anonymousland-synapse/synapse/handlers/room_member.py

# -*- coding: utf-8 -*-
# Copyright 2016 OpenMarket Ltd
# Copyright 2018 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.

import abc
import logging
from http import HTTPStatus
from typing import Dict, Iterable, List, Optional, Tuple

from synapse import types
from synapse.api.constants import EventTypes, Membership
from synapse.api.errors import AuthError, Codes, SynapseError
from synapse.events import EventBase
from synapse.events.snapshot import EventContext
from synapse.replication.http.membership import (
    ReplicationLocallyRejectInviteRestServlet,
)
from synapse.types import Collection, Requester, RoomAlias, RoomID, UserID
from synapse.util.async_helpers import Linearizer
from synapse.util.distributor import user_joined_room, user_left_room

from ._base import BaseHandler

logger = logging.getLogger(__name__)


class RoomMemberHandler(object):
    # TODO(paul): This handler currently contains a messy conflation of
    #   low-level API that works on UserID objects and so on, and REST-level
    #   API that takes ID strings and returns pagination chunks. These concerns
    #   ought to be separated out a lot better.

    __metaclass__ = abc.ABCMeta

    def __init__(self, hs):
        self.hs = hs
        self.store = hs.get_datastore()
        self.auth = hs.get_auth()
        self.state_handler = hs.get_state_handler()
        self.config = hs.config

        self.federation_handler = hs.get_handlers().federation_handler
        self.directory_handler = hs.get_handlers().directory_handler
        self.identity_handler = hs.get_handlers().identity_handler
        self.registration_handler = hs.get_registration_handler()
        self.profile_handler = hs.get_profile_handler()
        self.event_creation_handler = hs.get_event_creation_handler()

        self.member_linearizer = Linearizer(name="member")

        self.clock = hs.get_clock()
        self.spam_checker = hs.get_spam_checker()
        self.third_party_event_rules = hs.get_third_party_event_rules()
        self._server_notices_mxid = self.config.server_notices_mxid
        self._enable_lookup = hs.config.enable_3pid_lookup
        self.allow_per_room_profiles = self.config.allow_per_room_profiles

        self._event_stream_writer_instance = hs.config.worker.writers.events
        self._is_on_event_persistence_instance = (
            self._event_stream_writer_instance == hs.get_instance_name()
        )
        if self._is_on_event_persistence_instance:
            self.persist_event_storage = hs.get_storage().persistence
        else:
            self._locally_reject_client = ReplicationLocallyRejectInviteRestServlet.make_client(
                hs
            )

        # This is only used to get at ratelimit function, and
        # maybe_kick_guest_users. It's fine there are multiple of these as
        # it doesn't store state.
        self.base_handler = BaseHandler(hs)

    @abc.abstractmethod
    async def _remote_join(
        self,
        requester: Requester,
        remote_room_hosts: List[str],
        room_id: str,
        user: UserID,
        content: dict,
    ) -> Tuple[str, int]:
        """Try and join a room that this server is not in

        Args:
            requester
            remote_room_hosts: List of servers that can be used to join via.
            room_id: Room that we are trying to join
            user: User who is trying to join
            content: A dict that should be used as the content of the join event.
        """
        raise NotImplementedError()

    @abc.abstractmethod
    async def _remote_reject_invite(
        self,
        requester: Requester,
        remote_room_hosts: List[str],
        room_id: str,
        target: UserID,
        content: dict,
    ) -> Tuple[Optional[str], int]:
        """Attempt to reject an invite for a room this server is not in. If we
        fail to do so we locally mark the invite as rejected.

        Args:
            requester
            remote_room_hosts: List of servers to use to try and reject invite
            room_id
            target: The user rejecting the invite
            content: The content for the rejection event

        Returns:
            A dictionary to be returned to the client, may
            include event_id etc, or nothing if we locally rejected
        """
        raise NotImplementedError()

    async def locally_reject_invite(self, user_id: str, room_id: str) -> int:
        """Mark the invite has having been rejected even though we failed to
        create a leave event for it.
        """
        if self._is_on_event_persistence_instance:
            return await self.persist_event_storage.locally_reject_invite(
                user_id, room_id
            )
        else:
            result = await self._locally_reject_client(
                instance_name=self._event_stream_writer_instance,
                user_id=user_id,
                room_id=room_id,
            )
            return result["stream_id"]

    @abc.abstractmethod
    async def _user_joined_room(self, target: UserID, room_id: str) -> None:
        """Notifies distributor on master process that the user has joined the
        room.

