test_sync.py

#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
from typing import Collection, ContextManager, List, Optional
from unittest.mock import AsyncMock, Mock, patch

from parameterized import parameterized

from twisted.test.proto_helpers import MemoryReactor

from synapse.api.constants import EventTypes, JoinRules
from synapse.api.errors import Codes, ResourceLimitError
from synapse.api.filtering import FilterCollection, Filtering
from synapse.api.room_versions import RoomVersion, RoomVersions
from synapse.events import EventBase
from synapse.events.snapshot import EventContext
from synapse.federation.federation_base import event_from_pdu_json
from synapse.handlers.sync import SyncConfig, SyncResult
from synapse.rest import admin
from synapse.rest.client import knock, login, room
from synapse.server import HomeServer
from synapse.types import JsonDict, UserID, create_requester
from synapse.util import Clock

import tests.unittest
import tests.utils


class SyncTestCase(tests.unittest.HomeserverTestCase):
    """Tests Sync Handler."""

    servlets = [
        admin.register_servlets,
        knock.register_servlets,
        login.register_servlets,
        room.register_servlets,
    ]

    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
        self.sync_handler = self.hs.get_sync_handler()
        self.store = self.hs.get_datastores().main

        # AuthBlocking reads from the hs' config on initialization. We need to
        # modify its config instead of the hs'
        self.auth_blocking = self.hs.get_auth_blocking()

    def test_wait_for_sync_for_user_auth_blocking(self) -> None:
        user_id1 = "@user1:test"
        user_id2 = "@user2:test"
        sync_config = generate_sync_config(user_id1)
        requester = create_requester(user_id1)

        self.reactor.advance(100)  # So we get not 0 time
        self.auth_blocking._limit_usage_by_mau = True
        self.auth_blocking._max_mau_value = 1

        # Check that the happy case does not throw errors
        self.get_success(self.store.upsert_monthly_active_user(user_id1))
        self.get_success(
            self.sync_handler.wait_for_sync_for_user(requester, sync_config)
        )

        # Test that global lock works
        self.auth_blocking._hs_disabled = True
        e = self.get_failure(
            self.sync_handler.wait_for_sync_for_user(requester, sync_config),
            ResourceLimitError,
        )
        self.assertEqual(e.value.errcode, Codes.RESOURCE_LIMIT_EXCEEDED)

        self.auth_blocking._hs_disabled = False

        sync_config = generate_sync_config(user_id2)
        requester = create_requester(user_id2)

        e = self.get_failure(
            self.sync_handler.wait_for_sync_for_user(requester, sync_config),
            ResourceLimitError,
        )
        self.assertEqual(e.value.errcode, Codes.RESOURCE_LIMIT_EXCEEDED)

    def test_unknown_room_version(self) -> None:
        """
        A room with an unknown room version should not break sync (and should be excluded).
        """
        inviter = self.register_user("creator", "pass", admin=True)
        inviter_tok = self.login("@creator:test", "pass")

        user = self.register_user("user", "pass")
        tok = self.login("user", "pass")

        # Do an initial sync on a different device.
        requester = create_requester(user)
        initial_result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                requester, sync_config=generate_sync_config(user, device_id="dev")
            )
        )

        # Create a room as the user.
        joined_room = self.helper.create_room_as(user, tok=tok)

        # Invite the user to the room as someone else.
        invite_room = self.helper.create_room_as(inviter, tok=inviter_tok)
        self.helper.invite(invite_room, targ=user, tok=inviter_tok)

        knock_room = self.helper.create_room_as(
            inviter, room_version=RoomVersions.V7.identifier, tok=inviter_tok
        )
        self.helper.send_state(
            knock_room,
            EventTypes.JoinRules,
            {"join_rule": JoinRules.KNOCK},
            tok=inviter_tok,
        )
        channel = self.make_request(
            "POST",
            "/_matrix/client/r0/knock/%s" % (knock_room,),
            b"{}",
            tok,
        )
        self.assertEqual(200, channel.code, channel.result)

