synapse/synapse/handlers/room_member.py

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

import abc
import logging

from signedjson.key import decode_verify_key_bytes
from signedjson.sign import verify_signed_json
from twisted.internet import defer
from unpaddedbase64 import decode_base64

import synapse.types
from synapse.api.constants import (
    EventTypes, Membership,
)
from synapse.api.errors import AuthError, SynapseError, Codes
from synapse.types import UserID, RoomID
from synapse.util.async import Linearizer
from synapse.util.distributor import user_left_room, user_joined_room


logger = logging.getLogger(__name__)

id_server_scheme = "https://"


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.simple_http_client = hs.get_simple_http_client()

        self.federation_handler = hs.get_handlers().federation_handler
        self.directory_handler = hs.get_handlers().directory_handler
        self.registration_handler = hs.get_handlers().registration_handler
        self.profile_handler = hs.get_profile_handler()
        self.event_creation_hander = hs.get_event_creation_handler()

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

        self.clock = hs.get_clock()
        self.spam_checker = hs.get_spam_checker()

    @abc.abstractmethod
    def _remote_join(self, requester, remote_room_hosts, room_id, user, content):
        """Try and join a room that this server is not in

        Args:
            requester (Requester)
            remote_room_hosts (list[str]): List of servers that can be used
                to join via.
            room_id (str): Room that we are trying to join
            user (UserID): User who is trying to join
            content (dict): A dict that should be used as the content of the
                join event.

        Returns:
            Deferred
        """
        raise NotImplementedError()

    @abc.abstractmethod
    def _remote_reject_invite(self, remote_room_hosts, room_id, target):
        """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 (Requester)
            remote_room_hosts (list[str]): List of servers to use to try and
                reject invite
            room_id (str)
            target (UserID): The user rejecting the invite

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

    @abc.abstractmethod
    def get_or_register_3pid_guest(self, requester, medium, address, inviter_user_id):
        """Get a guest access token for a 3PID, creating a guest account if
        one doesn't already exist.

        Args:
            requester (Requester)
            medium (str)
            address (str)
            inviter_user_id (str): The user ID who is trying to invite the
                3PID

        Returns:
            Deferred[(str, str)]: A 2-tuple of `(user_id, access_token)` of the
            3PID guest account.
        """
        raise NotImplementedError()

    @abc.abstractmethod
    def _user_joined_room(self, target, room_id):
        """Notifies distributor on master process that the user has joined the
        room.

        Args:
            target (UserID)
            room_id (str)

        Returns:
            Deferred|None
        """
        raise NotImplementedError()

    @abc.abstractmethod
    def _user_left_room(self, target, room_id):
        """Notifies distributor on master process that the user has left the
        room.

        Args:
            target (UserID)
            room_id (str)

        Returns:
            Deferred|None
        """
        raise NotImplementedError()

    @defer.inlineCallbacks
    def _local_membership_update(
        self, requester, target, room_id, membership,
        prev_event_ids,
        txn_id=None,
        ratelimit=True,
        content=None,
    ):
        if content is None:
            content = {}

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

        event, context = yield self.event_creation_hander.create_event(
            requester,
            {
                "type": EventTypes.Member,
                "content": content,
                "room_id": room_id,
                "sender": requester.user.to_string(),
                "state_key": target.to_string(),

                # For backwards compatibility:
                "membership": membership,
            },
            token_id=requester.access_token_id,
            txn_id=txn_id,
            prev_event_ids=prev_event_ids,
        )

        # Check if this event matches the previous membership event for the user.
        duplicate = yield self.event_creation_hander.deduplicate_state_event(
            event, context,
        )
        if duplicate is not None:
            # Discard the new event since this membership change is a no-op.
            defer.returnValue(duplicate)

        yield self.event_creation_hander.handle_new_client_event(
            requester,
            event,
            context,
            extra_users=[target],
            ratelimit=ratelimit,
        )

        prev_member_event_id = context.prev_state_ids.get(
            (EventTypes.Member, target.to_string()),
            None
        )

        if event.membership == Membership.JOIN:
            # Only fire user_joined_room if the user has acutally 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 = yield self.store.get_event(prev_member_event_id)
                newly_joined = prev_member_event.membership != Membership.JOIN
            if newly_joined:
                yield self._user_joined_room(target, room_id)
        elif event.membership == Membership.LEAVE:
            if prev_member_event_id:
                prev_member_event = yield self.store.get_event(prev_member_event_id)
                if prev_member_event.membership == Membership.JOIN:
                    yield self._user_left_room(target, room_id)

        defer.returnValue(event)

