diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index abbb71424d..6e40e2c216 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1,6 +1,5 @@
-# Copyright 2014-2016 OpenMarket Ltd
-# Copyright 2017-2018 New Vector Ltd
-# Copyright 2019 The Matrix.org Foundation C.I.C.
+# Copyright 2014-2021 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.
@@ -1550,6 +1549,77 @@ class FederationHandler(BaseHandler):
run_in_background(self._handle_queued_pdus, room_queue)
+ @log_function
+ async def do_knock(
+ self,
+ target_hosts: List[str],
+ room_id: str,
+ knockee: str,
+ content: JsonDict,
+ ) -> Tuple[str, int]:
+ """Sends the knock to the remote server.
+
+ This first triggers a make_knock request that returns a partial
+ event that we can fill out and sign. This is then sent to the
+ remote server via send_knock.
+
+ Knock events must be signed by the knockee's server before distributing.
+
+ Args:
+ target_hosts: A list of hosts that we want to try knocking through.
+ room_id: The ID of the room to knock on.
+ knockee: The ID of the user who is knocking.
+ content: The content of the knock event.
+
+ Returns:
+ A tuple of (event ID, stream ID).
+
+ Raises:
+ SynapseError: If the chosen remote server returns a 3xx/4xx code.
+ RuntimeError: If no servers were reachable.
+ """
+ logger.debug("Knocking on room %s on behalf of user %s", room_id, knockee)
+
+ # Inform the remote server of the room versions we support
+ supported_room_versions = list(KNOWN_ROOM_VERSIONS.keys())
+
+ # Ask the remote server to create a valid knock event for us. Once received,
+ # we sign the event
+ params = {"ver": supported_room_versions} # type: Dict[str, Iterable[str]]
+ origin, event, event_format_version = await self._make_and_verify_event(
+ target_hosts, room_id, knockee, Membership.KNOCK, content, params=params
+ )
+
+ # Record the room ID and its version so that we have a record of the room
+ await self._maybe_store_room_on_outlier_membership(
+ room_id=event.room_id, room_version=event_format_version
+ )
+
+ # Initially try the host that we successfully called /make_knock on
+ try:
+ target_hosts.remove(origin)
+ target_hosts.insert(0, origin)
+ except ValueError:
+ pass
+
+ # Send the signed event back to the room, and potentially receive some
+ # further information about the room in the form of partial state events
+ stripped_room_state = await self.federation_client.send_knock(
+ target_hosts, event
+ )
+
+ # Store any stripped room state events in the "unsigned" key of the event.
+ # This is a bit of a hack and is cribbing off of invites. Basically we
+ # store the room state here and retrieve it again when this event appears
+ # in the invitee's sync stream. It is stripped out for all other local users.
+ event.unsigned["knock_room_state"] = stripped_room_state["knock_state_events"]
+
+ context = await self.state_handler.compute_event_context(event)
+ stream_id = await self.persist_events_and_notify(
+ event.room_id, [(event, context)]
+ )
+ return event.event_id, stream_id
+
async def _handle_queued_pdus(
self, room_queue: List[Tuple[EventBase, str]]
) -> None:
@@ -1915,6 +1985,116 @@ class FederationHandler(BaseHandler):
return None
+ @log_function
+ async def on_make_knock_request(
+ self, origin: str, room_id: str, user_id: str
+ ) -> EventBase:
+ """We've received a make_knock request, so we create a partial
+ knock event for the room and return that. We do *not* persist or
+ process it 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.
+
+ Returns:
+ The partial knock event.
+ """
+ if get_domain_from_id(user_id) != origin:
+ logger.info(
+ "Get /xyz.amorgan.knock/make_knock request for user %r"
+ "from different origin %s, ignoring",
+ user_id,
+ origin,
+ )
+ raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
+
+ room_version = await self.store.get_room_version_id(room_id)
+
+ builder = self.event_builder_factory.new(
+ room_version,
+ {
+ "type": EventTypes.Member,
+ "content": {"membership": Membership.KNOCK},
+ "room_id": room_id,
+ "sender": user_id,
+ "state_key": user_id,
+ },
+ )
+
+ event, context = await self.event_creation_handler.create_new_client_event(
+ builder=builder
+ )
+
+ event_allowed = await self.third_party_event_rules.check_event_allowed(
+ event, context
+ )
+ if not event_allowed:
+ logger.warning("Creation of knock %s forbidden by third-party rules", event)
+ raise SynapseError(
+ 403, "This event is not allowed in this context", Codes.FORBIDDEN
+ )
+
+ try:
+ # The remote hasn't signed it yet, obviously. We'll do the full checks
+ # when we get the event back in `on_send_knock_request`
+ await self.auth.check_from_context(
+ room_version, event, context, do_sig_check=False
+ )
+ except AuthError as e:
+ logger.warning("Failed to create new knock %r because %s", event, e)
+ raise e
+
+ return event
+
+ @log_function
+ async def on_send_knock_request(
+ self, origin: str, event: EventBase
+ ) -> EventContext:
+ """
+ We have received a knock event for a room. Verify that event and send it into the room
+ on the knocking homeserver's behalf.
+
+ Args:
+ origin: The remote homeserver of the knocking user.
+ event: The knocking member event that has been signed by the remote homeserver.
+
+ Returns:
+ The context of the event after inserting it into the room graph.
+ """
+ logger.debug(
+ "on_send_knock_request: Got event: %s, signatures: %s",
+ event.event_id,
+ event.signatures,
+ )
+
+ if get_domain_from_id(event.sender) != origin:
+ logger.info(
+ "Got /xyz.amorgan.knock/send_knock request for user %r "
+ "from different origin %s",
+ event.sender,
+ origin,
+ )
+ raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
+
+ event.internal_metadata.outlier = False
+
+ context = await self.state_handler.compute_event_context(event)
+
+ await self._auth_and_persist_event(origin, event, context)
+
+ event_allowed = await self.third_party_event_rules.check_event_allowed(
+ event, context
+ )
+ if not event_allowed:
+ logger.info("Sending of knock %s forbidden by third-party rules", event)
+ raise SynapseError(
+ 403, "This event is not allowed in this context", Codes.FORBIDDEN
+ )
+
+ return context
+
async def get_state_for_pdu(self, room_id: str, event_id: str) -> List[EventBase]:
"""Returns the state at the event. i.e. not including said event."""
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