Network: QUdpSocket setSocketOption seems not work

renaud.h

Hi

I have tryed to set different values for ttl option of an QUdpSocket to send multicast messages.
But when I verify with Wireshark I allways see ttl=1

setSocketOption is void function so I try step by step debugging and I found that setSocketOption fail :

in "void QAbstractSocket::setSocketOption(QAbstractSocket::SocketOption option, const QVariant &value)"

"if (QSslSocket sslSocket = qobject_cast<QSslSocket>(this))"
is false
so "sslSocket->setSocketOption" is not called
"if (!d_func()->socketEngine)"
is true
so it returns and "d_func()->socketEngine->setOption" is not called

thus option is not set.

I tryed the qt 4.8 multicast sender and I saw the same thing.
(http://qt-project.org/doc/qt-4.8/network-multicastsender.html)

Here is my environnement:
compile OS: Windows XP
execute OS: Windows XP
Qt version: 4.8.1
compiler: mingw
build type: debug

notes:
I did the same test under linux mint 12 and had the same problem.
I had the same problem also with Qt version 4.8.0

Does anyone encountered this problem ?
Is this a bug ?
Is there a workaround ?

Thanks
Renaud

KA51O

I'm having the same problem with a QTcpSocket.
I create a new socket and then try to set QAbstractSocket::KeepAliveOption to 1.
@
m_pTcpSocket = new QTcpSocket(this);
m_pTcpSocket->setSocketOption(QAbstractSocket::KeepAliveOption, 1);
int test = m_pTcpSocket->socketOption(QAbstractSocket::KeepAliveOption).toInt();
@
it stays at 0.

The problem for me is the same as Renauds. In QAbstractSocket::setSocketOption(..) the check
@
if (!d_func()->socketEngine)
return;
@
always causes the function to return without changing the socket option.

Anyone got an idea what I might be doing wrong?

KA51O

Found the problem. You can only set the socket option after the connected signal.
So this works:
@
SomeClass::ConnectToSomething()
{
m_pTcpSocket = new QTcpSocket(this);
m_pTcpSocket->connectToHost(m_sHost, m_uPort);
}

SomeClass::SlotOnConnectedSignalReceived()
{
m_pTcpSocket->setSocketOption(QAbstractSocket::KeepAliveOption, 1);
int test = m_pTcpSocket->socketOption(QAbstractSocket::KeepAliveOption).toInt();
}
@
This doesn't work:
@
m_pTcpSocket = new QTcpSocket(this);
m_pTcpSocket->setSocketOption(QAbstractSocket::KeepAliveOption, 1);
int test = m_pTcpSocket->socketOption(QAbstractSocket::KeepAliveOption).toInt();
m_pTcpSocket->connectToHost(m_sHost, m_uPort);
@

Croxman

Hi,
setSocketOption is useful function. I have used it for extension rcv and snd buffer in QUdpSocket, because i had problem with fast incoming packets and losing it, here is the code:

udpSocket->setSocketOption(QAbstractSocket::SendBufferSizeSocketOption, SNDBUF_SIZE_UDP);
udpSocket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption, RCVBUF_SIZE_UDP);

It works fine, when app are running on the same PC with local addresses 127.0.0.1. If I trying it on two PC throw local network, that functions doesn´t work. Default buffer for QUdpSocket has 8 kB and it is very few. I am using Qt ver 5.3.
Thanks for your advice,
Petr