anonymousland-synapse/synapse/handlers/room.py

# -*- coding: utf-8 -*-
# Copyright 2014 - 2016 OpenMarket Ltd
# Copyright 2018-2019 New Vector Ltd
# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Contains functions for performing events on rooms."""

import itertools
import logging
import math
import random
import string
from collections import OrderedDict
from typing import TYPE_CHECKING, Any, Awaitable, Dict, List, Optional, Tuple

from synapse.api.constants import (
    EventTypes,
    JoinRules,
    Membership,
    RoomCreationPreset,
    RoomEncryptionAlgorithms,
)
from synapse.api.errors import AuthError, Codes, NotFoundError, StoreError, SynapseError
from synapse.api.filtering import Filter
from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
from synapse.events import EventBase
from synapse.events.utils import copy_power_levels_contents
from synapse.http.endpoint import parse_and_validate_server_name
from synapse.storage.state import StateFilter
from synapse.types import (
    JsonDict,
    MutableStateMap,
    Requester,
    RoomAlias,
    RoomID,
    RoomStreamToken,
    StateMap,
    StreamToken,
    UserID,
    create_requester,
)
from synapse.util import stringutils
from synapse.util.async_helpers import Linearizer
from synapse.util.caches.response_cache import ResponseCache
from synapse.visibility import filter_events_for_client

from ._base import BaseHandler

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)

id_server_scheme = "https://"

FIVE_MINUTES_IN_MS = 5 * 60 * 1000


class RoomCreationHandler(BaseHandler):
    def __init__(self, hs: "HomeServer"):
        super().__init__(hs)

        self.spam_checker = hs.get_spam_checker()
        self.event_creation_handler = hs.get_event_creation_handler()
        self.room_member_handler = hs.get_room_member_handler()
        self.config = hs.config

        # Room state based off defined presets
        self._presets_dict = {
            RoomCreationPreset.PRIVATE_CHAT: {
                "join_rules": JoinRules.INVITE,
                "history_visibility": "shared",
                "original_invitees_have_ops": False,
                "guest_can_join": True,
                "power_level_content_override": {"invite": 0},
            },
            RoomCreationPreset.TRUSTED_PRIVATE_CHAT: {
                "join_rules": JoinRules.INVITE,
                "history_visibility": "shared",
                "original_invitees_have_ops": True,
                "guest_can_join": True,
                "power_level_content_override": {"invite": 0},
            },
            RoomCreationPreset.PUBLIC_CHAT: {
                "join_rules": JoinRules.PUBLIC,
                "history_visibility": "shared",
                "original_invitees_have_ops": False,
                "guest_can_join": False,
                "power_level_content_override": {},
            },
        }  # type: Dict[str, Dict[str, Any]]

        # Modify presets to selectively enable encryption by default per homeserver config
        for preset_name, preset_config in self._presets_dict.items():
            encrypted = (
                preset_name
                in self.config.encryption_enabled_by_default_for_room_presets
            )
            preset_config["encrypted"] = encrypted

        self._replication = hs.get_replication_data_handler()

        # linearizer to stop two upgrades happening at once
        self._upgrade_linearizer = Linearizer("room_upgrade_linearizer")

        # If a user tries to update the same room multiple times in quick
        # succession, only process the first attempt and return its result to
        # subsequent requests
        self._upgrade_response_cache = ResponseCache(
            hs, "room_upgrade", timeout_ms=FIVE_MINUTES_IN_MS
        )
        self._server_notices_mxid = hs.config.server_notices_mxid

        self.third_party_event_rules = hs.get_third_party_event_rules()

    async def upgrade_room(
        self, requester: Requester, old_room_id: str, new_version: RoomVersion
    ) -> str:
        """Replace a room with a new room with a different version

        Args:
            requester: the user requesting the upgrade
            old_room_id: the id of the room to be replaced
            new_version: the new room version to use

        Returns:
            the new room id

        Raises:
            ShadowBanError if the requester is shadow-banned.
        """
        await self.ratelimit(requester)

        user_id = requester.user.to_string()

        # Check if this room is already being upgraded by another person
        for key in self._upgrade_response_cache.pending_result_cache:
            if key[0] == old_room_id and key[1] != user_id:
                # Two different people are trying to upgrade the same room.
                # Send the second an error.
                #
                # Note that this of course only gets caught if both users are
                # on the same homeserver.
                raise SynapseError(
                    400, "An upgrade for this room is currently in progress"
                )

        # Upgrade the room
        #
        # If this user has sent multiple upgrade requests for the same room
        # and one of them is not complete yet, cache the response and
        # return it to all subsequent requests
        ret = await self._upgrade_response_cache.wrap(
            (old_room_id, user_id),
            self._upgrade_room,
            requester,
            old_room_id,
            new_version,  # args for _upgrade_room
        )

        return ret

    async def _upgrade_room(
        self, requester: Requester, old_room_id: str, new_version: RoomVersion
    ):
        """
        Args:
            requester: the user requesting the upgrade
            old_room_id: the id of the room to be replaced
            new_versions: the version to upgrade the room to