        Args:
            target
            room_id
        """
        raise NotImplementedError()

    @abc.abstractmethod
    async def _user_left_room(self, target: UserID, room_id: str) -> None:
        """Notifies distributor on master process that the user has left the
        room.

        Args:
            target
            room_id
        """
        raise NotImplementedError()

    async def _local_membership_update(
        self,
        requester: Requester,
        target: UserID,
        room_id: str,
        membership: str,
        prev_event_ids: Collection[str],
        txn_id: Optional[str] = None,
        ratelimit: bool = True,
        content: Optional[dict] = None,
        require_consent: bool = True,
    ) -> Tuple[str, int]:
        user_id = target.to_string()

        if content is None:
            content = {}

        content["membership"] = membership
        if requester.is_guest:
            content["kind"] = "guest"

        event, context = await self.event_creation_handler.create_event(
            requester,
            {
                "type": EventTypes.Member,
                "content": content,
                "room_id": room_id,
                "sender": requester.user.to_string(),
                "state_key": user_id,
                # For backwards compatibility:
                "membership": membership,
            },
            token_id=requester.access_token_id,
            txn_id=txn_id,
            prev_event_ids=prev_event_ids,
            require_consent=require_consent,
        )

        # Check if this event matches the previous membership event for the user.
        duplicate = await self.event_creation_handler.deduplicate_state_event(
            event, context
        )
        if duplicate is not None:
            # Discard the new event since this membership change is a no-op.
            _, stream_id = await self.store.get_event_ordering(duplicate.event_id)
            return duplicate.event_id, stream_id

        stream_id = await self.event_creation_handler.handle_new_client_event(
            requester, event, context, extra_users=[target], ratelimit=ratelimit
        )

        prev_state_ids = await context.get_prev_state_ids()

        prev_member_event_id = prev_state_ids.get((EventTypes.Member, user_id), None)

        if event.membership == Membership.JOIN:
            # Only fire user_joined_room if the user has actually joined the
            # room. Don't bother if the user is just changing their profile
            # info.
            newly_joined = True
            if prev_member_event_id:
                prev_member_event = await self.store.get_event(prev_member_event_id)
                newly_joined = prev_member_event.membership != Membership.JOIN
            if newly_joined:
                await self._user_joined_room(target, room_id)
        elif event.membership == Membership.LEAVE:
            if prev_member_event_id:
                prev_member_event = await self.store.get_event(prev_member_event_id)
                if prev_member_event.membership == Membership.JOIN:
                    await self._user_left_room(target, room_id)

        return event.event_id, stream_id

    async def copy_room_tags_and_direct_to_room(
        self, old_room_id, new_room_id, user_id
    ) -> None:
        """Copies the tags and direct room state from one room to another.

        Args:
            old_room_id: The room ID of the old room.
            new_room_id: The room ID of the new room.
            user_id: The user's ID.
        """
        # Retrieve user account data for predecessor room
        user_account_data, _ = await self.store.get_account_data_for_user(user_id)

        # Copy direct message state if applicable
        direct_rooms = user_account_data.get("m.direct", {})

        # Check which key this room is under
        if isinstance(direct_rooms, dict):
            for key, room_id_list in direct_rooms.items():
                if old_room_id in room_id_list and new_room_id not in room_id_list:
                    # Add new room_id to this key
                    direct_rooms[key].append(new_room_id)

                    # Save back to user's m.direct account data
                    await self.store.add_account_data_for_user(
                        user_id, "m.direct", direct_rooms
                    )
                    break

