text: # Copyright 2015-2021 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 copy
  import itertools
  import logging
  from typing import (
      TYPE_CHECKING,
      Awaitable,
      Callable,
      Collection,
      Container,
      Dict,
      Iterable,
      List,
      Mapping,
      Optional,
      Sequence,
      Tuple,
      TypeVar,
      Union,
  )
  
  import attr
  from prometheus_client import Counter
  
  from synapse.api.constants import EventTypes, Membership
  from synapse.api.errors import (
      CodeMessageException,
      Codes,
      FederationDeniedError,
      HttpResponseException,
      SynapseError,
      UnsupportedRoomVersionError,
  )
  from synapse.api.room_versions import (
      KNOWN_ROOM_VERSIONS,
      EventFormatVersions,
      RoomVersion,
      RoomVersions,
  )
  from synapse.events import EventBase, builder
  from synapse.federation.federation_base import FederationBase, event_from_pdu_json
  from synapse.federation.transport.client import SendJoinResponse
  from synapse.logging.utils import log_function
  from synapse.types import JsonDict, get_domain_from_id
  from synapse.util.async_helpers import concurrently_execute
  from synapse.util.caches.expiringcache import ExpiringCache
  from synapse.util.retryutils import NotRetryingDestination
  
  if TYPE_CHECKING:
      from synapse.server import HomeServer
  
  logger = logging.getLogger(__name__)
  
  sent_queries_counter = Counter("synapse_federation_client_sent_queries", "", ["type"])
  
  
  PDU_RETRY_TIME_MS = 1 * 60 * 1000
  
  T = TypeVar("T")
  
  
  class InvalidResponseError(RuntimeError):
      """Helper for _try_destination_list: indicates that the server returned a response
      we couldn't parse
      """
  
  
  @attr.s(slots=True, frozen=True, auto_attribs=True)
  class SendJoinResult:
      # The event to persist.
      event: EventBase
      # A string giving the server the event was sent to.
      origin: str
      state: List[EventBase]
      auth_chain: List[EventBase]
  
  
  class FederationClient(FederationBase):
      def __init__(self, hs: "HomeServer"):
          super().__init__(hs)
  
          self.pdu_destination_tried: Dict[str, Dict[str, int]] = {}
          self._clock.looping_call(self._clear_tried_cache, 60 * 1000)
          self.state = hs.get_state_handler()
          self.transport_layer = hs.get_federation_transport_client()
  
          self.hostname = hs.hostname
          self.signing_key = hs.signing_key
  
          self._get_pdu_cache: ExpiringCache[str, EventBase] = ExpiringCache(
              cache_name="get_pdu_cache",
              clock=self._clock,
              max_len=1000,
              expiry_ms=120 * 1000,
              reset_expiry_on_get=False,
          )
  
      def _clear_tried_cache(self):
          """Clear pdu_destination_tried cache"""
          now = self._clock.time_msec()
  
          old_dict = self.pdu_destination_tried
          self.pdu_destination_tried = {}
  
          for event_id, destination_dict in old_dict.items():
              destination_dict = {
                  dest: time
                  for dest, time in destination_dict.items()
                  if time + PDU_RETRY_TIME_MS > now
              }
              if destination_dict:
                  self.pdu_destination_tried[event_id] = destination_dict
  
      @log_function
      async def make_query(
          self,
          destination: str,
          query_type: str,
          args: dict,
          retry_on_dns_fail: bool = False,
          ignore_backoff: bool = False,
      ) -> JsonDict:
          """Sends a federation Query to a remote homeserver of the given type
          and arguments.
  
          Args:
              destination: Domain name of the remote homeserver
              query_type: Category of the query type; should match the
                  handler name used in register_query_handler().
              args: Mapping of strings to strings containing the details
                  of the query request.
              ignore_backoff: true to ignore the historical backoff data
                  and try the request anyway.
  
          Returns:
              The JSON object from the response
          """
          sent_queries_counter.labels(query_type).inc()
  
          return await self.transport_layer.make_query(
              destination,
              query_type,
              args,
              retry_on_dns_fail=retry_on_dns_fail,
              ignore_backoff=ignore_backoff,
          )
  
      @log_function
      async def query_client_keys(
          self, destination: str, content: JsonDict, timeout: int
      ) -> JsonDict:
          """Query device keys for a device hosted on a remote server.
  
          Args:
              destination: Domain name of the remote homeserver
              content: The query content.
  
          Returns:
              The JSON object from the response
          """
          sent_queries_counter.labels("client_device_keys").inc()
          return await self.transport_layer.query_client_keys(
              destination, content, timeout
          )
  
      @log_function
      async def query_user_devices(
          self, destination: str, user_id: str, timeout: int = 30000
      ) -> JsonDict:
          """Query the device keys for a list of user ids hosted on a remote
          server.
          """
          sent_queries_counter.labels("user_devices").inc()
          return await self.transport_layer.query_user_devices(
              destination, user_id, timeout
          )
  
      @log_function
      async def claim_client_keys(
          self, destination: str, content: JsonDict, timeout: int
      ) -> JsonDict:
          """Claims one-time keys for a device hosted on a remote server.
  
