Add knocking support (#81)

Implement knocking as defined by https://github.com/matrix-org/matrix-doc/pull/2403

This is the base knocking stuff, taken from https://github.com/matrix-org/synapse/pull/6739
and does not include any public room directory changes.

While knocking hasn't merged yet on mainline due to waiting on getting Complement
into Synapse's CI, the code has been well-tested.

1 files changed, 59 insertions, 1 deletions

diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py

index 302b2f69bc..895ac59d36 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -1,5 +1,7 @@
 # -*- coding: utf-8 -*-
 # Copyright 2015, 2016 OpenMarket Ltd
+# Copyrignt 2020 Sorunome
+# Copyrignt 2020 The Matrix.org Foundation 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.
@@ -539,7 +541,7 @@ class FederationClient(FederationBase):
 
             RuntimeError: if no servers were reachable.
         """
-        valid_memberships = {Membership.JOIN, Membership.LEAVE}
+        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"
@@ -879,6 +881,62 @@ class FederationClient(FederationBase):
         # 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(
+            "xyz.amorgan.knock/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_v2(
+            destination=destination,
+            room_id=pdu.room_id,
+            event_id=pdu.event_id,
+            content=pdu.get_pdu_json(time_now),
+        )
+
     def get_public_rooms(
         self,
         remote_server: str,