        # Copy room tags if applicable
        room_tags = await self.store.get_tags_for_room(user_id, old_room_id)

        # Copy each room tag to the new room
        for tag, tag_content in room_tags.items():
            await self.store.add_tag_to_room(user_id, new_room_id, tag, tag_content)

    async def update_membership(
        self,
        requester: Requester,
        target: UserID,
        room_id: str,
        action: str,
        txn_id: Optional[str] = None,
        remote_room_hosts: Optional[List[str]] = None,
        third_party_signed: Optional[dict] = None,
        ratelimit: bool = True,
        content: Optional[dict] = None,
        require_consent: bool = True,
    ) -> Tuple[Optional[str], int]:
        key = (room_id,)

        with (await self.member_linearizer.queue(key)):
            result = await self._update_membership(
                requester,
                target,
                room_id,
                action,
                txn_id=txn_id,
                remote_room_hosts=remote_room_hosts,
                third_party_signed=third_party_signed,
                ratelimit=ratelimit,
                content=content,
                require_consent=require_consent,
            )

        return result

    async def _update_membership(
        self,
        requester: Requester,
        target: UserID,
        room_id: str,
        action: str,
        txn_id: Optional[str] = None,
        remote_room_hosts: Optional[List[str]] = None,
        third_party_signed: Optional[dict] = None,
        ratelimit: bool = True,
        content: Optional[dict] = None,
        require_consent: bool = True,
    ) -> Tuple[Optional[str], int]:
        content_specified = bool(content)
        if content is None:
            content = {}
        else:
            # We do a copy here as we potentially change some keys
            # later on.
            content = dict(content)

        if not self.allow_per_room_profiles:
            # Strip profile data, knowing that new profile data will be added to the
            # event's content in event_creation_handler.create_event() using the target's
            # global profile.
            content.pop("displayname", None)
            content.pop("avatar_url", None)

        effective_membership_state = action
        if action in ["kick", "unban"]:
            effective_membership_state = "leave"

        # if this is a join with a 3pid signature, we may need to turn a 3pid
        # invite into a normal invite before we can handle the join.
        if third_party_signed is not None:
            await self.federation_handler.exchange_third_party_invite(
                third_party_signed["sender"],
                target.to_string(),
                room_id,
                third_party_signed,
            )

        if not remote_room_hosts:
            remote_room_hosts = []

        if effective_membership_state not in ("leave", "ban"):
            is_blocked = await self.store.is_room_blocked(room_id)
            if is_blocked:
                raise SynapseError(403, "This room has been blocked on this server")

        if effective_membership_state == Membership.INVITE:
            # block any attempts to invite the server notices mxid
            if target.to_string() == self._server_notices_mxid:
                raise SynapseError(HTTPStatus.FORBIDDEN, "Cannot invite this user")

            block_invite = False

            if (
                self._server_notices_mxid is not None
                and requester.user.to_string() == self._server_notices_mxid
            ):
                # allow the server notices mxid to send invites
                is_requester_admin = True

            else:
                is_requester_admin = await self.auth.is_server_admin(requester.user)

            if not is_requester_admin:
                if self.config.block_non_admin_invites:
                    logger.info(
                        "Blocking invite: user is not admin and non-admin "
                        "invites disabled"
                    )
                    block_invite = True

                if not self.spam_checker.user_may_invite(
                    requester.user.to_string(), target.to_string(), room_id
                ):
                    logger.info("Blocking invite due to spam checker")
                    block_invite = True

            if block_invite:
                raise SynapseError(403, "Invites have been disabled on this server")

        latest_event_ids = await self.store.get_prev_events_for_room(room_id)

        current_state_ids = await self.state_handler.get_current_state_ids(
            room_id, latest_event_ids=latest_event_ids
        )

