synapse-product/synapse/federation/federation_server.py

# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2018 New Vector Ltd
# Copyright 2019 Matrix.org Federation C.I.C
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
import random
from typing import (
    TYPE_CHECKING,
    Any,
    Awaitable,
    Callable,
    Dict,
    Iterable,
    List,
    Optional,
    Tuple,
    Union,
)

from prometheus_client import Counter, Gauge, Histogram

from twisted.internet import defer
from twisted.internet.abstract import isIPAddress
from twisted.python import failure

from synapse.api.constants import EduTypes, EventTypes
from synapse.api.errors import (
    AuthError,
    Codes,
    FederationError,
    IncompatibleRoomVersionError,
    NotFoundError,
    SynapseError,
    UnsupportedRoomVersionError,
)
from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
from synapse.events import EventBase
from synapse.federation.federation_base import FederationBase, event_from_pdu_json
from synapse.federation.persistence import TransactionActions
from synapse.federation.units import Edu, Transaction
from synapse.http.servlet import assert_params_in_dict
from synapse.logging.context import (
    make_deferred_yieldable,
    nested_logging_context,
    run_in_background,
)
from synapse.logging.opentracing import log_kv, start_active_span_from_edu, trace
from synapse.logging.utils import log_function
from synapse.replication.http.federation import (
    ReplicationFederationSendEduRestServlet,
    ReplicationGetQueryRestServlet,
)
from synapse.types import JsonDict
from synapse.util import glob_to_regex, json_decoder, unwrapFirstError
from synapse.util.async_helpers import Linearizer, concurrently_execute
from synapse.util.caches.response_cache import ResponseCache
from synapse.util.stringutils import parse_server_name

if TYPE_CHECKING:
    from synapse.server import HomeServer

# when processing incoming transactions, we try to handle multiple rooms in
# parallel, up to this limit.
TRANSACTION_CONCURRENCY_LIMIT = 10

logger = logging.getLogger(__name__)

received_pdus_counter = Counter("synapse_federation_server_received_pdus", "")

received_edus_counter = Counter("synapse_federation_server_received_edus", "")

received_queries_counter = Counter(
    "synapse_federation_server_received_queries", "", ["type"]
)

pdu_process_time = Histogram(
    "synapse_federation_server_pdu_process_time",
    "Time taken to process an event",
)

last_pdu_ts_metric = Gauge(
    "synapse_federation_last_received_pdu_time",
    "The timestamp of the last PDU which was successfully received from the given domain",
    labelnames=("server_name",),
)


class FederationServer(FederationBase):
    def __init__(self, hs: "HomeServer"):
        super().__init__(hs)

        self.auth = hs.get_auth()
        self.handler = hs.get_federation_handler()
        self.state = hs.get_state_handler()

        self.device_handler = hs.get_device_handler()

        # Ensure the following handlers are loaded since they register callbacks
        # with FederationHandlerRegistry.
        hs.get_directory_handler()

        self._server_linearizer = Linearizer("fed_server")

        # origins that we are currently processing a transaction from.
        # a dict from origin to txn id.
        self._active_transactions = {}  # type: Dict[str, str]

        # We cache results for transaction with the same ID
        self._transaction_resp_cache = ResponseCache(
            hs.get_clock(), "fed_txn_handler", timeout_ms=30000
        )  # type: ResponseCache[Tuple[str, str]]

        self.transaction_actions = TransactionActions(self.store)

        self.registry = hs.get_federation_registry()

        # We cache responses to state queries, as they take a while and often
        # come in waves.
        self._state_resp_cache = ResponseCache(
            hs.get_clock(), "state_resp", timeout_ms=30000
        )  # type: ResponseCache[Tuple[str, Optional[str]]]
        self._state_ids_resp_cache = ResponseCache(
            hs.get_clock(), "state_ids_resp", timeout_ms=30000
        )  # type: ResponseCache[Tuple[str, str]]

        self._federation_metrics_domains = (
            hs.config.federation.federation_metrics_domains
        )

        self._room_prejoin_state_types = hs.config.api.room_prejoin_state

    async def on_backfill_request(
        self, origin: str, room_id: str, versions: List[str], limit: int
    ) -> Tuple[int, Dict[str, Any]]:
        with (await self._server_linearizer.queue((origin, room_id))):
            origin_host, _ = parse_server_name(origin)
            await self.check_server_matches_acl(origin_host, room_id)