        # The rooms should appear in the sync response.
        result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                requester, sync_config=generate_sync_config(user)
            )
        )
        self.assertIn(joined_room, [r.room_id for r in result.joined])
        self.assertIn(invite_room, [r.room_id for r in result.invited])
        self.assertIn(knock_room, [r.room_id for r in result.knocked])

        # Test a incremental sync (by providing a since_token).
        result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                requester,
                sync_config=generate_sync_config(user, device_id="dev"),
                since_token=initial_result.next_batch,
            )
        )
        self.assertIn(joined_room, [r.room_id for r in result.joined])
        self.assertIn(invite_room, [r.room_id for r in result.invited])
        self.assertIn(knock_room, [r.room_id for r in result.knocked])

        # Poke the database and update the room version to an unknown one.
        for room_id in (joined_room, invite_room, knock_room):
            self.get_success(
                self.hs.get_datastores().main.db_pool.simple_update(
                    "rooms",
                    keyvalues={"room_id": room_id},
                    updatevalues={"room_version": "unknown-room-version"},
                    desc="updated-room-version",
                )
            )

        # Blow away caches (supported room versions can only change due to a restart).
        self.store.get_rooms_for_user_with_stream_ordering.invalidate_all()
        self.store.get_rooms_for_user.invalidate_all()
        self.store._get_event_cache.clear()
        self.store._event_ref.clear()

        # The rooms should be excluded from the sync response.
        # Get a new request key.
        result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                requester, sync_config=generate_sync_config(user)
            )
        )
        self.assertNotIn(joined_room, [r.room_id for r in result.joined])
        self.assertNotIn(invite_room, [r.room_id for r in result.invited])
        self.assertNotIn(knock_room, [r.room_id for r in result.knocked])

        # The rooms should also not be in an incremental sync.
        result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                requester,
                sync_config=generate_sync_config(user, device_id="dev"),
                since_token=initial_result.next_batch,
            )
        )
        self.assertNotIn(joined_room, [r.room_id for r in result.joined])
        self.assertNotIn(invite_room, [r.room_id for r in result.invited])
        self.assertNotIn(knock_room, [r.room_id for r in result.knocked])

    def test_ban_wins_race_with_join(self) -> None:
        """Rooms shouldn't appear under "joined" if a join loses a race to a ban.

        A complicated edge case. Imagine the following scenario:

        * you attempt to join a room
        * racing with that is a ban which comes in over federation, which ends up with
          an earlier stream_ordering than the join.
        * you get a sync response with a sync token which is _after_ the ban, but before
          the join
        * now your join lands; it is a valid event because its `prev_event`s predate the
          ban, but will not make it into current_state_events (because bans win over
          joins in state res, essentially).
        * When we do a sync from the incremental sync, the only event in the timeline
          is your join ... and yet you aren't joined.

        The ban coming in over federation isn't crucial for this behaviour; the key
        requirements are:
        1. the homeserver generates a join event with prev_events that precede the ban
           (so that it passes the "are you banned" test)
        2. the join event has a stream_ordering after that of the ban.

        We use monkeypatching to artificially trigger condition (1).
        """
        # A local user Alice creates a room.
        owner = self.register_user("alice", "password")
        owner_tok = self.login(owner, "password")
        room_id = self.helper.create_room_as(owner, is_public=True, tok=owner_tok)

        # Do a sync as Alice to get the latest event in the room.
        alice_sync_result: SyncResult = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                create_requester(owner), generate_sync_config(owner)
            )
        )
        self.assertEqual(len(alice_sync_result.joined), 1)
        self.assertEqual(alice_sync_result.joined[0].room_id, room_id)
        last_room_creation_event_id = (
            alice_sync_result.joined[0].timeline.events[-1].event_id
        )

        # Eve, a ne'er-do-well, registers.
        eve = self.register_user("eve", "password")
        eve_token = self.login(eve, "password")

        # Alice preemptively bans Eve.
        self.helper.ban(room_id, owner, eve, tok=owner_tok)

        # Eve syncs.
        eve_requester = create_requester(eve)
        eve_sync_config = generate_sync_config(eve)
        eve_sync_after_ban: SyncResult = self.get_success(
            self.sync_handler.wait_for_sync_for_user(eve_requester, eve_sync_config)
        )

