summary refs log tree commit diff
path: root/synapse/handlers/device.py
blob: 46ee834407412a1570e31eb13e5fc2f0448eea78 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
# Copyright 2016 OpenMarket Ltd
# Copyright 2019 New Vector Ltd
# Copyright 2019,2020 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
from typing import TYPE_CHECKING, Collection, Dict, Iterable, List, Optional, Set, Tuple

from synapse.api import errors
from synapse.api.constants import EventTypes
from synapse.api.errors import (
    Codes,
    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 (
    JsonDict,
    StreamToken,
    UserID,
    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

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)

MAX_DEVICE_DISPLAY_NAME_LEN = 100


class DeviceWorkerHandler(BaseHandler):
    def __init__(self, hs: "HomeServer"):
        super().__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
    async def get_devices_by_user(self, user_id: str) -> List[JsonDict]:
        """
        Retrieve the given user's devices

        Args:
            user_id: The user ID to query for devices.
        Returns:
            info on each device
        """

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

        ips = await 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
    async def get_device(self, user_id: str, device_id: str) -> JsonDict:
        """Retrieve the given device

        Args:
            user_id: The user to get the device from
            device_id: The device to fetch.

        Returns:
            info on the device
        Raises:
            errors.NotFoundError: if the device was not found
        """
        try:
            device = await self.store.get_device(user_id, device_id)
        except errors.StoreError:
            raise errors.NotFoundError
        ips = await 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

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

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

        room_ids = await 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 = await 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 = await 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 = await 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 = from_token.room_key.stream

        possibly_changed = set(changed)
        possibly_left = set()
        for room_id in rooms_changed:
            current_state_ids = await 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 etype, state_key in current_state_ids.keys():
                    if etype != EventTypes.Member:
                        continue
                    possibly_left.add(state_key)
                continue

            # Fetch the current state at the time.
            try:
                event_ids = await self.store.get_forward_extremities_for_room_at_stream_ordering(
                    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 etype, state_key in current_state_ids.keys():
                    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 = await 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 prev_state_ids.values():
                member_event = state_dict.get((EventTypes.Member, user_id), None)
                if not member_event or member_event != current_member_id:
                    for etype, state_key in current_state_ids.keys():
                        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 current_state_ids.items():
                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 prev_state_ids.values():
                    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 = set()
            possibly_left = set()

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

        log_kv(result)

        return result

    async def on_federation_query_user_devices(self, user_id: str) -> JsonDict:
        stream_id, devices = await self.store.get_e2e_device_keys_for_federation_query(
            user_id
        )
        master_key = await self.store.get_e2e_cross_signing_key(user_id, "master")
        self_signing_key = await 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: "HomeServer"):
        super().__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)

    def _check_device_name_length(self, name: Optional[str]):
        """
        Checks whether a device name is longer than the maximum allowed length.

        Args:
            name: The name of the device.

        Raises:
            SynapseError: if the device name is too long.
        """
        if name and len(name) > MAX_DEVICE_DISPLAY_NAME_LEN:
            raise SynapseError(
                400,
                "Device display name is too long (max %i)"
                % (MAX_DEVICE_DISPLAY_NAME_LEN,),
                errcode=Codes.TOO_LARGE,
            )

    async def check_device_registered(
        self,
        user_id: str,
        device_id: Optional[str],
        initial_device_display_name: Optional[str] = None,
    ) -> str:
        """
        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:  @user:id
            device_id: device id supplied by client
            initial_device_display_name: device display name from client
        Returns:
            device id (generated if none was supplied)
        """

        self._check_device_name_length(initial_device_display_name)

        if device_id is not None:
            new_device = await self.store.store_device(
                user_id=user_id,
                device_id=device_id,
                initial_device_display_name=initial_device_display_name,
            )
            if new_device:
                await 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:
            new_device_id = stringutils.random_string(10).upper()
            new_device = await self.store.store_device(
                user_id=user_id,
                device_id=new_device_id,
                initial_device_display_name=initial_device_display_name,
            )
            if new_device:
                await self.notify_device_update(user_id, [new_device_id])
                return new_device_id
            attempts += 1

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

    @trace
    async def delete_device(self, user_id: str, device_id: str) -> None:
        """Delete the given device

