handleUndecodable method

@override void handleUndecodable(List<int> data)

Called for an incoming data frame no codec could decode.

The default reports a SessionEventType.error event. Sessions may override it to answer the peer (for example, a relay session diagnoses a CRDT-aware sync client that connected to the wrong server).

Implementation

@override
void handleUndecodable(List<int> data) {
  final type = Message.getTypeOrNull(data);

  // Core-protocol frames (below the relay range) reaching a relay server are
  // almost always a CRDT-aware sync client connected to the wrong server.
  // The relay does not decode them (they carry no relay semantics), so they
  // surface here as undecodable — answer with a diagnostic instead of a
  // silent drop. Ping/pong/error decode fine and never reach this path.
  if (type != null && type < RelayMessageType.relayHello.value) {
    unawaited(
      sendMessage(
        Message.error(
          documentId: _documentIdOf(data) ?? '',
          code: Protocol.errorInvalidMessage,
          message: 'This server runs the relay protocol: '
              'the CRDT-aware sync protocol is not supported. '
              'Connect with a relay client.',
        ),
      ),
    );
    return;
  }

  super.handleUndecodable(data);
}