code: private boolean checkLongPollingOrder(HttpAcceptSession session) {
          if (firstWriter && !validateSequenceNo && longpoll(session)) {
              String message = "Out of order long-polling request, must not be first";
              setCloseException(new IOException(message));
              HttpStatus status = HttpStatus.CLIENT_BAD_REQUEST;
              session.setStatus(status);
              session.setWriteHeader(HEADER_CONTENT_LENGTH, "0");
              session.close(true);
              return false;
          }
          return true;
      }
docs: If the first write request is long-polling, then it is out of order