text: # Copyright 2016-2020 The Matrix.org Foundation C.I.C.
  # Copyright 2020 Sorunome
  #
  # 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
  import random
  from http import HTTPStatus
  from typing import TYPE_CHECKING, Iterable, List, Optional, Set, Tuple
  
  from synapse import types
  from synapse.api.constants import (
      AccountDataTypes,
      EventContentFields,
      EventTypes,
      Membership,
  )
  from synapse.api.errors import (
      AuthError,
      Codes,
      LimitExceededError,
      ShadowBanError,
      SynapseError,
  )
  from synapse.api.ratelimiting import Ratelimiter
  from synapse.event_auth import get_named_level, get_power_level_event
  from synapse.events import EventBase
  from synapse.events.snapshot import EventContext
  from synapse.handlers.profile import MAX_AVATAR_URL_LEN, MAX_DISPLAYNAME_LEN
  from synapse.types import (
      JsonDict,
      Requester,
      RoomAlias,
      RoomID,
      StateMap,
      UserID,
      get_domain_from_id,
  )
  from synapse.util.async_helpers import Linearizer
  from synapse.util.distributor import user_left_room
  
  from ._base import BaseHandler
  
  if TYPE_CHECKING:
      from synapse.server import HomeServer
  
  
  logger = logging.getLogger(__name__)
  
  
  class RoomMemberHandler(metaclass=abc.ABCMeta):
      # 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.
  
      def __init__(self, hs: "HomeServer"):
          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_federation_handler()
          self.directory_handler = hs.get_directory_handler()
          self.identity_handler = hs.get_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.account_data_handler = hs.get_account_data_handler()
          self.event_auth_handler = hs.get_event_auth_handler()
  
          self.member_linearizer: 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._join_rate_limiter_local = Ratelimiter(
              store=self.store,
              clock=self.clock,
              rate_hz=hs.config.ratelimiting.rc_joins_local.per_second,
              burst_count=hs.config.ratelimiting.rc_joins_local.burst_count,
          )
          self._join_rate_limiter_remote = Ratelimiter(
              store=self.store,
              clock=self.clock,
              rate_hz=hs.config.ratelimiting.rc_joins_remote.per_second,
              burst_count=hs.config.ratelimiting.rc_joins_remote.burst_count,
          )
  
          self._invites_per_room_limiter = Ratelimiter(
              store=self.store,
              clock=self.clock,
              rate_hz=hs.config.ratelimiting.rc_invites_per_room.per_second,
              burst_count=hs.config.ratelimiting.rc_invites_per_room.burst_count,
          )
          self._invites_per_user_limiter = Ratelimiter(
              store=self.store,
              clock=self.clock,
              rate_hz=hs.config.ratelimiting.rc_invites_per_user.per_second,
              burst_count=hs.config.ratelimiting.rc_invites_per_user.burst_count,
          )
  
          # 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_knock(
          self,
          remote_room_hosts: List[str],
          room_id: str,
          user: UserID,
          content: dict,
      ) -> Tuple[str, int]:
          """Try and knock on a room that this server is not in
  
          Args:
              remote_room_hosts: List of servers that can be used to knock via.
              room_id: Room that we are trying to knock on.
              user: User who is trying to knock.
              content: A dict that should be used as the content of the knock event.
          """
          raise NotImplementedError()
  
      @abc.abstractmethod
      async def remote_reject_invite(
          self,
          invite_event_id: str,
          txn_id: Optional[str],
          requester: Requester,
          content: JsonDict,
      ) -> Tuple[str, int]:
          """
          Rejects an out-of-band invite we have received from a remote server
  
          Args:
              invite_event_id: ID of the invite to be rejected
              txn_id: optional transaction ID supplied by the client
              requester: user making the rejection request, according to the access token
              content: additional content to include in the rejection event.
                 Normally an empty dict.
  