            pdus = await self.handler.on_backfill_request(
                origin, room_id, versions, limit
            )

            res = self._transaction_from_pdus(pdus).get_dict()

        return 200, res

    async def on_incoming_transaction(
        self, origin: str, transaction_data: JsonDict
    ) -> Tuple[int, Dict[str, Any]]:
        # keep this as early as possible to make the calculated origin ts as
        # accurate as possible.
        request_time = self._clock.time_msec()

        transaction = Transaction(**transaction_data)
        transaction_id = transaction.transaction_id  # type: ignore

        if not transaction_id:
            raise Exception("Transaction missing transaction_id")

        logger.debug("[%s] Got transaction", transaction_id)

        # Reject malformed transactions early: reject if too many PDUs/EDUs
        if len(transaction.pdus) > 50 or (  # type: ignore
            hasattr(transaction, "edus") and len(transaction.edus) > 100  # type: ignore
        ):
            logger.info("Transaction PDU or EDU count too large. Returning 400")
            return 400, {}

        # we only process one transaction from each origin at a time. We need to do
        # this check here, rather than in _on_incoming_transaction_inner so that we
        # don't cache the rejection in _transaction_resp_cache (so that if the txn
        # arrives again later, we can process it).
        current_transaction = self._active_transactions.get(origin)
        if current_transaction and current_transaction != transaction_id:
            logger.warning(
                "Received another txn %s from %s while still processing %s",
                transaction_id,
                origin,
                current_transaction,
            )
            return 429, {
                "errcode": Codes.UNKNOWN,
                "error": "Too many concurrent transactions",
            }

        # CRITICAL SECTION: we must now not await until we populate _active_transactions
        # in _on_incoming_transaction_inner.

        # We wrap in a ResponseCache so that we de-duplicate retried
        # transactions.
        return await self._transaction_resp_cache.wrap(
            (origin, transaction_id),
            self._on_incoming_transaction_inner,
            origin,
            transaction,
            request_time,
        )

    async def _on_incoming_transaction_inner(
        self, origin: str, transaction: Transaction, request_time: int
    ) -> Tuple[int, Dict[str, Any]]:
        # CRITICAL SECTION: the first thing we must do (before awaiting) is
        # add an entry to _active_transactions.
        assert origin not in self._active_transactions
        self._active_transactions[origin] = transaction.transaction_id  # type: ignore

        try:
            result = await self._handle_incoming_transaction(
                origin, transaction, request_time
            )
            return result
        finally:
            del self._active_transactions[origin]

    async def _handle_incoming_transaction(
        self, origin: str, transaction: Transaction, request_time: int
    ) -> Tuple[int, Dict[str, Any]]:
        """Process an incoming transaction and return the HTTP response

        Args:
            origin: the server making the request
            transaction: incoming transaction
            request_time: timestamp that the HTTP request arrived at

        Returns:
            HTTP response code and body
        """
        response = await self.transaction_actions.have_responded(origin, transaction)

        if response:
            logger.debug(
                "[%s] We've already responded to this request",
                transaction.transaction_id,  # type: ignore
            )
            return response

        logger.debug("[%s] Transaction is new", transaction.transaction_id)  # type: ignore

        # We process PDUs and EDUs in parallel. This is important as we don't
        # want to block things like to device messages from reaching clients
        # behind the potentially expensive handling of PDUs.
        pdu_results, _ = await make_deferred_yieldable(
            defer.gatherResults(
                [
                    run_in_background(
                        self._handle_pdus_in_txn, origin, transaction, request_time
                    ),
                    run_in_background(self._handle_edus_in_txn, origin, transaction),
                ],
                consumeErrors=True,
            ).addErrback(unwrapFirstError)
        )

        response = {"pdus": pdu_results}

        logger.debug("Returning: %s", str(response))

        await self.transaction_actions.set_response(origin, transaction, 200, response)
        return 200, response

    async def _handle_pdus_in_txn(
        self, origin: str, transaction: Transaction, request_time: int
    ) -> Dict[str, dict]:
        """Process the PDUs in a received transaction.

