QWebSocket from QTcpSocket

Question

I've written a small web server using QTcpServer, etc... It works fine so I wanted to get a bit further and implement Qt's WebSocket functionality. I want the WebSocket-Server to be reachable on the same port as my web server (due to limitations at my clients network).

My WebSocket-Server should be accessible at /admin/socket so I need a way to 'upgrade' a QTcpSocket (accessible from the request handler for /admin/socket) to a QWebSocket. QWebSocket has this functionality in this constructor which is used by this upgrade method in QWebSocketServerPrivate but it is all private and only used internally by the QWebSocketServer.

Is there a way to achieve what I described above? Do I have to implement my own WebSocket handler?

Answer 1

You need to copy the requisite files from Qt's sources into your project, wrap the QWebSocket into a namespace so it won't clash with Qt's own, and make the constructor non-private. That's the only way to achieve that without writing a lot of your own code, and without invoking undefined behavior.

To use your type, make it visible via using; it will hide the Qt's ::QObject then:

#include <QtCore>

namespace Foo { class QObject {}; }

int main() {
   using Foo::QObject;

   //         ours vvvvvvv        Qt's vvvvvvv
   Q_ASSERT(sizeof(QObject) < sizeof(::QObject));
}

Qt comes with a source code for a reason: you're supposed to use it when it makes sense!

Answer 2

Actually you can also use QWebSocketServer with your own web server. You should not use listen of this QWebSocketServer because your own server is already listening on some port. Instead you simply call handleConnection of this QWebSocketServer instance and pass the QTcpSocket from some request instead of letting the request be handled by your own server.

The problem is that QWebSocketServer::handleConnection expects that no data has been read from the QTcpSocket in order to access the TCP request method, URL and headers. But since you do not want to pass all sockets to the QWebSocketServer, you need to peek the data from the QTcpSocket, make your decision (handle by your own server or let QWebSocketServer handle it) e.g. by searching for Upgrade: websocket (case insensitive) or by examining the URL. Then you can either pass the QTcpSocket to your QWebSocketServer instance or execute your own handler for normal HTTP responses. In case you already fully read the HTTP header by using peek, you can simply call skip on the socket in the latter case.