        # TODO: Refactor into dictionary of explicitly allowed transitions
        # between old and new state, with specific error messages for some
        # transitions and generic otherwise
        old_state_id = current_state_ids.get((EventTypes.Member, target.to_string()))
        if old_state_id:
            old_state = await self.store.get_event(old_state_id, allow_none=True)
            old_membership = old_state.content.get("membership") if old_state else None
            if action == "unban" and old_membership != "ban":
                raise SynapseError(
                    403,
                    "Cannot unban user who was not banned"
                    " (membership=%s)" % old_membership,
                    errcode=Codes.BAD_STATE,
                )
            if old_membership == "ban" and action != "unban":
                raise SynapseError(
                    403,
                    "Cannot %s user who was banned" % (action,),
                    errcode=Codes.BAD_STATE,
                )

            if old_state:
                same_content = content == old_state.content
                same_membership = old_membership == effective_membership_state
                same_sender = requester.user.to_string() == old_state.sender
                if same_sender and same_membership and same_content:
                    _, stream_id = await self.store.get_event_ordering(
                        old_state.event_id
                    )
                    return (
                        old_state.event_id,
                        stream_id,
                    )

            if old_membership in ["ban", "leave"] and action == "kick":
                raise AuthError(403, "The target user is not in the room")

            # we don't allow people to reject invites to the server notice
            # room, but they can leave it once they are joined.
            if (
                old_membership == Membership.INVITE
                and effective_membership_state == Membership.LEAVE
            ):
                is_blocked = await self._is_server_notice_room(room_id)
                if is_blocked:
                    raise SynapseError(
                        HTTPStatus.FORBIDDEN,
                        "You cannot reject this invite",
                        errcode=Codes.CANNOT_LEAVE_SERVER_NOTICE_ROOM,
                    )
        else:
            if action == "kick":
                raise AuthError(403, "The target user is not in the room")

        is_host_in_room = await self._is_host_in_room(current_state_ids)

        if effective_membership_state == Membership.JOIN:
            if requester.is_guest:
                guest_can_join = await self._can_guest_join(current_state_ids)
                if not guest_can_join:
                    # This should be an auth check, but guests are a local concept,
                    # so don't really fit into the general auth process.
                    raise AuthError(403, "Guest access not allowed")

            if not is_host_in_room:
                inviter = await self._get_inviter(target.to_string(), room_id)
                if inviter and not self.hs.is_mine(inviter):
                    remote_room_hosts.append(inviter.domain)

                content["membership"] = Membership.JOIN

                profile = self.profile_handler
                if not content_specified:
                    content["displayname"] = await profile.get_displayname(target)
                    content["avatar_url"] = await profile.get_avatar_url(target)

                if requester.is_guest:
                    content["kind"] = "guest"

                remote_join_response = await self._remote_join(
                    requester, remote_room_hosts, room_id, target, content
                )

                return remote_join_response

        elif effective_membership_state == Membership.LEAVE:
            if not is_host_in_room:
                # perhaps we've been invited
                inviter = await self._get_inviter(target.to_string(), room_id)
                if not inviter:
                    raise SynapseError(404, "Not a known room")

                if self.hs.is_mine(inviter):
                    # the inviter was on our server, but has now left. Carry on
                    # with the normal rejection codepath.
                    #
                    # This is a bit of a hack, because the room might still be
                    # active on other servers.
                    pass
                else:
                    # send the rejection to the inviter's HS.
                    remote_room_hosts = remote_room_hosts + [inviter.domain]
                    return await self._remote_reject_invite(
                        requester, remote_room_hosts, room_id, target, content,
                    )

        return await self._local_membership_update(
            requester=requester,
            target=target,
            room_id=room_id,
            membership=effective_membership_state,
            txn_id=txn_id,
            ratelimit=ratelimit,
            prev_event_ids=latest_event_ids,
            content=content,
            require_consent=require_consent,
        )

    async def transfer_room_state_on_room_upgrade(
        self, old_room_id: str, room_id: str
    ) -> None:
        """Upon our server becoming aware of an upgraded room, either by upgrading a room
        ourselves or joining one, we can transfer over information from the previous room.

        Copies user state (tags/push rules) for every local user that was in the old room, as
        well as migrating the room directory state.

