Merge pull request #6553 from matrix-org/babolivier/fix-context-filter

 Use the filtered version of an event when responding to /context requests for that event

2 files changed, 7 insertions, 3 deletions

diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 22768e97ff..60b8bbc7a5 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -907,7 +907,10 @@ class RoomContextHandler(object):
 
         results["events_before"] = yield filter_evts(results["events_before"])
         results["events_after"] = yield filter_evts(results["events_after"])
-        results["event"] = event
+        # filter_evts can return a pruned event in case the user is allowed to see that
+        # there's something there but not see the content, so use the event that's in
+        # `filtered` rather than the event we retrieved from the datastore.
+        results["event"] = filtered[0]
 
         if results["events_after"]:
             last_event_id = results["events_after"][-1].event_id
@@ -938,7 +941,7 @@ class RoomContextHandler(object):
         if event_filter:
             state_events = event_filter.filter(state_events)
 
-        results["state"] = state_events
+        results["state"] = yield filter_evts(state_events)
 
         # We use a dummy token here as we only care about the room portion of
         # the token, which we replace.
diff --git a/synapse/visibility.py b/synapse/visibility.py
index dffe943b28..100dc47a8a 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -52,7 +52,8 @@ def filter_events_for_client(
     apply_retention_policies=True,
 ):
     """
-    Check which events a user is allowed to see
+    Check which events a user is allowed to see. If the user can see the event but its
+    sender asked for their data to be erased, prune the content of the event.
 
     Args:
         storage