          Returns:
              event id, stream_id of the leave event
          """
          raise NotImplementedError()
  
      @abc.abstractmethod
      async def remote_rescind_knock(
          self,
          knock_event_id: str,
          txn_id: Optional[str],
          requester: Requester,
          content: JsonDict,
      ) -> Tuple[str, int]:
          """Rescind a local knock made on a remote room.
  
          Args:
              knock_event_id: The ID of the knock event to rescind.
              txn_id: An optional transaction ID supplied by the client.
              requester: The user making the request, according to the access token.
              content: The content of the generated leave event.
  
          Returns:
              A tuple containing (event_id, stream_id of the leave event).
          """
          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()
  
      @abc.abstractmethod
      async def forget(self, user: UserID, room_id: str) -> None:
          raise NotImplementedError()
  
      async def ratelimit_multiple_invites(
          self,
          requester: Optional[Requester],
          room_id: Optional[str],
          n_invites: int,
          update: bool = True,
      ):
          """Ratelimit more than one invite sent by the given requester in the given room.
  
          Args:
              requester: The requester sending the invites.
              room_id: The room the invites are being sent in.
              n_invites: The amount of invites to ratelimit for.
              update: Whether to update the ratelimiter's cache.
  
          Raises:
              LimitExceededError: The requester can't send that many invites in the room.
          """
          await self._invites_per_room_limiter.ratelimit(
              requester,
              room_id,
              update=update,
              n_actions=n_invites,
          )
  
      async def ratelimit_invite(
          self,
          requester: Optional[Requester],
          room_id: Optional[str],
          invitee_user_id: str,
      ):
          """Ratelimit invites by room and by target user.
  
          If room ID is missing then we just rate limit by target user.
          """
          if room_id:
              await self._invites_per_room_limiter.ratelimit(requester, room_id)
  
          await self._invites_per_user_limiter.ratelimit(requester, invitee_user_id)
  
      async def _local_membership_update(
          self,
          requester: Requester,
          target: UserID,
          room_id: str,
          membership: str,
          prev_event_ids: List[str],
          auth_event_ids: Optional[List[str]] = None,
          txn_id: Optional[str] = None,
          ratelimit: bool = True,
          content: Optional[dict] = None,
          require_consent: bool = True,
          outlier: bool = False,
      ) -> Tuple[str, int]:
          """
          Internal membership update function to get an existing event or create
          and persist a new event for the new membership change.
  
          Args:
              requester:
              target:
              room_id:
              membership:
              prev_event_ids: The event IDs to use as the prev events
  
              auth_event_ids:
                  The event ids to use as the auth_events for the new event.
                  Should normally be left as None, which will cause them to be calculated
                  based on the room state at the prev_events.
  
              txn_id:
              ratelimit:
              content:
              require_consent:
  
              outlier: Indicates whether the event is an `outlier`, i.e. if
                  it's from an arbitrary point and floating in the DAG as
                  opposed to being inline with the current DAG.
  
          Returns:
              Tuple of event ID and stream ordering position
          """
  
          user_id = target.to_string()
  
          if content is None:
              content = {}
  
          content["membership"] = membership
          if requester.is_guest:
              content["kind"] = "guest"
  
          # Check if we already have an event with a matching transaction ID. (We
          # do this check just before we persist an event as well, but may as well
          # do it up front for efficiency.)
          if txn_id and requester.access_token_id:
              existing_event_id = await self.store.get_event_id_from_transaction_id(
                  room_id,
                  requester.user.to_string(),
                  requester.access_token_id,
                  txn_id,
              )
              if existing_event_id:
                  event_pos = await self.store.get_position_for_event(existing_event_id)
                  return existing_event_id, event_pos.stream
  
          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,
              },
              txn_id=txn_id,
              prev_event_ids=prev_event_ids,
              auth_event_ids=auth_event_ids,
              require_consent=require_consent,
              outlier=outlier,
          )
  
          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:
              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
  