        Args:
            old_room_id: The ID of the old room
            room_id: The ID of the new room
        """
        logger.info("Transferring room state from %s to %s", old_room_id, room_id)

        # Find all local users that were in the old room and copy over each user's state
        users = await self.store.get_users_in_room(old_room_id)
        await self.copy_user_state_on_room_upgrade(old_room_id, room_id, users)

        # Add new room to the room directory if the old room was there
        # Remove old room from the room directory
        old_room = await self.store.get_room(old_room_id)
        if old_room and old_room["is_public"]:
            await self.store.set_room_is_public(old_room_id, False)
            await self.store.set_room_is_public(room_id, True)

        # Transfer alias mappings in the room directory
        await self.store.update_aliases_for_room(old_room_id, room_id)

        # Check if any groups we own contain the predecessor room
        local_group_ids = await self.store.get_local_groups_for_room(old_room_id)
        for group_id in local_group_ids:
            # Add new the new room to those groups
            await self.store.add_room_to_group(group_id, room_id, old_room["is_public"])

            # Remove the old room from those groups
            await self.store.remove_room_from_group(group_id, old_room_id)

    async def copy_user_state_on_room_upgrade(
        self, old_room_id: str, new_room_id: str, user_ids: Iterable[str]
    ) -> None:
        """Copy user-specific information when they join a new room when that new room is the
        result of a room upgrade

        Args:
            old_room_id: The ID of upgraded room
            new_room_id: The ID of the new room
            user_ids: User IDs to copy state for
        """

        logger.debug(
            "Copying over room tags and push rules from %s to %s for users %s",
            old_room_id,
            new_room_id,
            user_ids,
        )

        for user_id in user_ids:
            try:
                # It is an upgraded room. Copy over old tags
                await self.copy_room_tags_and_direct_to_room(
                    old_room_id, new_room_id, user_id
                )
                # Copy over push rules
                await self.store.copy_push_rules_from_room_to_room_for_user(
                    old_room_id, new_room_id, user_id
                )
            except Exception:
                logger.exception(
                    "Error copying tags and/or push rules from rooms %s to %s for user %s. "
                    "Skipping...",
                    old_room_id,
                    new_room_id,
                    user_id,
                )
                continue

    async def send_membership_event(
        self,
        requester: Requester,
        event: EventBase,
        context: EventContext,
        ratelimit: bool = True,
    ):
        """
        Change the membership status of a user in a room.

        Args:
            requester: The local user who requested the membership
                event. If None, certain checks, like whether this homeserver can
                act as the sender, will be skipped.
            event: The membership event.
            context: The context of the event.
            ratelimit: Whether to rate limit this request.
        Raises:
            SynapseError if there was a problem changing the membership.
        """
        target_user = UserID.from_string(event.state_key)
        room_id = event.room_id

        if requester is not None:
            sender = UserID.from_string(event.sender)
            assert (
                sender == requester.user
            ), "Sender (%s) must be same as requester (%s)" % (sender, requester.user)
            assert self.hs.is_mine(sender), "Sender must be our own: %s" % (sender,)
        else:
            requester = types.create_requester(target_user)

        prev_event = await self.event_creation_handler.deduplicate_state_event(
            event, context
        )
        if prev_event is not None:
            return

        prev_state_ids = await context.get_prev_state_ids()
        if event.membership == Membership.JOIN:
            if requester.is_guest:
                guest_can_join = await self._can_guest_join(prev_state_ids)
                if not guest_can_join:
                    # This should be an auth check, but guests are a local concept,
                    # so don't really fit into the general auth process.
                    raise AuthError(403, "Guest access not allowed")

        if event.membership not in (Membership.LEAVE, Membership.BAN):
            is_blocked = await self.store.is_room_blocked(room_id)
            if is_blocked:
                raise SynapseError(403, "This room has been blocked on this server")

        await self.event_creation_handler.handle_new_client_event(
            requester, event, context, extra_users=[target_user], ratelimit=ratelimit
        )

        prev_member_event_id = prev_state_ids.get(
            (EventTypes.Member, event.state_key), None
        )

