synapse/synapse/federation/federation_server.py

# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2018 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
import re

import six
from six import iteritems

from canonicaljson import json
from prometheus_client import Counter

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

from synapse.api.constants import EventTypes
from synapse.api.errors import (
    AuthError,
    FederationError,
    IncompatibleRoomVersionError,
    NotFoundError,
    SynapseError,
)
from synapse.crypto.event_signing import compute_event_signature
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.endpoint import parse_server_name
from synapse.replication.http.federation import (
    ReplicationFederationSendEduRestServlet,
    ReplicationGetQueryRestServlet,
)
from synapse.types import get_domain_from_id
from synapse.util.async_helpers import Linearizer, concurrently_execute
from synapse.util.caches.response_cache import ResponseCache
from synapse.util.logutils import log_function

# 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"]
)


class FederationServer(FederationBase):

    def __init__(self, hs):
        super(FederationServer, self).__init__(hs)

        self.auth = hs.get_auth()
        self.handler = hs.get_handlers().federation_handler

        self._server_linearizer = Linearizer("fed_server")
        self._transaction_linearizer = Linearizer("fed_txn_handler")

        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, "state_resp", timeout_ms=30000)

    @defer.inlineCallbacks
    @log_function
    def on_backfill_request(self, origin, room_id, versions, limit):
        with (yield self._server_linearizer.queue((origin, room_id))):
            origin_host, _ = parse_server_name(origin)
            yield self.check_server_matches_acl(origin_host, room_id)

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

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

        defer.returnValue((200, res))

    @defer.inlineCallbacks
    @log_function
    def on_incoming_transaction(self, origin, transaction_data):
        # 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)

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

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

        # use a linearizer to ensure that we don't process the same transaction
        # multiple times in parallel.
        with (yield self._transaction_linearizer.queue(
                (origin, transaction.transaction_id),
        )):
            result = yield self._handle_incoming_transaction(
                origin, transaction, request_time,
            )

        defer.returnValue(result)

    @defer.inlineCallbacks
    def _handle_incoming_transaction(self, origin, transaction, request_time):
        """ Process an incoming transaction and return the HTTP response

        Args:
            origin (unicode): the server making the request
            transaction (Transaction): incoming transaction
            request_time (int): timestamp that the HTTP request arrived at

        Returns:
            Deferred[(int, object)]: http response code and body
        """
        response = yield self.transaction_actions.have_responded(origin, transaction)

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

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

        received_pdus_counter.inc(len(transaction.pdus))

        origin_host, _ = parse_server_name(origin)

        pdus_by_room = {}

        for p in transaction.pdus:
            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"]

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

        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.

        @defer.inlineCallbacks
        def process_pdus_for_room(room_id):
            logger.debug("Processing PDUs for %s", room_id)
            try:
                yield self.check_server_matches_acl(origin_host, room_id)
            except AuthError as e:
                logger.warn(
                    "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]:
                event_id = pdu.event_id
                try:
                    yield self._handle_received_pdu(
                        origin, pdu
                    )
                    pdu_results[event_id] = {}
                except FederationError as e:
                    logger.warn("Error handling PDU %s: %s", event_id, e)
                    pdu_results[event_id] = {"error": str(e)}
                except Exception as e:
                    f = failure.Failure()
                    pdu_results[event_id] = {"error": str(e)}
                    logger.error(
                        "Failed to handle PDU %s: %s",
                        event_id, f.getTraceback().rstrip(),
                    )

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

        if hasattr(transaction, "edus"):
            for edu in (Edu(**x) for x in transaction.edus):
                yield self.received_edu(
                    origin,
                    edu.edu_type,
                    edu.content
                )

        response = {
            "pdus": pdu_results,
        }

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

        yield self.transaction_actions.set_response(
            origin,
            transaction,
            200, response
        )
        defer.returnValue((200, response))

    @defer.inlineCallbacks
    def received_edu(self, origin, edu_type, content):
        received_edus_counter.inc()
        yield self.registry.on_edu(edu_type, origin, content)

    @defer.inlineCallbacks
    @log_function
    def on_context_state_request(self, origin, room_id, event_id):
        if not event_id:
            raise NotImplementedError("Specify an event")

