UDP communication readyread

Damian7546

Hi,
I try do UDP communication.

Firstly I'm sending to broadcast addres 192.0.1.255 with frame to get IP addres device wihich I should exchange data.
This recive properly IP addres, after them I send data to binded device sendData so in ready read I get only one datagram (Len=1).. But rest of data I do not have in my readyread... I should get other data (Len=28,Len=28, Len=74.....) Like below:

my code below:


MyUdpCom::MyUdpCom(QObject *parent)
    : QObject{parent}
{
    socket = new QUdpSocket(this);
    socket->bind(QHostAddress::LocalHost, 5010);
    connect(socket, &QUdpSocket::readyRead, this, &MyUdpCom::readyRead);

}
void MyUdpCom::bindWithDevice(QByteArray name, QByteArray ipAddr)
{
    QByteArray buff;
    buff += name;
    buff += ipAddr; 
    socket->writeDatagram(buff, QHostAddress("192.0.1.255"), 5000);
}

void MyUdpCom::sendData(QString ipAddr)
{
    socket->writeDatagram(buff, QHostAddress(ipAddr), 5010);

}
void MyUdpCom::readyRead()
{
    QByteArray buff;
    buff.resize(socket->pendingDatagramSize());

    QHostAddress sender;
    quint16 senderPort;

    socket->readDatagram(buff.data(), buff.size(),&sender, &senderPort);

    qDebug() << "Message from sender: " << sender.toString();
    qDebug() << "Message port: " << senderPort;
    qDebug() << "Message" << buff;

    if (buff.at(0) == 0x2F){
        qDebug() << "We have Ip addres destination";
        sendData(sender.toString());
    }
}

main:

    MyUdpCom server;
    MyUdpCom client;
    client.bindWithDevice("devMy01","192.0.1.169");

Damian7546

@JonB mayby the fact that remte device change UDP port when transmit next frames...? From 59185 (3row form log) to 12810(4,5,6...row from log) ?
It can be a problem ?

JonB

@Damian7546
In readyRead() you should loop for possible multiple datagrams received:

while (socket->hasPendingDatagrams()) 
{
      QByteArray buf(socket->pendingDatagramSize(), Qt::Uninitialized);
      socket->readDatagram(buf.data(), buf.size(), &sender, &senderPort);

Does that resolve your issue?

Damian7546

@JonB No, I still the same problem.. In my qt app I recived only first and third row form wireshark log published in my first post.

Below updated readyRead() function:

void MyUdpCom::readyRead()
{
    QHostAddress sender;
    quint16 senderPort;
    
    while (socket->hasPendingDatagrams())
    {
        QByteArray buff(socket->pendingDatagramSize(), Qt::Uninitialized);
        socket->readDatagram(buff.data(), buff.size(), &sender, &senderPort);
        
        qDebug() << "Message from sender: " << sender.toString();
        qDebug() << "Message port: " << senderPort;
        qDebug() << "Message" << buff;
        
        if (buff.at(0) == 0x2F){
            qDebug() << "We have Ip addres destination";
            sendData(sender.toString());
        }
    }
}

JonB

@Damian7546
Well that's already an improvement since you said you only received one datagram and now you receive two.

Does your software still work if try commenting out the sendData(sender.toString()); just to see whether that affects reception?

You say " I recived only first and third row form wireshark log" but row #2 has different source/destination addresses from the others. If you mean you also did not receive rows #4 onward then this does not apply.

Other than this I know that UDP does not guarantee delivery so normally missing datagrams can happen. I do not know whether the fact that wireshark shows various packets/datagrams means that no loss should occur.

Damian7546

@JonB
My host IP: 192.0.1.169
From my host I write UDP frame to broadcast address: 192.0.1.255
and I get recive from 192.0.1.167... row 1 from log

Next I write from my host to 192.0.1.167 - sendData(sender.toString()); , where sender.toString() is 192.0.1.167 ... row 2 from log

Next I get data from 192.0.1.167 - row 3 from log...
and after that silence....
Other data 4,5,6,7..rows from log doesn't receive to my app....

I can't not call sendData(sender.toString()); because the device will not send data to my host (3 to 6 rows from log).
In this function I only send data like below:

void MyUdpCom::sendData(QString ipAddr)
{
    QByteArray buff;
    buff += "01202032403420445550"
    buff += crc(buff);
    socket->writeDatagram(buff, QHostAddress(ipAddr), 5010);
    
}

Damian7546

@JonB Any idea?
Maybe this is a problem with creating client and server UDP:

 MyUdpCom server;
 MyUdpCom client;
 client.bindWithDevice("devMy01","192.0.1.169");

If I call function inside MyUdpComm, I do twice times ? and this generate problems ... Any idea how to do client and server in one object ?

Damian7546

@JonB mayby the fact that remte device change UDP port when transmit next frames...? From 59185 (3row form log) to 12810(4,5,6...row from log) ?
It can be a problem ?