QAbstractSocket::setSocketOption not working for QAbstractSocket::SendBufferSizeSocketOption

[Athil]

I tried to use QAbstractSocket::setSocketOption for setting the send buffer size in the following manner:

code snippet:
int sizebeforeincreasing = pTcpsocket->socketOption(QAbstractSocket::SendBufferSizeSocketOption).toInt();
std::cout << "size before:" sizebeforeincreasing << "\n";
pTcpsocket->setSocketOption(QAbstractSocket::SendBufferSizeSocketOption, 2 * 1024 * 1024);
int sizeafterincreasing = pTcpsocket->socketOption(QAbstractSocket::SendBufferSizeSocketOption).toInt();

std:: cout << "size after:" sizeafterincreasing << "\n";

output:
size before : 65536
size after : 65536

[JonB]

@Athil
https://stackoverflow.com/questions/53933227/increase-receive-buffer-size-for-qtcpsocket reports similar behaviour for QAbstractSocket::ReceiveBufferSizeSocketOption on QTcpSocket. Maybe same for SendBufferSizeSocketOption?? If you have to, you might try the appropriate call on the low-level socket descriptor and see whether that does work?

[Christian Ehrlicher]

SO_SNDBUF is limited by the OS. For Linux see e.g. here: http://man7.org/linux/man-pages/man7/socket.7.html

[Athil]

@JonB said in QAbstractSocket::setSocketOption not working for QAbstractSocket::SendBufferSizeSocketOption:

https://stackoverflow.com/questions/53933227/increase-receive-buffer-size-for-qtcpsocket

I tried for ReceiveBufferSizeSocketOption, it is working. Only SendBufferSizeSocketOption is not working.

[JonB]

@Athil
Did you read the link posted above by @Christian-Ehrlicher? Are you sure your attempt to increase the send buffer size is not exceeding any specified OS maximum?

Otherwise, if it were me I'd write a 10 line C program to check what happens if you call the OS level function with SO_SNDBUF; if that does nothing it's not a Qt issue.

[Athil]

@JonB I wrote a sample code using SO_SNDBUF, i was able change the send buffer size using the native api "setsockopt"

[JonB]

@Athil
Then since you're not getting the answer you want here can only suggest: if you compile Qt yourself then step through debugger, or browse source code, to see what it's actually doing?

[Athil]

@JonB Found out the reason
case QNativeSocketEngine::SendBufferSocketOption:
// see QTBUG-30478 SO_SNDBUF should not be used on Vista or later
return false;

This is from qt source code

[JonB]

@Athil
There you are! So worth looking at source :)

But that shows return false;, I thought you said you had checked the function return result and it was returning true?