Bring auto-accept invite logic into Synapse (#17147)

This PR ports the logic from the
[synapse_auto_accept_invite](https://github.com/matrix-org/synapse-auto-accept-invite)
module into synapse.

I went with the naive approach of injecting the "module" next to where
third party modules are currently loaded. If there is a better/preferred
way to handle this, I'm all ears. It wasn't obvious to me if there was a
better location to add this logic that would cleanly apply to all
incoming invite events.

Relies on https://github.com/element-hq/synapse/pull/17166 to fix linter
errors.

3 files changed, 665 insertions, 0 deletions

diff --git a/tests/events/test_auto_accept_invites.py b/tests/events/test_auto_accept_invites.py
new file mode 100644
index 0000000000..7fb4d4fa90
--- /dev/null
+++ b/tests/events/test_auto_accept_invites.py
@@ -0,0 +1,657 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright 2021 The Matrix.org Foundation C.I.C
+# Copyright (C) 2024 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]
+#
+#
+import asyncio
+from asyncio import Future
+from http import HTTPStatus
+from typing import Any, Awaitable, Dict, List, Optional, Tuple, TypeVar, cast
+from unittest.mock import Mock
+
+import attr
+from parameterized import parameterized
+
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.api.constants import EventTypes
+from synapse.api.errors import SynapseError
+from synapse.config.auto_accept_invites import AutoAcceptInvitesConfig
+from synapse.events.auto_accept_invites import InviteAutoAccepter
+from synapse.federation.federation_base import event_from_pdu_json
+from synapse.handlers.sync import JoinedSyncResult, SyncRequestKey, SyncVersion
+from synapse.module_api import ModuleApi
+from synapse.rest import admin
+from synapse.rest.client import login, room
+from synapse.server import HomeServer
+from synapse.types import StreamToken, create_requester
+from synapse.util import Clock
+
+from tests.handlers.test_sync import generate_sync_config
+from tests.unittest import (
+    FederatingHomeserverTestCase,
+    HomeserverTestCase,
+    TestCase,
+    override_config,
+)
+
+
+class AutoAcceptInvitesTestCase(FederatingHomeserverTestCase):
+    """
+    Integration test cases for auto-accepting invites.
+    """
+
+    servlets = [
+        admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
+        hs = self.setup_test_homeserver()
+        self.handler = hs.get_federation_handler()
+        self.store = hs.get_datastores().main
+        return hs
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.sync_handler = self.hs.get_sync_handler()
+        self.module_api = hs.get_module_api()
+
+    @parameterized.expand(
+        [
+            [False],
+            [True],
+        ]
+    )
+    @override_config(
+        {
+            "auto_accept_invites": {
+                "enabled": True,
+            },
+        }
+    )
+    def test_auto_accept_invites(self, direct_room: bool) -> None:
+        """Test that a user automatically joins a room when invited, if the
+        module is enabled.
+        """
+        # A local user who sends an invite
+        inviting_user_id = self.register_user("inviter", "pass")
+        inviting_user_tok = self.login("inviter", "pass")
+
+        # A local user who receives an invite
+        invited_user_id = self.register_user("invitee", "pass")
+        self.login("invitee", "pass")
+
+        # Create a room and send an invite to the other user
+        room_id = self.helper.create_room_as(
+            inviting_user_id,
+            is_public=False,
+            tok=inviting_user_tok,
+        )
+
+        self.helper.invite(
+            room_id,
+            inviting_user_id,
+            invited_user_id,
+            tok=inviting_user_tok,
+            extra_data={"is_direct": direct_room},
+        )
+
+        # Check that the invite receiving user has automatically joined the room when syncing
+        join_updates, _ = sync_join(self, invited_user_id)
+        self.assertEqual(len(join_updates), 1)
+
+        join_update: JoinedSyncResult = join_updates[0]
+        self.assertEqual(join_update.room_id, room_id)
+
+    @override_config(
+        {
+            "auto_accept_invites": {
+                "enabled": False,
+            },
+        }
+    )
+    def test_module_not_enabled(self) -> None:
+        """Test that a user does not automatically join a room when invited,
+        if the module is not enabled.
