Add support for updating state

synapse/events/snapshot.py

@@ -228,6 +228,25 @@ class EventContext(object):
         else:
             self._prev_state_ids = self._current_state_ids
 
+    @defer.inlineCallbacks
+    def update_state(self, state_group, prev_state_ids, current_state_ids,
+                     delta_ids):
+        """Replace the state in the context
+        """
+
+        # We need to make sure we wait for any ongoing fetching of state
+        # to complete so that the updated state doesn't get clobbered
+        if self._fetching_state_deferred:
+            yield make_deferred_yieldable(self._fetching_state_deferred)
+
+        self.state_group = state_group
+        self._prev_state_ids = prev_state_ids
+        self._current_state_ids = current_state_ids
+        self.delta_ids = delta_ids
+
+        # We need to ensure that that we've marked as having fetched the state
+        self._fetching_state_deferred = defer.succeed(None)
+
 
 def _encode_state_dict(state_dict):
     """Since dicts of (type, state_key) -> event_id cannot be serialized in

synapse/handlers/federation.py

@@ -1975,21 +1975,35 @@ class FederationHandler(BaseHandler):
             k: a.event_id for k, a in iteritems(auth_events)
             if k != event_key
         }
-        context.current_state_ids = dict(context.current_state_ids)
+        current_state_ids = yield context.get_current_state_ids(self.store)
-        context.current_state_ids.update(state_updates)
+        current_state_ids = dict(current_state_ids)
+
+        current_state_ids.update(state_updates)
+
         if context.delta_ids is not None:
-            context.delta_ids = dict(context.delta_ids)
+            delta_ids = dict(context.delta_ids)
-            context.delta_ids.update(state_updates)
+            delta_ids.update(state_updates)
-        context.prev_state_ids = dict(context.prev_state_ids)
+
-        context.prev_state_ids.update({
+        prev_state_ids = yield context.get_prev_state_ids(self.store)
+        prev_state_ids = dict(prev_state_ids)
+
+        prev_state_ids.update({
             k: a.event_id for k, a in iteritems(auth_events)
         })
-        context.state_group = yield self.store.store_state_group(
+
+        state_group = yield self.store.store_state_group(
             event.event_id,
             event.room_id,
             prev_group=context.prev_group,
-            delta_ids=context.delta_ids,
+            delta_ids=delta_ids,
-            current_state_ids=context.current_state_ids,
+            current_state_ids=current_state_ids,
+        )
+
+        yield context.update_state(
+            state_group=state_group,
+            current_state_ids=current_state_ids,
+            prev_state_ids=prev_state_ids,
+            delta_ids=delta_ids,
         )
 
     @defer.inlineCallbacks