Implement the lazy_load_members room state filter parameter

changelog.d/2970.feature

@@ -0,0 +1 @@
+add support for the lazy_loaded_members filter as per MSC1227

synapse/api/filtering.py

@@ -113,7 +113,10 @@
         },
         "contains_url": {
             "type": "boolean"
-        }
+        },
+        "lazy_load_members": {
+            "type": "boolean"
+        },
     }
 }
 
@@ -261,6 +264,9 @@ def presence_limit(self):
     def ephemeral_limit(self):
         return self._room_ephemeral_filter.limit()
 
+    def lazy_load_members(self):
+        return self._room_state_filter.lazy_load_members()
+
     def filter_presence(self, events):
         return self._presence_filter.filter(events)
 
@@ -417,6 +423,9 @@ def filter(self, events):
     def limit(self):
         return self.filter_json.get("limit", 10)
 
+    def lazy_load_members(self):
+        return self.filter_json.get("lazy_load_members", False)
+
 
 def _matches_wildcard(actual_value, filter_value):
     if filter_value.endswith("*"):

synapse/handlers/sync.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
-# Copyright 2015 - 2016 OpenMarket Ltd
+# Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2018 New Vector Ltd
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -416,29 +417,44 @@ def _load_filtered_recents(self, room_id, sync_config, now_token,
         ))
 
     @defer.inlineCallbacks
-    def get_state_after_event(self, event):
+    def get_state_after_event(self, event, types=None, filtered_types=None):
         """
         Get the room state after the given event
 
         Args:
             event(synapse.events.EventBase): event of interest
+            types(list[(str, str|None)]|None): List of (type, state_key) tuples
+                which are used to filter the state fetched. If `state_key` is None,
+                all events are returned of the given type.
+                May be None, which matches any key.
+            filtered_types(list[str]|None): Only apply filtering via `types` to this
+                list of event types.  Other types of events are returned unfiltered.
+                If None, `types` filtering is applied to all events.
 
         Returns:
             A Deferred map from ((type, state_key)->Event)
         """
-        state_ids = yield self.store.get_state_ids_for_event(event.event_id)
+        state_ids = yield self.store.get_state_ids_for_event(
+            event.event_id, types, filtered_types=filtered_types,
+        )
         if event.is_state():
             state_ids = state_ids.copy()
             state_ids[(event.type, event.state_key)] = event.event_id
         defer.returnValue(state_ids)
 
     @defer.inlineCallbacks
-    def get_state_at(self, room_id, stream_position):
+    def get_state_at(self, room_id, stream_position, types=None, filtered_types=None):
         """ Get the room state at a particular stream position
 
         Args:
             room_id(str): room for which to get state
             stream_position(StreamToken): point at which to get state
+            types(list[(str, str|None)]|None): List of (type, state_key) tuples
+                which are used to filter the state fetched. If `state_key` is None,
+                all events are returned of the given type.
+            filtered_types(list[str]|None): Only apply filtering via `types` to this
+                list of event types.  Other types of events are returned unfiltered.
+                If None, `types` filtering is applied to all events.
 
         Returns:
             A Deferred map from ((type, state_key)->Event)
@@ -453,7 +469,9 @@ def get_state_at(self, room_id, stream_position):
 
         if last_events:
             last_event = last_events[-1]
-            state = yield self.get_state_after_event(last_event)
+            state = yield self.get_state_after_event(
+                last_event, types, filtered_types=filtered_types,
+            )
 
         else:
             # no events in this room - so presumably no state
@@ -485,18 +503,42 @@ def compute_state_delta(self, room_id, batch, sync_config, since_token, now_toke
         # TODO(mjark) Check for new redactions in the state events.
 
         with Measure(self.clock, "compute_state_delta"):
+
+            types = None
+            lazy_load_members = sync_config.filter_collection.lazy_load_members()
+            filtered_types = None
+
+            if lazy_load_members:
+                # We only request state for the members needed to display the
+                # timeline:
+
+                types = [
+                    (EventTypes.Member, state_key)
+                    for state_key in set(
+                        event.sender  # FIXME: we also care about invite targets etc.
+                        for event in batch.events
+                    )
+                ]
+
+                # only apply the filtering to room members
+                filtered_types = [EventTypes.Member]
+
             if full_state:
                 if batch:
                     current_state_ids = yield self.store.get_state_ids_for_event(
-                        batch.events[-1].event_id
+                        batch.events[-1].event_id, types=types,
+                        filtered_types=filtered_types,
                     )
 
