, user_ids):
        """Notify a user that they have made new signatures of other users.

        Args:
            from_user_id (str): the user who made the signature
            user_ids (list[str]): the users IDs that have new signatures
        """

        position = yield self.store.add_user_signature_change_to_streams(
            from_user_id, user_ids
        )

        self.notifier.on_new_event("device_list_key", position, users=[from_user_id])

    @defer.inlineCallbacks
    def user_left_room(self, user, room_id):
        user_id = user.to_string()
        room_ids = yield self.store.get_rooms_for_user(user_id)
        if not room_ids:
            # We no longer share rooms with this user, so we'll no longer
            # receive device updates. Mark this in DB.
            yield self.store.mark_remote_user_device_list_as_unsubscribed(user_id)


def _update_device_from_client_ips(device, client_ips):
    ip = client_ips.get((device["user_id"], device["device_id"]), {})
    device.update({"last_seen_ts": ip.get("last_seen"), "last_seen_ip": ip.get("ip")})


class DeviceListUpdater(object):
    "Handles incoming device list updates from federation and updates the DB"

    def __init__(self, hs, device_handler):
        self.store = hs.get_datastore()
        self.federation = hs.get_federation_client()
        self.clock = hs.get_clock()
        self.device_handler = device_handler

        self._remote_edu_linearizer = Linearizer(name="remote_device_list")

        # user_id -> list of updates waiting to be handled.
        self._pending_updates = {}

        # Recently seen stream ids. We don't bother keeping these in the DB,
        # but they're useful to have them about to reduce the number of spurious
        # resyncs.
        self._seen_updates = ExpiringCache(
            cache_name="device_update_edu",
            clock=self.clock,
            max_len=10000,
            expiry_ms=30 * 60 * 1000,
            iterable=True,
        )

        # Attempt to resync out of sync device lists every 30s.
        self._resync_retry_in_progress = False
        self.clock.looping_call(
            run_as_background_process,
            30 * 1000,
            func=self._maybe_retry_device_resync,
            desc="_maybe_retry_device_resync",
        )

    @trace
    @defer.inlineCallbacks
    def incoming_device_list_update(self, origin, edu_content):
        """Called on incoming device list update from federation. Responsible
        for parsing the EDU and adding to pending updates list.
        """

        set_tag("origin", origin)
        set_tag("edu_content", edu_content)
        user_id = edu_content.pop("user_id")
        device_id = edu_content.pop("device_id")
        stream_id = str(edu_content.pop("stream_id"))  # They may come as ints
        prev_ids = edu_content.pop("prev_id", [])
        prev_ids = [str(p) for p in prev_ids]  # They may come as ints

        if get_domain_from_id(user_id) != origin:
            # TODO: Raise?
            logger.warning(
                "Got device list update edu for %r/%r from %r",
                user_id,
                device_id,
                origin,
            )

            set_tag("error", True)
            log_kv(
                {
                    "message": "Got a device list update edu from a user and "
                    "device which does not match the origin of the request.",
                    "user_id": user_id,
                    "device_id": device_id,
                }
            )
            return

        room_ids = yield self.store.get_rooms_for_user(user_id)
        if not room_ids:
            # We don't share any rooms with this user. Ignore update, as we
            # probably won't get any further updates.
            set_tag("error", True)
            log_kv(
                {
                    "message": "Got an update from a user for which "
                    "we don't share any rooms",
                    "other user_id": user_id,
                }
            )
            logger.warning(
                "Got device list update edu for %r/%r, but don't share a room",
                user_id,
                device_id,
            )
            return

        logger.debug("Received device list update for %r/%r", user_id, device_id)

        self._pending_updates.setdefault(user_id, []).append(
            (device_id, stream_id, prev_ids, edu_content)
        )

        yield self._handle_device_updates(user_id)

    @measure_func("_incoming_device_list_update")
    @defer.inlineCallbacks
    def _handle_device_updates(self, user_id):
        "Actually handle pending updates."

        with (yield self._remote_edu_linearizer.queue(user_id)):
            pending_updates = self._pending_updates.pop(user_id, [])
            if not pending_updates:
                # This can happen since we batch updates
                return

            for device_id, stream_id, prev_ids, content in pending_updates:
                logger.debug(
                    "Handling update %r/%r, ID: %r, prev: %r ",
                    user_id,
                    device_id,
                    stream_id,
                    prev_ids,
                )

