synapse/tests/state/test_v2.py

# Copyright 2018 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import itertools
from typing import (
    Collection,
    Dict,
    Iterable,
    List,
    Mapping,
    Optional,
    Set,
    Tuple,
    TypeVar,
)

import attr

from twisted.internet import defer

from synapse.api.constants import EventTypes, JoinRules, Membership
from synapse.api.room_versions import RoomVersions
from synapse.event_auth import auth_types_for_event
from synapse.events import EventBase, make_event_from_dict
from synapse.state.v2 import (
    _get_auth_chain_difference,
    lexicographical_topological_sort,
    resolve_events_with_store,
)
from synapse.types import EventID, StateMap

from tests import unittest

ALICE = "@alice:example.com"
BOB = "@bob:example.com"
CHARLIE = "@charlie:example.com"
EVELYN = "@evelyn:example.com"
ZARA = "@zara:example.com"

ROOM_ID = "!test:example.com"

MEMBERSHIP_CONTENT_JOIN = {"membership": Membership.JOIN}
MEMBERSHIP_CONTENT_BAN = {"membership": Membership.BAN}


ORIGIN_SERVER_TS = 0


class FakeClock:
    def sleep(self, msec: float) -> "defer.Deferred[None]":
        return defer.succeed(None)


class FakeEvent:
    """A fake event we use as a convenience.

    NOTE: Again as a convenience we use "node_ids" rather than event_ids to
    refer to events. The event_id has node_id as localpart and example.com
    as domain.
    """

    def __init__(
        self,
        id: str,
        sender: str,
        type: str,
        state_key: Optional[str],
        content: Mapping[str, object],
    ):
        self.node_id = id
        self.event_id = EventID(id, "example.com").to_string()
        self.sender = sender
        self.type = type
        self.state_key = state_key
        self.content = content
        self.room_id = ROOM_ID

    def to_event(self, auth_events: List[str], prev_events: List[str]) -> EventBase:
        """Given the auth_events and prev_events, convert to a Frozen Event

        Args:
            auth_events: list of event_ids
            prev_events: list of event_ids

        Returns:
            FrozenEvent
        """
        global ORIGIN_SERVER_TS

        ts = ORIGIN_SERVER_TS
        ORIGIN_SERVER_TS = ORIGIN_SERVER_TS + 1

        event_dict = {
            "auth_events": [(a, {}) for a in auth_events],
            "prev_events": [(p, {}) for p in prev_events],
            "event_id": self.event_id,
            "sender": self.sender,
            "type": self.type,
            "content": self.content,
            "origin_server_ts": ts,
            "room_id": ROOM_ID,
        }

        if self.state_key is not None:
            event_dict["state_key"] = self.state_key

        return make_event_from_dict(event_dict)


# All graphs start with this set of events
INITIAL_EVENTS = [
    FakeEvent(
        id="CREATE",
        sender=ALICE,
        type=EventTypes.Create,
        state_key="",
        content={"creator": ALICE},
    ),
    FakeEvent(
        id="IMA",
        sender=ALICE,
        type=EventTypes.Member,
        state_key=ALICE,
        content=MEMBERSHIP_CONTENT_JOIN,
    ),
    FakeEvent(
        id="IPOWER",
        sender=ALICE,
        type=EventTypes.PowerLevels,
        state_key="",
        content={"users": {ALICE: 100}},
    ),
    FakeEvent(
        id="IJR",
        sender=ALICE,
        type=EventTypes.JoinRules,
        state_key="",
        content={"join_rule": JoinRules.PUBLIC},
    ),
    FakeEvent(
        id="IMB",
        sender=BOB,
        type=EventTypes.Member,
        state_key=BOB,
        content=MEMBERSHIP_CONTENT_JOIN,
    ),
    FakeEvent(
        id="IMC",
        sender=CHARLIE,
        type=EventTypes.Member,
        state_key=CHARLIE,
        content=MEMBERSHIP_CONTENT_JOIN,
    ),
    FakeEvent(
        id="IMZ",
        sender=ZARA,
        type=EventTypes.Member,
        state_key=ZARA,
        content=MEMBERSHIP_CONTENT_JOIN,
    ),
    FakeEvent(
        id="START", sender=ZARA, type=EventTypes.Message, state_key=None, content={}
    ),
    FakeEvent(
        id="END", sender=ZARA, type=EventTypes.Message, state_key=None, content={}
    ),
]