        # Sanity check this sync result. We shouldn't be joined to the room.
        self.assertEqual(eve_sync_after_ban.joined, [])

        # Eve tries to join the room. We monkey patch the internal logic which selects
        # the prev_events used when creating the join event, such that the ban does not
        # precede the join.
        with self._patch_get_latest_events([last_room_creation_event_id]):
            self.helper.join(room_id, eve, tok=eve_token)

        # Eve makes a second, incremental sync.
        eve_incremental_sync_after_join: SyncResult = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                eve_requester,
                eve_sync_config,
                since_token=eve_sync_after_ban.next_batch,
            )
        )
        # Eve should not see herself as joined to the room.
        self.assertEqual(eve_incremental_sync_after_join.joined, [])

        # If we did a third initial sync, we should _still_ see eve is not joined to the room.
        eve_initial_sync_after_join: SyncResult = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                eve_requester,
                eve_sync_config,
                since_token=None,
            )
        )
        self.assertEqual(eve_initial_sync_after_join.joined, [])

    def test_state_includes_changes_on_forks(self) -> None:
        """State changes that happen on a fork of the DAG must be included in `state`

        Given the following DAG:

             E1
           ↗    ↖
          |      S2
          |      ↑
        --|------|----
          |      |
          E3     |
           ↖    /
             E4

        ... and a filter that means we only return 2 events, represented by the dashed
        horizontal line: `S2` must be included in the `state` section.
        """
        alice = self.register_user("alice", "password")
        alice_tok = self.login(alice, "password")
        alice_requester = create_requester(alice)
        room_id = self.helper.create_room_as(alice, is_public=True, tok=alice_tok)

        # Do an initial sync as Alice to get a known starting point.
        initial_sync_result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                alice_requester, generate_sync_config(alice)
            )
        )
        last_room_creation_event_id = (
            initial_sync_result.joined[0].timeline.events[-1].event_id
        )

        # Send a state event, and a regular event, both using the same prev ID
        with self._patch_get_latest_events([last_room_creation_event_id]):
            s2_event = self.helper.send_state(room_id, "s2", {}, tok=alice_tok)[
                "event_id"
            ]
            e3_event = self.helper.send(room_id, "e3", tok=alice_tok)["event_id"]

        # Send a final event, joining the two branches of the dag
        e4_event = self.helper.send(room_id, "e4", tok=alice_tok)["event_id"]

        # do an incremental sync, with a filter that will ensure we only get two of
        # the three new events.
        incremental_sync = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                alice_requester,
                generate_sync_config(
                    alice,
                    filter_collection=FilterCollection(
                        self.hs, {"room": {"timeline": {"limit": 2}}}
                    ),
                ),
                since_token=initial_sync_result.next_batch,
            )
        )

        # The state event should appear in the 'state' section of the response.
        room_sync = incremental_sync.joined[0]
        self.assertEqual(room_sync.room_id, room_id)
        self.assertTrue(room_sync.timeline.limited)
        self.assertEqual(
            [e.event_id for e in room_sync.timeline.events],
            [e3_event, e4_event],
        )
        self.assertEqual(
            [e.event_id for e in room_sync.state.values()],
            [s2_event],
        )

    def test_state_includes_changes_on_forks_when_events_excluded(self) -> None:
        """A variation on the previous test, but where one event is filtered

        The DAG is the same as the previous test, but E4 is excluded by the filter.

