diff --git a/changelog.d/13416.misc b/changelog.d/13416.misc
new file mode 100644
index 0000000000..2904e73376
--- /dev/null
+++ b/changelog.d/13416.misc
@@ -0,0 +1 @@
+Faster Room Joins: prevent Synapse from answering federated join requests for a room which it has not fully joined yet.
\ No newline at end of file
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 1d60137411..db4b83a505 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -843,8 +843,25 @@ class FederationServer(FederationBase):
Codes.BAD_JSON,
)
+ # Note that get_room_version throws if the room does not exist here.
room_version = await self.store.get_room_version(room_id)
+ if await self.store.is_partial_state_room(room_id):
+ # If our server is still only partially joined, we can't give a complete
+ # response to /send_join, /send_knock or /send_leave.
+ # This is because we will not be able to provide the server list (for partial
+ # joins) or the full state (for full joins).
+ # Return a 404 as we would if we weren't in the room at all.
+ logger.info(
+ f"Rejecting /send_{membership_type} to %s because it's a partial state room",
+ room_id,
+ )
+ raise SynapseError(
+ 404,
+ f"Unable to handle /send_{membership_type} right now; this server is not fully joined.",
+ errcode=Codes.NOT_FOUND,
+ )
+
if membership_type == Membership.KNOCK and not room_version.msc2403_knocking:
raise SynapseError(
403,
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 30f1585a85..5042236742 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -754,6 +754,23 @@ class FederationHandler:
# (and return a 404 otherwise)
room_version = await self.store.get_room_version(room_id)
+ if await self.store.is_partial_state_room(room_id):
+ # If our server is still only partially joined, we can't give a complete
+ # response to /make_join, so return a 404 as we would if we weren't in the
+ # room at all.
+ # The main reason we can't respond properly is that we need to know about
+ # the auth events for the join event that we would return.
+ # We also should not bother entertaining the /make_join since we cannot
+ # handle the /send_join.
+ logger.info(
+ "Rejecting /make_join to %s because it's a partial state room", room_id
+ )
+ raise SynapseError(
+ 404,
+ "Unable to handle /make_join right now; this server is not fully joined.",
+ errcode=Codes.NOT_FOUND,
+ )
+
# now check that we are *still* in the room
is_in_room = await self._event_auth_handler.check_host_in_room(
room_id, self.server_name
|
