Implement rejected events (#1426)

* WIP Event rejection

* Still send back errors for rejected events

Instead, discard them at the federationapi /send layer rather than
re-implementing checks at the clientapi/PerformJoin layer.

* Implement rejected events

Critically, rejected events CAN cause state resolution to happen
as it can merge forks in the DAG. This is fine, _provided_ we
do not add the rejected event when performing state resolution,
which is what this PR does. It also fixes the error handling
when NotAllowed happens, as we were checking too early and needlessly
handling NotAllowed in more than one place.

* Update test to match reality

* Modify InputRoomEvents to no longer return an error

Errors do not serialise across HTTP boundaries in polylith mode,
so instead set fields on the InputRoomEventsResponse. Add `Err()`
function to make the API shape basically the same.

* Remove redundant returns; linting

* Update blacklist

1 files changed, 8 insertions, 5 deletions

diff --git a/roomserver/storage/sqlite3/events_table.go b/roomserver/storage/sqlite3/events_table.go
index a866c85d..773e9ade 100644
--- a/roomserver/storage/sqlite3/events_table.go
+++ b/roomserver/storage/sqlite3/events_table.go
@@ -41,13 +41,14 @@ const eventsSchema = `
     depth INTEGER NOT NULL,
     event_id TEXT NOT NULL UNIQUE,
     reference_sha256 BLOB NOT NULL,
-    auth_event_nids TEXT NOT NULL DEFAULT '[]'
+	auth_event_nids TEXT NOT NULL DEFAULT '[]',
+	is_rejected BOOLEAN NOT NULL DEFAULT FALSE
   );
 `
 
 const insertEventSQL = `
-	INSERT INTO roomserver_events (room_nid, event_type_nid, event_state_key_nid, event_id, reference_sha256, auth_event_nids, depth)
-	  VALUES ($1, $2, $3, $4, $5, $6, $7)
+	INSERT INTO roomserver_events (room_nid, event_type_nid, event_state_key_nid, event_id, reference_sha256, auth_event_nids, depth, is_rejected)
+	  VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
 	  ON CONFLICT DO NOTHING;
 `
 
@@ -63,7 +64,7 @@ const bulkSelectStateEventByIDSQL = "" +
 	" ORDER BY event_type_nid, event_state_key_nid ASC"
 
 const bulkSelectStateAtEventByIDSQL = "" +
-	"SELECT event_type_nid, event_state_key_nid, event_nid, state_snapshot_nid FROM roomserver_events" +
+	"SELECT event_type_nid, event_state_key_nid, event_nid, state_snapshot_nid, is_rejected FROM roomserver_events" +
 	" WHERE event_id IN ($1)"
 
 const updateEventStateSQL = "" +
@@ -150,13 +151,14 @@ func (s *eventStatements) InsertEvent(
 	referenceSHA256 []byte,
 	authEventNIDs []types.EventNID,
 	depth int64,
+	isRejected bool,
 ) (types.EventNID, types.StateSnapshotNID, error) {
 	// attempt to insert: the last_row_id is the event NID
 	var eventNID int64
 	insertStmt := sqlutil.TxStmt(txn, s.insertEventStmt)
 	result, err := insertStmt.ExecContext(
 		ctx, int64(roomNID), int64(eventTypeNID), int64(eventStateKeyNID),
-		eventID, referenceSHA256, eventNIDsAsArray(authEventNIDs), depth,
+		eventID, referenceSHA256, eventNIDsAsArray(authEventNIDs), depth, isRejected,
 	)
 	if err != nil {
 		return 0, 0, err
@@ -261,6 +263,7 @@ func (s *eventStatements) BulkSelectStateAtEventByID(
 			&result.EventStateKeyNID,
 			&result.EventNID,
 			&result.BeforeStateSnapshotNID,
+			&result.IsRejected,
 		); err != nil {
 			return nil, err
 		}