        Raises:
            ShadowBanError if the requester is shadow-banned.
        """
        user_id = requester.user.to_string()

        # start by allocating a new room id
        r = await self.store.get_room(old_room_id)
        if r is None:
            raise NotFoundError("Unknown room id %s" % (old_room_id,))
        new_room_id = await self._generate_room_id(
            creator_id=user_id, is_public=r["is_public"], room_version=new_version,
        )

        logger.info("Creating new room %s to replace %s", new_room_id, old_room_id)

        # we create and auth the tombstone event before properly creating the new
        # room, to check our user has perms in the old room.
        (
            tombstone_event,
            tombstone_context,
        ) = await self.event_creation_handler.create_event(
            requester,
            {
                "type": EventTypes.Tombstone,
                "state_key": "",
                "room_id": old_room_id,
                "sender": user_id,
                "content": {
                    "body": "This room has been replaced",
                    "replacement_room": new_room_id,
                },
            },
            token_id=requester.access_token_id,
        )
        old_room_version = await self.store.get_room_version_id(old_room_id)
        await self.auth.check_from_context(
            old_room_version, tombstone_event, tombstone_context
        )

        await self.clone_existing_room(
            requester,
            old_room_id=old_room_id,
            new_room_id=new_room_id,
            new_room_version=new_version,
            tombstone_event_id=tombstone_event.event_id,
        )

        # now send the tombstone
        await self.event_creation_handler.send_nonmember_event(
            requester, tombstone_event, tombstone_context
        )

        old_room_state = await tombstone_context.get_current_state_ids()

        # We know the tombstone event isn't an outlier so it has current state.
        assert old_room_state is not None

        # update any aliases
        await self._move_aliases_to_new_room(
            requester, old_room_id, new_room_id, old_room_state
        )

        # Copy over user push rules, tags and migrate room directory state
        await self.room_member_handler.transfer_room_state_on_room_upgrade(
            old_room_id, new_room_id
        )

        # finally, shut down the PLs in the old room, and update them in the new
        # room.
        await self._update_upgraded_room_pls(
            requester, old_room_id, new_room_id, old_room_state,
        )

        return new_room_id

    async def _update_upgraded_room_pls(
        self,
        requester: Requester,
        old_room_id: str,
        new_room_id: str,
        old_room_state: StateMap[str],
    ) -> None:
        """Send updated power levels in both rooms after an upgrade

        Args:
            requester: the user requesting the upgrade
            old_room_id: the id of the room to be replaced
            new_room_id: the id of the replacement room
            old_room_state: the state map for the old room

        Raises:
            ShadowBanError if the requester is shadow-banned.
        """
        old_room_pl_event_id = old_room_state.get((EventTypes.PowerLevels, ""))

        if old_room_pl_event_id is None:
            logger.warning(
                "Not supported: upgrading a room with no PL event. Not setting PLs "
                "in old room."
            )
            return

        old_room_pl_state = await self.store.get_event(old_room_pl_event_id)

        # we try to stop regular users from speaking by setting the PL required
        # to send regular events and invites to 'Moderator' level. That's normally
        # 50, but if the default PL in a room is 50 or more, then we set the
        # required PL above that.

        pl_content = dict(old_room_pl_state.content)
        users_default = int(pl_content.get("users_default", 0))
        restricted_level = max(users_default + 1, 50)

        updated = False
        for v in ("invite", "events_default"):
            current = int(pl_content.get(v, 0))
            if current < restricted_level:
                logger.debug(
                    "Setting level for %s in %s to %i (was %i)",
                    v,
                    old_room_id,
                    restricted_level,
                    current,
                )
                pl_content[v] = restricted_level
                updated = True
            else:
                logger.debug("Not setting level for %s (already %i)", v, current)

        if updated:
            try:
                await self.event_creation_handler.create_and_send_nonmember_event(
                    requester,
                    {
                        "type": EventTypes.PowerLevels,
                        "state_key": "",
                        "room_id": old_room_id,
                        "sender": requester.user.to_string(),
                        "content": pl_content,
                    },
                    ratelimit=False,
                )
            except AuthError as e:
                logger.warning("Unable to update PLs in old room: %s", e)

        await self.event_creation_handler.create_and_send_nonmember_event(
            requester,
            {
                "type": EventTypes.PowerLevels,
                "state_key": "",
                "room_id": new_room_id,
                "sender": requester.user.to_string(),
                "content": old_room_pl_state.content,
            },
            ratelimit=False,
        )

    async def clone_existing_room(
        self,
        requester: Requester,
        old_room_id: str,
        new_room_id: str,
        new_room_version: RoomVersion,
        tombstone_event_id: str,
    ) -> None:
        """Populate a new room based on an old room

        Args:
            requester: the user requesting the upgrade
            old_room_id : the id of the room to be replaced
            new_room_id: the id to give the new room (should already have been
                created with _gemerate_room_id())
            new_room_version: the new room version to use
            tombstone_event_id: the ID of the tombstone event in the old room.
        """
        user_id = requester.user.to_string()

        if not self.spam_checker.user_may_create_room(user_id):
            raise SynapseError(403, "You are not permitted to create rooms")

        creation_content = {
            "room_version": new_room_version.identifier,
            "predecessor": {"room_id": old_room_id, "event_id": tombstone_event_id},
        }