    @defer.inlineCallbacks
    def update_membership(
            self,
            requester,
            target,
            room_id,
            action,
            txn_id=None,
            remote_room_hosts=None,
            third_party_signed=None,
            ratelimit=True,
            content=None,
    ):
        key = (room_id,)

        with (yield self.member_linearizer.queue(key)):
            result = yield 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,
            )

        defer.returnValue(result)

    @defer.inlineCallbacks
    def _update_membership(
            self,
            requester,
            target,
            room_id,
            action,
            txn_id=None,
            remote_room_hosts=None,
            third_party_signed=None,
            ratelimit=True,
            content=None,
    ):
        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)

        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:
            yield 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 = yield 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 == "invite":
            block_invite = False
            is_requester_admin = yield 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 = yield self.store.get_latest_event_ids_in_room(room_id)
        current_state_ids = yield self.state_handler.get_current_state_ids(
            room_id, latest_event_ids=latest_event_ids,
        )

        old_state_id = current_state_ids.get((EventTypes.Member, target.to_string()))
        if old_state_id:
            old_state = yield 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:
                    defer.returnValue(old_state)

        is_host_in_room = yield self._is_host_in_room(current_state_ids)

        if effective_membership_state == Membership.JOIN:
            if requester.is_guest:
                guest_can_join = yield 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 = yield 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"] = yield profile.get_displayname(target)
                    content["avatar_url"] = yield profile.get_avatar_url(target)

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

                ret = yield self._remote_join(
                    requester, remote_room_hosts, room_id, target, content
                )
                defer.returnValue(ret)

        elif effective_membership_state == Membership.LEAVE:
            if not is_host_in_room:
                # perhaps we've been invited
                inviter = yield 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]
                    res = yield self._remote_reject_invite(
                        requester, remote_room_hosts, room_id, target,
                    )
                    defer.returnValue(res)

        res = yield 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,
        )
        defer.returnValue(res)

    @defer.inlineCallbacks
    def send_membership_event(
            self,
            requester,
            event,
            context,
            remote_room_hosts=None,
            ratelimit=True,
    ):
        """
        Change the membership status of a user in a room.

        Args:
            requester (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 (SynapseEvent): The membership event.
            context: The context of the event.
            is_guest (bool): Whether the sender is a guest.
            room_hosts ([str]): Homeservers which are likely to already be in
                the room, and could be danced with in order to join this
                homeserver for the first time.
            ratelimit (bool): Whether to rate limit this request.
        Raises:
            SynapseError if there was a problem changing the membership.
        """
        remote_room_hosts = remote_room_hosts or []

        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 = synapse.types.create_requester(target_user)

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

        if event.membership == Membership.JOIN:
            if requester.is_guest:
                guest_can_join = yield self._can_guest_join(context.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 = yield self.store.is_room_blocked(room_id)
            if is_blocked:
                raise SynapseError(403, "This room has been blocked on this server")

        yield self.event_creation_hander.handle_new_client_event(
            requester,
            event,
            context,
            extra_users=[target_user],
            ratelimit=ratelimit,
        )

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

        if event.membership == Membership.JOIN:
            # Only fire user_joined_room if the user has acutally 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 = yield self.store.get_event(prev_member_event_id)
                newly_joined = prev_member_event.membership != Membership.JOIN
            if newly_joined:
                yield self._user_joined_room(target_user, room_id)
        elif event.membership == Membership.LEAVE:
            if prev_member_event_id:
                prev_member_event = yield self.store.get_event(prev_member_event_id)
                if prev_member_event.membership == Membership.JOIN:
                    yield self._user_left_room(target_user, room_id)

    @defer.inlineCallbacks
    def _can_guest_join(self, current_state_ids):
        """
        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:
            defer.returnValue(False)

        guest_access = yield self.store.get_event(guest_access_id)

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

    @defer.inlineCallbacks
    def lookup_room_alias(self, room_alias):
        """
        Get the room ID associated with a room alias.

