code: @Override
    public void upgrade(Object protocol)
    {
      Objects.requireNonNull(protocol);
  
      if (protocol instanceof ServiceWebSocket) {
        ServiceWebSocket<?,?> webSocket = (ServiceWebSocket<?,?>) protocol;
  
        upgradeWebSocket(webSocket);
      }
      else {
        throw new IllegalArgumentException(protocol.toString());
      }
    }
docs: Starts an upgrade of the HTTP request to a protocol on raw TCP.