        if event.membership == Membership.JOIN:
            # Only fire user_joined_room if the user has actually joined the
            # room. Don't bother if the user is just changing their profile
            # info.
            newly_joined = True
            if prev_member_event_id:
                prev_member_event = await self.store.get_event(prev_member_event_id)
                newly_joined = prev_member_event.membership != Membership.JOIN
            if newly_joined:
                await self._user_joined_room(target_user, room_id)
        elif event.membership == Membership.LEAVE:
            if prev_member_event_id:
                prev_member_event = await self.store.get_event(prev_member_event_id)
                if prev_member_event.membership == Membership.JOIN:
                    await self._user_left_room(target_user, room_id)

    async def _can_guest_join(
        self, current_state_ids: Dict[Tuple[str, str], str]
    ) -> bool:
        """
        Returns whether a guest can join a room based on its current state.
        """
        guest_access_id = current_state_ids.get((EventTypes.GuestAccess, ""), None)
        if not guest_access_id:
            return False

        guest_access = await self.store.get_event(guest_access_id)

        return (
            guest_access
            and guest_access.content
            and "guest_access" in guest_access.content
            and guest_access.content["guest_access"] == "can_join"
        )

    async def lookup_room_alias(
        self, room_alias: RoomAlias
    ) -> Tuple[RoomID, List[str]]:
        """
        Get the room ID associated with a room alias.

        Args:
            room_alias: The alias to look up.
        Returns:
            A tuple of:
                The room ID as a RoomID object.
                Hosts likely to be participating in the room ([str]).
        Raises:
            SynapseError if room alias could not be found.
        """
        directory_handler = self.directory_handler
        mapping = await directory_handler.get_association(room_alias)

        if not mapping:
            raise SynapseError(404, "No such room alias")

        room_id = mapping["room_id"]
        servers = mapping["servers"]

        # put the server which owns the alias at the front of the server list.
        if room_alias.domain in servers:
            servers.remove(room_alias.domain)
        servers.insert(0, room_alias.domain)

        return RoomID.from_string(room_id), servers

    async def _get_inviter(self, user_id: str, room_id: str) -> Optional[UserID]:
        invite = await self.store.get_invite_for_local_user_in_room(
            user_id=user_id, room_id=room_id
        )
        if invite:
            return UserID.from_string(invite.sender)
        return None

    async def do_3pid_invite(
        self,
        room_id: str,
        inviter: UserID,
        medium: str,
        address: str,
        id_server: str,
        requester: Requester,
        txn_id: Optional[str],
        id_access_token: Optional[str] = None,
    ) -> int:
        if self.config.block_non_admin_invites:
            is_requester_admin = await self.auth.is_server_admin(requester.user)
            if not is_requester_admin:
                raise SynapseError(
                    403, "Invites have been disabled on this server", Codes.FORBIDDEN
                )

        # We need to rate limit *before* we send out any 3PID invites, so we
        # can't just rely on the standard ratelimiting of events.
        await self.base_handler.ratelimit(requester)

        can_invite = await self.third_party_event_rules.check_threepid_can_be_invited(
            medium, address, room_id
        )
        if not can_invite:
            raise SynapseError(
                403,
                "This third-party identifier can not be invited in this room",
                Codes.FORBIDDEN,
            )

        if not self._enable_lookup:
            raise SynapseError(
                403, "Looking up third-party identifiers is denied from this server"
            )

        invitee = await self.identity_handler.lookup_3pid(
            id_server, medium, address, id_access_token
        )

        if invitee:
            _, stream_id = await self.update_membership(
                requester, UserID.from_string(invitee), room_id, "invite", txn_id=txn_id
            )
        else:
            stream_id = await self._make_and_store_3pid_invite(
                requester,
                id_server,
                medium,
                address,
                room_id,
                inviter,
                txn_id=txn_id,
                id_access_token=id_access_token,
            )

        return stream_id

    async def _make_and_store_3pid_invite(
        self,
        requester: Requester,
        id_server: str,
        medium: str,
        address: str,
        room_id: str,
        user: UserID,
        txn_id: Optional[str],
        id_access_token: Optional[str] = None,
    ) -> int:
        room_state = await self.state_handler.get_current_state(room_id)

        inviter_display_name = ""
        inviter_avatar_url = ""
        member_event = room_state.get((EventTypes.Member, user.to_string()))
        if member_event:
            inviter_display_name = member_event.content.get("displayname", "")
            inviter_avatar_url = member_event.content.get("avatar_url", "")