        Args:
            origin: the server making the request
            transaction: incoming transaction
            request_time: timestamp that the HTTP request arrived at

        Returns:
            A map from event ID of a processed PDU to any errors we should
            report back to the sending server.
        """

        received_pdus_counter.inc(len(transaction.pdus))  # type: ignore

        origin_host, _ = parse_server_name(origin)

        pdus_by_room = {}  # type: Dict[str, List[EventBase]]

        newest_pdu_ts = 0

        for p in transaction.pdus:  # type: ignore
            # FIXME (richardv): I don't think this works:
            #  https://github.com/matrix-org/synapse/issues/8429
            if "unsigned" in p:
                unsigned = p["unsigned"]
                if "age" in unsigned:
                    p["age"] = unsigned["age"]
            if "age" in p:
                p["age_ts"] = request_time - int(p["age"])
                del p["age"]

            # We try and pull out an event ID so that if later checks fail we
            # can log something sensible. We don't mandate an event ID here in
            # case future event formats get rid of the key.
            possible_event_id = p.get("event_id", "<Unknown>")

            # Now we get the room ID so that we can check that we know the
            # version of the room.
            room_id = p.get("room_id")
            if not room_id:
                logger.info(
                    "Ignoring PDU as does not have a room_id. Event ID: %s",
                    possible_event_id,
                )
                continue

            try:
                room_version = await self.store.get_room_version(room_id)
            except NotFoundError:
                logger.info("Ignoring PDU for unknown room_id: %s", room_id)
                continue
            except UnsupportedRoomVersionError as e:
                # this can happen if support for a given room version is withdrawn,
                # so that we still get events for said room.
                logger.info("Ignoring PDU: %s", e)
                continue

            event = event_from_pdu_json(p, room_version)
            pdus_by_room.setdefault(room_id, []).append(event)

            if event.origin_server_ts > newest_pdu_ts:
                newest_pdu_ts = event.origin_server_ts

        pdu_results = {}

        # we can process different rooms in parallel (which is useful if they
        # require callouts to other servers to fetch missing events), but
        # impose a limit to avoid going too crazy with ram/cpu.

        async def process_pdus_for_room(room_id: str):
            with nested_logging_context(room_id):
                logger.debug("Processing PDUs for %s", room_id)

                try:
                    await self.check_server_matches_acl(origin_host, room_id)
                except AuthError as e:
                    logger.warning(
                        "Ignoring PDUs for room %s from banned server", room_id
                    )
                    for pdu in pdus_by_room[room_id]:
                        event_id = pdu.event_id
                        pdu_results[event_id] = e.error_dict()
                    return

                for pdu in pdus_by_room[room_id]:
                    pdu_results[pdu.event_id] = await process_pdu(pdu)

        async def process_pdu(pdu: EventBase) -> JsonDict:
            event_id = pdu.event_id
            with pdu_process_time.time():
                with nested_logging_context(event_id):
                    try:
                        await self._handle_received_pdu(origin, pdu)
                        return {}
                    except FederationError as e:
                        logger.warning("Error handling PDU %s: %s", event_id, e)
                        return {"error": str(e)}
                    except Exception as e:
                        f = failure.Failure()
                        logger.error(
                            "Failed to handle PDU %s",
                            event_id,
                            exc_info=(f.type, f.value, f.getTracebackObject()),  # type: ignore
                        )
                        return {"error": str(e)}

        await concurrently_execute(
            process_pdus_for_room, pdus_by_room.keys(), TRANSACTION_CONCURRENCY_LIMIT
        )

        if newest_pdu_ts and origin in self._federation_metrics_domains:
            last_pdu_ts_metric.labels(server_name=origin).set(newest_pdu_ts / 1000)

        return pdu_results

    async def _handle_edus_in_txn(self, origin: str, transaction: Transaction):
        """Process the EDUs in a received transaction."""

        async def _process_edu(edu_dict):
            received_edus_counter.inc()

            edu = Edu(
                origin=origin,
                destination=self.server_name,
                edu_type=edu_dict["edu_type"],
                content=edu_dict["content"],
            )
            await self.registry.on_edu(edu.edu_type, origin, edu.content)

        await concurrently_execute(
            _process_edu,
            getattr(transaction, "edus", []),
            TRANSACTION_CONCURRENCY_LIMIT,
        )

    async def on_room_state_request(
        self, origin: str, room_id: str, event_id: Optional[str]
    ) -> Tuple[int, Dict[str, Any]]:
        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, room_id)

        in_room = await self.auth.check_host_in_room(room_id, origin)
        if not in_room:
            raise AuthError(403, "Host not in room.")