          Args:
              destination: Domain name of the remote homeserver
              content: The query content.
  
          Returns:
              The JSON object from the response
          """
          sent_queries_counter.labels("client_one_time_keys").inc()
          return await self.transport_layer.claim_client_keys(
              destination, content, timeout
          )
  
      async def backfill(
          self, dest: str, room_id: str, limit: int, extremities: Iterable[str]
      ) -> Optional[List[EventBase]]:
          """Requests some more historic PDUs for the given room from the
          given destination server.
  
          Args:
              dest: The remote homeserver to ask.
              room_id: The room_id to backfill.
              limit: The maximum number of events to return.
              extremities: our current backwards extremities, to backfill from
          """
          logger.debug("backfill extrem=%s", extremities)
  
          # If there are no extremities then we've (probably) reached the start.
          if not extremities:
              return None
  
          transaction_data = await self.transport_layer.backfill(
              dest, room_id, extremities, limit
          )
  
          logger.debug("backfill transaction_data=%r", transaction_data)
  
          room_version = await self.store.get_room_version(room_id)
  
          pdus = [
              event_from_pdu_json(p, room_version, outlier=False)
              for p in transaction_data["pdus"]
          ]
  
          # Check signatures and hash of pdus, removing any from the list that fail checks
          pdus[:] = await self._check_sigs_and_hash_and_fetch(
              dest, pdus, outlier=True, room_version=room_version
          )
  
          return pdus
  
      async def get_pdu(
          self,
          destinations: Iterable[str],
          event_id: str,
          room_version: RoomVersion,
          outlier: bool = False,
          timeout: Optional[int] = None,
      ) -> Optional[EventBase]:
          """Requests the PDU with given origin and ID from the remote home
          servers.
  
          Will attempt to get the PDU from each destination in the list until
          one succeeds.
  
          Args:
              destinations: Which homeservers to query
              event_id: event to fetch
              room_version: version of the room
              outlier: Indicates whether the PDU is an `outlier`, i.e. if
                  it's from an arbitrary point in the context as opposed to part
                  of the current block of PDUs. Defaults to `False`
              timeout: How long to try (in ms) each destination for before
                  moving to the next destination. None indicates no timeout.
  
          Returns:
              The requested PDU, or None if we were unable to find it.
          """
  
          # TODO: Rate limit the number of times we try and get the same event.
  
          ev = self._get_pdu_cache.get(event_id)
          if ev:
              return ev
  
          pdu_attempts = self.pdu_destination_tried.setdefault(event_id, {})
  
          signed_pdu = None
          for destination in destinations:
              now = self._clock.time_msec()
              last_attempt = pdu_attempts.get(destination, 0)
              if last_attempt + PDU_RETRY_TIME_MS > now:
                  continue
  
              try:
                  transaction_data = await self.transport_layer.get_event(
                      destination, event_id, timeout=timeout
                  )
  
                  logger.debug(
                      "retrieved event id %s from %s: %r",
                      event_id,
                      destination,
                      transaction_data,
                  )
  
                  pdu_list: List[EventBase] = [
                      event_from_pdu_json(p, room_version, outlier=outlier)
                      for p in transaction_data["pdus"]
                  ]
  
                  if pdu_list and pdu_list[0]:
                      pdu = pdu_list[0]
  
                      # Check signatures are correct.
                      signed_pdu = await self._check_sigs_and_hash(room_version, pdu)
  
                      break
  
                  pdu_attempts[destination] = now
  
              except SynapseError as e:
                  logger.info(
                      "Failed to get PDU %s from %s because %s", event_id, destination, e
                  )
                  continue
              except NotRetryingDestination as e:
                  logger.info(str(e))
                  continue
              except FederationDeniedError as e:
                  logger.info(str(e))
                  continue
              except Exception as e:
                  pdu_attempts[destination] = now
  
                  logger.info(
                      "Failed to get PDU %s from %s because %s", event_id, destination, e
                  )
                  continue
  
          if signed_pdu:
              self._get_pdu_cache[event_id] = signed_pdu
  
          return signed_pdu
  
      async def get_room_state_ids(
          self, destination: str, room_id: str, event_id: str
      ) -> Tuple[List[str], List[str]]:
          """Calls the /state_ids endpoint to fetch the state at a particular point
          in the room, and the auth events for the given event
  
          Returns:
              a tuple of (state event_ids, auth event_ids)
          """
          result = await self.transport_layer.get_room_state_ids(
              destination, room_id, event_id=event_id
          )
  
          state_event_ids = result["pdu_ids"]
          auth_event_ids = result.get("auth_chain_ids", [])
  
          if not isinstance(state_event_ids, list) or not isinstance(
              auth_event_ids, list
          ):
              raise Exception("invalid response from /state_ids")
  
          return state_event_ids, auth_event_ids
  
      async def _check_sigs_and_hash_and_fetch(
          self,
          origin: str,
          pdus: Collection[EventBase],
          room_version: RoomVersion,
          outlier: bool = False,
      ) -> List[EventBase]:
          """Takes a list of PDUs and checks the signatures and hashes of each
          one. If a PDU fails its signature check then we check if we have it in
          the database and if not then request if from the originating server of
          that PDU.
  
