从UDP连接接收结构化数据

Question

I use Kolor Application for play 3D movie.this application send player status on the UDP port.

UDP messages can be used by any other application. For example, a 3D audio engine can use these informations to produce 3D sound in accordance with video playback made by Kolor Eyes.

UDP messages are in JSON format ( http://www.json.org/ ). So you have to use a JSON parser to decode the message.

Here is the current structure of UDP message :

"id": "ked" --- message identifier
"yaw": float --- yaw in radians
"pitch": float --- pitch in radians
"roll": float --- roll in radians
"url": string --- current video url
"state": enum --- playback state, integer possible values are : 0 (StoppedState), 1 (PlayingState), 2 (PausedState)
"position": int --- current video playback position in milliseconds

I create c# application To receive data from UDP port and convert this to ASCII String

static void Main(string[] args)
{         
    int localPort = 7755;
    IPEndPoint remoteSender = new IPEndPoint(IPAddress.Any, 0);                 
    // Create UDP client
    UdpClient client = new UdpClient(localPort);
    UdpState state = new UdpState(client, remoteSender);
    // Start async receiving
    client.BeginReceive(new AsyncCallback(DataReceived), state);
    // Wait for any key to terminate application
    Console.ReadKey();
    client.Close();
}
private static void DataReceived(IAsyncResult ar)
{
    UdpClient c = (UdpClient)((UdpState)ar.AsyncState).c;
    IPEndPoint wantedIpEndPoint = (IPEndPoint)((UdpState)(ar.AsyncState)).e;
    IPEndPoint receivedIpEndPoint = new IPEndPoint(IPAddress.Any, 0);
    Byte[] receiveBytes = c.EndReceive(ar, ref receivedIpEndPoint);

    // Check sender
    bool isRightHost = (wantedIpEndPoint.Address.Equals(receivedIpEndPoint.Address)) || wantedIpEndPoint.Address.Equals(IPAddress.Any);
    bool isRightPort = (wantedIpEndPoint.Port == receivedIpEndPoint.Port) || wantedIpEndPoint.Port == 0;
    if (isRightHost && isRightPort)
    {               
        string receivedText = Encoding.Default.GetString(receyiveBytes);
        Console.WriteLine(receivedText);
    }
    // Restart listening for udp data packages
    c.BeginReceive(new AsyncCallback(DataReceived), ar.AsyncState);

}

But output result in console show incorrect result

  qbjs☺   E   ☼   ¬   >☻  ☻ id♥ ked   ↕♣  ♣ pitch         U← position  '    ♦ roll
  ♥ url   ) file:///C:/Users/iman/Desktop/FIN_hi2.mp4 '¶  ♥ yaw           ♀   ∟
  0   @   T   `   ~

Answer 1

The messages sent by KolorEyes are not encoded as JSON, but some binary derivative. It may be Qt Binary Json (qbjs), but I cannot find much info about that.

Qt5 internally transform JSON documents into a binary representation, and this is what gets transmitted over UDP. http://doc.qt.io/qt-5/qjsondocument.html

This gives me the JSON document, in a Qt5 app:

void MainWindow::initSocket()
{
    udpSocket = new QUdpSocket(this);
    udpSocket->bind(QHostAddress::LocalHost, 7755);

    connect(udpSocket, SIGNAL(readyRead()),
            this, SLOT(readPendingDatagrams()));
}

void MainWindow::readPendingDatagrams()
{
    while (udpSocket->hasPendingDatagrams()) {
        QByteArray datagram;
        datagram.resize(udpSocket->pendingDatagramSize());
        QHostAddress sender;
        quint16 senderPort;

        udpSocket->readDatagram(datagram.data(), datagram.size(),
                            &sender, &senderPort);

        QJsonDocument document = QJsonDocument::fromBinaryData(datagram);
        qDebug() << document;
    }
}