        # Check if old room was non-federatable

        # Get old room's create event
        old_room_create_event = await self.store.get_create_event_for_room(old_room_id)

        # Check if the create event specified a non-federatable room
        if not old_room_create_event.content.get("m.federate", True):
            # If so, mark the new room as non-federatable as well
            creation_content["m.federate"] = False

        initial_state = {}

        # Replicate relevant room events
        types_to_copy = (
            (EventTypes.JoinRules, ""),
            (EventTypes.Name, ""),
            (EventTypes.Topic, ""),
            (EventTypes.RoomHistoryVisibility, ""),
            (EventTypes.GuestAccess, ""),
            (EventTypes.RoomAvatar, ""),
            (EventTypes.RoomEncryption, ""),
            (EventTypes.ServerACL, ""),
            (EventTypes.RelatedGroups, ""),
            (EventTypes.PowerLevels, ""),
        )

        old_room_state_ids = await self.store.get_filtered_current_state_ids(
            old_room_id, StateFilter.from_types(types_to_copy)
        )
        # map from event_id to BaseEvent
        old_room_state_events = await self.store.get_events(old_room_state_ids.values())

        for k, old_event_id in old_room_state_ids.items():
            old_event = old_room_state_events.get(old_event_id)
            if old_event:
                initial_state[k] = old_event.content

        # deep-copy the power-levels event before we start modifying it
        # note that if frozen_dicts are enabled, `power_levels` will be a frozen
        # dict so we can't just copy.deepcopy it.
        initial_state[
            (EventTypes.PowerLevels, "")
        ] = power_levels = copy_power_levels_contents(
            initial_state[(EventTypes.PowerLevels, "")]
        )

        # Resolve the minimum power level required to send any state event
        # We will give the upgrading user this power level temporarily (if necessary) such that
        # they are able to copy all of the state events over, then revert them back to their
        # original power level afterwards in _update_upgraded_room_pls

        # Copy over user power levels now as this will not be possible with >100PL users once
        # the room has been created

        # Calculate the minimum power level needed to clone the room
        event_power_levels = power_levels.get("events", {})
        state_default = power_levels.get("state_default", 0)
        ban = power_levels.get("ban")
        needed_power_level = max(state_default, ban, max(event_power_levels.values()))

        # Raise the requester's power level in the new room if necessary
        current_power_level = power_levels["users"][user_id]
        if current_power_level < needed_power_level:
            power_levels["users"][user_id] = needed_power_level

        await self._send_events_for_new_room(
            requester,
            new_room_id,
            # we expect to override all the presets with initial_state, so this is
            # somewhat arbitrary.
            preset_config=RoomCreationPreset.PRIVATE_CHAT,
            invite_list=[],
            initial_state=initial_state,
            creation_content=creation_content,
        )

        # Transfer membership events
        old_room_member_state_ids = await self.store.get_filtered_current_state_ids(
            old_room_id, StateFilter.from_types([(EventTypes.Member, None)])
        )

        # map from event_id to BaseEvent
        old_room_member_state_events = await self.store.get_events(
            old_room_member_state_ids.values()
        )
        for old_event in old_room_member_state_events.values():
            # Only transfer ban events
            if (
                "membership" in old_event.content
                and old_event.content["membership"] == "ban"
            ):
                await self.room_member_handler.update_membership(
                    requester,
                    UserID.from_string(old_event["state_key"]),
                    new_room_id,
                    "ban",
                    ratelimit=False,
                    content=old_event.content,
                )

        # XXX invites/joins
        # XXX 3pid invites

    async def _move_aliases_to_new_room(
        self,
        requester: Requester,
        old_room_id: str,
        new_room_id: str,
        old_room_state: StateMap[str],
    ):
        # check to see if we have a canonical alias.
        canonical_alias_event = None
        canonical_alias_event_id = old_room_state.get((EventTypes.CanonicalAlias, ""))
        if canonical_alias_event_id:
            canonical_alias_event = await self.store.get_event(canonical_alias_event_id)

        await self.store.update_aliases_for_room(old_room_id, new_room_id)

        if not canonical_alias_event:
            return

        # If there is a canonical alias we need to update the one in the old
        # room and set one in the new one.
        old_canonical_alias_content = dict(canonical_alias_event.content)
        new_canonical_alias_content = {}

        canonical = canonical_alias_event.content.get("alias")
        if canonical and self.hs.is_mine_id(canonical):
            new_canonical_alias_content["alias"] = canonical
            old_canonical_alias_content.pop("alias", None)

