Add parameter to control whether we do a faster join

When the local homeserver is already joined to a room and wants to
perform another remote join, we may find it useful to do a non-partial
state join if we already have the full state for the room.

Signed-off-by: Sean Quah <seanq@matrix.org>

changelog.d/14843.misc

@@ -0,0 +1 @@
+Add an `omit_members` option to control whether the federation client performs a faster join.

synapse/federation/federation_client.py

@@ -1014,7 +1014,11 @@ async def send_request(destination: str) -> Tuple[str, EventBase, RoomVersion]:
         )
 
     async def send_join(
-        self, destinations: Iterable[str], pdu: EventBase, room_version: RoomVersion
+        self,
+        destinations: Iterable[str],
+        pdu: EventBase,
+        room_version: RoomVersion,
+        partial_state: bool = True,
     ) -> SendJoinResult:
         """Sends a join event to one of a list of homeservers.
 
@@ -1027,6 +1031,10 @@ async def send_join(
             pdu: event to be sent
             room_version: the version of the room (according to the server that
                 did the make_join)
+            partial_state: whether to ask the remote server to omit membership state
+                events from the response. If the remote server complies,
+                `partial_state` in the send join result will be set. Defaults to
+                `True`.
 
         Returns:
             The result of the send join request.
@@ -1037,7 +1045,9 @@ async def send_join(
         """
 
         async def send_request(destination: str) -> SendJoinResult:
-            response = await self._do_send_join(room_version, destination, pdu)
+            response = await self._do_send_join(
+                room_version, destination, pdu, omit_members=partial_state
+            )
 
             # If an event was returned (and expected to be returned):
             #
@@ -1177,7 +1187,11 @@ async def _execute(pdu: EventBase) -> None:
         )
 
     async def _do_send_join(
-        self, room_version: RoomVersion, destination: str, pdu: EventBase
+        self,
+        room_version: RoomVersion,
+        destination: str,
+        pdu: EventBase,
+        omit_members: bool,
     ) -> SendJoinResponse:
         time_now = self._clock.time_msec()
 
@@ -1188,6 +1202,7 @@ async def _do_send_join(
                 room_id=pdu.room_id,
                 event_id=pdu.event_id,
                 content=pdu.get_pdu_json(time_now),
+                omit_members=omit_members,
             )
         except HttpResponseException as e:
             # If an error is received that is due to an unrecognised endpoint,

synapse/federation/transport/client.py

@@ -351,13 +351,16 @@ async def send_join_v2(
         room_id: str,
         event_id: str,
         content: JsonDict,
+        omit_members: bool,
     ) -> "SendJoinResponse":
         path = _create_v2_path("/send_join/%s/%s", room_id, event_id)
         query_params: Dict[str, str] = {}
         if self._faster_joins_enabled:
             # lazy-load state on join
-            query_params["org.matrix.msc3706.partial_state"] = "true"
-            query_params["omit_members"] = "true"
+            query_params["org.matrix.msc3706.partial_state"] = (
+                "true" if omit_members else "false"
+            )
+            query_params["omit_members"] = "true" if omit_members else "false"
 
         return await self.client.put_json(
             destination=destination,