        # if user has no display name, default to their MXID
        if not inviter_display_name:
            inviter_display_name = user.to_string()

        canonical_room_alias = ""
        canonical_alias_event = room_state.get((EventTypes.CanonicalAlias, ""))
        if canonical_alias_event:
            canonical_room_alias = canonical_alias_event.content.get("alias", "")

        room_name = ""
        room_name_event = room_state.get((EventTypes.Name, ""))
        if room_name_event:
            room_name = room_name_event.content.get("name", "")

        room_join_rules = ""
        join_rules_event = room_state.get((EventTypes.JoinRules, ""))
        if join_rules_event:
            room_join_rules = join_rules_event.content.get("join_rule", "")

        room_avatar_url = ""
        room_avatar_event = room_state.get((EventTypes.RoomAvatar, ""))
        if room_avatar_event:
            room_avatar_url = room_avatar_event.content.get("url", "")

        (
            token,
            public_keys,
            fallback_public_key,
            display_name,
        ) = await self.identity_handler.ask_id_server_for_third_party_invite(
            requester=requester,
            id_server=id_server,
            medium=medium,
            address=address,
            room_id=room_id,
            inviter_user_id=user.to_string(),
            room_alias=canonical_room_alias,
            room_avatar_url=room_avatar_url,
            room_join_rules=room_join_rules,
            room_name=room_name,
            inviter_display_name=inviter_display_name,
            inviter_avatar_url=inviter_avatar_url,
            id_access_token=id_access_token,
        )

        (
            event,
            stream_id,
        ) = await self.event_creation_handler.create_and_send_nonmember_event(
            requester,
            {
                "type": EventTypes.ThirdPartyInvite,
                "content": {
                    "display_name": display_name,
                    "public_keys": public_keys,
                    # For backwards compatibility:
                    "key_validity_url": fallback_public_key["key_validity_url"],
                    "public_key": fallback_public_key["public_key"],
                },
                "room_id": room_id,
                "sender": user.to_string(),
                "state_key": token,
            },
            ratelimit=False,
            txn_id=txn_id,
        )
        return stream_id

    async def _is_host_in_room(
        self, current_state_ids: Dict[Tuple[str, str], str]
    ) -> bool:
        # Have we just created the room, and is this about to be the very
        # first member event?
        create_event_id = current_state_ids.get(("m.room.create", ""))
        if len(current_state_ids) == 1 and create_event_id:
            # We can only get here if we're in the process of creating the room
            return True

        for etype, state_key in current_state_ids:
            if etype != EventTypes.Member or not self.hs.is_mine_id(state_key):
                continue

            event_id = current_state_ids[(etype, state_key)]
            event = await self.store.get_event(event_id, allow_none=True)
            if not event:
                continue

            if event.membership == Membership.JOIN:
                return True

        return False

    async def _is_server_notice_room(self, room_id: str) -> bool:
        if self._server_notices_mxid is None:
            return False
        user_ids = await self.store.get_users_in_room(room_id)
        return self._server_notices_mxid in user_ids


class RoomMemberMasterHandler(RoomMemberHandler):
    def __init__(self, hs):
        super(RoomMemberMasterHandler, self).__init__(hs)

        self.distributor = hs.get_distributor()
        self.distributor.declare("user_joined_room")
        self.distributor.declare("user_left_room")

    async def _is_remote_room_too_complex(
        self, room_id: str, remote_room_hosts: List[str]
    ) -> Optional[bool]:
        """
        Check if complexity of a remote room is too great.

        Args:
            room_id
            remote_room_hosts

        Returns: bool of whether the complexity is too great, or None
            if unable to be fetched
        """
        max_complexity = self.hs.config.limit_remote_rooms.complexity
        complexity = await self.federation_handler.get_room_complexity(
            remote_room_hosts, room_id
        )

        if complexity:
            return complexity["v1"] > max_complexity
        return None

    async def _is_local_room_too_complex(self, room_id: str) -> bool:
        """
        Check if the complexity of a local room is too great.