        # we grab the linearizer to protect ourselves from servers which hammer
        # us. In theory we might already have the response to this query
        # in the cache so we could return it without waiting for the linearizer
        # - but that's non-trivial to get right, and anyway somewhat defeats
        # the point of the linearizer.
        with (await self._server_linearizer.queue((origin, room_id))):
            resp = dict(
                await self._state_resp_cache.wrap(
                    (room_id, event_id),
                    self._on_context_state_request_compute,
                    room_id,
                    event_id,
                )
            )

        room_version = await self.store.get_room_version_id(room_id)
        resp["room_version"] = room_version

        return 200, resp

    async def on_state_ids_request(
        self, origin: str, room_id: str, event_id: str
    ) -> Tuple[int, Dict[str, Any]]:
        if not event_id:
            raise NotImplementedError("Specify an event")

        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, room_id)

        in_room = await self.auth.check_host_in_room(room_id, origin)
        if not in_room:
            raise AuthError(403, "Host not in room.")

        resp = await self._state_ids_resp_cache.wrap(
            (room_id, event_id),
            self._on_state_ids_request_compute,
            room_id,
            event_id,
        )

        return 200, resp

    async def _on_state_ids_request_compute(self, room_id, event_id):
        state_ids = await self.handler.get_state_ids_for_pdu(room_id, event_id)
        auth_chain_ids = await self.store.get_auth_chain_ids(room_id, state_ids)
        return {"pdu_ids": state_ids, "auth_chain_ids": auth_chain_ids}

    async def _on_context_state_request_compute(
        self, room_id: str, event_id: Optional[str]
    ) -> Dict[str, list]:
        if event_id:
            pdus = await self.handler.get_state_for_pdu(
                room_id, event_id
            )  # type: Iterable[EventBase]
        else:
            pdus = (await self.state.get_current_state(room_id)).values()

        auth_chain = await self.store.get_auth_chain(
            room_id, [pdu.event_id for pdu in pdus]
        )

        return {
            "pdus": [pdu.get_pdu_json() for pdu in pdus],
            "auth_chain": [pdu.get_pdu_json() for pdu in auth_chain],
        }

    async def on_pdu_request(
        self, origin: str, event_id: str
    ) -> Tuple[int, Union[JsonDict, str]]:
        pdu = await self.handler.get_persisted_pdu(origin, event_id)

        if pdu:
            return 200, self._transaction_from_pdus([pdu]).get_dict()
        else:
            return 404, ""

    async def on_query_request(
        self, query_type: str, args: Dict[str, str]
    ) -> Tuple[int, Dict[str, Any]]:
        received_queries_counter.labels(query_type).inc()
        resp = await self.registry.on_query(query_type, args)
        return 200, resp

    async def on_make_join_request(
        self, origin: str, room_id: str, user_id: str, supported_versions: List[str]
    ) -> Dict[str, Any]:
        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, room_id)

        room_version = await self.store.get_room_version_id(room_id)
        if room_version not in supported_versions:
            logger.warning(
                "Room version %s not in %s", room_version, supported_versions
            )
            raise IncompatibleRoomVersionError(room_version=room_version)

        pdu = await self.handler.on_make_join_request(origin, room_id, user_id)
        time_now = self._clock.time_msec()
        return {"event": pdu.get_pdu_json(time_now), "room_version": room_version}

    async def on_invite_request(
        self, origin: str, content: JsonDict, room_version_id: str
    ) -> Dict[str, Any]:
        room_version = KNOWN_ROOM_VERSIONS.get(room_version_id)
        if not room_version:
            raise SynapseError(
                400,
                "Homeserver does not support this room version",
                Codes.UNSUPPORTED_ROOM_VERSION,
            )

        pdu = event_from_pdu_json(content, room_version)
        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, pdu.room_id)
        pdu = await self._check_sigs_and_hash(room_version, pdu)
        ret_pdu = await self.handler.on_invite_request(origin, pdu, room_version)
        time_now = self._clock.time_msec()
        return {"event": ret_pdu.get_pdu_json(time_now)}

    async def on_send_join_request(
        self, origin: str, content: JsonDict
    ) -> Dict[str, Any]:
        logger.debug("on_send_join_request: content: %s", content)

        assert_params_in_dict(content, ["room_id"])
        room_version = await self.store.get_room_version(content["room_id"])
        pdu = event_from_pdu_json(content, room_version)

