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

5 files changed, 26 insertions, 12 deletions

diff --git a/roomserver/storage/interface.go b/roomserver/storage/interface.go
index be724da6..10a380e8 100644
--- a/roomserver/storage/interface.go
+++ b/roomserver/storage/interface.go
@@ -70,6 +70,7 @@ type Database interface {
 	// Stores a matrix room event in the database. Returns the room NID, the state snapshot and the redacted event ID if any, or an error.
 	StoreEvent(
 		ctx context.Context, event gomatrixserverlib.Event, txnAndSessionID *api.TransactionID, authEventNIDs []types.EventNID,
+		isRejected bool,
 	) (types.RoomNID, types.StateAtEvent, *gomatrixserverlib.Event, string, error)
 	// Look up the state entries for a list of string event IDs
 	// Returns an error if the there is an error talking to the database
diff --git a/roomserver/storage/postgres/events_table.go b/roomserver/storage/postgres/events_table.go
index e66efb09..c8eb8e2d 100644
--- a/roomserver/storage/postgres/events_table.go
+++ b/roomserver/storage/postgres/events_table.go
@@ -65,13 +65,14 @@ CREATE TABLE IF NOT EXISTS roomserver_events (
     -- Needed for setting reference hashes when sending new events.
     reference_sha256 BYTEA NOT NULL,
     -- A list of numeric IDs for events that can authenticate this event.
-    auth_event_nids BIGINT[] NOT NULL
+	auth_event_nids BIGINT[] NOT NULL,
+	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 ON CONSTRAINT roomserver_event_id_unique" +
 	" DO NOTHING" +
 	" RETURNING event_nid, state_snapshot_nid"
@@ -88,7 +89,7 @@ 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 = ANY($1)"
 
 const updateEventStateSQL = "" +
@@ -174,12 +175,14 @@ func (s *eventStatements) InsertEvent(
 	referenceSHA256 []byte,
 	authEventNIDs []types.EventNID,
 	depth int64,
+	isRejected bool,
 ) (types.EventNID, types.StateSnapshotNID, error) {
 	var eventNID int64
 	var stateNID int64
 	err := s.insertEventStmt.QueryRowContext(
 		ctx, int64(roomNID), int64(eventTypeNID), int64(eventStateKeyNID),
 		eventID, referenceSHA256, eventNIDsAsArray(authEventNIDs), depth,
+		isRejected,
 	).Scan(&eventNID, &stateNID)
 	return types.EventNID(eventNID), types.StateSnapshotNID(stateNID), err
 }
@@ -255,6 +258,7 @@ func (s *eventStatements) BulkSelectStateAtEventByID(
 			&result.EventStateKeyNID,
 			&result.EventNID,
 			&result.BeforeStateSnapshotNID,
+			&result.IsRejected,
 		); err != nil {
 			return nil, err
 		}
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index 262b0f2f..e710b99b 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -382,7 +382,7 @@ func (d *Database) GetLatestEventsForUpdate(
 // nolint:gocyclo
 func (d *Database) StoreEvent(
 	ctx context.Context, event gomatrixserverlib.Event,
-	txnAndSessionID *api.TransactionID, authEventNIDs []types.EventNID,
+	txnAndSessionID *api.TransactionID, authEventNIDs []types.EventNID, isRejected bool,
 ) (types.RoomNID, types.StateAtEvent, *gomatrixserverlib.Event, string, error) {
 	var (
 		roomNID          types.RoomNID
@@ -446,6 +446,7 @@ func (d *Database) StoreEvent(
 			event.EventReference().EventSHA256,
 			authEventNIDs,
 			event.Depth(),
+			isRejected,
 		); err != nil {
 			if err == sql.ErrNoRows {
 				// We've already inserted the event so select the numeric event ID
@@ -459,7 +460,9 @@ func (d *Database) StoreEvent(
 		if err = d.EventJSONTable.InsertEventJSON(ctx, txn, eventNID, event.JSON()); err != nil {
 			return fmt.Errorf("d.EventJSONTable.InsertEventJSON: %w", err)
 		}
-		redactionEvent, redactedEventID, err = d.handleRedactions(ctx, txn, eventNID, event)
+		if !isRejected { // ignore rejected redaction events
+			redactionEvent, redactedEventID, err = d.handleRedactions(ctx, txn, eventNID, event)
+		}
 		return nil
 	})
 	if err != nil {
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
 		}
diff --git a/roomserver/storage/tables/interface.go b/roomserver/storage/tables/interface.go
index adb06212..eba878ba 100644
--- a/roomserver/storage/tables/interface.go
+++ b/roomserver/storage/tables/interface.go
@@ -34,7 +34,10 @@ type EventStateKeys interface {
 }
 
 type Events interface {
-	InsertEvent(c context.Context, txn *sql.Tx, i types.RoomNID, j types.EventTypeNID, k types.EventStateKeyNID, eventID string, referenceSHA256 []byte, authEventNIDs []types.EventNID, depth int64) (types.EventNID, types.StateSnapshotNID, error)
+	InsertEvent(
+		ctx context.Context, txn *sql.Tx, i types.RoomNID, j types.EventTypeNID, k types.EventStateKeyNID, eventID string,
+		referenceSHA256 []byte, authEventNIDs []types.EventNID, depth int64, isRejected bool,
+	) (types.EventNID, types.StateSnapshotNID, error)
 	SelectEvent(ctx context.Context, txn *sql.Tx, eventID string) (types.EventNID, types.StateSnapshotNID, error)
 	// bulkSelectStateEventByID lookups a list of state events by event ID.
 	// If any of the requested events are missing from the database it returns a types.MissingEventError