Add /state_ids federation API

The new API only returns the event_ids for the state, as most
requesters will already have the vast majority of the events already.

2 files changed, 34 insertions, 0 deletions

diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py

index ebb698e278..3d088e43cb 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -55,6 +55,28 @@ class TransportLayerClient(object):
         )
 
     @log_function
+    def get_room_state_ids(self, destination, room_id, event_id):
+        """ Requests all state for a given room from the given server at the
+        given event. Returns the state's event_id's
+
+        Args:
+            destination (str): The host name of the remote home server we want
+                to get the state from.
+            context (str): The name of the context we want the state of
+            event_id (str): The event we want the context at.
+
+        Returns:
+            Deferred: Results in a dict received from the remote homeserver.
+        """
+        logger.debug("get_room_state_ids dest=%s, room=%s",
+                     destination, room_id)
+
+        path = PREFIX + "/state_ids/%s/" % room_id
+        return self.client.get_json(
+            destination, path=path, args={"event_id": event_id},
+        )
+
+    @log_function
     def get_event(self, destination, event_id, timeout=None):
         """ Requests the pdu with give id and origin from the given server.
 
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py

index 26fa88ae84..3ae7c48457 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -271,6 +271,17 @@ class FederationStateServlet(BaseFederationServlet):
         )
 
 
+class FederationStateIdsServlet(BaseFederationServlet):
+    PATH = "/state_ids/(?P<room_id>[^/]*)/"
+
+    def on_GET(self, origin, content, query, room_id):
+        return self.handler.on_state_ids_request(
+            origin,
+            room_id,
+            query.get("event_id", [None])[0],
+        )
+
+
 class FederationBackfillServlet(BaseFederationServlet):
     PATH = "/backfill/(?P<context>[^/]*)/"
 
@@ -538,6 +549,7 @@ SERVLET_CLASSES = (
     FederationPullServlet,
     FederationEventServlet,
     FederationStateServlet,
+    FederationStateIdsServlet,
     FederationBackfillServlet,
     FederationQueryServlet,
     FederationMakeJoinServlet,