        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, pdu.room_id)

        logger.debug("on_send_join_request: pdu sigs: %s", pdu.signatures)

        pdu = await self._check_sigs_and_hash(room_version, pdu)

        res_pdus = await self.handler.on_send_join_request(origin, pdu)
        time_now = self._clock.time_msec()
        return {
            "state": [p.get_pdu_json(time_now) for p in res_pdus["state"]],
            "auth_chain": [p.get_pdu_json(time_now) for p in res_pdus["auth_chain"]],
        }

    async def on_make_leave_request(
        self, origin: str, room_id: str, user_id: str
    ) -> Dict[str, Any]:
        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, room_id)
        pdu = await self.handler.on_make_leave_request(origin, room_id, user_id)

        room_version = await self.store.get_room_version_id(room_id)

        time_now = self._clock.time_msec()
        return {"event": pdu.get_pdu_json(time_now), "room_version": room_version}

    async def on_send_leave_request(self, origin: str, content: JsonDict) -> dict:
        logger.debug("on_send_leave_request: content: %s", content)

        assert_params_in_dict(content, ["room_id"])
        room_version = await self.store.get_room_version(content["room_id"])
        pdu = event_from_pdu_json(content, room_version)

        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, pdu.room_id)

        logger.debug("on_send_leave_request: pdu sigs: %s", pdu.signatures)

        pdu = await self._check_sigs_and_hash(room_version, pdu)

        await self.handler.on_send_leave_request(origin, pdu)
        return {}

    async def on_make_knock_request(
        self, origin: str, room_id: str, user_id: str, supported_versions: List[str]
    ) -> Dict[str, Union[EventBase, str]]:
        """We've received a /make_knock/ request, so we create a partial knock
        event for the room and hand that back, along with the room version, to the knocking
        homeserver. We do *not* persist or process this event until the other server has
        signed it and sent it back.

        Args:
            origin: The (verified) server name of the requesting server.
            room_id: The room to create the knock event in.
            user_id: The user to create the knock for.
            supported_versions: The room versions supported by the requesting server.

        Returns:
            The partial knock event.
        """
        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, room_id)

        room_version = await self.store.get_room_version(room_id)

        # Check that this room version is supported by the remote homeserver
        if room_version.identifier not in supported_versions:
            logger.warning(
                "Room version %s not in %s", room_version.identifier, supported_versions
            )
            raise IncompatibleRoomVersionError(room_version=room_version.identifier)

        # Check that this room supports knocking as defined by its room version
        if not room_version.msc2403_knocking:
            raise SynapseError(
                403,
                "This room version does not support knocking",
                errcode=Codes.FORBIDDEN,
            )

        pdu = await self.handler.on_make_knock_request(origin, room_id, user_id)
        time_now = self._clock.time_msec()
        return {
            "event": pdu.get_pdu_json(time_now),
            "room_version": room_version.identifier,
        }

    async def on_send_knock_request(
        self,
        origin: str,
        content: JsonDict,
        room_id: str,
    ) -> Dict[str, List[JsonDict]]:
        """
        We have received a knock event for a room. Verify and send the event into the room
        on the knocking homeserver's behalf. Then reply with some stripped state from the
        room for the knockee.

        Args:
            origin: The remote homeserver of the knocking user.
            content: The content of the request.
            room_id: The ID of the room to knock on.

        Returns:
            The stripped room state.
        """
        logger.debug("on_send_knock_request: content: %s", content)

        room_version = await self.store.get_room_version(room_id)

        # Check that this room supports knocking as defined by its room version
        if not room_version.msc2403_knocking:
            raise SynapseError(
                403,
                "This room version does not support knocking",
                errcode=Codes.FORBIDDEN,
            )

        pdu = event_from_pdu_json(content, room_version)

        origin_host, _ = parse_server_name(origin)
        await self.check_server_matches_acl(origin_host, pdu.room_id)

        logger.debug("on_send_knock_request: pdu sigs: %s", pdu.signatures)

        pdu = await self._check_sigs_and_hash(room_version, pdu)

        # Handle the event, and retrieve the EventContext
        event_context = await self.handler.on_send_knock_request(origin, pdu)

