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 DialogIO() {
    // delegate all but sendLine
    boolean isStillConnected() { ret io.isStillConnected(); }
    String readLineImpl() { ret io.readLineImpl(); }
    boolean isLocalConnection() { ret io.isLocalConnection(); }
    Socket getSocket() { ret io.getSocket(); }
    void close() { io.close(); }

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