              # Only rate-limit if the user actually joined the room, otherwise we'll end
              # up blocking profile updates.
              if newly_joined and ratelimit:
                  time_now_s = self.clock.time()
                  (
                      allowed,
                      time_allowed,
                  ) = await self._join_rate_limiter_local.can_do_action(requester)
  
                  if not allowed:
                      raise LimitExceededError(
                          retry_after_ms=int(1000 * (time_allowed - time_now_s))
                      )
  
          result_event = await self.event_creation_handler.handle_new_client_event(
              requester,
              event,
              context,
              extra_users=[target],
              ratelimit=ratelimit,
          )
  
          if 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)
  
          # we know it was persisted, so should have a stream ordering
          assert result_event.internal_metadata.stream_ordering
          return result_event.event_id, result_event.internal_metadata.stream_ordering
  
      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(AccountDataTypes.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.account_data_handler.add_account_data_for_user(
                          user_id, AccountDataTypes.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.account_data_handler.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,
          outlier: bool = False,
          prev_event_ids: Optional[List[str]] = None,
          auth_event_ids: Optional[List[str]] = None,
      ) -> Tuple[str, int]:
          """Update a user's membership in a room.
  
          Params:
              requester: The user who is performing the update.
              target: The user whose membership is being updated.
              room_id: The room ID whose membership is being updated.
              action: The membership change, see synapse.api.constants.Membership.
              txn_id: The transaction ID, if given.
              remote_room_hosts: Remote servers to send the update to.
              third_party_signed: Information from a 3PID invite.
              ratelimit: Whether to rate limit the request.
              content: The content of the created event.
              require_consent: Whether consent is required.
              outlier: Indicates whether the event is an `outlier`, i.e. if
                  it's from an arbitrary point and floating in the DAG as
                  opposed to being inline with the current DAG.
              prev_event_ids: The event IDs to use as the prev events
              auth_event_ids:
                  The event ids to use as the auth_events for the new event.
                  Should normally be left as None, which will cause them to be calculated
                  based on the room state at the prev_events.
  
          Returns:
              A tuple of the new event ID and stream ID.
  
          Raises:
              ShadowBanError if a shadow-banned requester attempts to send an invite.
          """
          if action == Membership.INVITE and requester.shadow_banned:
              # We randomly sleep a bit just to annoy the requester.
              await self.clock.sleep(random.randint(1, 10))
              raise ShadowBanError()
  
          key = (room_id,)
  
          with (await self.member_linearizer.queue(key)):
              result = await self.update_membership_locked(
                  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,
                  outlier=outlier,
                  prev_event_ids=prev_event_ids,
                  auth_event_ids=auth_event_ids,
              )
  
          return result
  
      async def update_membership_locked(
          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,
          outlier: bool = False,
          prev_event_ids: Optional[List[str]] = None,
          auth_event_ids: Optional[List[str]] = None,
      ) -> Tuple[str, int]:
          """Helper for update_membership.
  
          Assumes that the membership linearizer is already held for the room.
  
          Args:
              requester:
              target:
              room_id:
              action:
              txn_id:
              remote_room_hosts:
              third_party_signed:
              ratelimit:
              content:
              require_consent:
              outlier: Indicates whether the event is an `outlier`, i.e. if
                  it's from an arbitrary point and floating in the DAG as
                  opposed to being inline with the current DAG.
              prev_event_ids: The event IDs to use as the prev events
              auth_event_ids:
                  The event ids to use as the auth_events for the new event.
                  Should normally be left as None, which will cause them to be calculated
                  based on the room state at the prev_events.
  