        # Retrieve stripped state events from the room and send them back to the remote
        # server. This will allow the remote server's clients to display information
        # related to the room while the knock request is pending.
        stripped_room_state = (
            await self.store.get_stripped_room_state_from_event_context(
                event_context, self._room_prejoin_state_types
            )
        )
        return {"knock_state_events": stripped_room_state}

    async def on_event_auth(
        self, origin: str, room_id: str, event_id: str
    ) -> Tuple[int, Dict[str, Any]]:
        with (await self._server_linearizer.queue((origin, room_id))):
            origin_host, _ = parse_server_name(origin)
            await self.check_server_matches_acl(origin_host, room_id)

            time_now = self._clock.time_msec()
            auth_pdus = await self.handler.on_event_auth(event_id)
            res = {"auth_chain": [a.get_pdu_json(time_now) for a in auth_pdus]}
        return 200, res

    @log_function
    async def on_query_client_keys(
        self, origin: str, content: Dict[str, str]
    ) -> Tuple[int, Dict[str, Any]]:
        return await self.on_query_request("client_keys", content)

    async def on_query_user_devices(
        self, origin: str, user_id: str
    ) -> Tuple[int, Dict[str, Any]]:
        keys = await self.device_handler.on_federation_query_user_devices(user_id)
        return 200, keys

    @trace
    async def on_claim_client_keys(
        self, origin: str, content: JsonDict
    ) -> Dict[str, Any]:
        query = []
        for user_id, device_keys in content.get("one_time_keys", {}).items():
            for device_id, algorithm in device_keys.items():
                query.append((user_id, device_id, algorithm))

        log_kv({"message": "Claiming one time keys.", "user, device pairs": query})
        results = await self.store.claim_e2e_one_time_keys(query)

        json_result = {}  # type: Dict[str, Dict[str, dict]]
        for user_id, device_keys in results.items():
            for device_id, keys in device_keys.items():
                for key_id, json_str in keys.items():
                    json_result.setdefault(user_id, {})[device_id] = {
                        key_id: json_decoder.decode(json_str)
                    }

        logger.info(
            "Claimed one-time-keys: %s",
            ",".join(
                (
                    "%s for %s:%s" % (key_id, user_id, device_id)
                    for user_id, user_keys in json_result.items()
                    for device_id, device_keys in user_keys.items()
                    for key_id, _ in device_keys.items()
                )
            ),
        )

        return {"one_time_keys": json_result}

    async def on_get_missing_events(
        self,
        origin: str,
        room_id: str,
        earliest_events: List[str],
        latest_events: List[str],
        limit: int,
    ) -> Dict[str, list]:
        with (await self._server_linearizer.queue((origin, room_id))):
            origin_host, _ = parse_server_name(origin)
            await self.check_server_matches_acl(origin_host, room_id)

            logger.debug(
                "on_get_missing_events: earliest_events: %r, latest_events: %r,"
                " limit: %d",
                earliest_events,
                latest_events,
                limit,
            )

            missing_events = await self.handler.on_get_missing_events(
                origin, room_id, earliest_events, latest_events, limit
            )

            if len(missing_events) < 5:
                logger.debug(
                    "Returning %d events: %r", len(missing_events), missing_events
                )
            else:
                logger.debug("Returning %d events", len(missing_events))

            time_now = self._clock.time_msec()

        return {"events": [ev.get_pdu_json(time_now) for ev in missing_events]}

    @log_function
    async def on_openid_userinfo(self, token: str) -> Optional[str]:
        ts_now_ms = self._clock.time_msec()
        return await self.store.get_user_id_for_open_id_token(token, ts_now_ms)

    def _transaction_from_pdus(self, pdu_list: List[EventBase]) -> Transaction:
        """Returns a new Transaction containing the given PDUs suitable for
        transmission.
        """
        time_now = self._clock.time_msec()
        pdus = [p.get_pdu_json(time_now) for p in pdu_list]
        return Transaction(
            origin=self.server_name,
            pdus=pdus,
            origin_server_ts=int(time_now),
            destination=None,
        )

    async def _handle_received_pdu(self, origin: str, pdu: EventBase) -> None:
        """Process a PDU received in a federation /send/ transaction.

        If the event is invalid, then this method throws a FederationError.
        (The error will then be logged and sent back to the sender (which
        probably won't do anything with it), and other events in the
        transaction will be processed as normal).

        It is likely that we'll then receive other events which refer to
        this rejected_event in their prev_events, etc.  When that happens,
        we'll attempt to fetch the rejected event again, which will presumably
        fail, so those second-generation events will also get rejected.