        Args:
            room_id: The room ID to check for complexity.
        """
        max_complexity = self.hs.config.limit_remote_rooms.complexity
        complexity = await self.store.get_room_complexity(room_id)

        return complexity["v1"] > max_complexity

    async def _remote_join(
        self,
        requester: Requester,
        remote_room_hosts: List[str],
        room_id: str,
        user: UserID,
        content: dict,
    ) -> Tuple[str, int]:
        """Implements RoomMemberHandler._remote_join
        """
        # filter ourselves out of remote_room_hosts: do_invite_join ignores it
        # and if it is the only entry we'd like to return a 404 rather than a
        # 500.
        remote_room_hosts = [
            host for host in remote_room_hosts if host != self.hs.hostname
        ]

        if len(remote_room_hosts) == 0:
            raise SynapseError(404, "No known servers")

        if self.hs.config.limit_remote_rooms.enabled:
            # Fetch the room complexity
            too_complex = await self._is_remote_room_too_complex(
                room_id, remote_room_hosts
            )
            if too_complex is True:
                raise SynapseError(
                    code=400,
                    msg=self.hs.config.limit_remote_rooms.complexity_error,
                    errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
                )

        # We don't do an auth check if we are doing an invite
        # join dance for now, since we're kinda implicitly checking
        # that we are allowed to join when we decide whether or not we
        # need to do the invite/join dance.
        event_id, stream_id = await self.federation_handler.do_invite_join(
            remote_room_hosts, room_id, user.to_string(), content
        )
        await self._user_joined_room(user, room_id)

        # Check the room we just joined wasn't too large, if we didn't fetch the
        # complexity of it before.
        if self.hs.config.limit_remote_rooms.enabled:
            if too_complex is False:
                # We checked, and we're under the limit.
                return event_id, stream_id

            # Check again, but with the local state events
            too_complex = await self._is_local_room_too_complex(room_id)

            if too_complex is False:
                # We're under the limit.
                return event_id, stream_id

            # The room is too large. Leave.
            requester = types.create_requester(user, None, False, None)
            await self.update_membership(
                requester=requester, target=user, room_id=room_id, action="leave"
            )
            raise SynapseError(
                code=400,
                msg=self.hs.config.limit_remote_rooms.complexity_error,
                errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
            )

        return event_id, stream_id

    async def _remote_reject_invite(
        self,
        requester: Requester,
        remote_room_hosts: List[str],
        room_id: str,
        target: UserID,
        content: dict,
    ) -> Tuple[Optional[str], int]:
        """Implements RoomMemberHandler._remote_reject_invite
        """
        fed_handler = self.federation_handler
        try:
            event, stream_id = await fed_handler.do_remotely_reject_invite(
                remote_room_hosts, room_id, target.to_string(), content=content,
            )
            return event.event_id, stream_id
        except Exception as e:
            # if we were unable to reject the exception, just mark
            # it as rejected on our end and plough ahead.
            #
            # The 'except' clause is very broad, but we need to
            # capture everything from DNS failures upwards
            #
            logger.warning("Failed to reject invite: %s", e)

            stream_id = await self.locally_reject_invite(target.to_string(), room_id)
            return None, stream_id

    async def _user_joined_room(self, target: UserID, room_id: str) -> None:
        """Implements RoomMemberHandler._user_joined_room
        """
        user_joined_room(self.distributor, target, room_id)

    async def _user_left_room(self, target: UserID, room_id: str) -> None:
        """Implements RoomMemberHandler._user_left_room
        """
        user_left_room(self.distributor, target, room_id)

    async def forget(self, user: UserID, room_id: str) -> None:
        user_id = user.to_string()

        member = await self.state_handler.get_current_state(
            room_id=room_id, event_type=EventTypes.Member, state_key=user_id
        )
        membership = member.membership if member else None

        if membership is not None and membership not in [
            Membership.LEAVE,
            Membership.BAN,
        ]:
            raise SynapseError(400, "User %s in room %s" % (user_id, room_id))

        if membership:
            await self.store.forget(user_id, room_id)