          Returns:
              A tuple of the new event ID and stream ID.
          """
          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)
  
          # allow the server notices mxid to set room-level profile
          is_requester_server_notices_user = (
              self._server_notices_mxid is not None
              and requester.user.to_string() == self._server_notices_mxid
          )
  
          if (
              not self.allow_per_room_profiles and not is_requester_server_notices_user
          ) or requester.shadow_banned:
              # 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)
  
          if len(content.get("displayname") or "") > MAX_DISPLAYNAME_LEN:
              raise SynapseError(
                  400,
                  f"Displayname is too long (max {MAX_DISPLAYNAME_LEN})",
                  errcode=Codes.BAD_JSON,
              )
  
          if len(content.get("avatar_url") or "") > MAX_AVATAR_URL_LEN:
              raise SynapseError(
                  400,
                  f"Avatar URL is too long (max {MAX_AVATAR_URL_LEN})",
                  errcode=Codes.BAD_JSON,
              )
  
          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:
              target_id = target.to_string()
              if ratelimit:
                  await self.ratelimit_invite(requester, room_id, target_id)
  
              # block any attempts to invite the server notices mxid
              if target_id == 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 await self.spam_checker.user_may_invite(
                      requester.user.to_string(), target_id, 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")
  
          if prev_event_ids:
              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=prev_event_ids,
                  auth_event_ids=auth_event_ids,
                  content=content,
                  require_consent=require_consent,
                  outlier=outlier,
              )
  
          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:
                      # duplicate event.
                      # we know it was persisted, so must have a stream ordering.
                      assert old_state.internal_metadata.stream_ordering
                      return (
                          old_state.event_id,
                          old_state.internal_metadata.stream_ordering,
                      )
  
              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")
  
              # Check if a remote join should be performed.
              remote_join, remote_room_hosts = await self._should_perform_remote_join(
                  target.to_string(), room_id, remote_room_hosts, content, is_host_in_room
              )
              if remote_join:
                  if ratelimit:
                      time_now_s = self.clock.time()
                      (
                          allowed,
                          time_allowed,
                      ) = await self._join_rate_limiter_remote.can_do_action(
                          requester,
                      )
  
                      if not allowed:
                          raise LimitExceededError(
                              retry_after_ms=int(1000 * (time_allowed - time_now_s))
                          )
  
                  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:
                  # Figure out the user's current membership state for the room
                  (
                      current_membership_type,
                      current_membership_event_id,
                  ) = await self.store.get_local_current_membership_for_user_in_room(
                      target.to_string(), room_id
                  )
                  if not current_membership_type or not current_membership_event_id:
                      logger.info(
                          "%s sent a leave request to %s, but that is not an active room "
                          "on this server, or there is no pending invite or knock",
                          target,
                          room_id,
                      )
  
                      raise SynapseError(404, "Not a known room")
  
                  # perhaps we've been invited
                  if current_membership_type == Membership.INVITE:
                      invite = await self.store.get_event(current_membership_event_id)
                      logger.info(
                          "%s rejects invite to %s from %s",
                          target,
                          room_id,
                          invite.sender,
                      )
  
                      if not self.hs.is_mine_id(invite.sender):
                          # send the rejection to the inviter's HS (with fallback to
                          # local event)
                          return await self.remote_reject_invite(
                              invite.event_id,
                              txn_id,
                              requester,
                              content,
                          )
  
                      # the inviter was on our server, but has now left. Carry on
                      # with the normal rejection codepath, which will also send the
                      # rejection out to any other servers we believe are still in the room.
  
                      # thanks to overzealous cleaning up of event_forward_extremities in
                      # `delete_old_current_state_events`, it's possible to end up with no
                      # forward extremities here. If that happens, let's just hang the
                      # rejection off the invite event.
                      #
                      # see: https://github.com/matrix-org/synapse/issues/7139
                      if len(latest_event_ids) == 0:
                          latest_event_ids = [invite.event_id]
  