             E1
           ↗    ↖
          |      S2
          |      ↑
        --|------|----
          |      |
          E3     |
           ↖    /
            (E4)

        """

        alice = self.register_user("alice", "password")
        alice_tok = self.login(alice, "password")
        alice_requester = create_requester(alice)
        room_id = self.helper.create_room_as(alice, is_public=True, tok=alice_tok)

        # Do an initial sync as Alice to get a known starting point.
        initial_sync_result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                alice_requester, generate_sync_config(alice)
            )
        )
        last_room_creation_event_id = (
            initial_sync_result.joined[0].timeline.events[-1].event_id
        )

        # Send a state event, and a regular event, both using the same prev ID
        with self._patch_get_latest_events([last_room_creation_event_id]):
            s2_event = self.helper.send_state(room_id, "s2", {}, tok=alice_tok)[
                "event_id"
            ]
            e3_event = self.helper.send(room_id, "e3", tok=alice_tok)["event_id"]

        # Send a final event, joining the two branches of the dag
        self.helper.send(room_id, "e4", type="not_a_normal_message", tok=alice_tok)[
            "event_id"
        ]

        # do an incremental sync, with a filter that will only return E3, excluding S2
        # and E4.
        incremental_sync = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                alice_requester,
                generate_sync_config(
                    alice,
                    filter_collection=FilterCollection(
                        self.hs,
                        {
                            "room": {
                                "timeline": {
                                    "limit": 1,
                                    "not_types": ["not_a_normal_message"],
                                }
                            }
                        },
                    ),
                ),
                since_token=initial_sync_result.next_batch,
            )
        )

        # The state event should appear in the 'state' section of the response.
        room_sync = incremental_sync.joined[0]
        self.assertEqual(room_sync.room_id, room_id)
        self.assertTrue(room_sync.timeline.limited)
        self.assertEqual(
            [e.event_id for e in room_sync.timeline.events],
            [e3_event],
        )
        self.assertEqual(
            [e.event_id for e in room_sync.state.values()],
            [s2_event],
        )

    def test_state_includes_changes_on_ungappy_syncs(self) -> None:
        """Test `state` where the sync is not gappy.

        We start with a DAG like this:

             E1
           ↗    ↖
          |      S2
          |
        --|---
          |
          E3

        ... and initialsync with `limit=1`, represented by the horizontal dashed line.
        At this point, we do not expect S2 to appear in the response at all (since
        it is excluded from the timeline by the `limit`, and the state is based on the
        state after the most recent event before the sync token (E3), which doesn't
        include S2.

        Now more events arrive, and we do an incremental sync:

             E1
           ↗    ↖
          |      S2
          |      ↑
          E3     |
          ↑      |
        --|------|----
          |      |
          E4     |
           ↖    /
             E5

        This is the last chance for us to tell the client about S2, so it *must* be
        included in the response.
        """
        alice = self.register_user("alice", "password")
        alice_tok = self.login(alice, "password")
        alice_requester = create_requester(alice)
        room_id = self.helper.create_room_as(alice, is_public=True, tok=alice_tok)

        # Do an initial sync to get a known starting point.
        initial_sync_result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                alice_requester, generate_sync_config(alice)
            )
        )
        last_room_creation_event_id = (
            initial_sync_result.joined[0].timeline.events[-1].event_id
        )

        # Send a state event, and a regular event, both using the same prev ID
        with self._patch_get_latest_events([last_room_creation_event_id]):
            s2_event = self.helper.send_state(room_id, "s2", {}, tok=alice_tok)[
                "event_id"
            ]
            e3_event = self.helper.send(room_id, "e3", tok=alice_tok)["event_id"]

        # Another initial sync, with limit=1
        initial_sync_result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                alice_requester,
                generate_sync_config(
                    alice,
                    filter_collection=FilterCollection(
                        self.hs, {"room": {"timeline": {"limit": 1}}}
                    ),
                ),
            )
        )
        room_sync = initial_sync_result.joined[0]
        self.assertEqual(room_sync.room_id, room_id)
        self.assertEqual(
            [e.event_id for e in room_sync.timeline.events],
            [e3_event],
        )
        self.assertNotIn(s2_event, [e.event_id for e in room_sync.state.values()])

        # More events, E4 and E5
        with self._patch_get_latest_events([e3_event]):
            e4_event = self.helper.send(room_id, "e4", tok=alice_tok)["event_id"]
        e5_event = self.helper.send(room_id, "e5", tok=alice_tok)["event_id"]

