QTcpServer, addresses and IPv6

Return value QHostAddress of QTcpSocket::localAddress() and QTcpSocket::peerAddress() is incorrect using with QTcpServer. No matter inside overrided incomingConnection() or in the newConnection() signal. There is the issue QTBUG-47348. In that incident, the author did not manage to explain to the developers what exactly the problem was.

QTcpSocket::localAddress() and QTcpSocket::peerAddress() allways return protocol() == QAbstractSocket::IPv6Protocol. In conjunction with QTcpServer only. When QTcpSocket is used as a client, everything is fine.

It's very easy to reproduce this problem using standat Qt examples fortuneclient and fortuneserver.

For Server:

Add 

    qDebug() << clientConnection->localAddress().toString();
    qDebug() << clientConnection->localAddress().protocol();
    qDebug() << clientConnection->peerAddress().toString();    
    qDebug() << clientConnection->peerAddress().protocol();

after

QTcpSocket *clientConnection = tcpServer->nextPendingConnection();

inside 

void Server::sendFortune()

For Client:

Add 

qDebug() << tcpSocket->localAddress().toString(); 
qDebug() << tcpSocket->localAddress().protocol(); 
qDebug() << tcpSocket->peerAddress().toString(); 
qDebug() << tcpSocket->peerAddress().protocol();

in the very beginning of

void Client::readFortune()

Start this examples and look at results. 

For address 127.0.0.1

Client output:

"127.0.0.1"
QAbstractSocket::IPv4Protocol
"127.0.0.1"
QAbstractSocket::IPv4Protocol

Server output:

"::ffff:127.0.0.1"
QAbstractSocket::IPv6Protocol
"::ffff:127.0.0.1"
QAbstractSocket::IPv6Protocol

For address 192.168.2.1

Client output:

"192.168.2.1"
QAbstractSocket::IPv4Protocol
"192.168.2.1"
QAbstractSocket::IPv4Protocol

Server output:

"::ffff:192.168.2.1"
QAbstractSocket::IPv6Protocol
"::ffff:192.168.2.1"
QAbstractSocket::IPv6Protocol

And so on and so on.

There is no way to determine the correct protocol version and clear IP-address on the server side. Arguments about the fact that this is how it was intended (not a bug but a feature) do not stand up to criticism, because everything works correctly on the client side.

Probably, the core of the problem in QTcpSocket::setSocketDescriptor().