        # We convert to a list as it will be a Tuple.
        old_alt_aliases = list(old_canonical_alias_content.get("alt_aliases", []))
        if old_alt_aliases:
            old_canonical_alias_content["alt_aliases"] = old_alt_aliases
            new_alt_aliases = new_canonical_alias_content.setdefault("alt_aliases", [])
            for alias in canonical_alias_event.content.get("alt_aliases", []):
                try:
                    if self.hs.is_mine_id(alias):
                        new_alt_aliases.append(alias)
                        old_alt_aliases.remove(alias)
                except Exception:
                    logger.info(
                        "Invalid alias %s in canonical alias event %s",
                        alias,
                        canonical_alias_event_id,
                    )

            if not old_alt_aliases:
                old_canonical_alias_content.pop("alt_aliases")

        # If a canonical alias event existed for the old room, fire a canonical
        # alias event for the new room with a copy of the information.
        try:
            await self.event_creation_handler.create_and_send_nonmember_event(
                requester,
                {
                    "type": EventTypes.CanonicalAlias,
                    "state_key": "",
                    "room_id": old_room_id,
                    "sender": requester.user.to_string(),
                    "content": old_canonical_alias_content,
                },
                ratelimit=False,
            )
        except SynapseError as e:
            # again I'm not really expecting this to fail, but if it does, I'd rather
            # we returned the new room to the client at this point.
            logger.error("Unable to send updated alias events in old room: %s", e)

        try:
            await self.event_creation_handler.create_and_send_nonmember_event(
                requester,
                {
                    "type": EventTypes.CanonicalAlias,
                    "state_key": "",
                    "room_id": new_room_id,
                    "sender": requester.user.to_string(),
                    "content": new_canonical_alias_content,
                },
                ratelimit=False,
            )
        except SynapseError as e:
            # again I'm not really expecting this to fail, but if it does, I'd rather
            # we returned the new room to the client at this point.
            logger.error("Unable to send updated alias events in new room: %s", e)

    async def create_room(
        self,
        requester: Requester,
        config: JsonDict,
        ratelimit: bool = True,
        creator_join_profile: Optional[JsonDict] = None,
    ) -> Tuple[dict, int]:
        """ Creates a new room.

        Args:
            requester:
                The user who requested the room creation.
            config : A dict of configuration options.
            ratelimit: set to False to disable the rate limiter

            creator_join_profile:
                Set to override the displayname and avatar for the creating
                user in this room. If unset, displayname and avatar will be
                derived from the user's profile. If set, should contain the
                values to go in the body of the 'join' event (typically
                `avatar_url` and/or `displayname`.

        Returns:
                First, a dict containing the keys `room_id` and, if an alias
                was, requested, `room_alias`. Secondly, the stream_id of the
                last persisted event.
        Raises:
            SynapseError if the room ID couldn't be stored, or something went
            horribly wrong.
            ResourceLimitError if server is blocked to some resource being
            exceeded
        """
        user_id = requester.user.to_string()

        await self.auth.check_auth_blocking(user_id)

        if (
            self._server_notices_mxid is not None
            and requester.user.to_string() == self._server_notices_mxid
        ):
            # allow the server notices mxid to create rooms
            is_requester_admin = True
        else:
            is_requester_admin = await self.auth.is_server_admin(requester.user)

        # Check whether the third party rules allows/changes the room create
        # request.
        event_allowed = await self.third_party_event_rules.on_create_room(
            requester, config, is_requester_admin=is_requester_admin
        )
        if not event_allowed:
            raise SynapseError(
                403, "You are not permitted to create rooms", Codes.FORBIDDEN
            )

        if not is_requester_admin and not self.spam_checker.user_may_create_room(
            user_id
        ):
            raise SynapseError(403, "You are not permitted to create rooms")

        if ratelimit:
            await self.ratelimit(requester)

        room_version_id = config.get(
            "room_version", self.config.default_room_version.identifier
        )

        if not isinstance(room_version_id, str):
            raise SynapseError(400, "room_version must be a string", Codes.BAD_JSON)

        room_version = KNOWN_ROOM_VERSIONS.get(room_version_id)
        if room_version is None:
            raise SynapseError(
                400,
                "Your homeserver does not support this room version",
                Codes.UNSUPPORTED_ROOM_VERSION,
            )

        room_alias = None
        if "room_alias_name" in config:
            for wchar in string.whitespace:
                if wchar in config["room_alias_name"]:
                    raise SynapseError(400, "Invalid characters in room alias")

            room_alias = RoomAlias(config["room_alias_name"], self.hs.hostname)
            mapping = await self.store.get_association_from_room_alias(room_alias)

            if mapping:
                raise SynapseError(400, "Room alias already taken", Codes.ROOM_IN_USE)

        invite_3pid_list = config.get("invite_3pid", [])
        invite_list = config.get("invite", [])
        for i in invite_list:
            try:
                uid = UserID.from_string(i)
                parse_and_validate_server_name(uid.domain)
            except Exception:
                raise SynapseError(400, "Invalid user_id: %s" % (i,))

        if (invite_list or invite_3pid_list) and requester.shadow_banned:
            # We randomly sleep a bit just to annoy the requester.
            await self.clock.sleep(random.randint(1, 10))

