static abstract class DialogIO implements AutoCloseable {

  String line;

  boolean eos, loud, noClose;

  Lock lock = lock();

  abstract String readLineImpl();

  abstract boolean isStillConnected();

  abstract void sendLine(String line);

  abstract boolean isLocalConnection();

  abstract Socket getSocket();

  int getPort() { Socket s = getSocket(); ret s == null ? 0 : s.getPort(); }

  boolean helloRead;

  int shortenOutputTo = 500;

  String readLineNoBlock() {

    String l = line;

    line = null;

    return l;

  }

  boolean waitForLine() ctex {

    ping();

    if (line != null) return true;

    //print("Readline");

    line = readLineImpl();

    //print("Readline done: " + line);

    if (line == null) eos = true;

    return line != null;

  }

  String readLine() {

    waitForLine();

    helloRead = true;

    return readLineNoBlock();

  }

  String ask(String s, Object... args) {

    if (loud) ret askLoudly(s, args);

    if (!helloRead) readLine();

    if (args.length != 0) s = format3(s, args);

    sendLine(s);

    return readLine();

  }

  String askLoudly(String s, Object... args) {

    if (!helloRead) readLine();

    if (args.length != 0) s = format3(s, args);

    print("> " + shorten(s, shortenOutputTo));

    sendLine(s);

    String answer = readLine();

    print("< " + shorten(answer, shortenOutputTo));

    return answer;

  }

  void pushback(String l) {

    if (line != null)

      fail();

    line = l;

    helloRead = false;

  }

}

static abstract class DialogHandler is IDialogHandler {}

interface IDialogHandler {

  void run(DialogIO io);

}