            # Given a list of updates we check if we need to resync. This
            # happens if we've missed updates.
            resync = yield self._need_to_do_resync(user_id, pending_updates)

            if logger.isEnabledFor(logging.INFO):
                logger.info(
                    "Received device list update for %s, requiring resync: %s. Devices: %s",
                    user_id,
                    resync,
                    ", ".join(u[0] for u in pending_updates),
                )

            if resync:
                yield self.user_device_resync(user_id)
            else:
                # Simply update the single device, since we know that is the only
                # change (because of the single prev_id matching the current cache)
                for device_id, stream_id, prev_ids, content in pending_updates:
                    yield self.store.update_remote_device_list_cache_entry(
                        user_id, device_id, content, stream_id
                    )

                yield self.device_handler.notify_device_update(
                    user_id, [device_id for device_id, _, _, _ in pending_updates]
                )

                self._seen_updates.setdefault(user_id, set()).update(
                    stream_id for _, stream_id, _, _ in pending_updates
                )

    @defer.inlineCallbacks
    def _need_to_do_resync(self, user_id, updates):
        """Given a list of updates for a user figure out if we need to do a full
        resync, or whether we have enough data that we can just apply the delta.
        """
        seen_updates = self._seen_updates.get(user_id, set())

        extremity = yield self.store.get_device_list_last_stream_id_for_remote(user_id)

        logger.debug("Current extremity for %r: %r", user_id, extremity)

        stream_id_in_updates = set()  # stream_ids in updates list
        for _, stream_id, prev_ids, _ in updates:
            if not prev_ids:
                # We always do a resync if there are no previous IDs
                return True

            for prev_id in prev_ids:
                if prev_id == extremity:
                    continue
                elif prev_id in seen_updates:
                    continue
                elif prev_id in stream_id_in_updates:
                    continue
                else:
                    return True

            stream_id_in_updates.add(stream_id)

        return False

    @defer.inlineCallbacks
    def _maybe_retry_device_resync(self):
        """Retry to resync device lists that are out of sync, except if another retry is
        in progress.
        """
        if self._resync_retry_in_progress:
            return

        try:
            # Prevent another call of this function to retry resyncing device lists so
            # we don't send too many requests.
            self._resync_retry_in_progress = True
            # Get all of the users that need resyncing.
            need_resync = yield self.store.get_user_ids_requiring_device_list_resync()
            # Iterate over the set of user IDs.
            for user_id in need_resync:
                try:
                    # Try to resync the current user's devices list.
                    result = yield self.user_device_resync(
                        user_id=user_id, mark_failed_as_stale=False,
                    )

                    # user_device_resync only returns a result if it managed to
                    # successfully resync and update the database. Updating the table
                    # of users requiring resync isn't necessary here as
                    # user_device_resync already does it (through
                    # self.store.update_remote_device_list_cache).
                    if result:
                        logger.debug(
                            "Successfully resynced the device list for %s", user_id,
                        )
                except Exception as e:
                    # If there was an issue resyncing this user, e.g. if the remote
                    # server sent a malformed result, just log the error instead of
                    # aborting all the subsequent resyncs.
                    logger.debug(
                        "Could not resync the device list for %s: %s", user_id, e,
                    )
        finally:
            # Allow future calls to retry resyncinc out of sync device lists.
            self._resync_retry_in_progress = False

    @defer.inlineCallbacks
    def user_device_resync(self, user_id, mark_failed_as_stale=True):
        """Fetches all devices for a user and updates the device cache with them.

        Args:
            user_id (str): The user's id whose device_list will be updated.
            mark_failed_as_stale (bool): Whether to mark the user's device list as stale
                if the attempt to resync failed.
        Returns:
            Deferred[dict]: a dict with device info as under the "devices" in the result of this
            request:
            https://matrix.org/docs/spec/server_server/r0.1.2#get-matrix-federation-v1-user-devices-userid
        """
        logger.debug("Attempting to resync the device list for %s", user_id)
        log_kv({"message": "Doing resync to update device list."})
        # Fetch all devices for the user.
        origin = get_domain_from_id(user_id)
        try:
            result = yield self.federation.query_user_devices(origin, user_id)
        except NotRetryingDestination:
            if mark_failed_as_stale:
                # Mark the remote user's device list as stale so we know we need to retry
                # it later.
                yield self.store.mark_remote_user_device_cache_as_stale(user_id)

            return
        except (RequestSendFailed, HttpResponseException) as e:
            logger.warning(
                "Failed to handle device list update for %s: %s", user_id, e,
            )

            if mark_failed_as_stale:
                # Mark the remote user's device list as stale so we know we need to retry
                # it later.
                yield self.store.mark_remote_user_device_cache_as_stale(user_id)