            # Allow the request to go through, but remove any associated invites.
            invite_3pid_list = []
            invite_list = []

        await self.event_creation_handler.assert_accepted_privacy_policy(requester)

        power_level_content_override = config.get("power_level_content_override")
        if (
            power_level_content_override
            and "users" in power_level_content_override
            and user_id not in power_level_content_override["users"]
        ):
            raise SynapseError(
                400,
                "Not a valid power_level_content_override: 'users' did not contain %s"
                % (user_id,),
            )

        visibility = config.get("visibility", None)
        is_public = visibility == "public"

        room_id = await self._generate_room_id(
            creator_id=user_id, is_public=is_public, room_version=room_version,
        )

        directory_handler = self.hs.get_handlers().directory_handler
        if room_alias:
            await directory_handler.create_association(
                requester=requester,
                room_id=room_id,
                room_alias=room_alias,
                servers=[self.hs.hostname],
                check_membership=False,
            )

        if is_public:
            if not self.config.is_publishing_room_allowed(user_id, room_id, room_alias):
                # Lets just return a generic message, as there may be all sorts of
                # reasons why we said no. TODO: Allow configurable error messages
                # per alias creation rule?
                raise SynapseError(403, "Not allowed to publish room")

        preset_config = config.get(
            "preset",
            RoomCreationPreset.PRIVATE_CHAT
            if visibility == "private"
            else RoomCreationPreset.PUBLIC_CHAT,
        )

        raw_initial_state = config.get("initial_state", [])

        initial_state = OrderedDict()
        for val in raw_initial_state:
            initial_state[(val["type"], val.get("state_key", ""))] = val["content"]

        creation_content = config.get("creation_content", {})

        # override any attempt to set room versions via the creation_content
        creation_content["room_version"] = room_version.identifier

        last_stream_id = await self._send_events_for_new_room(
            requester,
            room_id,
            preset_config=preset_config,
            invite_list=invite_list,
            initial_state=initial_state,
            creation_content=creation_content,
            room_alias=room_alias,
            power_level_content_override=power_level_content_override,
            creator_join_profile=creator_join_profile,
        )

        if "name" in config:
            name = config["name"]
            (
                _,
                last_stream_id,
            ) = await self.event_creation_handler.create_and_send_nonmember_event(
                requester,
                {
                    "type": EventTypes.Name,
                    "room_id": room_id,
                    "sender": user_id,
                    "state_key": "",
                    "content": {"name": name},
                },
                ratelimit=False,
            )

        if "topic" in config:
            topic = config["topic"]
            (
                _,
                last_stream_id,
            ) = await self.event_creation_handler.create_and_send_nonmember_event(
                requester,
                {
                    "type": EventTypes.Topic,
                    "room_id": room_id,
                    "sender": user_id,
                    "state_key": "",
                    "content": {"topic": topic},
                },
                ratelimit=False,
            )

        for invitee in invite_list:
            content = {}
            is_direct = config.get("is_direct", None)
            if is_direct:
                content["is_direct"] = is_direct

            # Note that update_membership with an action of "invite" can raise a
            # ShadowBanError, but this was handled above by emptying invite_list.
            _, last_stream_id = await self.room_member_handler.update_membership(
                requester,
                UserID.from_string(invitee),
                room_id,
                "invite",
                ratelimit=False,
                content=content,
            )

        for invite_3pid in invite_3pid_list:
            id_server = invite_3pid["id_server"]
            id_access_token = invite_3pid.get("id_access_token")  # optional
            address = invite_3pid["address"]
            medium = invite_3pid["medium"]
            # Note that do_3pid_invite can raise a  ShadowBanError, but this was
            # handled above by emptying invite_3pid_list.
            last_stream_id = await self.hs.get_room_member_handler().do_3pid_invite(
                room_id,
                requester.user,
                medium,
                address,
                id_server,
                requester,
                txn_id=None,
                id_access_token=id_access_token,
            )

        result = {"room_id": room_id}

        if room_alias:
            result["room_alias"] = room_alias.to_string()

        # Always wait for room creation to progate before returning
        await self._replication.wait_for_stream_position(
            self.hs.config.worker.events_shard_config.get_instance(room_id),
            "events",
            last_stream_id,
        )

        return result, last_stream_id

    async def _send_events_for_new_room(
        self,
        creator: Requester,
        room_id: str,
        preset_config: str,
        invite_list: List[str],
        initial_state: MutableStateMap,
        creation_content: JsonDict,
        room_alias: Optional[RoomAlias] = None,
        power_level_content_override: Optional[JsonDict] = None,
        creator_join_profile: Optional[JsonDict] = None,
    ) -> int:
        """Sends the initial events into a new room.

        `power_level_content_override` doesn't apply when initial state has
        power level state event content.