          If a PDU fails its content hash check then it is redacted.
  
          The given list of PDUs are not modified, instead the function returns
          a new list.
  
          Args:
              origin
              pdu
              room_version
              outlier: Whether the events are outliers or not
  
          Returns:
              A list of PDUs that have valid signatures and hashes.
          """
  
          # We limit how many PDUs we check at once, as if we try to do hundreds
          # of thousands of PDUs at once we see large memory spikes.
  
          valid_pdus = []
  
          async def _execute(pdu: EventBase) -> None:
              valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
                  pdu=pdu,
                  origin=origin,
                  outlier=outlier,
                  room_version=room_version,
              )
  
              if valid_pdu:
                  valid_pdus.append(valid_pdu)
  
          await concurrently_execute(_execute, pdus, 10000)
  
          return valid_pdus
  
      async def _check_sigs_and_hash_and_fetch_one(
          self,
          pdu: EventBase,
          origin: str,
          room_version: RoomVersion,
          outlier: bool = False,
      ) -> Optional[EventBase]:
          """Takes a PDU and checks its signatures and hashes. If the PDU fails
          its signature check then we check if we have it in the database and if
          not then request if from the originating server of that PDU.
  
          If then PDU fails its content hash check then it is redacted.
  
          Args:
              origin
              pdu
              room_version
              outlier: Whether the events are outliers or not
              include_none: Whether to include None in the returned list
                  for events that have failed their checks
  
          Returns:
              The PDU (possibly redacted) if it has valid signatures and hashes.
          """
  
          res = None
          try:
              res = await self._check_sigs_and_hash(room_version, pdu)
          except SynapseError:
              pass
  
          if not res:
              # Check local db.
              res = await self.store.get_event(
                  pdu.event_id, allow_rejected=True, allow_none=True
              )
  
          pdu_origin = get_domain_from_id(pdu.sender)
          if not res and pdu_origin != origin:
              try:
                  res = await self.get_pdu(
                      destinations=[pdu_origin],
                      event_id=pdu.event_id,
                      room_version=room_version,
                      outlier=outlier,
                      timeout=10000,
                  )
              except SynapseError:
                  pass
  
          if not res:
              logger.warning(
                  "Failed to find copy of %s with valid signature", pdu.event_id
              )
  
          return res
  
      async def get_event_auth(
          self, destination: str, room_id: str, event_id: str
      ) -> List[EventBase]:
          res = await self.transport_layer.get_event_auth(destination, room_id, event_id)
  
          room_version = await self.store.get_room_version(room_id)
  
          auth_chain = [
              event_from_pdu_json(p, room_version, outlier=True)
              for p in res["auth_chain"]
          ]
  
          signed_auth = await self._check_sigs_and_hash_and_fetch(
              destination, auth_chain, outlier=True, room_version=room_version
          )
  
          signed_auth.sort(key=lambda e: e.depth)
  
          return signed_auth
  
      def _is_unknown_endpoint(
          self, e: HttpResponseException, synapse_error: Optional[SynapseError] = None
      ) -> bool:
          """
          Returns true if the response was due to an endpoint being unimplemented.
  
          Args:
              e: The error response received from the remote server.
              synapse_error: The above error converted to a SynapseError. This is
                  automatically generated if not provided.
  
          """
          if synapse_error is None:
              synapse_error = e.to_synapse_error()
          # There is no good way to detect an "unknown" endpoint.
          #
          # Dendrite returns a 404 (with no body); synapse returns a 400
          # with M_UNRECOGNISED.
          return e.code == 404 or (
              e.code == 400 and synapse_error.errcode == Codes.UNRECOGNIZED
          )
  
      async def _try_destination_list(
          self,
          description: str,
          destinations: Iterable[str],
          callback: Callable[[str], Awaitable[T]],
          failover_errcodes: Optional[Container[str]] = None,
          failover_on_unknown_endpoint: bool = False,
      ) -> T:
          """Try an operation on a series of servers, until it succeeds
  
          Args:
              description: description of the operation we're doing, for logging
  
              destinations: list of server_names to try
  
              callback:  Function to run for each server. Passed a single
                  argument: the server_name to try.
  
                  If the callback raises a CodeMessageException with a 300/400 code or
                  an UnsupportedRoomVersionError, attempts to perform the operation
                  stop immediately and the exception is reraised.
  
                  Otherwise, if the callback raises an Exception the error is logged and the
                  next server tried. Normally the stacktrace is logged but this is
                  suppressed if the exception is an InvalidResponseError.
  
              failover_errcodes: Error codes (specific to this endpoint) which should
                  cause a failover when received as part of an HTTP 400 error.
  
              failover_on_unknown_endpoint: if True, we will try other servers if it looks
                  like a server doesn't support the endpoint. This is typically useful
                  if the endpoint in question is new or experimental.
  