        Args:
            user_id: The user to delete the device from.
            device_id: The device to delete.
        """

        try:
            await 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

        await self._auth_handler.delete_access_tokens_for_user(
            user_id, device_id=device_id
        )

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

        await self.notify_device_update(user_id, [device_id])

    @trace
    async def delete_all_devices_for_user(
        self, user_id: str, except_device_id: Optional[str] = None
    ) -> None:
        """Delete all of the user's devices

        Args:
            user_id: The user to remove all devices from
            except_device_id: optional device id which should not be deleted
        """
        device_map = await 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]
        await self.delete_devices(user_id, device_ids)

    async def delete_devices(self, user_id: str, device_ids: List[str]) -> None:
        """Delete several devices

        Args:
            user_id: The user to delete devices from.
            device_ids: The list of device IDs to delete
        """

        try:
            await 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:
            await self._auth_handler.delete_access_tokens_for_user(
                user_id, device_id=device_id
            )
            await self.store.delete_e2e_keys_by_device(
                user_id=user_id, device_id=device_id
            )

        await self.notify_device_update(user_id, device_ids)

    async def update_device(self, user_id: str, device_id: str, content: dict) -> None:
        """Update the given device

        Args:
            user_id: The user to update devices of.
            device_id: The device to update.
            content: body of update request
        """

        # Reject a new displayname which is too long.
        new_display_name = content.get("display_name")

        self._check_device_name_length(new_display_name)

        try:
            await self.store.update_device(
                user_id, device_id, new_display_name=new_display_name
            )
            await 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")
    async def notify_device_update(
        self, user_id: str, device_ids: Collection[str]
    ) -> None:
        """Notify that a user's device(s) has changed. Pokes the notifier, and
        remote servers if the user is local.
        """
        if not device_ids:
            # No changes to notify about, so this is a no-op.
            return

        users_who_share_room = await self.store.get_users_who_share_room_with_user(
            user_id
        )

        hosts: Set[str] = 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 = await self.store.add_device_change_to_streams(
            user_id, device_ids, list(hosts)
        )

        if not position:
            # This should only happen if there are no updates, so we bail.
            return

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

        room_ids = await 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.
        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})

    async def notify_user_signature_update(
        self, from_user_id: str, user_ids: List[str]
    ) -> None:
        """Notify a user that they have made new signatures of other users.

        Args:
            from_user_id: the user who made the signature
            user_ids: the users IDs that have new signatures
        """

        position = await 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])

    async def user_left_room(self, user: UserID, room_id: str) -> None:
        user_id = user.to_string()
        room_ids = await 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.
            await self.store.mark_remote_user_device_list_as_unsubscribed(user_id)

    async def store_dehydrated_device(
        self,
        user_id: str,
        device_data: JsonDict,
        initial_device_display_name: Optional[str] = None,
    ) -> str:
        """Store a dehydrated device for a user.  If the user had a previous
        dehydrated device, it is removed.

        Args:
            user_id: the user that we are storing the device for
            device_data: the dehydrated device information
            initial_device_display_name: The display name to use for the device
        Returns:
            device id of the dehydrated device
        """
        device_id = await self.check_device_registered(
            user_id,
            None,
            initial_device_display_name,
        )
        old_device_id = await self.store.store_dehydrated_device(
            user_id, device_id, device_data
        )
        if old_device_id is not None:
            await self.delete_device(user_id, old_device_id)
        return device_id

    async def get_dehydrated_device(
        self, user_id: str
    ) -> Optional[Tuple[str, JsonDict]]:
        """Retrieve the information for a dehydrated device.

        Args:
            user_id: the user whose dehydrated device we are looking for
        Returns:
            a tuple whose first item is the device ID, and the second item is
            the dehydrated device information
        """
        return await self.store.get_dehydrated_device(user_id)

    async def rehydrate_device(
        self, user_id: str, access_token: str, device_id: str
    ) -> dict:
        """Process a rehydration request from the user.