+        """
+        # A local user who sends an invite
+        inviting_user_id = self.register_user("inviter", "pass")
+        inviting_user_tok = self.login("inviter", "pass")
+
+        # A local user who receives an invite
+        invited_user_id = self.register_user("invitee", "pass")
+        self.login("invitee", "pass")
+
+        # Create a room and send an invite to the other user
+        room_id = self.helper.create_room_as(
+            inviting_user_id, is_public=False, tok=inviting_user_tok
+        )
+
+        self.helper.invite(
+            room_id,
+            inviting_user_id,
+            invited_user_id,
+            tok=inviting_user_tok,
+        )
+
+        # Check that the invite receiving user has not automatically joined the room when syncing
+        join_updates, _ = sync_join(self, invited_user_id)
+        self.assertEqual(len(join_updates), 0)
+
+    @override_config(
+        {
+            "auto_accept_invites": {
+                "enabled": True,
+            },
+        }
+    )
+    def test_invite_from_remote_user(self) -> None:
+        """Test that an invite from a remote user results in the invited user
+        automatically joining the room.
+        """
+        # A remote user who sends the invite
+        remote_server = "otherserver"
+        remote_user = "@otheruser:" + remote_server
+
+        # A local user who creates the room
+        creator_user_id = self.register_user("creator", "pass")
+        creator_user_tok = self.login("creator", "pass")
+
+        # A local user who receives an invite
+        invited_user_id = self.register_user("invitee", "pass")
+        self.login("invitee", "pass")
+
+        room_id = self.helper.create_room_as(
+            room_creator=creator_user_id, tok=creator_user_tok
+        )
+        room_version = self.get_success(self.store.get_room_version(room_id))
+
+        invite_event = event_from_pdu_json(
+            {
+                "type": EventTypes.Member,
+                "content": {"membership": "invite"},
+                "room_id": room_id,
+                "sender": remote_user,
+                "state_key": invited_user_id,
+                "depth": 32,
+                "prev_events": [],
+                "auth_events": [],
+                "origin_server_ts": self.clock.time_msec(),
+            },
+            room_version,
+        )
+        self.get_success(
+            self.handler.on_invite_request(
+                remote_server,
+                invite_event,
+                invite_event.room_version,
+            )
+        )
+
+        # Check that the invite receiving user has automatically joined the room when syncing
+        join_updates, _ = sync_join(self, invited_user_id)
+        self.assertEqual(len(join_updates), 1)
+
+        join_update: JoinedSyncResult = join_updates[0]
+        self.assertEqual(join_update.room_id, room_id)
+
+    @parameterized.expand(
+        [
+            [False, False],
+            [True, True],
+        ]
+    )
+    @override_config(
+        {
+            "auto_accept_invites": {
+                "enabled": True,
+                "only_for_direct_messages": True,
+            },
+        }
+    )
+    def test_accept_invite_direct_message(
+        self,
+        direct_room: bool,
+        expect_auto_join: bool,
+    ) -> None:
+        """Tests that, if the module is configured to only accept DM invites, invites to DM rooms are still
+        automatically accepted. Otherwise they are rejected.
+        """
+        # A local user who sends an invite
+        inviting_user_id = self.register_user("inviter", "pass")
+        inviting_user_tok = self.login("inviter", "pass")
+
+        # A local user who receives an invite
+        invited_user_id = self.register_user("invitee", "pass")
+        self.login("invitee", "pass")
+
+        # Create a room and send an invite to the other user
+        room_id = self.helper.create_room_as(
+            inviting_user_id,
+            is_public=False,
+            tok=inviting_user_tok,
+        )
+
+        self.helper.invite(
+            room_id,
+            inviting_user_id,
+            invited_user_id,
+            tok=inviting_user_tok,
+            extra_data={"is_direct": direct_room},
+        )
+
+        if expect_auto_join:
+            # Check that the invite receiving user has automatically joined the room when syncing
+            join_updates, _ = sync_join(self, invited_user_id)
+            self.assertEqual(len(join_updates), 1)
+
+            join_update: JoinedSyncResult = join_updates[0]
+            self.assertEqual(join_update.room_id, room_id)
+        else:
+            # Check that the invite receiving user has not automatically joined the room when syncing
+            join_updates, _ = sync_join(self, invited_user_id)
+            self.assertEqual(len(join_updates), 0)
+
+    @parameterized.expand(
+        [
+            [False, True],
+            [True, False],
+        ]
+    )
+    @override_config(
+        {
+            "auto_accept_invites": {
+                "enabled": True,
+                "only_from_local_users": True,
+            },
+        }
+    )
+    def test_accept_invite_local_user(
+        self, remote_inviter: bool, expect_auto_join: bool
+    ) -> None:
+        """Tests that, if the module is configured to only accept invites from local users, invites
+        from local users are still automatically accepted. Otherwise they are rejected.