INITIAL_EDGES = ["START", "IMZ", "IMC", "IMB", "IJR", "IPOWER", "IMA", "CREATE"]


class StateTestCase(unittest.TestCase):
    def test_ban_vs_pl(self) -> None:
        events = [
            FakeEvent(
                id="PA",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="MA",
                sender=ALICE,
                type=EventTypes.Member,
                state_key=ALICE,
                content={"membership": Membership.JOIN},
            ),
            FakeEvent(
                id="MB",
                sender=ALICE,
                type=EventTypes.Member,
                state_key=BOB,
                content={"membership": Membership.BAN},
            ),
            FakeEvent(
                id="PB",
                sender=BOB,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
        ]

        edges = [["END", "MB", "MA", "PA", "START"], ["END", "PB", "PA"]]

        expected_state_ids = ["PA", "MA", "MB"]

        self.do_check(events, edges, expected_state_ids)

    def test_join_rule_evasion(self) -> None:
        events = [
            FakeEvent(
                id="JR",
                sender=ALICE,
                type=EventTypes.JoinRules,
                state_key="",
                content={"join_rules": JoinRules.PRIVATE},
            ),
            FakeEvent(
                id="ME",
                sender=EVELYN,
                type=EventTypes.Member,
                state_key=EVELYN,
                content={"membership": Membership.JOIN},
            ),
        ]

        edges = [["END", "JR", "START"], ["END", "ME", "START"]]

        expected_state_ids = ["JR"]

        self.do_check(events, edges, expected_state_ids)

    def test_offtopic_pl(self) -> None:
        events = [
            FakeEvent(
                id="PA",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="PB",
                sender=BOB,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50, CHARLIE: 50}},
            ),
            FakeEvent(
                id="PC",
                sender=CHARLIE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50, CHARLIE: 0}},
            ),
        ]

        edges = [["END", "PC", "PB", "PA", "START"], ["END", "PA"]]

        expected_state_ids = ["PC"]

        self.do_check(events, edges, expected_state_ids)

    def test_topic_basic(self) -> None:
        events = [
            FakeEvent(
                id="T1", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="PA1",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="T2", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="PA2",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 0}},
            ),
            FakeEvent(
                id="PB",
                sender=BOB,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="T3", sender=BOB, type=EventTypes.Topic, state_key="", content={}
            ),
        ]

        edges = [["END", "PA2", "T2", "PA1", "T1", "START"], ["END", "T3", "PB", "PA1"]]

        expected_state_ids = ["PA2", "T2"]

        self.do_check(events, edges, expected_state_ids)

    def test_topic_reset(self) -> None:
        events = [
            FakeEvent(
                id="T1", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="PA",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="T2", sender=BOB, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="MB",
                sender=ALICE,
                type=EventTypes.Member,
                state_key=BOB,
                content={"membership": Membership.BAN},
            ),
        ]

        edges = [["END", "MB", "T2", "PA", "T1", "START"], ["END", "T1"]]

        expected_state_ids = ["T1", "MB", "PA"]

        self.do_check(events, edges, expected_state_ids)

    def test_topic(self) -> None:
        events = [
            FakeEvent(
                id="T1", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="PA1",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="T2", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="PA2",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 0}},
            ),
            FakeEvent(
                id="PB",
                sender=BOB,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="T3", sender=BOB, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="MZ1",
                sender=ZARA,
                type=EventTypes.Message,
                state_key=None,
                content={},
            ),
            FakeEvent(
                id="T4", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
        ]

        edges = [
            ["END", "T4", "MZ1", "PA2", "T2", "PA1", "T1", "START"],
            ["END", "MZ1", "T3", "PB", "PA1"],
        ]

        expected_state_ids = ["T4", "PA2"]

        self.do_check(events, edges, expected_state_ids)

    def test_mainline_sort(self) -> None:
        """Tests that the mainline ordering works correctly."""

        events = [
            FakeEvent(
                id="T1", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="PA1",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="T2", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="PA2",
                sender=ALICE,
                type=EventTypes.PowerLevels,
                state_key="",
                content={
                    "users": {ALICE: 100, BOB: 50},
                    "events": {EventTypes.PowerLevels: 100},
                },
            ),
            FakeEvent(
                id="PB",
                sender=BOB,
                type=EventTypes.PowerLevels,
                state_key="",
                content={"users": {ALICE: 100, BOB: 50}},
            ),
            FakeEvent(
                id="T3", sender=BOB, type=EventTypes.Topic, state_key="", content={}
            ),
            FakeEvent(
                id="T4", sender=ALICE, type=EventTypes.Topic, state_key="", content={}
            ),
        ]

        edges = [
            ["END", "T3", "PA2", "T2", "PA1", "T1", "START"],
            ["END", "T4", "PB", "PA1"],
        ]