          Returns:
              The result of callback, if it succeeds
  
          Raises:
              SynapseError if the chosen remote server returns a 300/400 code, or
              no servers were reachable.
          """
          if failover_errcodes is None:
              failover_errcodes = ()
  
          for destination in destinations:
              if destination == self.server_name:
                  continue
  
              try:
                  return await callback(destination)
              except InvalidResponseError as e:
                  logger.warning("Failed to %s via %s: %s", description, destination, e)
              except UnsupportedRoomVersionError:
                  raise
              except HttpResponseException as e:
                  synapse_error = e.to_synapse_error()
                  failover = False
  
                  # Failover should occur:
                  #
                  # * On internal server errors.
                  # * If the destination responds that it cannot complete the request.
                  # * If the destination doesn't implemented the endpoint for some reason.
                  if 500 <= e.code < 600:
                      failover = True
  
                  elif e.code == 400 and synapse_error.errcode in failover_errcodes:
                      failover = True
  
                  elif failover_on_unknown_endpoint and self._is_unknown_endpoint(
                      e, synapse_error
                  ):
                      failover = True
  
                  if not failover:
                      raise synapse_error from e
  
                  logger.warning(
                      "Failed to %s via %s: %i %s",
                      description,
                      destination,
                      e.code,
                      e.args[0],
                  )
              except Exception:
                  logger.warning(
                      "Failed to %s via %s", description, destination, exc_info=True
                  )
  
          raise SynapseError(502, "Failed to %s via any server" % (description,))
  
      async def make_membership_event(
          self,
          destinations: Iterable[str],
          room_id: str,
          user_id: str,
          membership: str,
          content: dict,
          params: Optional[Mapping[str, Union[str, Iterable[str]]]],
      ) -> Tuple[str, EventBase, RoomVersion]:
          """
          Creates an m.room.member event, with context, without participating in the room.
  
          Does so by asking one of the already participating servers to create an
          event with proper context.
  
          Returns a fully signed and hashed event.
  
          Note that this does not append any events to any graphs.
  
          Args:
              destinations: Candidate homeservers which are probably
                  participating in the room.
              room_id: The room in which the event will happen.
              user_id: The user whose membership is being evented.
              membership: The "membership" property of the event. Must be one of
                  "join" or "leave".
              content: Any additional data to put into the content field of the
                  event.
              params: Query parameters to include in the request.
  
          Returns:
              `(origin, event, room_version)` where origin is the remote
              homeserver which generated the event, and room_version is the
              version of the room.
  
          Raises:
              UnsupportedRoomVersionError: if remote responds with
                  a room version we don't understand.
  
              SynapseError: if the chosen remote server returns a 300/400 code, or
                  no servers successfully handle the request.
          """
          valid_memberships = {Membership.JOIN, Membership.LEAVE, Membership.KNOCK}
  
          if membership not in valid_memberships:
              raise RuntimeError(
                  "make_membership_event called with membership='%s', must be one of %s"
                  % (membership, ",".join(valid_memberships))
              )
  
          async def send_request(destination: str) -> Tuple[str, EventBase, RoomVersion]:
              ret = await self.transport_layer.make_membership_event(
                  destination, room_id, user_id, membership, params
              )
  
              # Note: If not supplied, the room version may be either v1 or v2,
              # however either way the event format version will be v1.
              room_version_id = ret.get("room_version", RoomVersions.V1.identifier)
              room_version = KNOWN_ROOM_VERSIONS.get(room_version_id)
              if not room_version:
                  raise UnsupportedRoomVersionError()
  
              if not room_version.msc2403_knocking and membership == Membership.KNOCK:
                  raise SynapseError(
                      400,
                      "This room version does not support knocking",
                      errcode=Codes.FORBIDDEN,
                  )
  
              pdu_dict = ret.get("event", None)
              if not isinstance(pdu_dict, dict):
                  raise InvalidResponseError("Bad 'event' field in response")
  
              logger.debug("Got response to make_%s: %s", membership, pdu_dict)
  
              pdu_dict["content"].update(content)
  
              # The protoevent received over the JSON wire may not have all
              # the required fields. Lets just gloss over that because
              # there's some we never care about
              if "prev_state" not in pdu_dict:
                  pdu_dict["prev_state"] = []
  
              ev = builder.create_local_event_from_event_dict(
                  self._clock,
                  self.hostname,
                  self.signing_key,
                  room_version=room_version,
                  event_dict=pdu_dict,
              )
  
              return destination, ev, room_version
  
          # MSC3083 defines additional error codes for room joins. Unfortunately
          # we do not yet know the room version, assume these will only be returned
          # by valid room versions.
          failover_errcodes = (
              (Codes.UNABLE_AUTHORISE_JOIN, Codes.UNABLE_TO_GRANT_JOIN)
              if membership == Membership.JOIN
              else None
          )
  
          return await self._try_destination_list(
              "make_" + membership,
              destinations,
              send_request,
              failover_errcodes=failover_errcodes,
          )
  
      async def send_join(
          self, destinations: Iterable[str], pdu: EventBase, room_version: RoomVersion
      ) -> SendJoinResult:
          """Sends a join event to one of a list of homeservers.
  