+        """
+        # A local user who sends an invite
+        creator_user_id = self.register_user("inviter", "pass")
+        creator_user_tok = self.login("inviter", "pass")
+
+        # A local user who receives an invite
+        invited_user_id = self.register_user("invitee", "pass")
+        self.login("invitee", "pass")
+
+        # Create a room and send an invite to the other user
+        room_id = self.helper.create_room_as(
+            creator_user_id, is_public=False, tok=creator_user_tok
+        )
+
+        if remote_inviter:
+            room_version = self.get_success(self.store.get_room_version(room_id))
+
+            # A remote user who sends the invite
+            remote_server = "otherserver"
+            remote_user = "@otheruser:" + remote_server
+
+            invite_event = event_from_pdu_json(
+                {
+                    "type": EventTypes.Member,
+                    "content": {"membership": "invite"},
+                    "room_id": room_id,
+                    "sender": remote_user,
+                    "state_key": invited_user_id,
+                    "depth": 32,
+                    "prev_events": [],
+                    "auth_events": [],
+                    "origin_server_ts": self.clock.time_msec(),
+                },
+                room_version,
+            )
+            self.get_success(
+                self.handler.on_invite_request(
+                    remote_server,
+                    invite_event,
+                    invite_event.room_version,
+                )
+            )
+        else:
+            self.helper.invite(
+                room_id,
+                creator_user_id,
+                invited_user_id,
+                tok=creator_user_tok,
+            )
+
+        if expect_auto_join:
+            # Check that the invite receiving user has automatically joined the room when syncing
+            join_updates, _ = sync_join(self, invited_user_id)
+            self.assertEqual(len(join_updates), 1)
+
+            join_update: JoinedSyncResult = join_updates[0]
+            self.assertEqual(join_update.room_id, room_id)
+        else:
+            # Check that the invite receiving user has not automatically joined the room when syncing
+            join_updates, _ = sync_join(self, invited_user_id)
+            self.assertEqual(len(join_updates), 0)
+
+
+_request_key = 0
+
+
+def generate_request_key() -> SyncRequestKey:
+    global _request_key
+    _request_key += 1
+    return ("request_key", _request_key)
+
+
+def sync_join(
+    testcase: HomeserverTestCase,
+    user_id: str,
+    since_token: Optional[StreamToken] = None,
+) -> Tuple[List[JoinedSyncResult], StreamToken]:
+    """Perform a sync request for the given user and return the user join updates
+    they've received, as well as the next_batch token.
+
+    This method assumes testcase.sync_handler points to the homeserver's sync handler.
+
+    Args:
+        testcase: The testcase that is currently being run.
+        user_id: The ID of the user to generate a sync response for.
+        since_token: An optional token to indicate from at what point to sync from.
+
+    Returns:
+        A tuple containing a list of join updates, and the sync response's
+        next_batch token.
+    """
+    requester = create_requester(user_id)
+    sync_config = generate_sync_config(requester.user.to_string())
+    sync_result = testcase.get_success(
+        testcase.hs.get_sync_handler().wait_for_sync_for_user(
+            requester,
+            sync_config,
+            SyncVersion.SYNC_V2,
+            generate_request_key(),
+            since_token,
+        )
+    )
+
+    return sync_result.joined, sync_result.next_batch
+
+
+class InviteAutoAccepterInternalTestCase(TestCase):
+    """
+    Test cases which exercise the internals of the InviteAutoAccepter.
+    """
+
+    def setUp(self) -> None:
+        self.module = create_module()
+        self.user_id = "@peter:test"
+        self.invitee = "@lesley:test"
+        self.remote_invitee = "@thomas:remote"
+
+        # We know our module API is a mock, but mypy doesn't.
+        self.mocked_update_membership: Mock = self.module._api.update_room_membership  # type: ignore[assignment]
+
+    async def test_accept_invite_with_failures(self) -> None:
+        """Tests that receiving an invite for a local user makes the module attempt to
+        make the invitee join the room. This test verifies that it works if the call to
+        update membership returns exceptions before successfully completing and returning an event.
+        """
+        invite = MockEvent(
+            sender="@inviter:test",
+            state_key="@invitee:test",
+            type="m.room.member",
+            content={"membership": "invite"},
+        )
+
+        join_event = MockEvent(
+            sender="someone",
+            state_key="someone",
+            type="m.room.member",
+            content={"membership": "join"},
+        )
+        # the first two calls raise an exception while the third call is successful
+        self.mocked_update_membership.side_effect = [
+            SynapseError(HTTPStatus.FORBIDDEN, "Forbidden"),
+            SynapseError(HTTPStatus.FORBIDDEN, "Forbidden"),
+            make_awaitable(join_event),
+        ]
+
+        # Stop mypy from complaining that we give on_new_event a MockEvent rather than an
+        # EventBase.
