When we see a difference in current state, actually use state conflict resolution algorithm

synapse/handlers/federation.py

@@ -858,6 +858,40 @@ class FederationHandler(BaseHandler):
             # Do auth conflict res.
             logger.debug("Different auth: %s", different_auth)
 
+            different_events = yield defer.gatherResults(
+                [
+                    self.store.get_event(
+                        d,
+                        allow_none=True,
+                        allow_rejected=False,
+                    )
+                    for d in different_auth
+                    if d in have_events and not have_events[d]
+                ],
+                consumeErrors=True
+            )
+
+            if different_events:
+                local_view = dict(auth_events)
+                remote_view = dict(auth_events)
+                remote_view.update({
+                    (d.type, d.state_key) for d in different_events
+                })
+
+                new_state, _ = self.state.resolve_events(
+                    [local_view, remote_view],
+                    event
+                )
+
+                auth_events.update(new_state)
+
+                current_state = set(e.event_id for e in auth_events.values())
+                different_auth = event_auth_events - current_state
+
+                context.current_state.update(auth_events)
+                context.state_group = None
+
+        if different_auth and not event.internal_metadata.is_outlier():
             # Only do auth resolution if we have something new to say.
             # We can't rove an auth failure.
             do_resolution = False

synapse/state.py

@@ -259,13 +259,37 @@ class StateHandler(object):
 
             defer.returnValue((name, state, prev_states))
 
+        new_state, prev_states = self._resolve_events(
+            state_groups.values(), event_type, state_key
+        )
+
+        if self._state_cache is not None:
+            cache = _StateCacheEntry(
+                state=new_state,
+                state_group=None,
+                ts=self.clock.time_msec()
+            )
+
+            self._state_cache[frozenset(event_ids)] = cache
+
+        defer.returnValue((None, new_state, prev_states))
+
+    def resolve_events(self, state_sets, event):
+        if event.is_state():
+            return self._resolve_events(
+                state_sets, event.type, event.state_key
+            )
+        else:
+            return self._resolve_events(state_sets)
+
+    def _resolve_events(self, state_sets, event_type=None, state_key=""):
         state = {}
-        for group, g_state in state_groups.items():
-            for s in g_state:
+        for st in state_sets:
+            for e in st:
                 state.setdefault(
-                    (s.type, s.state_key),
+                    (e.type, e.state_key),
                     {}
-                )[s.event_id] = s
+                )[e.event_id] = e
 
         unconflicted_state = {
             k: v.values()[0] for k, v in state.items()
@@ -302,16 +326,7 @@ class StateHandler(object):
         new_state = unconflicted_state
         new_state.update(resolved_state)
 
-        if self._state_cache is not None:
-            cache = _StateCacheEntry(
-                state=new_state,
-                state_group=None,
-                ts=self.clock.time_msec()
-            )
-
-            self._state_cache[frozenset(event_ids)] = cache
-
-        defer.returnValue((None, new_state, prev_states))
+        return new_state, prev_states
 
     @log_function
     def _resolve_state_events(self, conflicted_state, auth_events):