        Returns:
            The stream_id of the last event persisted.
        """

        creator_id = creator.user.to_string()

        event_keys = {"room_id": room_id, "sender": creator_id, "state_key": ""}

        def create(etype: str, content: JsonDict, **kwargs) -> JsonDict:
            e = {"type": etype, "content": content}

            e.update(event_keys)
            e.update(kwargs)

            return e

        async def send(etype: str, content: JsonDict, **kwargs) -> int:
            event = create(etype, content, **kwargs)
            logger.debug("Sending %s in new room", etype)
            # Allow these events to be sent even if the user is shadow-banned to
            # allow the room creation to complete.
            (
                _,
                last_stream_id,
            ) = await self.event_creation_handler.create_and_send_nonmember_event(
                creator, event, ratelimit=False, ignore_shadow_ban=True,
            )
            return last_stream_id

        config = self._presets_dict[preset_config]

        creation_content.update({"creator": creator_id})
        await send(etype=EventTypes.Create, content=creation_content)

        logger.debug("Sending %s in new room", EventTypes.Member)
        await self.room_member_handler.update_membership(
            creator,
            creator.user,
            room_id,
            "join",
            ratelimit=False,
            content=creator_join_profile,
        )

        # We treat the power levels override specially as this needs to be one
        # of the first events that get sent into a room.
        pl_content = initial_state.pop((EventTypes.PowerLevels, ""), None)
        if pl_content is not None:
            last_sent_stream_id = await send(
                etype=EventTypes.PowerLevels, content=pl_content
            )
        else:
            power_level_content = {
                "users": {creator_id: 100},
                "users_default": 0,
                "events": {
                    EventTypes.Name: 50,
                    EventTypes.PowerLevels: 100,
                    EventTypes.RoomHistoryVisibility: 100,
                    EventTypes.CanonicalAlias: 50,
                    EventTypes.RoomAvatar: 50,
                    EventTypes.Tombstone: 100,
                    EventTypes.ServerACL: 100,
                    EventTypes.RoomEncryption: 100,
                },
                "events_default": 0,
                "state_default": 50,
                "ban": 50,
                "kick": 50,
                "redact": 50,
                "invite": 50,
            }  # type: JsonDict

            if config["original_invitees_have_ops"]:
                for invitee in invite_list:
                    power_level_content["users"][invitee] = 100

            # Power levels overrides are defined per chat preset
            power_level_content.update(config["power_level_content_override"])

            if power_level_content_override:
                power_level_content.update(power_level_content_override)

            last_sent_stream_id = await send(
                etype=EventTypes.PowerLevels, content=power_level_content
            )

        if room_alias and (EventTypes.CanonicalAlias, "") not in initial_state:
            last_sent_stream_id = await send(
                etype=EventTypes.CanonicalAlias,
                content={"alias": room_alias.to_string()},
            )

        if (EventTypes.JoinRules, "") not in initial_state:
            last_sent_stream_id = await send(
                etype=EventTypes.JoinRules, content={"join_rule": config["join_rules"]}
            )

        if (EventTypes.RoomHistoryVisibility, "") not in initial_state:
            last_sent_stream_id = await send(
                etype=EventTypes.RoomHistoryVisibility,
                content={"history_visibility": config["history_visibility"]},
            )

        if config["guest_can_join"]:
            if (EventTypes.GuestAccess, "") not in initial_state:
                last_sent_stream_id = await send(
                    etype=EventTypes.GuestAccess, content={"guest_access": "can_join"}
                )

        for (etype, state_key), content in initial_state.items():
            last_sent_stream_id = await send(
                etype=etype, state_key=state_key, content=content
            )

        if config["encrypted"]:
            last_sent_stream_id = await send(
                etype=EventTypes.RoomEncryption,
                state_key="",
                content={"algorithm": RoomEncryptionAlgorithms.DEFAULT},
            )

        return last_sent_stream_id

    async def _generate_room_id(
        self, creator_id: str, is_public: bool, room_version: RoomVersion,
    ):
        # autogen room IDs and try to create it. We may clash, so just
        # try a few times till one goes through, giving up eventually.
        attempts = 0
        while attempts < 5:
            try:
                random_string = stringutils.random_string(18)
                gen_room_id = RoomID(random_string, self.hs.hostname).to_string()
                if isinstance(gen_room_id, bytes):
                    gen_room_id = gen_room_id.decode("utf-8")
                await self.store.store_room(
                    room_id=gen_room_id,
                    room_creator_user_id=creator_id,
                    is_public=is_public,
                    room_version=room_version,
                )
                return gen_room_id
            except StoreError:
                attempts += 1
        raise StoreError(500, "Couldn't generate a room ID.")


class RoomContextHandler:
    def __init__(self, hs: "HomeServer"):
        self.hs = hs
        self.store = hs.get_datastore()
        self.storage = hs.get_storage()
        self.state_store = self.storage.state

    async def get_event_context(
        self,
        user: UserID,
        room_id: str,
        event_id: str,
        limit: int,
        event_filter: Optional[Filter],
    ) -> Optional[JsonDict]:
        """Retrieves events, pagination tokens and state around a given event
        in a room.