        # Now incremental sync
        incremental_sync = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                alice_requester,
                generate_sync_config(alice),
                since_token=initial_sync_result.next_batch,
            )
        )

        # The state event should appear in the 'state' section of the response.
        room_sync = incremental_sync.joined[0]
        self.assertEqual(room_sync.room_id, room_id)
        self.assertFalse(room_sync.timeline.limited)
        self.assertEqual(
            [e.event_id for e in room_sync.timeline.events],
            [e4_event, e5_event],
        )
        self.assertEqual(
            [e.event_id for e in room_sync.state.values()],
            [s2_event],
        )

    @parameterized.expand(
        [
            (False, False),
            (True, False),
            (False, True),
            (True, True),
        ]
    )
    def test_archived_rooms_do_not_include_state_after_leave(
        self, initial_sync: bool, empty_timeline: bool
    ) -> None:
        """If the user leaves the room, state changes that happen after they leave are not returned.

        We try with both a zero and a normal timeline limit,
        and we try both an initial sync and an incremental sync for both.
        """
        if empty_timeline and not initial_sync:
            # FIXME synapse doesn't return the room at all in this situation!
            self.skipTest("Synapse does not correctly handle this case")

        # Alice creates the room, and bob joins.
        alice = self.register_user("alice", "password")
        alice_tok = self.login(alice, "password")

        bob = self.register_user("bob", "password")
        bob_tok = self.login(bob, "password")
        bob_requester = create_requester(bob)

        room_id = self.helper.create_room_as(alice, is_public=True, tok=alice_tok)
        self.helper.join(room_id, bob, tok=bob_tok)

        initial_sync_result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                bob_requester, generate_sync_config(bob)
            )
        )

        # Alice sends a message and a state
        before_message_event = self.helper.send(room_id, "before", tok=alice_tok)[
            "event_id"
        ]
        before_state_event = self.helper.send_state(
            room_id, "test_state", {"body": "before"}, tok=alice_tok
        )["event_id"]

        # Bob leaves
        leave_event = self.helper.leave(room_id, bob, tok=bob_tok)["event_id"]

        # Alice sends some more stuff
        self.helper.send(room_id, "after", tok=alice_tok)["event_id"]
        self.helper.send_state(room_id, "test_state", {"body": "after"}, tok=alice_tok)[
            "event_id"
        ]

        # And now, Bob resyncs.
        filter_dict: JsonDict = {"room": {"include_leave": True}}
        if empty_timeline:
            filter_dict["room"]["timeline"] = {"limit": 0}
        sync_room_result = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                bob_requester,
                generate_sync_config(
                    bob, filter_collection=FilterCollection(self.hs, filter_dict)
                ),
                since_token=None if initial_sync else initial_sync_result.next_batch,
            )
        ).archived[0]

        if empty_timeline:
            # The timeline should be empty
            self.assertEqual(sync_room_result.timeline.events, [])

            # And the state should include the leave event...
            self.assertEqual(
                sync_room_result.state[("m.room.member", bob)].event_id, leave_event
            )
            # ... and the state change before he left.
            self.assertEqual(
                sync_room_result.state[("test_state", "")].event_id, before_state_event
            )
        else:
            # The last three events in the timeline should be those leading up to the
            # leave
            self.assertEqual(
                [e.event_id for e in sync_room_result.timeline.events[-3:]],
                [before_message_event, before_state_event, leave_event],
            )
            # ... And the state should be empty
            self.assertEqual(sync_room_result.state, {})

    def _patch_get_latest_events(self, latest_events: List[str]) -> ContextManager:
        """Monkey-patch `get_prev_events_for_room`