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

        in_room = yield 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 (yield self._server_linearizer.queue((origin, room_id))):
            resp = yield self._state_resp_cache.wrap(
                (room_id, event_id),
                self._on_context_state_request_compute,
                room_id, event_id,
            )

        defer.returnValue((200, resp))

    @defer.inlineCallbacks
    def on_state_ids_request(self, origin, room_id, event_id):
        if not event_id:
            raise NotImplementedError("Specify an event")

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

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

        state_ids = yield self.handler.get_state_ids_for_pdu(
            room_id, event_id,
        )
        auth_chain_ids = yield self.store.get_auth_chain_ids(state_ids)

        defer.returnValue((200, {
            "pdu_ids": state_ids,
            "auth_chain_ids": auth_chain_ids,
        }))

    @defer.inlineCallbacks
    def _on_context_state_request_compute(self, room_id, event_id):
        pdus = yield self.handler.get_state_for_pdu(
            room_id, event_id,
        )
        auth_chain = yield self.store.get_auth_chain(
            [pdu.event_id for pdu in pdus]
        )

        for event in auth_chain:
            # We sign these again because there was a bug where we
            # incorrectly signed things the first time round
            if self.hs.is_mine_id(event.event_id):
                event.signatures.update(
                    compute_event_signature(
                        event,
                        self.hs.hostname,
                        self.hs.config.signing_key[0]
                    )
                )

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

    @defer.inlineCallbacks
    @log_function
    def on_pdu_request(self, origin, event_id):
        pdu = yield self.handler.get_persisted_pdu(origin, event_id)

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

    @defer.inlineCallbacks
    @log_function
    def on_pull_request(self, origin, versions):
        raise NotImplementedError("Pull transactions not implemented")

    @defer.inlineCallbacks
    def on_query_request(self, query_type, args):
        received_queries_counter.labels(query_type).inc()
        resp = yield self.registry.on_query(query_type, args)
        defer.returnValue((200, resp))

    @defer.inlineCallbacks
    def on_make_join_request(self, origin, room_id, user_id, supported_versions):
        origin_host, _ = parse_server_name(origin)
        yield self.check_server_matches_acl(origin_host, room_id)

        room_version = yield self.store.get_room_version(room_id)
        if room_version not in supported_versions:
            logger.warn("Room version %s not in %s", room_version, supported_versions)
            raise IncompatibleRoomVersionError(room_version=room_version)

        pdu = yield self.handler.on_make_join_request(room_id, user_id)
        time_now = self._clock.time_msec()
        defer.returnValue({
            "event": pdu.get_pdu_json(time_now),
            "room_version": room_version,
        })

    @defer.inlineCallbacks
    def on_invite_request(self, origin, content):
        pdu = event_from_pdu_json(content)
        origin_host, _ = parse_server_name(origin)
        yield self.check_server_matches_acl(origin_host, pdu.room_id)
        ret_pdu = yield self.handler.on_invite_request(origin, pdu)
        time_now = self._clock.time_msec()
        defer.returnValue((200, {"event": ret_pdu.get_pdu_json(time_now)}))

    @defer.inlineCallbacks
    def on_send_join_request(self, origin, content):
        logger.debug("on_send_join_request: content: %s", content)
        pdu = event_from_pdu_json(content)

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

        logger.debug("on_send_join_request: pdu sigs: %s", pdu.signatures)
        res_pdus = yield self.handler.on_send_join_request(origin, pdu)
        time_now = self._clock.time_msec()
        defer.returnValue((200, {
            "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"]
            ],
        }))

    @defer.inlineCallbacks
    def on_make_leave_request(self, origin, room_id, user_id):
        origin_host, _ = parse_server_name(origin)
        yield self.check_server_matches_acl(origin_host, room_id)
        pdu = yield self.handler.on_make_leave_request(room_id, user_id)
        time_now = self._clock.time_msec()
        defer.returnValue({"event": pdu.get_pdu_json(time_now)})

    @defer.inlineCallbacks
    def on_send_leave_request(self, origin, content):
        logger.debug("on_send_leave_request: content: %s", content)
        pdu = event_from_pdu_json(content)

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

        logger.debug("on_send_leave_request: pdu sigs: %s", pdu.signatures)
        yield self.handler.on_send_leave_request(origin, pdu)
        defer.returnValue((200, {}))