        Args:
            user
            room_id
            event_id
            limit: The maximum number of events to return in total
                (excluding state).
            event_filter: the filter to apply to the events returned
                (excluding the target event_id)

        Returns:
            dict, or None if the event isn't found
        """
        before_limit = math.floor(limit / 2.0)
        after_limit = limit - before_limit

        users = await self.store.get_users_in_room(room_id)
        is_peeking = user.to_string() not in users

        def filter_evts(events):
            return filter_events_for_client(
                self.storage, user.to_string(), events, is_peeking=is_peeking
            )

        event = await self.store.get_event(
            event_id, get_prev_content=True, allow_none=True
        )
        if not event:
            return None

        filtered = await filter_evts([event])
        if not filtered:
            raise AuthError(403, "You don't have permission to access that event.")

        results = await self.store.get_events_around(
            room_id, event_id, before_limit, after_limit, event_filter
        )

        if event_filter:
            results["events_before"] = event_filter.filter(results["events_before"])
            results["events_after"] = event_filter.filter(results["events_after"])

        results["events_before"] = await filter_evts(results["events_before"])
        results["events_after"] = await filter_evts(results["events_after"])
        # filter_evts can return a pruned event in case the user is allowed to see that
        # there's something there but not see the content, so use the event that's in
        # `filtered` rather than the event we retrieved from the datastore.
        results["event"] = filtered[0]

        if results["events_after"]:
            last_event_id = results["events_after"][-1].event_id
        else:
            last_event_id = event_id

        if event_filter and event_filter.lazy_load_members():
            state_filter = StateFilter.from_lazy_load_member_list(
                ev.sender
                for ev in itertools.chain(
                    results["events_before"],
                    (results["event"],),
                    results["events_after"],
                )
            )
        else:
            state_filter = StateFilter.all()

        # XXX: why do we return the state as of the last event rather than the
        # first? Shouldn't we be consistent with /sync?
        # https://github.com/matrix-org/matrix-doc/issues/687

        state = await self.state_store.get_state_for_events(
            [last_event_id], state_filter=state_filter
        )

        state_events = list(state[last_event_id].values())
        if event_filter:
            state_events = event_filter.filter(state_events)

        results["state"] = await filter_evts(state_events)

        # We use a dummy token here as we only care about the room portion of
        # the token, which we replace.
        token = StreamToken.START

        results["start"] = token.copy_and_replace(
            "room_key", results["start"]
        ).to_string()

        results["end"] = token.copy_and_replace("room_key", results["end"]).to_string()

        return results


class RoomEventSource:
    def __init__(self, hs: "HomeServer"):
        self.store = hs.get_datastore()

    async def get_new_events(
        self,
        user: UserID,
        from_key: RoomStreamToken,
        limit: int,
        room_ids: List[str],
        is_guest: bool,
        explicit_room_id: Optional[str] = None,
    ) -> Tuple[List[EventBase], RoomStreamToken]:
        # We just ignore the key for now.

        to_key = self.get_current_key()

        if from_key.topological:
            logger.warning("Stream has topological part!!!! %r", from_key)
            from_key = RoomStreamToken(None, from_key.stream)

        app_service = self.store.get_app_service_by_user_id(user.to_string())
        if app_service:
            # We no longer support AS users using /sync directly.
            # See https://github.com/matrix-org/matrix-doc/issues/1144
            raise NotImplementedError()
        else:
            room_events = await self.store.get_membership_changes_for_user(
                user.to_string(), from_key, to_key
            )

            room_to_events = await self.store.get_room_events_stream_for_rooms(
                room_ids=room_ids,
                from_key=from_key,
                to_key=to_key,
                limit=limit or 10,
                order="ASC",
            )

            events = list(room_events)
            events.extend(e for evs, _ in room_to_events.values() for e in evs)

            events.sort(key=lambda e: e.internal_metadata.order)

            if limit:
                events[:] = events[:limit]

            if events:
                end_key = RoomStreamToken.parse(events[-1].internal_metadata.after)
            else:
                end_key = to_key

        return (events, end_key)

    def get_current_key(self) -> RoomStreamToken:
        return RoomStreamToken(None, self.store.get_room_max_stream_ordering())

    def get_current_key_for_room(self, room_id: str) -> Awaitable[str]:
        return self.store.get_room_events_max_id(room_id)


class RoomShutdownHandler:

    DEFAULT_MESSAGE = (
        "Sharing illegal content on this server is not permitted and rooms in"
        " violation will be blocked."
    )
    DEFAULT_ROOM_NAME = "Content Violation Notification"

    def __init__(self, hs: "HomeServer"):
        self.hs = hs
        self.room_member_handler = hs.get_room_member_handler()
        self._room_creation_handler = hs.get_room_creation_handler()
        self._replication = hs.get_replication_data_handler()
        self.event_creation_handler = hs.get_event_creation_handler()
        self.state = hs.get_state_handler()
        self.store = hs.get_datastore()

    async def shutdown_room(
        self,
        room_id: str,
        requester_user_id: str,
        new_room_user_id: Optional[str] = None,
        new_room_name: Optional[str] = None,
        message: Optional[str] = None,
        block: bool = False,
    ) -> dict:
        """
        Shuts down a room. Moves all local users and room aliases automatically
        to a new room if `new_room_user_id` is set. Otherwise local users only
        leave the room without any information.