        # We expect T3 to be picked as the other topics are pointing at older
        # power levels. Note that without mainline ordering we'd pick T4 due to
        # it being sent *after* T3.
        expected_state_ids = ["T3", "PA2"]

        self.do_check(events, edges, expected_state_ids)

    def do_check(
        self,
        events: List[FakeEvent],
        edges: List[List[str]],
        expected_state_ids: List[str],
    ) -> None:
        """Take a list of events and edges and calculate the state of the
        graph at END, and asserts it matches `expected_state_ids`

        Args:
            events
            edges: A list of chains of event edges, e.g.
                `[[A, B, C]]` are edges A->B and B->C.
            expected_state_ids: The expected state at END, (excluding
                the keys that haven't changed since START).
        """
        # We want to sort the events into topological order for processing.
        graph: Dict[str, Set[str]] = {}

        fake_event_map: Dict[str, FakeEvent] = {}

        for ev in itertools.chain(INITIAL_EVENTS, events):
            graph[ev.node_id] = set()
            fake_event_map[ev.node_id] = ev

        for a, b in pairwise(INITIAL_EDGES):
            graph[a].add(b)

        for edge_list in edges:
            for a, b in pairwise(edge_list):
                graph[a].add(b)

        event_map: Dict[str, EventBase] = {}
        state_at_event: Dict[str, StateMap[str]] = {}

        # We copy the map as the sort consumes the graph
        graph_copy = {k: set(v) for k, v in graph.items()}

        for node_id in lexicographical_topological_sort(graph_copy, key=lambda e: e):
            fake_event = fake_event_map[node_id]
            event_id = fake_event.event_id

            prev_events = list(graph[node_id])

            if len(prev_events) == 0:
                state_before = {}
            elif len(prev_events) == 1:
                state_before = dict(state_at_event[prev_events[0]])
            else:
                state_d = resolve_events_with_store(
                    FakeClock(),
                    ROOM_ID,
                    RoomVersions.V2,
                    [state_at_event[n] for n in prev_events],
                    event_map=event_map,
                    state_res_store=TestStateResolutionStore(event_map),
                )

                state_before = self.successResultOf(defer.ensureDeferred(state_d))

            state_after = dict(state_before)
            if fake_event.state_key is not None:
                state_after[(fake_event.type, fake_event.state_key)] = event_id

            # This type ignore is a bit sad. Things we have tried:
            # 1. Define a `GenericEvent` Protocol satisfied by FakeEvent, EventBase and
            #    EventBuilder. But this is Hard because the relevant attributes are
            #    DictProperty[T] descriptors on EventBase but normal Ts on FakeEvent.
            # 2. Define a `GenericEvent` Protocol describing `FakeEvent` only, and
            #    change this function to accept Union[Event, EventBase, EventBuilder].
            #    This seems reasonable to me, but mypy isn't happy. I think that's
            #    a mypy bug, see https://github.com/python/mypy/issues/5570
            # Instead, resort to a type-ignore.
            auth_types = set(auth_types_for_event(RoomVersions.V6, fake_event))  # type: ignore[arg-type]

            auth_events = []
            for key in auth_types:
                if key in state_before:
                    auth_events.append(state_before[key])

            event = fake_event.to_event(auth_events, prev_events)

            state_at_event[node_id] = state_after
            event_map[event_id] = event

        expected_state = {}
        for node_id in expected_state_ids:
            # expected_state_ids are node IDs rather than event IDs,
            # so we have to convert
            event_id = EventID(node_id, "example.com").to_string()
            event = event_map[event_id]

            key = (event.type, event.state_key)

            expected_state[key] = event_id

        start_state = state_at_event["START"]
        end_state = {
            key: value
            for key, value in state_at_event["END"].items()
            if key in expected_state or start_state.get(key) != value
        }

        self.assertEqual(expected_state, end_state)


class LexicographicalTestCase(unittest.TestCase):
    def test_simple(self) -> None:
        graph: Dict[str, Set[str]] = {
            "l": {"o"},
            "m": {"n", "o"},
            "n": {"o"},
            "o": set(),
            "p": {"o"},
        }

        res = list(lexicographical_topological_sort(graph, key=lambda x: x))

        self.assertEqual(["o", "l", "n", "m", "p"], res)


class SimpleParamStateTestCase(unittest.TestCase):
    def setUp(self) -> None:
        # We build up a simple DAG.

