class ConnectionRefusedException {
  var message;
  ConnectionRefusedException(this.message);
}

class NoServiceFoundException {
  var message;
  NoServiceFoundException(this.message);
}

class InvalidFormatException {
  var message;
  InvalidFormatException(this.message);
}

class UnknownException {
  var message;
  UnknownException(this.message);
}