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);
}