        Returns a context manager which will replace the implementation of
        `get_prev_events_for_room` with one which returns `latest_events`.
        """
        return patch.object(
            self.hs.get_datastores().main,
            "get_prev_events_for_room",
            new_callable=AsyncMock,
            return_value=latest_events,
        )

    def test_call_invite_in_public_room_not_returned(self) -> None:
        user = self.register_user("alice", "password")
        tok = self.login(user, "password")
        room_id = self.helper.create_room_as(user, is_public=True, tok=tok)
        self.handler = self.hs.get_federation_handler()
        federation_event_handler = self.hs.get_federation_event_handler()

        async def _check_event_auth(
            origin: Optional[str], event: EventBase, context: EventContext
        ) -> None:
            pass

        federation_event_handler._check_event_auth = _check_event_auth  # type: ignore[method-assign]
        self.client = self.hs.get_federation_client()

        async def _check_sigs_and_hash_for_pulled_events_and_fetch(
            dest: str, pdus: Collection[EventBase], room_version: RoomVersion
        ) -> List[EventBase]:
            return list(pdus)

        self.client._check_sigs_and_hash_for_pulled_events_and_fetch = _check_sigs_and_hash_for_pulled_events_and_fetch  # type: ignore[assignment]

        prev_events = self.get_success(self.store.get_prev_events_for_room(room_id))

        # create a call invite event
        call_event = event_from_pdu_json(
            {
                "type": EventTypes.CallInvite,
                "content": {},
                "room_id": room_id,
                "sender": user,
                "depth": 32,
                "prev_events": prev_events,
                "auth_events": prev_events,
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V10,
        )

        self.assertEqual(
            self.get_success(
                federation_event_handler.on_receive_pdu("test.serv", call_event)
            ),
            None,
        )

        # check that it is in DB
        recent_event = self.get_success(self.store.get_prev_events_for_room(room_id))
        self.assertIn(call_event.event_id, recent_event)

        # but that it does not come down /sync in public room
        sync_result: SyncResult = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                create_requester(user), generate_sync_config(user)
            )
        )
        event_ids = []
        for event in sync_result.joined[0].timeline.events:
            event_ids.append(event.event_id)
        self.assertNotIn(call_event.event_id, event_ids)

        # it will come down in a private room, though
        user2 = self.register_user("bob", "password")
        tok2 = self.login(user2, "password")
        private_room_id = self.helper.create_room_as(
            user2, is_public=False, tok=tok2, extra_content={"preset": "private_chat"}
        )

        priv_prev_events = self.get_success(
            self.store.get_prev_events_for_room(private_room_id)
        )
        private_call_event = event_from_pdu_json(
            {
                "type": EventTypes.CallInvite,
                "content": {},
                "room_id": private_room_id,
                "sender": user,
                "depth": 32,
                "prev_events": priv_prev_events,
                "auth_events": priv_prev_events,
                "origin_server_ts": self.clock.time_msec(),
            },
            RoomVersions.V10,
        )

        self.assertEqual(
            self.get_success(
                federation_event_handler.on_receive_pdu("test.serv", private_call_event)
            ),
            None,
        )

        recent_events = self.get_success(
            self.store.get_prev_events_for_room(private_room_id)
        )
        self.assertIn(private_call_event.event_id, recent_events)

        private_sync_result: SyncResult = self.get_success(
            self.sync_handler.wait_for_sync_for_user(
                create_requester(user2), generate_sync_config(user2)
            )
        )
        priv_event_ids = []
        for event in private_sync_result.joined[0].timeline.events:
            priv_event_ids.append(event.event_id)

        self.assertIn(private_call_event.event_id, priv_event_ids)


_request_key = 0


def generate_sync_config(
    user_id: str,
    device_id: Optional[str] = "device_id",
    filter_collection: Optional[FilterCollection] = None,
) -> SyncConfig:
    """Generate a sync config (with a unique request key).

    Args:
        user_id: user who is syncing.
        device_id: device that is syncing. Defaults to "device_id".
        filter_collection: filter to apply. Defaults to the default filter (ie,
           return everything, with a default limit)
    """
    if filter_collection is None:
        filter_collection = Filtering(Mock()).DEFAULT_FILTER_COLLECTION

    global _request_key
    _request_key += 1
    return SyncConfig(
        user=UserID.from_string(user_id),
        filter_collection=filter_collection,
        is_guest=False,
        request_key=("request_key", _request_key),
        device_id=device_id,
    )