          Doing so will cause the remote server to add the event to the graph,
          and send the event out to the rest of the federation.
  
          Args:
              destinations: Candidate homeservers which are probably
                  participating in the room.
              pdu: event to be sent
              room_version: the version of the room (according to the server that
                  did the make_join)
  
          Returns:
              The result of the send join request.
  
          Raises:
              SynapseError: if the chosen remote server returns a 300/400 code, or
                  no servers successfully handle the request.
          """
  
          async def send_request(destination) -> SendJoinResult:
              response = await self._do_send_join(room_version, destination, pdu)
  
              # If an event was returned (and expected to be returned):
              #
              # * Ensure it has the same event ID (note that the event ID is a hash
              #   of the event fields for versions which support MSC3083).
              # * Ensure the signatures are good.
              #
              # Otherwise, fallback to the provided event.
              if room_version.msc3083_join_rules and response.event:
                  event = response.event
  
                  valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
                      pdu=event,
                      origin=destination,
                      outlier=True,
                      room_version=room_version,
                  )
  
                  if valid_pdu is None or event.event_id != pdu.event_id:
                      raise InvalidResponseError("Returned an invalid join event")
              else:
                  event = pdu
  
              state = response.state
              auth_chain = response.auth_events
  
              create_event = None
              for e in state:
                  if (e.type, e.state_key) == (EventTypes.Create, ""):
                      create_event = e
                      break
  
              if create_event is None:
                  # If the state doesn't have a create event then the room is
                  # invalid, and it would fail auth checks anyway.
                  raise InvalidResponseError("No create event in state")
  
              # the room version should be sane.
              create_room_version = create_event.content.get(
                  "room_version", RoomVersions.V1.identifier
              )
              if create_room_version != room_version.identifier:
                  # either the server that fulfilled the make_join, or the server that is
                  # handling the send_join, is lying.
                  raise InvalidResponseError(
                      "Unexpected room version %s in create event"
                      % (create_room_version,)
                  )
  
              logger.info(
                  "Processing from send_join %d events", len(state) + len(auth_chain)
              )
  
              # We now go and check the signatures and hashes for the event. Note
              # that we limit how many events we process at a time to keep the
              # memory overhead from exploding.
              valid_pdus_map: Dict[str, EventBase] = {}
  
              async def _execute(pdu: EventBase) -> None:
                  valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
                      pdu=pdu,
                      origin=destination,
                      outlier=True,
                      room_version=room_version,
                  )
  
                  if valid_pdu:
                      valid_pdus_map[valid_pdu.event_id] = valid_pdu
  
              await concurrently_execute(
                  _execute, itertools.chain(state, auth_chain), 10000
              )
  
              # NB: We *need* to copy to ensure that we don't have multiple
              # references being passed on, as that causes... issues.
              signed_state = [
                  copy.copy(valid_pdus_map[p.event_id])
                  for p in state
                  if p.event_id in valid_pdus_map
              ]
  
              signed_auth = [
                  valid_pdus_map[p.event_id]
                  for p in auth_chain
                  if p.event_id in valid_pdus_map
              ]
  
              # NB: We *need* to copy to ensure that we don't have multiple
              # references being passed on, as that causes... issues.
              for s in signed_state:
                  s.internal_metadata = copy.deepcopy(s.internal_metadata)
  
              # double-check that the same create event has ended up in the auth chain
              auth_chain_create_events = [
                  e.event_id
                  for e in signed_auth
                  if (e.type, e.state_key) == (EventTypes.Create, "")
              ]
              if auth_chain_create_events != [create_event.event_id]:
                  raise InvalidResponseError(
                      "Unexpected create event(s) in auth chain: %s"
                      % (auth_chain_create_events,)
                  )
  
              return SendJoinResult(
                  event=event,
                  state=signed_state,
                  auth_chain=signed_auth,
                  origin=destination,
              )
  
          # MSC3083 defines additional error codes for room joins.
          failover_errcodes = None
          if room_version.msc3083_join_rules:
              failover_errcodes = (
                  Codes.UNABLE_AUTHORISE_JOIN,
                  Codes.UNABLE_TO_GRANT_JOIN,
              )
  
