Make QWebSocket::QWebSocket(QTcpSocket...) public

The issue:

The current websocket implementation in Qt only allow to build a client websocket from the QWebSocket API (with QWebSocket::open()). The only way to create a server websocket is to use the class QWebSocketServer. While this class is a nice way to implement quickly a websocket server, it does not permit to re-use a real http server (3rd party library (as Qt doesn't provide anything for this purpose)) and add a websocket feature to it.

Currently the only way to achieve this, is to make a QWebSocketServer listen on another port or to use a proxy. This makes the QWebSocket hardly usable with an http server.

A previous feature request about this has been integrated into Qt 5.9: QTBUG-54276
The chosen solution was to create the function void QWebSocketServer::handleConnection(QTcpSocket *pTcpSocket)

However, to me, it is hardly usable since it forces to create an unwanted QWebSocketServer (which won't even listen anything) + we have to let inside the QTcpSocket buffer the hanshake data.

A solution:

It would be nice to have an PUBLIC API to "upgrade" a QTcpSocket into a QWebSocket (and this AFTER the http handshake done).
It almost means making "QWebSocket::QWebSocket(QTcpSocket...)" public.