        The new room will be created with the user specified by the
        `new_room_user_id` parameter as room administrator and will contain a
        message explaining what happened. Users invited to the new room will
        have power level `-10` by default, and thus be unable to speak.

        The local server will only have the power to move local user and room
        aliases to the new room. Users on other servers will be unaffected.

        Args:
            room_id: The ID of the room to shut down.
            requester_user_id:
                User who requested the action and put the room on the
                blocking list.
            new_room_user_id:
                If set, a new room will be created with this user ID
                as the creator and admin, and all users in the old room will be
                moved into that room. If not set, no new room will be created
                and the users will just be removed from the old room.
            new_room_name:
                A string representing the name of the room that new users will
                be invited to. Defaults to `Content Violation Notification`
            message:
                A string containing the first message that will be sent as
                `new_room_user_id` in the new room. Ideally this will clearly
                convey why the original room was shut down.
                Defaults to `Sharing illegal content on this server is not
                permitted and rooms in violation will be blocked.`
            block:
                If set to `true`, this room will be added to a blocking list,
                preventing future attempts to join the room. Defaults to `false`.

        Returns: a dict containing the following keys:
            kicked_users: An array of users (`user_id`) that were kicked.
            failed_to_kick_users:
                An array of users (`user_id`) that that were not kicked.
            local_aliases:
                An array of strings representing the local aliases that were
                migrated from the old room to the new.
            new_room_id: A string representing the room ID of the new room.
        """

        if not new_room_name:
            new_room_name = self.DEFAULT_ROOM_NAME
        if not message:
            message = self.DEFAULT_MESSAGE

        if not RoomID.is_valid(room_id):
            raise SynapseError(400, "%s is not a legal room ID" % (room_id,))

        if not await self.store.get_room(room_id):
            raise NotFoundError("Unknown room id %s" % (room_id,))

        # This will work even if the room is already blocked, but that is
        # desirable in case the first attempt at blocking the room failed below.
        if block:
            await self.store.block_room(room_id, requester_user_id)

        if new_room_user_id is not None:
            if not self.hs.is_mine_id(new_room_user_id):
                raise SynapseError(
                    400, "User must be our own: %s" % (new_room_user_id,)
                )

            room_creator_requester = create_requester(new_room_user_id)

            info, stream_id = await self._room_creation_handler.create_room(
                room_creator_requester,
                config={
                    "preset": RoomCreationPreset.PUBLIC_CHAT,
                    "name": new_room_name,
                    "power_level_content_override": {"users_default": -10},
                },
                ratelimit=False,
            )
            new_room_id = info["room_id"]

            logger.info(
                "Shutting down room %r, joining to new room: %r", room_id, new_room_id
            )

            # We now wait for the create room to come back in via replication so
            # that we can assume that all the joins/invites have propogated before
            # we try and auto join below.
            await self._replication.wait_for_stream_position(
                self.hs.config.worker.events_shard_config.get_instance(new_room_id),
                "events",
                stream_id,
            )
        else:
            new_room_id = None
            logger.info("Shutting down room %r", room_id)

        users = await self.state.get_current_users_in_room(room_id)
        kicked_users = []
        failed_to_kick_users = []
        for user_id in users:
            if not self.hs.is_mine_id(user_id):
                continue

            logger.info("Kicking %r from %r...", user_id, room_id)

            try:
                # Kick users from room
                target_requester = create_requester(user_id)
                _, stream_id = await self.room_member_handler.update_membership(
                    requester=target_requester,
                    target=target_requester.user,
                    room_id=room_id,
                    action=Membership.LEAVE,
                    content={},
                    ratelimit=False,
                    require_consent=False,
                )

                # Wait for leave to come in over replication before trying to forget.
                await self._replication.wait_for_stream_position(
                    self.hs.config.worker.events_shard_config.get_instance(room_id),
                    "events",
                    stream_id,
                )

                await self.room_member_handler.forget(target_requester.user, room_id)

                # Join users to new room
                if new_room_user_id:
                    await self.room_member_handler.update_membership(
                        requester=target_requester,
                        target=target_requester.user,
                        room_id=new_room_id,
                        action=Membership.JOIN,
                        content={},
                        ratelimit=False,
                        require_consent=False,
                    )

                kicked_users.append(user_id)
            except Exception:
                logger.exception(
                    "Failed to leave old room and join new room for %r", user_id
                )
                failed_to_kick_users.append(user_id)

        # Send message in new room and move aliases
        if new_room_user_id:
            await self.event_creation_handler.create_and_send_nonmember_event(
                room_creator_requester,
                {
                    "type": "m.room.message",
                    "content": {"body": message, "msgtype": "m.text"},
                    "room_id": new_room_id,
                    "sender": new_room_user_id,
                },
                ratelimit=False,
            )

            aliases_for_room = await self.store.get_aliases_for_room(room_id)

            await self.store.update_aliases_for_room(
                room_id, new_room_id, requester_user_id
            )
        else:
            aliases_for_room = []

        return {
            "kicked_users": kicked_users,
            "failed_to_kick_users": failed_to_kick_users,
            "local_aliases": aliases_for_room,
            "new_room_id": new_room_id,
        }