+        await self.module.on_new_event(event=invite)  # type: ignore[arg-type]
+
+        await self.retry_assertions(
+            self.mocked_update_membership,
+            3,
+            sender=invite.state_key,
+            target=invite.state_key,
+            room_id=invite.room_id,
+            new_membership="join",
+        )
+
+    async def test_accept_invite_failures(self) -> None:
+        """Tests that receiving an invite for a local user makes the module attempt to
+        make the invitee join the room. This test verifies that if the update_membership call
+        fails consistently, _retry_make_join will break the loop after the set number of retries and
+        execution will continue.
+        """
+        invite = MockEvent(
+            sender=self.user_id,
+            state_key=self.invitee,
+            type="m.room.member",
+            content={"membership": "invite"},
+        )
+        self.mocked_update_membership.side_effect = SynapseError(
+            HTTPStatus.FORBIDDEN, "Forbidden"
+        )
+
+        # Stop mypy from complaining that we give on_new_event a MockEvent rather than an
+        # EventBase.
+        await self.module.on_new_event(event=invite)  # type: ignore[arg-type]
+
+        await self.retry_assertions(
+            self.mocked_update_membership,
+            5,
+            sender=invite.state_key,
+            target=invite.state_key,
+            room_id=invite.room_id,
+            new_membership="join",
+        )
+
+    async def test_not_state(self) -> None:
+        """Tests that receiving an invite that's not a state event does nothing."""
+        invite = MockEvent(
+            sender=self.user_id, type="m.room.member", content={"membership": "invite"}
+        )
+
+        # Stop mypy from complaining that we give on_new_event a MockEvent rather than an
+        # EventBase.
+        await self.module.on_new_event(event=invite)  # type: ignore[arg-type]
+
+        self.mocked_update_membership.assert_not_called()
+
+    async def test_not_invite(self) -> None:
+        """Tests that receiving a membership update that's not an invite does nothing."""
+        invite = MockEvent(
+            sender=self.user_id,
+            state_key=self.user_id,
+            type="m.room.member",
+            content={"membership": "join"},
+        )
+
+        # Stop mypy from complaining that we give on_new_event a MockEvent rather than an
+        # EventBase.
+        await self.module.on_new_event(event=invite)  # type: ignore[arg-type]
+
+        self.mocked_update_membership.assert_not_called()
+
+    async def test_not_membership(self) -> None:
+        """Tests that receiving a state event that's not a membership update does
+        nothing.
+        """
+        invite = MockEvent(
+            sender=self.user_id,
+            state_key=self.user_id,
+            type="org.matrix.test",
+            content={"foo": "bar"},
+        )
+
+        # Stop mypy from complaining that we give on_new_event a MockEvent rather than an
+        # EventBase.
+        await self.module.on_new_event(event=invite)  # type: ignore[arg-type]
+
+        self.mocked_update_membership.assert_not_called()
+
+    def test_config_parse(self) -> None:
+        """Tests that a correct configuration parses."""
+        config = {
+            "auto_accept_invites": {
+                "enabled": True,
+                "only_for_direct_messages": True,
+                "only_from_local_users": True,
+            }
+        }
+        parsed_config = AutoAcceptInvitesConfig()
+        parsed_config.read_config(config)
+
+        self.assertTrue(parsed_config.enabled)
+        self.assertTrue(parsed_config.accept_invites_only_for_direct_messages)
+        self.assertTrue(parsed_config.accept_invites_only_from_local_users)
+
+    def test_runs_on_only_one_worker(self) -> None:
+        """
+        Tests that the module only runs on the specified worker.
+        """
+        # By default, we run on the main process...
+        main_module = create_module(
+            config_override={"auto_accept_invites": {"enabled": True}}, worker_name=None
+        )
+        cast(
+            Mock, main_module._api.register_third_party_rules_callbacks
+        ).assert_called_once()
+
+        # ...and not on other workers (like synchrotrons)...
+        sync_module = create_module(worker_name="synchrotron42")
+        cast(
+            Mock, sync_module._api.register_third_party_rules_callbacks
+        ).assert_not_called()
+
+        # ...unless we configured them to be the designated worker.
+        specified_module = create_module(
+            config_override={
+                "auto_accept_invites": {
+                    "enabled": True,
+                    "worker_to_run_on": "account_data1",
+                }
+            },
+            worker_name="account_data1",
+        )
+        cast(
+            Mock, specified_module._api.register_third_party_rules_callbacks
+        ).assert_called_once()
+
+    async def retry_assertions(
+        self, mock: Mock, call_count: int, **kwargs: Any
+    ) -> None:
+        """
+        This is a hacky way to ensure that the assertions are not called before the other coroutine
+        has a chance to call `update_room_membership`. It catches the exception caused by a failure,
+        and sleeps the thread before retrying, up until 5 tries.