        event_map = {}

        create_event = FakeEvent(
            id="CREATE",
            sender=ALICE,
            type=EventTypes.Create,
            state_key="",
            content={"creator": ALICE},
        ).to_event([], [])
        event_map[create_event.event_id] = create_event

        alice_member = FakeEvent(
            id="IMA",
            sender=ALICE,
            type=EventTypes.Member,
            state_key=ALICE,
            content=MEMBERSHIP_CONTENT_JOIN,
        ).to_event([create_event.event_id], [create_event.event_id])
        event_map[alice_member.event_id] = alice_member

        join_rules = FakeEvent(
            id="IJR",
            sender=ALICE,
            type=EventTypes.JoinRules,
            state_key="",
            content={"join_rule": JoinRules.PUBLIC},
        ).to_event(
            auth_events=[create_event.event_id, alice_member.event_id],
            prev_events=[alice_member.event_id],
        )
        event_map[join_rules.event_id] = join_rules

        # Bob and Charlie join at the same time, so there is a fork
        bob_member = FakeEvent(
            id="IMB",
            sender=BOB,
            type=EventTypes.Member,
            state_key=BOB,
            content=MEMBERSHIP_CONTENT_JOIN,
        ).to_event(
            auth_events=[create_event.event_id, join_rules.event_id],
            prev_events=[join_rules.event_id],
        )
        event_map[bob_member.event_id] = bob_member

        charlie_member = FakeEvent(
            id="IMC",
            sender=CHARLIE,
            type=EventTypes.Member,
            state_key=CHARLIE,
            content=MEMBERSHIP_CONTENT_JOIN,
        ).to_event(
            auth_events=[create_event.event_id, join_rules.event_id],
            prev_events=[join_rules.event_id],
        )
        event_map[charlie_member.event_id] = charlie_member

        self.event_map = event_map
        self.create_event = create_event
        self.alice_member = alice_member
        self.join_rules = join_rules
        self.bob_member = bob_member
        self.charlie_member = charlie_member

        self.state_at_bob = {
            (e.type, e.state_key): e.event_id
            for e in [create_event, alice_member, join_rules, bob_member]
        }

        self.state_at_charlie = {
            (e.type, e.state_key): e.event_id
            for e in [create_event, alice_member, join_rules, charlie_member]
        }

        self.expected_combined_state = {
            (e.type, e.state_key): e.event_id
            for e in [
                create_event,
                alice_member,
                join_rules,
                bob_member,
                charlie_member,
            ]
        }

    def test_event_map_none(self) -> None:
        # Test that we correctly handle passing `None` as the event_map

        state_d = resolve_events_with_store(
            FakeClock(),
            ROOM_ID,
            RoomVersions.V2,
            [self.state_at_bob, self.state_at_charlie],
            event_map=None,
            state_res_store=TestStateResolutionStore(self.event_map),
        )

        state = self.successResultOf(defer.ensureDeferred(state_d))

        self.assert_dict(self.expected_combined_state, state)


class AuthChainDifferenceTestCase(unittest.TestCase):
    """We test that `_get_auth_chain_difference` correctly handles unpersisted
    events.
    """

    def test_simple(self) -> None:
        # Test getting the auth difference for a simple chain with a single
        # unpersisted event:
        #
        #  Unpersisted | Persisted
        #              |
        #           C -|-> B -> A

        a = FakeEvent(
            id="A",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([], [])

        b = FakeEvent(
            id="B",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([a.event_id], [])

        c = FakeEvent(
            id="C",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([b.event_id], [])

        persisted_events = {a.event_id: a, b.event_id: b}
        unpersited_events = {c.event_id: c}

        state_sets = [{"a": a.event_id, "b": b.event_id}, {"c": c.event_id}]

        store = TestStateResolutionStore(persisted_events)

        diff_d = _get_auth_chain_difference(
            ROOM_ID, state_sets, unpersited_events, store
        )
        difference = self.successResultOf(defer.ensureDeferred(diff_d))