    @defer.inlineCallbacks
    def on_event_auth(self, origin, room_id, event_id):
        with (yield self._server_linearizer.queue((origin, room_id))):
            origin_host, _ = parse_server_name(origin)
            yield self.check_server_matches_acl(origin_host, room_id)

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

    @defer.inlineCallbacks
    def on_query_auth_request(self, origin, content, room_id, event_id):
        """
        Content is a dict with keys::
            auth_chain (list): A list of events that give the auth chain.
            missing (list): A list of event_ids indicating what the other
              side (`origin`) think we're missing.
            rejects (dict): A mapping from event_id to a 2-tuple of reason
              string and a proof (or None) of why the event was rejected.
              The keys of this dict give the list of events the `origin` has
              rejected.

        Args:
            origin (str)
            content (dict)
            event_id (str)

        Returns:
            Deferred: Results in `dict` with the same format as `content`
        """
        with (yield self._server_linearizer.queue((origin, room_id))):
            origin_host, _ = parse_server_name(origin)
            yield self.check_server_matches_acl(origin_host, room_id)

            auth_chain = [
                event_from_pdu_json(e)
                for e in content["auth_chain"]
            ]

            signed_auth = yield self._check_sigs_and_hash_and_fetch(
                origin, auth_chain, outlier=True
            )

            ret = yield self.handler.on_query_auth(
                origin,
                event_id,
                room_id,
                signed_auth,
                content.get("rejects", []),
                content.get("missing", []),
            )

            time_now = self._clock.time_msec()
            send_content = {
                "auth_chain": [
                    e.get_pdu_json(time_now)
                    for e in ret["auth_chain"]
                ],
                "rejects": ret.get("rejects", []),
                "missing": ret.get("missing", []),
            }

        defer.returnValue(
            (200, send_content)
        )

    @log_function
    def on_query_client_keys(self, origin, content):
        return self.on_query_request("client_keys", content)

    def on_query_user_devices(self, origin, user_id):
        return self.on_query_request("user_devices", user_id)

    @defer.inlineCallbacks
    @log_function
    def on_claim_client_keys(self, origin, content):
        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))

        results = yield self.store.claim_e2e_one_time_keys(query)

        json_result = {}
        for user_id, device_keys in results.items():
            for device_id, keys in device_keys.items():
                for key_id, json_bytes in keys.items():
                    json_result.setdefault(user_id, {})[device_id] = {
                        key_id: json.loads(json_bytes)
                    }

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

        defer.returnValue({"one_time_keys": json_result})

    @defer.inlineCallbacks
    @log_function
    def on_get_missing_events(self, origin, room_id, earliest_events,
                              latest_events, limit, min_depth):
        with (yield self._server_linearizer.queue((origin, room_id))):
            origin_host, _ = parse_server_name(origin)
            yield self.check_server_matches_acl(origin_host, room_id)

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

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

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

            time_now = self._clock.time_msec()

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

    @log_function
    def on_openid_userinfo(self, token):
        ts_now_ms = self._clock.time_msec()
        return self.store.get_user_id_for_open_id_token(token, ts_now_ms)

    def _transaction_from_pdus(self, pdu_list):
        """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,
        )

    @defer.inlineCallbacks
    def _handle_received_pdu(self, origin, pdu):
        """ 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 (str): server which sent the pdu
            pdu (FrozenEvent): received pdu

        Returns (Deferred): completes with None

        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)
        """
        # check that it's actually being sent from a valid destination to
        # workaround bug #1753 in 0.18.5 and 0.18.6
        if origin != get_domain_from_id(pdu.event_id):
            # We continue to accept join events from any server; this is
            # necessary for the federation join dance to work correctly.
            # (When we join over federation, the "helper" server is
            # responsible for sending out the join event, rather than the
            # origin. See bug #1893).
            if not (
                pdu.type == 'm.room.member' and
                pdu.content and
                pdu.content.get("membership", None) == 'join'
            ):
                logger.info(
                    "Discarding PDU %s from invalid origin %s",
                    pdu.event_id, origin
                )
                return
            else:
                logger.info(
                    "Accepting join PDU %s from %s",
                    pdu.event_id, origin
                )

