Remove the ability to query relations when the original event was redacted. (#5629)

Fixes #5594

Forbid viewing relations on an event once it has been redacted.

2 files changed, 23 insertions, 4 deletions

diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py

index d3de70e671..88ed6d764f 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -104,6 +104,17 @@ class _EventInternalMetadata(object):
         """
         return getattr(self, "proactively_send", True)
 
+    def is_redacted(self):
+        """Whether the event has been redacted.
+
+        This is used for efficiently checking whether an event has been
+        marked as redacted without needing to make another database call.
+
+        Returns:
+            bool
+        """
+        return getattr(self, "redacted", False)
+
 
 def _event_dict_property(key):
     # We want to be able to use hasattr with the event dict properties.
diff --git a/synapse/events/utils.py b/synapse/events/utils.py

index 987de5cab7..9487a886f5 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -52,10 +52,15 @@ def prune_event(event):
 
     from . import event_type_from_format_version
 
-    return event_type_from_format_version(event.format_version)(
+    pruned_event = event_type_from_format_version(event.format_version)(
         pruned_event_dict, event.internal_metadata.get_dict()
     )
 
+    # Mark the event as redacted
+    pruned_event.internal_metadata.redacted = True
+
+    return pruned_event
+
 
 def prune_event_dict(event_dict):
     """Redacts the event_dict in the same way as `prune_event`, except it
@@ -360,9 +365,12 @@ class EventClientSerializer(object):
         event_id = event.event_id
         serialized_event = serialize_event(event, time_now, **kwargs)
 
-        # If MSC1849 is enabled then we need to look if thre are any relations
-        # we need to bundle in with the event
-        if self.experimental_msc1849_support_enabled and bundle_aggregations:
+        # If MSC1849 is enabled then we need to look if there are any relations
+        # we need to bundle in with the event.
+        # Do not bundle relations if the event has been redacted
+        if not event.internal_metadata.is_redacted() and (
+            self.experimental_msc1849_support_enabled and bundle_aggregations
+        ):
             annotations = yield self.store.get_aggregation_groups_for_event(event_id)
             references = yield self.store.get_relations_for_event(
                 event_id, RelationTypes.REFERENCE, direction="f"