              # If the join is being authorised via allow rules, we need to send
              # the /send_join back to the same server that was originally used
              # with /make_join.
              if "join_authorised_via_users_server" in pdu.content:
                  destinations = [
                      get_domain_from_id(pdu.content["join_authorised_via_users_server"])
                  ]
  
          return await self._try_destination_list(
              "send_join", destinations, send_request, failover_errcodes=failover_errcodes
          )
  
      async def _do_send_join(
          self, room_version: RoomVersion, destination: str, pdu: EventBase
      ) -> SendJoinResponse:
          time_now = self._clock.time_msec()
  
          try:
              return await self.transport_layer.send_join_v2(
                  room_version=room_version,
                  destination=destination,
                  room_id=pdu.room_id,
                  event_id=pdu.event_id,
                  content=pdu.get_pdu_json(time_now),
              )
          except HttpResponseException as e:
              # If an error is received that is due to an unrecognised endpoint,
              # fallback to the v1 endpoint. Otherwise consider it a legitmate error
              # and raise.
              if not self._is_unknown_endpoint(e):
                  raise
  
          logger.debug("Couldn't send_join with the v2 API, falling back to the v1 API")
  
          return await self.transport_layer.send_join_v1(
              room_version=room_version,
              destination=destination,
              room_id=pdu.room_id,
              event_id=pdu.event_id,
              content=pdu.get_pdu_json(time_now),
          )
  
      async def send_invite(
          self,
          destination: str,
          room_id: str,
          event_id: str,
          pdu: EventBase,
      ) -> EventBase:
          room_version = await self.store.get_room_version(room_id)
  
          content = await self._do_send_invite(destination, pdu, room_version)
  
          pdu_dict = content["event"]
  
          logger.debug("Got response to send_invite: %s", pdu_dict)
  
          pdu = event_from_pdu_json(pdu_dict, room_version)
  
          # Check signatures are correct.
          pdu = await self._check_sigs_and_hash(room_version, pdu)
  
          # FIXME: We should handle signature failures more gracefully.
  
          return pdu
  
      async def _do_send_invite(
          self, destination: str, pdu: EventBase, room_version: RoomVersion
      ) -> JsonDict:
          """Actually sends the invite, first trying v2 API and falling back to
          v1 API if necessary.
  
          Returns:
              The event as a dict as returned by the remote server
  
          Raises:
              SynapseError: if the remote server returns an error or if the server
                  only supports the v1 endpoint and a room version other than "1"
                  or "2" is requested.
          """
          time_now = self._clock.time_msec()
  
          try:
              return await self.transport_layer.send_invite_v2(
                  destination=destination,
                  room_id=pdu.room_id,
                  event_id=pdu.event_id,
                  content={
                      "event": pdu.get_pdu_json(time_now),
                      "room_version": room_version.identifier,
                      "invite_room_state": pdu.unsigned.get("invite_room_state", []),
                  },
              )
          except HttpResponseException as e:
              # If an error is received that is due to an unrecognised endpoint,
              # fallback to the v1 endpoint if the room uses old-style event IDs.
              # Otherwise consider it a legitmate error and raise.
              err = e.to_synapse_error()
              if self._is_unknown_endpoint(e, err):
                  if room_version.event_format != EventFormatVersions.V1:
                      raise SynapseError(
                          400,
                          "User's homeserver does not support this room version",
                          Codes.UNSUPPORTED_ROOM_VERSION,
                      )
              else:
                  raise err
  
          # Didn't work, try v1 API.
          # Note the v1 API returns a tuple of `(200, content)`
  
          _, content = await self.transport_layer.send_invite_v1(
              destination=destination,
              room_id=pdu.room_id,
              event_id=pdu.event_id,
              content=pdu.get_pdu_json(time_now),
          )
          return content
  
      async def send_leave(self, destinations: Iterable[str], pdu: EventBase) -> None:
          """Sends a leave event to one of a list of homeservers.
  
          Doing so will cause the remote server to add the event to the graph,
          and send the event out to the rest of the federation.
  
          This is mostly useful to reject received invites.
  
          Args:
              destinations: Candidate homeservers which are probably
                  participating in the room.
              pdu: event to be sent
  
          Raises:
              SynapseError: if the chosen remote server returns a 300/400 code, or
                  no servers successfully handle the request.
          """
  
          async def send_request(destination: str) -> None:
              content = await self._do_send_leave(destination, pdu)
              logger.debug("Got content: %s", content)
  
          return await self._try_destination_list(
              "send_leave", destinations, send_request
          )
  
      async def _do_send_leave(self, destination: str, pdu: EventBase) -> JsonDict:
          time_now = self._clock.time_msec()
  
          try:
              return await self.transport_layer.send_leave_v2(
                  destination=destination,
                  room_id=pdu.room_id,
                  event_id=pdu.event_id,
                  content=pdu.get_pdu_json(time_now),
              )
          except HttpResponseException as e:
              # If an error is received that is due to an unrecognised endpoint,
              # fallback to the v1 endpoint. Otherwise consider it a legitmate error
              # and raise.
              if not self._is_unknown_endpoint(e):
                  raise
  
          logger.debug("Couldn't send_leave with the v2 API, falling back to the v1 API")
  
          resp = await self.transport_layer.send_leave_v1(
              destination=destination,
              room_id=pdu.room_id,
              event_id=pdu.event_id,
              content=pdu.get_pdu_json(time_now),
          )
  
          # We expect the v1 API to respond with [200, content], so we only return the
          # content.
          return resp[1]
  
      async def send_knock(self, destinations: List[str], pdu: EventBase) -> JsonDict:
          """Attempts to send a knock event to given a list of servers. Iterates
          through the list until one attempt succeeds.
  