        Eventually, we get to the point where there are more than 10 events
        between any new events and the original rejected event. Since we
        only try to backfill 10 events deep on received pdu, we then accept the
        new event, possibly introducing a discontinuity in the DAG, with new
        forward extremities, so normal service is approximately returned,
        until we try to backfill across the discontinuity.

        Args:
            origin: server which sent the pdu
            pdu: received pdu

        Raises: FederationError if the signatures / hash do not match, or
            if the event was unacceptable for any other reason (eg, too large,
            too many prev_events, couldn't find the prev_events)
        """

        # We've already checked that we know the room version by this point
        room_version = await self.store.get_room_version(pdu.room_id)

        # Check signature.
        try:
            pdu = await self._check_sigs_and_hash(room_version, pdu)
        except SynapseError as e:
            raise FederationError("ERROR", e.code, e.msg, affected=pdu.event_id)

        await self.handler.on_receive_pdu(origin, pdu, sent_to_us_directly=True)

    def __str__(self) -> str:
        return "<ReplicationLayer(%s)>" % self.server_name

    async def exchange_third_party_invite(
        self, sender_user_id: str, target_user_id: str, room_id: str, signed: Dict
    ) -> None:
        await self.handler.exchange_third_party_invite(
            sender_user_id, target_user_id, room_id, signed
        )

    async def on_exchange_third_party_invite_request(self, event_dict: Dict) -> None:
        await self.handler.on_exchange_third_party_invite_request(event_dict)

    async def check_server_matches_acl(self, server_name: str, room_id: str) -> None:
        """Check if the given server is allowed by the server ACLs in the room

        Args:
            server_name: name of server, *without any port part*
            room_id: ID of the room to check

        Raises:
            AuthError if the server does not match the ACL
        """
        state_ids = await self.store.get_current_state_ids(room_id)
        acl_event_id = state_ids.get((EventTypes.ServerACL, ""))

        if not acl_event_id:
            return

        acl_event = await self.store.get_event(acl_event_id)
        if server_matches_acl_event(server_name, acl_event):
            return

        raise AuthError(code=403, msg="Server is banned from room")


def server_matches_acl_event(server_name: str, acl_event: EventBase) -> bool:
    """Check if the given server is allowed by the ACL event

    Args:
        server_name: name of server, without any port part
        acl_event: m.room.server_acl event

    Returns:
        True if this server is allowed by the ACLs
    """
    logger.debug("Checking %s against acl %s", server_name, acl_event.content)

    # first of all, check if literal IPs are blocked, and if so, whether the
    # server name is a literal IP
    allow_ip_literals = acl_event.content.get("allow_ip_literals", True)
    if not isinstance(allow_ip_literals, bool):
        logger.warning("Ignoring non-bool allow_ip_literals flag")
        allow_ip_literals = True
    if not allow_ip_literals:
        # check for ipv6 literals. These start with '['.
        if server_name[0] == "[":
            return False

        # check for ipv4 literals. We can just lift the routine from twisted.
        if isIPAddress(server_name):
            return False

    # next,  check the deny list
    deny = acl_event.content.get("deny", [])
    if not isinstance(deny, (list, tuple)):
        logger.warning("Ignoring non-list deny ACL %s", deny)
        deny = []
    for e in deny:
        if _acl_entry_matches(server_name, e):
            # logger.info("%s matched deny rule %s", server_name, e)
            return False

    # then the allow list.
    allow = acl_event.content.get("allow", [])
    if not isinstance(allow, (list, tuple)):
        logger.warning("Ignoring non-list allow ACL %s", allow)
        allow = []
    for e in allow:
        if _acl_entry_matches(server_name, e):
            # logger.info("%s matched allow rule %s", server_name, e)
            return True

    # everything else should be rejected.
    # logger.info("%s fell through", server_name)
    return False


def _acl_entry_matches(server_name: str, acl_entry: Any) -> bool:
    if not isinstance(acl_entry, str):
        logger.warning(
            "Ignoring non-str ACL entry '%s' (is %s)", acl_entry, type(acl_entry)
        )
        return False
    regex = glob_to_regex(acl_entry)
    return bool(regex.match(server_name))


class FederationHandlerRegistry:
    """Allows classes to register themselves as handlers for a given EDU or
    query type for incoming federation traffic.
    """

    def __init__(self, hs: "HomeServer"):
        self.config = hs.config
        self.clock = hs.get_clock()
        self._instance_name = hs.get_instance_name()