        Args:
            room_alias (RoomAlias): 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 = yield directory_handler.get_association(room_alias)

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

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

        defer.returnValue((RoomID.from_string(room_id), servers))

    @defer.inlineCallbacks
    def _get_inviter(self, user_id, room_id):
        invite = yield self.store.get_invite_for_user_in_room(
            user_id=user_id,
            room_id=room_id,
        )
        if invite:
            defer.returnValue(UserID.from_string(invite.sender))

    @defer.inlineCallbacks
    def do_3pid_invite(
            self,
            room_id,
            inviter,
            medium,
            address,
            id_server,
            requester,
            txn_id
    ):
        if self.config.block_non_admin_invites:
            is_requester_admin = yield self.auth.is_server_admin(
                requester.user,
            )
            if not is_requester_admin:
                raise SynapseError(
                    403, "Invites have been disabled on this server",
                    Codes.FORBIDDEN,
                )

        invitee = yield self._lookup_3pid(
            id_server, medium, address
        )

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

    @defer.inlineCallbacks
    def _lookup_3pid(self, id_server, medium, address):
        """Looks up a 3pid in the passed identity server.

        Args:
            id_server (str): The server name (including port, if required)
                of the identity server to use.
            medium (str): The type of the third party identifier (e.g. "email").
            address (str): The third party identifier (e.g. "foo@example.com").

        Returns:
            str: the matrix ID of the 3pid, or None if it is not recognized.
        """
        try:
            data = yield self.simple_http_client.get_json(
                "%s%s/_matrix/identity/api/v1/lookup" % (id_server_scheme, id_server,),
                {
                    "medium": medium,
                    "address": address,
                }
            )

            if "mxid" in data:
                if "signatures" not in data:
                    raise AuthError(401, "No signatures on 3pid binding")
                yield self._verify_any_signature(data, id_server)
                defer.returnValue(data["mxid"])

        except IOError as e:
            logger.warn("Error from identity server lookup: %s" % (e,))
            defer.returnValue(None)

    @defer.inlineCallbacks
    def _verify_any_signature(self, data, server_hostname):
        if server_hostname not in data["signatures"]:
            raise AuthError(401, "No signature from server %s" % (server_hostname,))
        for key_name, signature in data["signatures"][server_hostname].items():
            key_data = yield self.simple_http_client.get_json(
                "%s%s/_matrix/identity/api/v1/pubkey/%s" %
                (id_server_scheme, server_hostname, key_name,),
            )
            if "public_key" not in key_data:
                raise AuthError(401, "No public key named %s from %s" %
                                (key_name, server_hostname,))
            verify_signed_json(
                data,
                server_hostname,
                decode_verify_key_bytes(key_name, decode_base64(key_data["public_key"]))
            )
            return

    @defer.inlineCallbacks
    def _make_and_store_3pid_invite(
            self,
            requester,
            id_server,
            medium,
            address,
            room_id,
            user,
            txn_id
    ):
        room_state = yield 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", "")

        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 = (
            yield self._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
            )
        )

        yield self.event_creation_hander.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,
            },
            txn_id=txn_id,
        )

    @defer.inlineCallbacks
    def _ask_id_server_for_third_party_invite(
            self,
            requester,
            id_server,
            medium,
            address,
            room_id,
            inviter_user_id,
            room_alias,
            room_avatar_url,
            room_join_rules,
            room_name,
            inviter_display_name,
            inviter_avatar_url
    ):
        """
        Asks an identity server for a third party invite.

        Args:
            requester (Requester)
            id_server (str): hostname + optional port for the identity server.
            medium (str): The literal string "email".
            address (str): The third party address being invited.
            room_id (str): The ID of the room to which the user is invited.
            inviter_user_id (str): The user ID of the inviter.
            room_alias (str): An alias for the room, for cosmetic notifications.
            room_avatar_url (str): The URL of the room's avatar, for cosmetic
                notifications.
            room_join_rules (str): The join rules of the email (e.g. "public").
            room_name (str): The m.room.name of the room.
            inviter_display_name (str): The current display name of the
                inviter.
            inviter_avatar_url (str): The URL of the inviter's avatar.