          Doing so will cause the remote server to add the event to the graph,
          and send the event out to the rest of the federation.
  
          Args:
              destinations: A list of candidate homeservers which are likely to be
                  participating in the room.
              pdu: The event to be sent.
  
          Returns:
              The remote homeserver return some state from the room. The response
              dictionary is in the form:
  
              {"knock_state_events": [<state event dict>, ...]}
  
              The list of state events may be empty.
  
          Raises:
              SynapseError: If the chosen remote server returns a 3xx/4xx code.
              RuntimeError: If no servers were reachable.
          """
  
          async def send_request(destination: str) -> JsonDict:
              return await self._do_send_knock(destination, pdu)
  
          return await self._try_destination_list(
              "send_knock", destinations, send_request
          )
  
      async def _do_send_knock(self, destination: str, pdu: EventBase) -> JsonDict:
          """Send a knock event to a remote homeserver.
  
          Args:
              destination: The homeserver to send to.
              pdu: The event to send.
  
          Returns:
              The remote homeserver can optionally return some state from the room. The response
              dictionary is in the form:
  
              {"knock_state_events": [<state event dict>, ...]}
  
              The list of state events may be empty.
          """
          time_now = self._clock.time_msec()
  
          return await self.transport_layer.send_knock_v1(
              destination=destination,
              room_id=pdu.room_id,
              event_id=pdu.event_id,
              content=pdu.get_pdu_json(time_now),
          )
  
      async def get_public_rooms(
          self,
          remote_server: str,
          limit: Optional[int] = None,
          since_token: Optional[str] = None,
          search_filter: Optional[Dict] = None,
          include_all_networks: bool = False,
          third_party_instance_id: Optional[str] = None,
      ) -> JsonDict:
          """Get the list of public rooms from a remote homeserver
  
          Args:
              remote_server: The name of the remote server
              limit: Maximum amount of rooms to return
              since_token: Used for result pagination
              search_filter: A filter dictionary to send the remote homeserver
                  and filter the result set
              include_all_networks: Whether to include results from all third party instances
              third_party_instance_id: Whether to only include results from a specific third
                  party instance
  
          Returns:
              The response from the remote server.
  
          Raises:
              HttpResponseException / RequestSendFailed: There was an exception
                  returned from the remote server
              SynapseException: M_FORBIDDEN when the remote server has disallowed publicRoom
                  requests over federation
  
          """
          return await self.transport_layer.get_public_rooms(
              remote_server,
              limit,
              since_token,
              search_filter,
              include_all_networks=include_all_networks,
              third_party_instance_id=third_party_instance_id,
          )
  
      async def get_missing_events(
          self,
          destination: str,
          room_id: str,
          earliest_events_ids: Iterable[str],
          latest_events: Iterable[EventBase],
          limit: int,
          min_depth: int,
          timeout: int,
      ) -> List[EventBase]:
          """Tries to fetch events we are missing. This is called when we receive
          an event without having received all of its ancestors.
  
          Args:
              destination
              room_id
              earliest_events_ids: List of event ids. Effectively the
                  events we expected to receive, but haven't. `get_missing_events`
                  should only return events that didn't happen before these.
              latest_events: List of events we have received that we don't
                  have all previous events for.
              limit: Maximum number of events to return.
              min_depth: Minimum depth of events to return.
              timeout: Max time to wait in ms
          """
          try:
              content = await self.transport_layer.get_missing_events(
                  destination=destination,
                  room_id=room_id,
                  earliest_events=earliest_events_ids,
                  latest_events=[e.event_id for e in latest_events],
                  limit=limit,
                  min_depth=min_depth,
                  timeout=timeout,
              )
  
              room_version = await self.store.get_room_version(room_id)
  
              events = [
                  event_from_pdu_json(e, room_version) for e in content.get("events", [])
              ]
  
              signed_events = await self._check_sigs_and_hash_and_fetch(
                  destination, events, outlier=False, room_version=room_version
              )
          except HttpResponseException as e:
              if not e.code == 400:
                  raise
  
              # We are probably hitting an old server that doesn't support
              # get_missing_events
              signed_events = []
  
          return signed_events
  
      async def forward_third_party_invite(
          self, destinations: Iterable[str], room_id: str, event_dict: JsonDict
      ) -> None:
          for destination in destinations:
              if destination == self.server_name:
                  continue
  
              try:
                  await self.transport_layer.exchange_third_party_invite(
                      destination=destination, room_id=room_id, event_dict=event_dict
                  )
                  return
              except CodeMessageException:
                  raise
              except Exception as e:
                  logger.exception(
                      "Failed to send_third_party_invite via %s: %s", destination, str(e)
                  )
  
          raise RuntimeError("Failed to send to any server.")
  
      async def get_room_complexity(
          self, destination: str, room_id: str
      ) -> Optional[JsonDict]:
          """
          Fetch the complexity of a remote room from another server.
  
          Args:
              destination: The remote server
              room_id: The room ID to ask about.
  