        Args:
            user_id: the user who is rehydrating the device
            access_token: the access token used for the request
            device_id: the ID of the device that will be rehydrated
        Returns:
            a dict containing {"success": True}
        """
        success = await self.store.remove_dehydrated_device(user_id, device_id)

        if not success:
            raise errors.NotFoundError()

        # If the dehydrated device was successfully deleted (the device ID
        # matched the stored dehydrated device), then modify the access
        # token to use the dehydrated device's ID and copy the old device
        # display name to the dehydrated device, and destroy the old device
        # ID
        old_device_id = await self.store.set_device_for_access_token(
            access_token, device_id
        )
        old_device = await self.store.get_device(user_id, old_device_id)
        await self.store.update_device(user_id, device_id, old_device["display_name"])
        # can't call self.delete_device because that will clobber the
        # access token so call the storage layer directly
        await self.store.delete_device(user_id, old_device_id)
        await self.store.delete_e2e_keys_by_device(
            user_id=user_id, device_id=old_device_id
        )

        # tell everyone that the old device is gone and that the dehydrated
        # device has a new display name
        await self.notify_device_update(user_id, [old_device_id, device_id])

        return {"success": True}


def _update_device_from_client_ips(
    device: JsonDict, client_ips: Dict[Tuple[str, str], JsonDict]
) -> None:
    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:
    "Handles incoming device list updates from federation and updates the DB"

    def __init__(self, hs: "HomeServer", device_handler: DeviceHandler):
        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: Dict[
            str, List[Tuple[str, str, Iterable[str], JsonDict]]
        ] = {}

        # 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[str, Set[str]] = 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
    async def incoming_device_list_update(
        self, origin: str, edu_content: JsonDict
    ) -> None:
        """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 = await 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)
        )

        await self._handle_device_updates(user_id)

    @measure_func("_incoming_device_list_update")
    async def _handle_device_updates(self, user_id: str) -> None:
        "Actually handle pending updates."

        with (await 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, _ 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 = await 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:
                await 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, _, content in pending_updates:
                    await self.store.update_remote_device_list_cache_entry(
                        user_id, device_id, content, stream_id
                    )

                await 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
                )

    async def _need_to_do_resync(
        self, user_id: str, updates: Iterable[Tuple[str, str, Iterable[str], JsonDict]]
    ) -> bool:
        """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: Set[str] = self._seen_updates.get(user_id, set())

        extremity = await 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

    @trace
    async def _maybe_retry_device_resync(self) -> None:
        """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 = await 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 = await 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

    async def user_device_resync(
        self, user_id: str, mark_failed_as_stale: bool = True
    ) -> Optional[JsonDict]:
        """Fetches all devices for a user and updates the device cache with them.

        Args:
            user_id: The user's id whose device_list will be updated.
            mark_failed_as_stale: Whether to mark the user's device list as stale
                if the attempt to resync failed.
        Returns:
            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 = await 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.
                await self.store.mark_remote_user_device_cache_as_stale(user_id)

            return None
        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.
                await 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 None
        except FederationDeniedError as e:
            set_tag("error", True)
            log_kv({"reason": "FederationDeniedError"})
            logger.info(e)
            return None
        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.
                await self.store.mark_remote_user_device_cache_as_stale(user_id)

            return None
        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")

        ignore_devices = False
        # 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 = []
            ignore_devices = True
        else:
            cached_devices = await self.store.get_cached_devices_for_user(user_id)
            if cached_devices == {d["device_id"]: d for d in devices}:
                logging.info(
                    "Skipping device list resync for %s, as our cache matches already",
                    user_id,
                )
                devices = []
                ignore_devices = True

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

        if not ignore_devices:
            await self.store.update_remote_device_list_cache(
                user_id, devices, stream_id
            )
        # mark the cache as valid, whether or not we actually processed any device
        # list updates.
        await self.store.mark_remote_user_device_cache_as_valid(user_id)
        device_ids = [device["device_id"] for device in devices]

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

        if device_ids:
            await 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}

        return result

    async def process_cross_signing_key_update(
        self,
        user_id: str,
        master_key: Optional[JsonDict],
        self_signing_key: Optional[JsonDict],
    ) -> List[str]:
        """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 = []

        current_keys_map = await self.store.get_e2e_cross_signing_keys_bulk([user_id])
        current_keys = current_keys_map.get(user_id) or {}

        if master_key and master_key != current_keys.get("master"):
            await 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 and self_signing_key != current_keys.get("self_signing"):
            await 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