Implement soft fail

synapse/events/__init__.py

@@ -77,6 +77,20 @@ class _EventInternalMetadata(object):
         """
         return getattr(self, "recheck_redaction", False)
 
+    def is_soft_failed(self):
+        """Whether the event has been soft failed.
+
+        Soft failed events should be handled as usual, except:
+            1. They should not go down sync or event streams, or generally
+               sent to clients.
+            2. They should not be added to the forward extremities (and
+               therefore not to current state).
+
+        Returns:
+            bool
+        """
+        return getattr(self, "soft_failed", False)
+
 
 def _event_dict_property(key):
     # We want to be able to use hasattr with the event dict properties.