QTcpSocket: selecting source interface using bind() for connection to remote host with connectToHost(): don't work, possible bug

sibislaw2

Hi, i want to use certain source interface for connection to remote host. I have
3 interfaces: eth0 (192.168.230.100), wlan0(10.0.9.100), and lo:

Assuming mSocket is class member:

@QTcpSocket mSocket;@

And in constructor we use:

@
bool ret = mSocket.bind(QHostAddress("10.0.9.100"));
@

And then in timer we try to connect:

@
void CamComponent::tryToConnect()
{
mSocket.connectToHost(QHostAddress(CameraIpAddr), CameraPort);
}
@

And after this i use TCPDUMP to view outgoing packets, and they dont have source IP 10.0.9.100. Using strace i had checked that Qt makes calls to:

socket()
bind()
socket() <- this causes problem, it's QT internal problem
connect()

Is this any possibility to workaround this ? Maybe by using own sockets, creating descriptor and providing it to QTcpSocket by @QAbstractSocket::setSocketDescriptor@ ? Is this bug covers also QAbstractSocket::setSocketDescriptor ?

IamSumit

Hi.
When you bind a socket using bind method then it randomly select a port number.Here i can see you didn't specify it.may be this cause an error because randomly selected port is not matched to your port.

Is your CameraIpAddr same as 10.0.9.100 ?

sibislaw2

It is not server socket. Addresses are randomly chosen by me, not real. The clue is that bind() dont work for connect to.

Eric Vialas

Just to exclude any constructor overloading trap, have you tried:

@
bool ret=mSocket.bind(QHostAddress(QLatin1String("10.0.9.100")));
@

?

sibislaw2

I think it is related to BUG:

https://bugreports.qt-project.org/browse/QTBUG-29732

So my question, how to workaround this, or when bug will be fixed ?