            # We abort on exceptions rather than accepting the update
            # as otherwise synapse will 'forget' that its device list
            # is out of date. If we bail then we will retry the resync
            # next time we get a device list update for this user_id.
            # This makes it more likely that the device lists will
            # eventually become consistent.
            return
        except FederationDeniedError as e:
            set_tag("error", True)
            log_kv({"reason": "FederationDeniedError"})
            logger.info(e)
            return
        except Exception as e:
            set_tag("error", True)
            log_kv(
                {"message": "Exception raised by federation request", "exception": e}
            )
            logger.exception("Failed to handle device list update for %s", user_id)

            if mark_failed_as_stale:
                # Mark the remote user's device list as stale so we know we need to retry
                # it later.
                yield self.store.mark_remote_user_device_cache_as_stale(user_id)

            return
        log_kv({"result": result})
        stream_id = result["stream_id"]
        devices = result["devices"]

        # Get the master key and the self-signing key for this user if provided in the
        # response (None if not in the response).
        # The response will not contain the user signing key, as this key is only used by
        # its owner, thus it doesn't make sense to send it over federation.
        master_key = result.get("master_key")
        self_signing_key = result.get("self_signing_key")

        # If the remote server has more than ~1000 devices for this user
        # we assume that something is going horribly wrong (e.g. a bot
        # that logs in and creates a new device every time it tries to
        # send a message).  Maintaining lots of devices per user in the
        # cache can cause serious performance issues as if this request
        # takes more than 60s to complete, internal replication from the
        # inbound federation worker to the synapse master may time out
        # causing the inbound federation to fail and causing the remote
        # server to retry, causing a DoS.  So in this scenario we give
        # up on storing the total list of devices and only handle the
        # delta instead.
        if len(devices) > 1000:
            logger.warning(
                "Ignoring device list snapshot for %s as it has >1K devs (%d)",
                user_id,
                len(devices),
            )
            devices = []

        for device in devices:
            logger.debug(
                "Handling resync update %r/%r, ID: %r",
                user_id,
                device["device_id"],
                stream_id,
            )

        yield self.store.update_remote_device_list_cache(user_id, devices, stream_id)
        device_ids = [device["device_id"] for device in devices]

        # Handle cross-signing keys.
        cross_signing_device_ids = yield self.process_cross_signing_key_update(
            user_id, master_key, self_signing_key,
        )
        device_ids = device_ids + cross_signing_device_ids

        yield self.device_handler.notify_device_update(user_id, device_ids)

        # We clobber the seen updates since we've re-synced from a given
        # point.
        self._seen_updates[user_id] = {stream_id}

        defer.returnValue(result)

    @defer.inlineCallbacks
    def process_cross_signing_key_update(
        self,
        user_id: str,
        master_key: Optional[Dict[str, Any]],
        self_signing_key: Optional[Dict[str, Any]],
    ) -> list:
        """Process the given new master and self-signing key for the given remote user.

        Args:
            user_id: The ID of the user these keys are for.
            master_key: The dict of the cross-signing master key as returned by the
                remote server.
            self_signing_key: The dict of the cross-signing self-signing key as returned
                by the remote server.

        Return:
            The device IDs for the given keys.
        """
        device_ids = []

        if master_key:
            yield self.store.set_e2e_cross_signing_key(user_id, "master", master_key)
            _, verify_key = get_verify_key_from_cross_signing_key(master_key)
            # verify_key is a VerifyKey from signedjson, which uses
            # .version to denote the portion of the key ID after the
            # algorithm and colon, which is the device ID
            device_ids.append(verify_key.version)
        if self_signing_key:
            yield self.store.set_e2e_cross_signing_key(
                user_id, "self_signing", self_signing_key
            )
            _, verify_key = get_verify_key_from_cross_signing_key(self_signing_key)
            device_ids.append(verify_key.version)

        return device_ids