        # These are safe to load in monolith mode, but will explode if we try
        # and use them. However we have guards before we use them to ensure that
        # we don't route to ourselves, and in monolith mode that will always be
        # the case.
        self._get_query_client = ReplicationGetQueryRestServlet.make_client(hs)
        self._send_edu = ReplicationFederationSendEduRestServlet.make_client(hs)

        self.edu_handlers = (
            {}
        )  # type: Dict[str, Callable[[str, dict], Awaitable[None]]]
        self.query_handlers = (
            {}
        )  # type: Dict[str, Callable[[dict], Awaitable[JsonDict]]]

        # Map from type to instance names that we should route EDU handling to.
        # We randomly choose one instance from the list to route to for each new
        # EDU received.
        self._edu_type_to_instance = {}  # type: Dict[str, List[str]]

    def register_edu_handler(
        self, edu_type: str, handler: Callable[[str, JsonDict], Awaitable[None]]
    ) -> None:
        """Sets the handler callable that will be used to handle an incoming
        federation EDU of the given type.

        Args:
            edu_type: The type of the incoming EDU to register handler for
            handler: A callable invoked on incoming EDU
                of the given type. The arguments are the origin server name and
                the EDU contents.
        """
        if edu_type in self.edu_handlers:
            raise KeyError("Already have an EDU handler for %s" % (edu_type,))

        logger.info("Registering federation EDU handler for %r", edu_type)

        self.edu_handlers[edu_type] = handler

    def register_query_handler(
        self, query_type: str, handler: Callable[[dict], Awaitable[JsonDict]]
    ) -> None:
        """Sets the handler callable that will be used to handle an incoming
        federation query of the given type.

        Args:
            query_type: Category name of the query, which should match
                the string used by make_query.
            handler: Invoked to handle
                incoming queries of this type. The return will be yielded
                on and the result used as the response to the query request.
        """
        if query_type in self.query_handlers:
            raise KeyError("Already have a Query handler for %s" % (query_type,))

        logger.info("Registering federation query handler for %r", query_type)

        self.query_handlers[query_type] = handler

    def register_instance_for_edu(self, edu_type: str, instance_name: str) -> None:
        """Register that the EDU handler is on a different instance than master."""
        self._edu_type_to_instance[edu_type] = [instance_name]

    def register_instances_for_edu(
        self, edu_type: str, instance_names: List[str]
    ) -> None:
        """Register that the EDU handler is on multiple instances."""
        self._edu_type_to_instance[edu_type] = instance_names

    async def on_edu(self, edu_type: str, origin: str, content: dict) -> None:
        if not self.config.use_presence and edu_type == EduTypes.Presence:
            return

        # Check if we have a handler on this instance
        handler = self.edu_handlers.get(edu_type)
        if handler:
            with start_active_span_from_edu(content, "handle_edu"):
                try:
                    await handler(origin, content)
                except SynapseError as e:
                    logger.info("Failed to handle edu %r: %r", edu_type, e)
                except Exception:
                    logger.exception("Failed to handle edu %r", edu_type)
            return

        # Check if we can route it somewhere else that isn't us
        instances = self._edu_type_to_instance.get(edu_type, ["master"])
        if self._instance_name not in instances:
            # Pick an instance randomly so that we don't overload one.
            route_to = random.choice(instances)

            try:
                await self._send_edu(
                    instance_name=route_to,
                    edu_type=edu_type,
                    origin=origin,
                    content=content,
                )
            except SynapseError as e:
                logger.info("Failed to handle edu %r: %r", edu_type, e)
            except Exception:
                logger.exception("Failed to handle edu %r", edu_type)
            return

        # Oh well, let's just log and move on.
        logger.warning("No handler registered for EDU type %s", edu_type)

    async def on_query(self, query_type: str, args: dict) -> JsonDict:
        handler = self.query_handlers.get(query_type)
        if handler:
            return await handler(args)

        # Check if we can route it somewhere else that isn't us
        if self._instance_name == "master":
            return await self._get_query_client(query_type=query_type, args=args)

        # Uh oh, no handler! Let's raise an exception so the request returns an
        # error.
        logger.warning("No handler registered for query type %s", query_type)
        raise NotFoundError("No handler for Query type '%s'" % (query_type,))