Problem with QUdpSocket bind with port lower than 1024

edoardo.videx

Hi to everyone!
I develop my desktop application with MacOS. My application use a udp port: 1002.
I know that all the unix system has a protected ports below 1024.

Initially i binded the ip and port in this way:

// create a QUDP socket
socket = new QUdpSocket(this);
port = 1002;
QHostAddress *addr;
addr = new QHostAddress(ThisHostIpAddress);

if(!socket->bind(*addr, port)){
    qDebug() << "I cannot bind socket with IP: " + ThisHostIpAddress + " and port: " + QString::number(port);
    qDebug() << socket->errorString();
}

this->socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption,8000000);

connect(socket, SIGNAL(readyRead()), this, SLOT(OnDataReceived()));

but in this way it didn't work.
So i tried to change the binded ip address as QHostAddress::AnyIPv4:

// create a QUDP socket
socket = new QUdpSocket(this);
port = 1002;
QHostAddress *addr;
addr = new QHostAddress(ThisHostIpAddress);

if(!socket->bind(QHostAddress::AnyIPv4, port)){
    qDebug() << "I cannot bind socket with IP: " + ThisHostIpAddress + " and port: " + QString::number(port);
    qDebug() << socket->errorString();
}

this->socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption,8000000);

connect(socket, SIGNAL(readyRead()), this, SLOT(OnDataReceived()));

In this way, it seems work.. but not in the correct way. I'll explain: if my computer has only one network card, it works! But if you've 2 or more network cards you cannot decide the network card for outgoing the packets but it's always the first one.

Someone can help me?

ChrisW67

The outgoing network interface will be whichever one has the least cost route to the destination IP, or the default gateway if no more specific route exists. Without knowing the destination IP, routing table and interfaces of your machine there's no way to be more specific.

J.Hilk

@edoardo-videx said in Problem with QUdpSocket bind with port lower than 1024:

I know that all the unix system has a protected ports below 1024.

and what do you think MacOS is ?

edoardo.videx

@J-Hilk macOS is based on unix.. but i need to know if exist a workaround..

JonB

@edoardo-videx
The "workaround" is why do you want to use a port lower than 1024

My application use a udp port: 1002.

Why? Change it to use > 1024....

edoardo.videx

@JonB I cannot change the port. But anyway if, for example, i want to do a custom HTTP server that use the port 80, is it not possible? It's really absurd.

edoardo.videx

@ChrisW67 i've problem when i send a broadcast packets (255.255.255.255) in this case i cannot select the network card but MacOS choose for me

Christian Ehrlicher

@edoardo-videx said in Problem with QUdpSocket bind with port lower than 1024:

It's really absurd.

All ports below 1024 are meant to be used with special rights. If you program don't have these rights you can't use them. Don't see anything absurd here...