                  # or perhaps this is a remote room that a local user has knocked on
                  elif current_membership_type == Membership.KNOCK:
                      knock = await self.store.get_event(current_membership_event_id)
                      return await self.remote_rescind_knock(
                          knock.event_id, txn_id, requester, content
                      )
  
          elif effective_membership_state == Membership.KNOCK:
              if not is_host_in_room:
                  # The knock needs to be sent over federation instead
                  remote_room_hosts.append(get_domain_from_id(room_id))
  
                  content["membership"] = Membership.KNOCK
  
                  profile = self.profile_handler
                  if "displayname" not in content:
                      content["displayname"] = await profile.get_displayname(target)
                  if "avatar_url" not in content:
                      content["avatar_url"] = await profile.get_avatar_url(target)
  
                  return await self.remote_knock(
                      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,
              auth_event_ids=auth_event_ids,
              content=content,
              require_consent=require_consent,
              outlier=outlier,
          )
  
      async def _should_perform_remote_join(
          self,
          user_id: str,
          room_id: str,
          remote_room_hosts: List[str],
          content: JsonDict,
          is_host_in_room: bool,
      ) -> Tuple[bool, List[str]]:
          """
          Check whether the server should do a remote join (as opposed to a local
          join) for a user.
  
          Generally a remote join is used if:
  
          * The server is not yet in the room.
          * The server is in the room, the room has restricted join rules, the user
            is not joined or invited to the room, and the server does not have
            another user who is capable of issuing invites.
  
          Args:
              user_id: The user joining the room.
              room_id: The room being joined.
              remote_room_hosts: A list of remote room hosts.
              content: The content to use as the event body of the join. This may
                  be modified.
              is_host_in_room: True if the host is in the room.
  
          Returns:
              A tuple of:
                  True if a remote join should be performed. False if the join can be
                  done locally.
  
                  A list of remote room hosts to use. This is an empty list if a
                  local join is to be done.
          """
          # If the host isn't in the room, pass through the prospective hosts.
          if not is_host_in_room:
              return True, remote_room_hosts
  
          # If the host is in the room, but not one of the authorised hosts
          # for restricted join rules, a remote join must be used.
          room_version = await self.store.get_room_version(room_id)
          current_state_ids = await self.store.get_current_state_ids(room_id)
  
          # If restricted join rules are not being used, a local join can always
          # be used.
          if not await self.event_auth_handler.has_restricted_join_rules(
              current_state_ids, room_version
          ):
              return False, []
  
          # If the user is invited to the room or already joined, the join
          # event can always be issued locally.
          prev_member_event_id = current_state_ids.get((EventTypes.Member, user_id), None)
          prev_member_event = None
          if prev_member_event_id:
              prev_member_event = await self.store.get_event(prev_member_event_id)
              if prev_member_event.membership in (
                  Membership.JOIN,
                  Membership.INVITE,
              ):
                  return False, []
  
          # If the local host has a user who can issue invites, then a local
          # join can be done.
          #
          # If not, generate a new list of remote hosts based on which
          # can issue invites.
          event_map = await self.store.get_events(current_state_ids.values())
          current_state = {
              state_key: event_map[event_id]
              for state_key, event_id in current_state_ids.items()
          }
          allowed_servers = get_servers_from_users(
              get_users_which_can_issue_invite(current_state)
          )
  
          # If the local server is not one of allowed servers, then a remote
          # join must be done. Return the list of prospective servers based on
          # which can issue invites.
          if self.hs.hostname not in allowed_servers:
              return True, list(allowed_servers)
  
          # Ensure the member should be allowed access via membership in a room.
          await self.event_auth_handler.check_restricted_join_rules(
              current_state_ids, room_version, user_id, prev_member_event
          )
  
          # If this is going to be a local join, additional information must
          # be included in the event content in order to efficiently validate
          # the event.
          content[
              "join_authorised_via_users_server"
          ] = await self.event_auth_handler.get_user_which_could_invite(
              room_id,
              current_state_ids,
          )
  
          return False, []
  
      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: Optional[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_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")
  
          event = 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.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: StateMap[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 bool(
              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:
          """Invite a 3PID to a room.
  
