Reapply redaction algo fix

- Remove m.room.aliases from v4 algo
- Only set preserved content keys if they exist (else they insert as 'null')

Author: kegsay

redactevent.go

@@ -54,7 +54,6 @@ var (
 		"m.room.create":             {"creator"},
 		"m.room.join_rules":         {"join_rule", "allow"},
 		"m.room.power_levels":       {"ban", "events", "events_default", "kick", "redact", "state_default", "users", "users_default"},
-		"m.room.aliases":            {"aliases"},
 		"m.room.history_visibility": {"history_visibility"},
 	}
 )
@@ -95,7 +94,10 @@ func redactEventJSON(eventJSON []byte, eventTypeToKeepContentFields map[string][
 	newContent := map[string]interface{}{}
 	keepContentFields := eventTypeToKeepContentFields[event.Type]
 	for _, contentKey := range keepContentFields {
-		newContent[contentKey] = event.Content[contentKey]
+		val, ok := event.Content[contentKey]
+		if ok {
+			newContent[contentKey] = val
+		}
 	}
 	// Replace the content with our new filtered content.
 	// This will zero out any keys that weren't copied in the loop above.

redactevent_test.go

@@ -33,4 +33,13 @@ func TestRedactionAlgorithmV4(t *testing.T) {
 	if !bytes.Equal(redactedv9, expectedv9) {
 		t.Fatalf("room version 9 redaction produced unexpected result\nexpected: %s\ngot: %s", string(expectedv9), string(redactedv9))
 	}
+
+	redactedv8withv9, err := MustGetRoomVersion(RoomVersionV9).RedactEventJSON(expectedv8)
+	if err != nil {
+		t.Fatal(err)
+	}
+	redactedv8withv9 = CanonicalJSONAssumeValid(redactedv8withv9)
+	if !bytes.Equal(redactedv8withv9, expectedv8) {
+		t.Fatalf("room version 8 redaction produced unexpected result\nexpected: %s\ngot: %s", string(expectedv8), string(redactedv8withv9))
+	}
 }