          Returns:
              Dict contains the complexity metric versions, while None means we
              could not fetch the complexity.
          """
          try:
              return await self.transport_layer.get_room_complexity(
                  destination=destination, room_id=room_id
              )
          except CodeMessageException as e:
              # We didn't manage to get it -- probably a 404. We are okay if other
              # servers don't give it to us.
              logger.debug(
                  "Failed to fetch room complexity via %s for %s, got a %d",
                  destination,
                  room_id,
                  e.code,
              )
          except Exception:
              logger.exception(
                  "Failed to fetch room complexity via %s for %s", destination, room_id
              )
  
          # If we don't manage to find it, return None. It's not an error if a
          # server doesn't give it to us.
          return None
  
      async def get_space_summary(
          self,
          destinations: Iterable[str],
          room_id: str,
          suggested_only: bool,
          max_rooms_per_space: Optional[int],
          exclude_rooms: List[str],
      ) -> "FederationSpaceSummaryResult":
          """
          Call other servers to get a summary of the given space
  
  
          Args:
              destinations: The remote servers. We will try them in turn, omitting any
                  that have been blacklisted.
  
              room_id: ID of the space to be queried
  
              suggested_only:  If true, ask the remote server to only return children
                  with the "suggested" flag set
  
              max_rooms_per_space: A limit on the number of children to return for each
                  space
  
              exclude_rooms: A list of room IDs to tell the remote server to skip
  
          Returns:
              a parsed FederationSpaceSummaryResult
  
          Raises:
              SynapseError if we were unable to get a valid summary from any of the
                 remote servers
          """
  
          async def send_request(destination: str) -> FederationSpaceSummaryResult:
              res = await self.transport_layer.get_space_summary(
                  destination=destination,
                  room_id=room_id,
                  suggested_only=suggested_only,
                  max_rooms_per_space=max_rooms_per_space,
                  exclude_rooms=exclude_rooms,
              )
  
              try:
                  return FederationSpaceSummaryResult.from_json_dict(res)
              except ValueError as e:
                  raise InvalidResponseError(str(e))
  
          return await self._try_destination_list(
              "fetch space summary",
              destinations,
              send_request,
              failover_on_unknown_endpoint=True,
          )
  
  
  @attr.s(frozen=True, slots=True, auto_attribs=True)
  class FederationSpaceSummaryEventResult:
      """Represents a single event in the result of a successful get_space_summary call.
  
      It's essentially just a serialised event object, but we do a bit of parsing and
      validation in `from_json_dict` and store some of the validated properties in
      object attributes.
      """
  
      event_type: str
      room_id: str
      state_key: str
      via: Sequence[str]
  
      # the raw data, including the above keys
      data: JsonDict
  
      @classmethod
      def from_json_dict(cls, d: JsonDict) -> "FederationSpaceSummaryEventResult":
          """Parse an event within the result of a /spaces/ request
  
          Args:
              d: json object to be parsed
  
          Raises:
              ValueError if d is not a valid event
          """
  
          event_type = d.get("type")
          if not isinstance(event_type, str):
              raise ValueError("Invalid event: 'event_type' must be a str")
  
          room_id = d.get("room_id")
          if not isinstance(room_id, str):
              raise ValueError("Invalid event: 'room_id' must be a str")
  
          state_key = d.get("state_key")
          if not isinstance(state_key, str):
              raise ValueError("Invalid event: 'state_key' must be a str")
  
          content = d.get("content")
          if not isinstance(content, dict):
              raise ValueError("Invalid event: 'content' must be a dict")
  
          via = content.get("via")
          if not isinstance(via, Sequence):
              raise ValueError("Invalid event: 'via' must be a list")
          if any(not isinstance(v, str) for v in via):
              raise ValueError("Invalid event: 'via' must be a list of strings")
  
          return cls(event_type, room_id, state_key, via, d)
  
  
  @attr.s(frozen=True, slots=True, auto_attribs=True)
  class FederationSpaceSummaryResult:
      """Represents the data returned by a successful get_space_summary call."""
  
      rooms: Sequence[JsonDict]
      events: Sequence[FederationSpaceSummaryEventResult]
  
      @classmethod
      def from_json_dict(cls, d: JsonDict) -> "FederationSpaceSummaryResult":
          """Parse the result of a /spaces/ request
  
          Args:
              d: json object to be parsed
  
          Raises:
              ValueError if d is not a valid /spaces/ response
          """
          rooms = d.get("rooms")
          if not isinstance(rooms, Sequence):
              raise ValueError("'rooms' must be a list")
          if any(not isinstance(r, dict) for r in rooms):
              raise ValueError("Invalid room in 'rooms' list")
  
          events = d.get("events")
          if not isinstance(events, Sequence):
              raise ValueError("'events' must be a list")
          if any(not isinstance(e, dict) for e in events):
              raise ValueError("Invalid event in 'events' list")
          parsed_events = [
              FederationSpaceSummaryEventResult.from_json_dict(e) for e in events
          ]
  
          return cls(rooms, parsed_events)
  