#include <QCoreApplication>
#include <QTimer>
#include <QUdpSocket>
#include <QHostAddress>
#include <QByteArray>
#include <QDebug>

//
// trivial UDP socket class that sends datagrams to a server and
// processes any replies that may turn up
//
class MyUdpSocket final : public QUdpSocket
{
  Q_OBJECT

public:
  MyUdpSocket (QObject* parent = nullptr)
    : QUdpSocket {parent}
  {
    // report socket errors
    connect (this, static_cast<void (MyUdpSocket::*) (MyUdpSocket::SocketError)> (&MyUdpSocket::error)
             , [this] (MyUdpSocket::SocketError const& err) {
               qDebug () << "socket error:" << err << ":" << errorString ();
             });
    connect (this, &MyUdpSocket::readyRead, this, &MyUdpSocket::get_reply);

    // bind to ephemeral port for any replies from server
    if (!bind ()) qDebug () << "bind failed";

    // send periodic datagrams to any server listening localhost:2237
    auto timer = new QTimer {this};
    connect (timer, &QTimer::timeout, [this]() {
        static const QByteArray ba {10, 'a'};
        auto bytes_sent = writeDatagram(ba, QHostAddress::LocalHost, 2237);
        qDebug () << "wrote" << bytes_sent << "byte datagram";
      });
    timer->start (2000);
  }

private:
  // process replies from server
  Q_SLOT void get_reply ()
  {
    int i {0};
    while (hasPendingDatagrams ())
      {
        buffer_.resize (pendingDatagramSize ());
        QHostAddress sender;
        quint16 sender_port;
        auto size = readDatagram (buffer_.data (), buffer_.size (), &sender, &sender_port);
        qDebug() << ++i << "read" << size << "of"
                 << buffer_.size () << "bytesAvailable()" << bytesAvailable ();
      }
  }

  QByteArray buffer_;
};

int main (int argc, char * argv[])
{
  QCoreApplication a {argc, argv};
  MyUdpSocket socket;
  return a.exec ();
}


#include "main.moc"