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

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

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

    @defer.inlineCallbacks
    def exchange_third_party_invite(
            self,
            sender_user_id,
            target_user_id,
            room_id,
            signed,
    ):
        ret = yield self.handler.exchange_third_party_invite(
            sender_user_id,
            target_user_id,
            room_id,
            signed,
        )
        defer.returnValue(ret)

    @defer.inlineCallbacks
    def on_exchange_third_party_invite_request(self, origin, room_id, event_dict):
        ret = yield self.handler.on_exchange_third_party_invite_request(
            origin, room_id, event_dict
        )
        defer.returnValue(ret)

    @defer.inlineCallbacks
    def check_server_matches_acl(self, server_name, room_id):
        """Check if the given server is allowed by the server ACLs in the room

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

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

        if not acl_event_id:
            return

        acl_event = yield 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, acl_event):
    """Check if the given server is allowed by the ACL event

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

    Returns:
        bool: 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.warn("Ignorning 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.warn("Ignorning 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.warn("Ignorning 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, acl_entry):
    if not isinstance(acl_entry, six.string_types):
        logger.warn("Ignoring non-str ACL entry '%s' (is %s)", acl_entry, type(acl_entry))
        return False
    regex = _glob_to_regex(acl_entry)
    return regex.match(server_name)


def _glob_to_regex(glob):
    res = ''
    for c in glob:
        if c == '*':
            res = res + '.*'
        elif c == '?':
            res = res + '.'
        else:
            res = res + re.escape(c)
    return re.compile(res + "\\Z", re.IGNORECASE)


class FederationHandlerRegistry(object):
    """Allows classes to register themselves as handlers for a given EDU or
    query type for incoming federation traffic.
    """
    def __init__(self):
        self.edu_handlers = {}
        self.query_handlers = {}

    def register_edu_handler(self, edu_type, handler):
        """Sets the handler callable that will be used to handle an incoming
        federation EDU of the given type.

        Args:
            edu_type (str): The type of the incoming EDU to register handler for
            handler (Callable[[str, dict]]): 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, handler):
        """Sets the handler callable that will be used to handle an incoming
        federation query of the given type.

        Args:
            query_type (str): Category name of the query, which should match
                the string used by make_query.
            handler (Callable[[dict], Deferred[dict]]): 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

    @defer.inlineCallbacks
    def on_edu(self, edu_type, origin, content):
        handler = self.edu_handlers.get(edu_type)
        if not handler:
            logger.warn("No handler registered for EDU type %s", edu_type)

        try:
            yield handler(origin, content)
        except SynapseError as e:
            logger.info("Failed to handle edu %r: %r", edu_type, e)
        except Exception as e:
            logger.exception("Failed to handle edu %r", edu_type)

    def on_query(self, query_type, args):
        handler = self.query_handlers.get(query_type)
        if not handler:
            logger.warn("No handler registered for query type %s", query_type)
            raise NotFoundError("No handler for Query type '%s'" % (query_type,))

        return handler(args)


class ReplicationFederationHandlerRegistry(FederationHandlerRegistry):
    """A FederationHandlerRegistry for worker processes.

    When receiving EDU or queries it will check if an appropriate handler has
    been registered on the worker, if there isn't one then it calls off to the
    master process.
    """

    def __init__(self, hs):
        self.config = hs.config
        self.http_client = hs.get_simple_http_client()
        self.clock = hs.get_clock()

        self._get_query_client = ReplicationGetQueryRestServlet.make_client(hs)
        self._send_edu = ReplicationFederationSendEduRestServlet.make_client(hs)

        super(ReplicationFederationHandlerRegistry, self).__init__()

    def on_edu(self, edu_type, origin, content):
        """Overrides FederationHandlerRegistry
        """
        handler = self.edu_handlers.get(edu_type)
        if handler:
            return super(ReplicationFederationHandlerRegistry, self).on_edu(
                edu_type, origin, content,
            )

        return self._send_edu(
            edu_type=edu_type,
            origin=origin,
            content=content,
        )

    def on_query(self, query_type, args):
        """Overrides FederationHandlerRegistry
        """
        handler = self.query_handlers.get(query_type)
        if handler:
            return handler(args)

        return self._get_query_client(
            query_type=query_type,
            args=args,
        )