Does QSslSocket disconnect after a period of idle time?

[wysota]

If the QAbstractSocket::KeepAliveOption is set on both peers, if one of the two tcp sockets does not receive a keep-alive packet back in time is this triggered up the Qt level ?

As already said, this is implemented by the operating system.

so in other words by setting the keep-alive option can we findout if the other peer is still there or gone ? and can/should we trust keep-alive?

Trust no-one. How can you be sure you're not talking to some alien implementation of the client? In networking you cannot dump any decision on your peer if you can't trust it. You have to be autonomous in your decisions. If you decide you need to receive some heart-beat from the client every 5 minutes and you don't receive it as expected then close the connection yourself without waiting for the tcp/ip stack to do it for you. And first of all understand how underlying protocols (at least tcp and ip) work, what they guarantee and what they don't guarantee.