+
+        Args:
+            call_count: the number of times the mock should have been called
+            mock: the mocked function we want to assert on
+            kwargs: keyword arguments to assert that the mock was called with
+        """
+
+        i = 0
+        while i < 5:
+            try:
+                # Check that the mocked method is called the expected amount of times and with the right
+                # arguments to attempt to make the user join the room.
+                mock.assert_called_with(**kwargs)
+                self.assertEqual(call_count, mock.call_count)
+                break
+            except AssertionError as e:
+                i += 1
+                if i == 5:
+                    # we've used up the tries, force the test to fail as we've already caught the exception
+                    self.fail(e)
+                await asyncio.sleep(1)
+
+
+@attr.s(auto_attribs=True)
+class MockEvent:
+    """Mocks an event. Only exposes properties the module uses."""
+
+    sender: str
+    type: str
+    content: Dict[str, Any]
+    room_id: str = "!someroom"
+    state_key: Optional[str] = None
+
+    def is_state(self) -> bool:
+        """Checks if the event is a state event by checking if it has a state key."""
+        return self.state_key is not None
+
+    @property
+    def membership(self) -> str:
+        """Extracts the membership from the event. Should only be called on an event
+        that's a membership event, and will raise a KeyError otherwise.
+        """
+        membership: str = self.content["membership"]
+        return membership
+
+
+T = TypeVar("T")
+TV = TypeVar("TV")
+
+
+async def make_awaitable(value: T) -> T:
+    return value
+
+
+def make_multiple_awaitable(result: TV) -> Awaitable[TV]:
+    """
+    Makes an awaitable, suitable for mocking an `async` function.
+    This uses Futures as they can be awaited multiple times so can be returned
+    to multiple callers.
+    """
+    future: Future[TV] = Future()
+    future.set_result(result)
+    return future
+
+
+def create_module(
+    config_override: Optional[Dict[str, Any]] = None, worker_name: Optional[str] = None
+) -> InviteAutoAccepter:
+    # Create a mock based on the ModuleApi spec, but override some mocked functions
+    # because some capabilities are needed for running the tests.
+    module_api = Mock(spec=ModuleApi)
+    module_api.is_mine.side_effect = lambda a: a.split(":")[1] == "test"
+    module_api.worker_name = worker_name
+    module_api.sleep.return_value = make_multiple_awaitable(None)
+
+    if config_override is None:
+        config_override = {}
+
+    config = AutoAcceptInvitesConfig()
+    config.read_config(config_override)
+
+    return InviteAutoAccepter(config, module_api)
diff --git a/tests/rest/client/utils.py b/tests/rest/client/utils.py
index fe00afe198..7362bde7ab 100644
--- a/tests/rest/client/utils.py
+++ b/tests/rest/client/utils.py
@@ -170,6 +170,7 @@ class RestHelper:
         targ: Optional[str] = None,
         expect_code: int = HTTPStatus.OK,
         tok: Optional[str] = None,
+        extra_data: Optional[dict] = None,
     ) -> JsonDict:
         return self.change_membership(
             room=room,
@@ -178,6 +179,7 @@ class RestHelper:
             tok=tok,
             membership=Membership.INVITE,
             expect_code=expect_code,
+            extra_data=extra_data,
         )
 
     def join(
diff --git a/tests/server.py b/tests/server.py
index 434be3d22c..f3a917f835 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -85,6 +85,7 @@ from twisted.web.server import Request, Site
 
 from synapse.config.database import DatabaseConnectionConfig
 from synapse.config.homeserver import HomeServerConfig
+from synapse.events.auto_accept_invites import InviteAutoAccepter
 from synapse.events.presence_router import load_legacy_presence_router
 from synapse.handlers.auth import load_legacy_password_auth_providers
 from synapse.http.site import SynapseRequest
@@ -1156,6 +1157,11 @@ def setup_test_homeserver(
     for module, module_config in hs.config.modules.loaded_modules:
         module(config=module_config, api=module_api)
 
+    if hs.config.auto_accept_invites.enabled:
+        # Start the local auto_accept_invites module.
+        m = InviteAutoAccepter(hs.config.auto_accept_invites, module_api)
+        logger.info("Loaded local module %s", m)
+
     load_legacy_spam_checkers(hs)
     load_legacy_third_party_event_rules(hs)
     load_legacy_presence_router(hs)