Factor _get_missing_events_for_pdu out of _handle_new_pdu

This should be functionally identical: it just seeks to improve readability by
reducing indentation.

synapse/federation/federation_server.py

@@ -574,11 +574,60 @@ class FederationServer(FederationBase):
                             pdu.room_id, len(prevs - seen),
                         )
 
+                        yield self._get_missing_events_for_pdu(
+                            origin, pdu, prevs, min_depth
+                        )
+
+            prevs = {e_id for e_id, _ in pdu.prev_events}
+            seen = set(have_seen.keys())
+            if prevs - seen:
+                logger.info(
+                    "Still missing %d events for room %r: %r...",
+                    len(prevs - seen), pdu.room_id, list(prevs - seen)[:5]
+                )
+                fetch_state = True
+
+        if fetch_state:
+            # We need to get the state at this event, since we haven't
+            # processed all the prev events.
+            logger.debug(
+                "_handle_new_pdu getting state for %s",
+                pdu.room_id
+            )
+            try:
+                state, auth_chain = yield self.get_state_for_room(
+                    origin, pdu.room_id, pdu.event_id,
+                )
+            except:
+                logger.exception("Failed to get state for event: %s", pdu.event_id)
+
+        yield self.handler.on_receive_pdu(
+            origin,
+            pdu,
+            state=state,
+            auth_chain=auth_chain,
+        )
+
+    @defer.inlineCallbacks
+    def _get_missing_events_for_pdu(self, origin, pdu, prevs, min_depth):
+        """
+        Args:
+            origin (str): Origin of the pdu. Will be called to get the missing events
+            pdu: received pdu
+            prevs (str[]): List of event ids which we are missing
+            min_depth (int): Minimum depth of events to return.
+
+        Returns:
+            Deferred<dict(str, str?)>: updated have_seen dictionary
+        """
         # We recalculate seen, since it may have changed.
         have_seen = yield self.store.have_events(prevs)
         seen = set(have_seen.keys())
 
-                        if prevs - seen:
+        if not prevs - seen:
+            # nothing left to do
+            defer.returnValue(have_seen)
+
         latest = yield self.store.get_latest_event_ids_in_room(
             pdu.room_id
         )
@@ -636,36 +685,7 @@ class FederationServer(FederationBase):
         have_seen = yield self.store.have_events(
             [ev for ev, _ in pdu.prev_events]
         )
-
+        defer.returnValue(have_seen)
-            prevs = {e_id for e_id, _ in pdu.prev_events}
-            seen = set(have_seen.keys())
-            if prevs - seen:
-                logger.info(
-                    "Still missing %d events for room %r: %r...",
-                    len(prevs - seen), pdu.room_id, list(prevs - seen)[:5]
-                )
-                fetch_state = True
-
-        if fetch_state:
-            # We need to get the state at this event, since we haven't
-            # processed all the prev events.
-            logger.debug(
-                "_handle_new_pdu getting state for %s",
-                pdu.room_id
-            )
-            try:
-                state, auth_chain = yield self.get_state_for_room(
-                    origin, pdu.room_id, pdu.event_id,
-                )
-            except:
-                logger.exception("Failed to get state for event: %s", pdu.event_id)
-
-        yield self.handler.on_receive_pdu(
-            origin,
-            pdu,
-            state=state,
-            auth_chain=auth_chain,
-        )
 
     def __str__(self):
         return "<ReplicationLayer(%s)>" % self.server_name