                     state_ids = yield self.store.get_state_ids_for_event(
-                        batch.events[0].event_id
+                        batch.events[0].event_id, types=types,
+                        filtered_types=filtered_types,
                     )
+
                 else:
                     current_state_ids = yield self.get_state_at(
-                        room_id, stream_position=now_token
+                        room_id, stream_position=now_token, types=types,
+                        filtered_types=filtered_types,
                     )
 
                     state_ids = current_state_ids
@@ -511,33 +553,58 @@ def compute_state_delta(self, room_id, batch, sync_config, since_token, now_toke
                     timeline_start=state_ids,
                     previous={},
                     current=current_state_ids,
+                    lazy_load_members=lazy_load_members,
                 )
             elif batch.limited:
                 state_at_previous_sync = yield self.get_state_at(
-                    room_id, stream_position=since_token
+                    room_id, stream_position=since_token, types=types,
+                    filtered_types=filtered_types,
                 )
 
                 current_state_ids = yield self.store.get_state_ids_for_event(
-                    batch.events[-1].event_id
+                    batch.events[-1].event_id, types=types,
+                    filtered_types=filtered_types,
                 )
 
                 state_at_timeline_start = yield self.store.get_state_ids_for_event(
-                    batch.events[0].event_id
+                    batch.events[0].event_id, types=types,
+                    filtered_types=filtered_types,
                 )
 
                 timeline_state = {
                     (event.type, event.state_key): event.event_id
                     for event in batch.events if event.is_state()
                 }
 
+                # TODO: optionally filter out redundant membership events at this
+                # point, to stop repeatedly sending members in every /sync as if
+                # the client isn't tracking them.
+                # When implemented, this should filter using event_ids (not mxids).
+                # In practice, limited syncs are
+                # relatively rare so it's not a total disaster to send redundant
+                # members down at this point. Redundant members are ones which
+                # repeatedly get sent down /sync because we don't know if the client
+                # is caching them or not.
+
                 state_ids = _calculate_state(
                     timeline_contains=timeline_state,
                     timeline_start=state_at_timeline_start,
                     previous=state_at_previous_sync,
                     current=current_state_ids,
+                    lazy_load_members=lazy_load_members,
                 )
             else:
                 state_ids = {}
+                if lazy_load_members:
+                    # TODO: filter out redundant members based on their mxids (not their
+                    # event_ids) at this point. We know we can do it based on mxid as this
+                    # is an non-gappy incremental sync.
+
+                    if types:
+                        state_ids = yield self.store.get_state_ids_for_event(
+                            batch.events[0].event_id, types=types,
+                            filtered_types=filtered_types,
+                        )
 
         state = {}
         if state_ids:
@@ -1448,7 +1515,9 @@ def _action_has_highlight(actions):
     return False
 
 
-def _calculate_state(timeline_contains, timeline_start, previous, current):
+def _calculate_state(
+    timeline_contains, timeline_start, previous, current, lazy_load_members,
+):
     """Works out what state to include in a sync response.
 
     Args:
@@ -1457,6 +1526,9 @@ def _calculate_state(timeline_contains, timeline_start, previous, current):
         previous (dict): state at the end of the previous sync (or empty dict
             if this is an initial sync)
         current (dict): state at the end of the timeline
+        lazy_load_members (bool): whether to return members from timeline_start
+            or not.  assumes that timeline_start has already been filtered to
+            include only the members the client needs to know about.
 
     Returns:
         dict
@@ -1472,9 +1544,25 @@ def _calculate_state(timeline_contains, timeline_start, previous, current):
     }
 
     c_ids = set(e for e in current.values())
-    tc_ids = set(e for e in timeline_contains.values())
-    p_ids = set(e for e in previous.values())
     ts_ids = set(e for e in timeline_start.values())
+    p_ids = set(e for e in previous.values())
+    tc_ids = set(e for e in timeline_contains.values())
+
+    # If we are lazyloading room members, we explicitly add the membership events
+    # for the senders in the timeline into the state block returned by /sync,
+    # as we may not have sent them to the client before.  We find these membership
+    # events by filtering them out of timeline_start, which has already been filtered
+    # to only include membership events for the senders in the timeline.
+    # In practice, we can do this by removing them from the p_ids list,
+    # which is the list of relevant state we know we have already sent to the client.
+    # see https://github.com/matrix-org/synapse/pull/2970
+    #            /files/efcdacad7d1b7f52f879179701c7e0d9b763511f#r204732809
+
+    if lazy_load_members:
+        p_ids.difference_update(
+            e for t, e in timeline_start.iteritems()
+            if t[0] == EventTypes.Member
+        )
 
     state_ids = ((c_ids | ts_ids) - p_ids) - tc_ids