Implement knock feature (#6739)

This PR aims to implement the knock feature as proposed in https://github.com/matrix-org/matrix-doc/pull/2403

Signed-off-by: Sorunome mail@sorunome.de
Signed-off-by: Andrew Morgan andrewm@element.io

1 files changed, 59 insertions, 3 deletions

diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 5b4f5d17f7..af0c679ed9 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -1,5 +1,5 @@
-# Copyright 2014-2016 OpenMarket Ltd
-# Copyright 2018 New Vector Ltd
+# 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.
@@ -47,6 +47,7 @@ class TransportLayerClient:
     def __init__(self, hs):
         self.server_name = hs.hostname
         self.client = hs.get_federation_http_client()
+        self._msc2403_enabled = hs.config.experimental.msc2403_enabled
 
     @log_function
     def get_room_state_ids(self, destination, room_id, event_id):
@@ -221,12 +222,28 @@ class TransportLayerClient:
             is not in our federation whitelist
         """
         valid_memberships = {Membership.JOIN, Membership.LEAVE}
+
+        # Allow knocking if the feature is enabled
+        if self._msc2403_enabled:
+            valid_memberships.add(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))
             )
-        path = _create_v1_path("/make_%s/%s/%s", membership, room_id, user_id)
+
+        # Knock currently uses an unstable prefix
+        if membership == Membership.KNOCK:
+            # Create a path in the form of /unstable/xyz.amorgan.knock/make_knock/...
+            path = _create_path(
+                FEDERATION_UNSTABLE_PREFIX + "/xyz.amorgan.knock",
+                "/make_knock/%s/%s",
+                room_id,
+                user_id,
+            )
+        else:
+            path = _create_v1_path("/make_%s/%s/%s", membership, room_id, user_id)
 
         ignore_backoff = False
         retry_on_dns_fail = False
@@ -322,6 +339,45 @@ class TransportLayerClient:
         return response
 
     @log_function
+    async def send_knock_v1(
+        self,
+        destination: str,
+        room_id: str,
+        event_id: str,
+        content: JsonDict,
+    ) -> JsonDict:
+        """
+        Sends a signed knock membership event to a remote server. This is the second
+        step for knocking after make_knock.
+
+        Args:
+            destination: The remote homeserver.
+            room_id: The ID of the room to knock on.
+            event_id: The ID of the knock membership event that we're sending.
+            content: The knock membership event that we're sending. Note that this is not the
+                `content` field of the membership event, but the entire signed membership event
+                itself represented as a JSON dict.
+
+        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.
+        """
+        path = _create_path(
+            FEDERATION_UNSTABLE_PREFIX + "/xyz.amorgan.knock",
+            "/send_knock/%s/%s",
+            room_id,
+            event_id,
+        )
+
+        return await self.client.put_json(
+            destination=destination, path=path, data=content
+        )
+
+    @log_function
     async def send_invite_v1(self, destination, room_id, event_id, content):
         path = _create_v1_path("/invite/%s/%s", room_id, event_id)