          Args:
              room_id: The room to invite the 3PID to.
              inviter: The user sending the invite.
              medium: The 3PID's medium.
              address: The 3PID's address.
              id_server: The identity server to use.
              requester: The user making the request.
              txn_id: The transaction ID this is part of, or None if this is not
                  part of a transaction.
              id_access_token: The optional identity server access token.
  
          Returns:
               The new stream ID.
  
          Raises:
              ShadowBanError if the requester has been shadow-banned.
          """
          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
                  )
  
          if requester.shadow_banned:
              # We randomly sleep a bit just to annoy the requester.
              await self.clock.sleep(random.randint(1, 10))
              raise ShadowBanError()
  
          # 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:
              # Note that update_membership with an action of "invite" can raise
              # a ShadowBanError, but this was done above already.
              _, 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_type = None
          room_create_event = room_state.get((EventTypes.Create, ""))
          if room_create_event:
              room_type = room_create_event.content.get(EventContentFields.ROOM_TYPE)
  
          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,
              room_type=room_type,
              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: StateMap[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: "HomeServer"):
          super().__init__(hs)
  
          self.distributor = hs.get_distributor()
          self.distributor.declare("user_left_room")
          self._server_name = hs.hostname
  
      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")
  
          check_complexity = self.hs.config.limit_remote_rooms.enabled
          if check_complexity and self.hs.config.limit_remote_rooms.admins_can_join:
              check_complexity = not await self.auth.is_server_admin(user)
  
          if check_complexity:
              # 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
          )
  
          # Check the room we just joined wasn't too large, if we didn't fetch the
          # complexity of it before.
          if check_complexity:
              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, authenticated_entity=self._server_name
              )
              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,
          invite_event_id: str,
          txn_id: Optional[str],
          requester: Requester,
          content: JsonDict,
      ) -> Tuple[str, int]:
          """
          Rejects an out-of-band invite received from a remote user
  
          Implements RoomMemberHandler.remote_reject_invite
          """
          invite_event = await self.store.get_event(invite_event_id)
          room_id = invite_event.room_id
          target_user = invite_event.state_key
  
          # first of all, try doing a rejection via the inviting server
          fed_handler = self.federation_handler
          try:
              inviter_id = UserID.from_string(invite_event.sender)
              event, stream_id = await fed_handler.do_remotely_reject_invite(
                  [inviter_id.domain], room_id, target_user, content=content
              )
              return event.event_id, stream_id
          except Exception as e:
              # if we were unable to reject the invite, we will generate our own
              # leave event.
              #
              # The 'except' clause is very broad, but we need to
              # capture everything from DNS failures upwards
              #
              logger.warning("Failed to reject invite: %s", e)
  
              return await self._generate_local_out_of_band_leave(
                  invite_event, txn_id, requester, content
              )
  
      async def remote_rescind_knock(
          self,
          knock_event_id: str,
          txn_id: Optional[str],
          requester: Requester,
          content: JsonDict,
      ) -> Tuple[str, int]:
          """
          Rescinds a local knock made on a remote room
  
          Args:
              knock_event_id: The ID of the knock event to rescind.
              txn_id: The transaction ID to use.
              requester: The originator of the request.
              content: The content of the leave event.
  
          Implements RoomMemberHandler.remote_rescind_knock
          """
          # TODO: We don't yet support rescinding knocks over federation
          # as we don't know which homeserver to send it to. An obvious
          # candidate is the remote homeserver we originally knocked through,
          # however we don't currently store that information.
  
          # Just rescind the knock locally
          knock_event = await self.store.get_event(knock_event_id)
          return await self._generate_local_out_of_band_leave(
              knock_event, txn_id, requester, content
          )
  
      async def _generate_local_out_of_band_leave(
          self,
          previous_membership_event: EventBase,
          txn_id: Optional[str],
          requester: Requester,
          content: JsonDict,
      ) -> Tuple[str, int]:
          """Generate a local leave event for a room
  
          This can be called after we e.g fail to reject an invite via a remote server.
          It generates an out-of-band membership event locally.
  