        self.assertEqual(difference, {c.event_id})

    def test_multiple_unpersisted_chain(self) -> None:
        # Test getting the auth difference for a simple chain with multiple
        # unpersisted events:
        #
        #  Unpersisted | Persisted
        #              |
        #      D -> C -|-> B -> A

        a = FakeEvent(
            id="A",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([], [])

        b = FakeEvent(
            id="B",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([a.event_id], [])

        c = FakeEvent(
            id="C",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([b.event_id], [])

        d = FakeEvent(
            id="D",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([c.event_id], [])

        persisted_events = {a.event_id: a, b.event_id: b}
        unpersited_events = {c.event_id: c, d.event_id: d}

        state_sets = [
            {"a": a.event_id, "b": b.event_id},
            {"c": c.event_id, "d": d.event_id},
        ]

        store = TestStateResolutionStore(persisted_events)

        diff_d = _get_auth_chain_difference(
            ROOM_ID, state_sets, unpersited_events, store
        )
        difference = self.successResultOf(defer.ensureDeferred(diff_d))

        self.assertEqual(difference, {d.event_id, c.event_id})

    def test_unpersisted_events_different_sets(self) -> None:
        # Test getting the auth difference for with multiple unpersisted events
        # in different branches:
        #
        #  Unpersisted | Persisted
        #              |
        #     D --> C -|-> B -> A
        #     E ----^ -|---^
        #              |

        a = FakeEvent(
            id="A",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([], [])

        b = FakeEvent(
            id="B",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([a.event_id], [])

        c = FakeEvent(
            id="C",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([b.event_id], [])

        d = FakeEvent(
            id="D",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([c.event_id], [])

        e = FakeEvent(
            id="E",
            sender=ALICE,
            type=EventTypes.Member,
            state_key="",
            content={},
        ).to_event([c.event_id, b.event_id], [])

        persisted_events = {a.event_id: a, b.event_id: b}
        unpersited_events = {c.event_id: c, d.event_id: d, e.event_id: e}

        state_sets = [
            {"a": a.event_id, "b": b.event_id, "e": e.event_id},
            {"c": c.event_id, "d": d.event_id},
        ]

        store = TestStateResolutionStore(persisted_events)

        diff_d = _get_auth_chain_difference(
            ROOM_ID, state_sets, unpersited_events, store
        )
        difference = self.successResultOf(defer.ensureDeferred(diff_d))

        self.assertEqual(difference, {d.event_id, e.event_id})


T = TypeVar("T")


def pairwise(iterable: Iterable[T]) -> Iterable[Tuple[T, T]]:
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = itertools.tee(iterable)
    next(b, None)
    return zip(a, b)


@attr.s
class TestStateResolutionStore:
    event_map: Dict[str, EventBase] = attr.ib()

    def get_events(
        self, event_ids: Collection[str], allow_rejected: bool = False
    ) -> "defer.Deferred[Dict[str, EventBase]]":
        """Get events from the database

        Args:
            event_ids: The event_ids of the events to fetch
            allow_rejected: If True return rejected events.

        Returns:
            Dict from event_id to event.
        """

        return defer.succeed(
            {eid: self.event_map[eid] for eid in event_ids if eid in self.event_map}
        )

    def _get_auth_chain(self, event_ids: Iterable[str]) -> List[str]:
        """Gets the full auth chain for a set of events (including rejected
        events).

        Includes the given event IDs in the result.

        Note that:
            1. All events must be state events.
            2. For v1 rooms this may not have the full auth chain in the
               presence of rejected events

        Args:
            event_ids: The event IDs of the events to fetch the auth
                chain for. Must be state events.
        Returns:
            List of event IDs of the auth chain.
        """

        # Simple DFS for auth chain
        result = set()
        stack = list(event_ids)
        while stack:
            event_id = stack.pop()
            if event_id in result:
                continue

            result.add(event_id)

            event = self.event_map[event_id]
            for aid in event.auth_event_ids():
                stack.append(aid)

        return list(result)

    def get_auth_chain_difference(
        self, room_id: str, auth_sets: List[Set[str]]
    ) -> "defer.Deferred[Set[str]]":
        chains = [frozenset(self._get_auth_chain(a)) for a in auth_sets]

        common = set(chains[0]).intersection(*chains[1:])
        return defer.succeed(set(chains[0]).union(*chains[1:]) - common)