1 files changed, 111 insertions, 2 deletions
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index b06387051c..65778fd4ee 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -314,6 +314,40 @@ class FederationClient(FederationBase):
             Deferred: Results in a list of PDUs.
         """
 
+        try:
+            # First we try and ask for just the IDs, as thats far quicker if
+            # we have most of the state and auth_chain already.
+            # However, this may 404 if the other side has an old synapse.
+            result = yield self.transport_layer.get_room_state_ids(
+                destination, room_id, event_id=event_id,
+            )
+
+            state_event_ids = result["pdu_ids"]
+            auth_event_ids = result.get("auth_chain_ids", [])
+
+            fetched_events, failed_to_fetch = yield self.get_events(
+                [destination], room_id, set(state_event_ids + auth_event_ids)
+            )
+
+            if failed_to_fetch:
+                logger.warn("Failed to get %r", failed_to_fetch)
+
+            event_map = {
+                ev.event_id: ev for ev in fetched_events
+            }
+
+            pdus = [event_map[e_id] for e_id in state_event_ids]
+            auth_chain = [event_map[e_id] for e_id in auth_event_ids]
+
+            auth_chain.sort(key=lambda e: e.depth)
+
+            defer.returnValue((pdus, auth_chain))
+        except HttpResponseException as e:
+            if e.code == 400 or e.code == 404:
+                logger.info("Failed to use get_room_state_ids API, falling back")
+            else:
+                raise e
+
         result = yield self.transport_layer.get_room_state(
             destination, room_id, event_id=event_id,
         )
@@ -327,12 +361,26 @@ class FederationClient(FederationBase):
             for p in result.get("auth_chain", [])
         ]
 
+        seen_events = yield self.store.get_events([
+            ev.event_id for ev in itertools.chain(pdus, auth_chain)
+        ])
+
         signed_pdus = yield self._check_sigs_and_hash_and_fetch(
-            destination, pdus, outlier=True
+            destination,
+            [p for p in pdus if p.event_id not in seen_events],
+            outlier=True
+        )
+        signed_pdus.extend(
+            seen_events[p.event_id] for p in pdus if p.event_id in seen_events
         )
 
         signed_auth = yield self._check_sigs_and_hash_and_fetch(
-            destination, auth_chain, outlier=True
+            destination,
+            [p for p in auth_chain if p.event_id not in seen_events],
+            outlier=True
+        )
+        signed_auth.extend(
+            seen_events[p.event_id] for p in auth_chain if p.event_id in seen_events
         )
 
         signed_auth.sort(key=lambda e: e.depth)
@@ -340,6 +388,67 @@ class FederationClient(FederationBase):
         defer.returnValue((signed_pdus, signed_auth))
 
     @defer.inlineCallbacks
+    def get_events(self, destinations, room_id, event_ids, return_local=True):
+        """Fetch events from some remote destinations, checking if we already
+        have them.
+
+        Args:
+            destinations (list)
+            room_id (str)
+            event_ids (list)
+            return_local (bool): Whether to include events we already have in
+                the DB in the returned list of events
+
+        Returns:
+            Deferred: A deferred resolving to a 2-tuple where the first is a list of
+            events and the second is a list of event ids that we failed to fetch.
+        """
+        if return_local:
+            seen_events = yield self.store.get_events(event_ids)
+            signed_events = seen_events.values()
+        else:
+            seen_events = yield self.store.have_events(event_ids)
+            signed_events = []
+
+        failed_to_fetch = set()
+
+        missing_events = set(event_ids)
+        for k in seen_events:
+            missing_events.discard(k)
+
+        if not missing_events:
+            defer.returnValue((signed_events, failed_to_fetch))
+
+        def random_server_list():
+            srvs = list(destinations)
+            random.shuffle(srvs)
+            return srvs
+
+        batch_size = 20
+        missing_events = list(missing_events)
+        for i in xrange(0, len(missing_events), batch_size):
+            batch = set(missing_events[i:i + batch_size])
+
+            deferreds = [
+                self.get_pdu(
+                    destinations=random_server_list(),
+                    event_id=e_id,
+                )
+                for e_id in batch
+            ]
+
+            res = yield defer.DeferredList(deferreds, consumeErrors=True)
+            for success, result in res:
+                if success:
+                    signed_events.append(result)
+                    batch.discard(result.event_id)
+
+            # We removed all events we successfully fetched from `batch`
+            failed_to_fetch.update(batch)
+
+        defer.returnValue((signed_events, failed_to_fetch))
+
+    @defer.inlineCallbacks
     @log_function
     def get_event_auth(self, destination, room_id, event_id):
         res = yield self.transport_layer.get_event_auth(