        Returns:
            A deferred tuple containing:
                token (str): The token which must be signed to prove authenticity.
                public_keys ([{"public_key": str, "key_validity_url": str}]):
                    public_key is a base64-encoded ed25519 public key.
                fallback_public_key: One element from public_keys.
                display_name (str): A user-friendly name to represent the invited
                    user.
        """

        is_url = "%s%s/_matrix/identity/api/v1/store-invite" % (
            id_server_scheme, id_server,
        )

        invite_config = {
            "medium": medium,
            "address": address,
            "room_id": room_id,
            "room_alias": room_alias,
            "room_avatar_url": room_avatar_url,
            "room_join_rules": room_join_rules,
            "room_name": room_name,
            "sender": inviter_user_id,
            "sender_display_name": inviter_display_name,
            "sender_avatar_url": inviter_avatar_url,
        }

        if self.config.invite_3pid_guest:
            guest_access_token, guest_user_id = yield self.get_or_register_3pid_guest(
                requester=requester,
                medium=medium,
                address=address,
                inviter_user_id=inviter_user_id,
            )

            invite_config.update({
                "guest_access_token": guest_access_token,
                "guest_user_id": guest_user_id,
            })

        data = yield self.simple_http_client.post_urlencoded_get_json(
            is_url,
            invite_config
        )
        # TODO: Check for success
        token = data["token"]
        public_keys = data.get("public_keys", [])
        if "public_key" in data:
            fallback_public_key = {
                "public_key": data["public_key"],
                "key_validity_url": "%s%s/_matrix/identity/api/v1/pubkey/isvalid" % (
                    id_server_scheme, id_server,
                ),
            }
        else:
            fallback_public_key = public_keys[0]

        if not public_keys:
            public_keys.append(fallback_public_key)
        display_name = data["display_name"]
        defer.returnValue((token, public_keys, fallback_public_key, display_name))

    @defer.inlineCallbacks
    def _is_host_in_room(self, current_state_ids):
        # 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:
            defer.returnValue(self.hs.is_mine_id(create_event_id))

        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 = yield self.store.get_event(event_id, allow_none=True)
            if not event:
                continue

            if event.membership == Membership.JOIN:
                defer.returnValue(True)

        defer.returnValue(False)


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")

    @defer.inlineCallbacks
    def _remote_join(self, requester, remote_room_hosts, room_id, user, content):
        """Implements RoomMemberHandler._remote_join
        """
        if len(remote_room_hosts) == 0:
            raise SynapseError(404, "No known servers")

        # 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.
        yield self.federation_handler.do_invite_join(
            remote_room_hosts,
            room_id,
            user.to_string(),
            content,
        )
        yield self._user_joined_room(user, room_id)

    @defer.inlineCallbacks
    def _remote_reject_invite(self, requester, remote_room_hosts, room_id, target):
        """Implements RoomMemberHandler._remote_reject_invite
        """
        fed_handler = self.federation_handler
        try:
            ret = yield fed_handler.do_remotely_reject_invite(
                remote_room_hosts,
                room_id,
                target.to_string(),
            )
            defer.returnValue(ret)
        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.warn("Failed to reject invite: %s", e)

            yield self.store.locally_reject_invite(
                target.to_string(), room_id
            )
            defer.returnValue({})

    def get_or_register_3pid_guest(self, requester, medium, address, inviter_user_id):
        """Implements RoomMemberHandler.get_or_register_3pid_guest
        """
        rg = self.registration_handler
        return rg.get_or_register_3pid_guest(medium, address, inviter_user_id)

    def _user_joined_room(self, target, room_id):
        """Implements RoomMemberHandler._user_joined_room
        """
        return user_joined_room(self.distributor, target, room_id)

    def _user_left_room(self, target, room_id):
        """Implements RoomMemberHandler._user_left_room
        """
        return user_left_room(self.distributor, target, room_id)

    @defer.inlineCallbacks
    def forget(self, user, room_id):
        user_id = user.to_string()

        member = yield 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:
            yield self.store.forget(user_id, room_id)