          Args:
              previous_membership_event: the previous membership event for this user
              txn_id: optional transaction ID supplied by the client
              requester: user making the request, according to the access token
              content: additional content to include in the leave event.
                 Normally an empty dict.
  
          Returns:
              A tuple containing (event_id, stream_id of the leave event)
          """
          room_id = previous_membership_event.room_id
          target_user = previous_membership_event.state_key
  
          content["membership"] = Membership.LEAVE
  
          event_dict = {
              "type": EventTypes.Member,
              "room_id": room_id,
              "sender": target_user,
              "content": content,
              "state_key": target_user,
          }
  
          # the auth events for the new event are the same as that of the previous event, plus
          # the event itself.
          #
          # the prev_events consist solely of the previous membership event.
          prev_event_ids = [previous_membership_event.event_id]
          auth_event_ids = previous_membership_event.auth_event_ids() + prev_event_ids
  
          event, context = await self.event_creation_handler.create_event(
              requester,
              event_dict,
              txn_id=txn_id,
              prev_event_ids=prev_event_ids,
              auth_event_ids=auth_event_ids,
          )
          event.internal_metadata.outlier = True
          event.internal_metadata.out_of_band_membership = True
  
          result_event = await self.event_creation_handler.handle_new_client_event(
              requester,
              event,
              context,
              extra_users=[UserID.from_string(target_user)],
          )
          # we know it was persisted, so must have a stream ordering
          assert result_event.internal_metadata.stream_ordering
  
          return result_event.event_id, result_event.internal_metadata.stream_ordering
  
      async def remote_knock(
          self,
          remote_room_hosts: List[str],
          room_id: str,
          user: UserID,
          content: dict,
      ) -> Tuple[str, int]:
          """Sends a knock to a room. Attempts to do so via one remote out of a given list.
  
          Args:
              remote_room_hosts: A list of homeservers to try knocking through.
              room_id: The ID of the room to knock on.
              user: The user to knock on behalf of.
              content: The content of the knock event.
  
          Returns:
              A tuple of (event ID, stream ID).
          """
          # filter ourselves out of remote_room_hosts
          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")
  
          return await self.federation_handler.do_knock(
              remote_room_hosts, room_id, user.to_string(), content=content
          )
  
      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)
  
  
  def get_users_which_can_issue_invite(auth_events: StateMap[EventBase]) -> List[str]:
      """
      Return the list of users which can issue invites.
  
      This is done by exploring the joined users and comparing their power levels
      to the necessyar power level to issue an invite.
  
      Args:
          auth_events: state in force at this point in the room
  
      Returns:
          The users which can issue invites.
      """
      invite_level = get_named_level(auth_events, "invite", 0)
      users_default_level = get_named_level(auth_events, "users_default", 0)
      power_level_event = get_power_level_event(auth_events)
  
      # Custom power-levels for users.
      if power_level_event:
          users = power_level_event.content.get("users", {})
      else:
          users = {}
  
      result = []
  
      # Check which members are able to invite by ensuring they're joined and have
      # the necessary power level.
      for (event_type, state_key), event in auth_events.items():
          if event_type != EventTypes.Member:
              continue
  
          if event.membership != Membership.JOIN:
              continue
  
          # Check if the user has a custom power level.
          if users.get(state_key, users_default_level) >= invite_level:
              result.append(state_key)
  
      return result
  
  
  def get_servers_from_users(users: List[str]) -> Set[str]:
      """
      Resolve a list of users into their servers.
  
      Args:
          users: A list of users.
  
      Returns:
          A set of servers.
      """
      servers = set()
      for user in users:
          try:
              servers.add(get_domain_from_id(user))
          except SynapseError:
              pass
      return servers
  