static DialogIO talkToSubBot(final long vport, final DialogIO io) {
  ret talkToSubBot(String.valueOf(vport), io);
}

static DialogIO talkToSubBot(final S subBot, final DialogIO io) {
  if (subBot == null) ret io;
  ret new talkToSubBot_IO(subBot, io);
}

sclass talkToSubBot_IO extends DialogIO {
  S subBot;
  DialogIO io;
  
  *(S *subBot, DialogIO *io) {}
  
  // delegate all but sendLine
  boolean isStillConnected() { ret io.isStillConnected(); }
  String readLineImpl() { ret io.readLineImpl(); }
  boolean isLocalConnection() { ret io.isLocalConnection(); }
  Socket getSocket() { ret io.getSocket(); }
  public void close() ctex { io.close(); }

  void sendLine(String line) {
    io.sendLine(format3("please forward to bot *: *", subBot, line));
  }
}