1 files changed, 43 insertions, 2 deletions
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index a422ddf633..3ffad672a7 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -20,7 +20,7 @@ from collections import namedtuple
 from ._base import SQLBaseStore
 from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
 
-from synapse.api.constants import Membership
+from synapse.api.constants import Membership, EventTypes
 from synapse.types import get_domain_from_id
 
 import logging
@@ -325,7 +325,8 @@ class RoomMemberStore(SQLBaseStore):
 
     @cachedInlineCallbacks(num_args=3)
     def was_forgotten_at(self, user_id, room_id, event_id):
-        """Returns whether user_id has elected to discard history for room_id at event_id.
+        """Returns whether user_id has elected to discard history for room_id at
+        event_id.
 
         event_id must be a membership event."""
         def f(txn):
@@ -358,3 +359,43 @@ class RoomMemberStore(SQLBaseStore):
             },
             desc="who_forgot"
         )
+
+    def get_joined_users_from_context(self, room_id, context):
+        state_group = context.state_group
+        if not state_group:
+            # If state_group is None it means it has yet to be assigned a
+            # state group, i.e. we need to make sure that calls with a state_group
+            # of None don't hit previous cached calls with a None state_group.
+            # To do this we set the state_group to a new object as object() != object()
+            state_group = object()
+
+        return self._get_joined_users_from_context(
+            room_id, state_group, context.current_state_ids
+        )
+
+    @cachedInlineCallbacks(num_args=2, cache_context=True)
+    def _get_joined_users_from_context(self, room_id, state_group, current_state_ids,
+                                       cache_context):
+        # We don't use `state_group`, its there so that we can cache based
+        # on it. However, its important that its never None, since two current_state's
+        # with a state_group of None are likely to be different.
+        # See bulk_get_push_rules_for_room for how we work around this.
+        assert state_group is not None
+
+        member_event_ids = [
+            e_id
+            for key, e_id in current_state_ids.iteritems()
+            if key[0] == EventTypes.Member
+        ]
+
+        rows = yield self._simple_select_many_batch(
+            table="room_memberships",
+            column="event_id",
+            iterable=member_event_ids,
+            retcols=['user_id'],
+            keyvalues={
+                "membership": Membership.JOIN,
+            }
+        )
+
+        defer.returnValue(set(row["user_id"] for row in rows))