How to connect chrome web extension with localhost server? - sockets

Question

I have a google chrome web extension that needs to communicate with a Qt desktop application - but how?
There is chrome's native messaging, but as I want to support multiple browsers/OS, this would be too much effort because it is only for chrome.
Then there is this post that suggests setting up a local server. This is what I did, see below.
I have set up a server with Qt with QTcpServer that uses QTcpSocket's on 127.0.0.1 (localhost). But a web extension can not listen to sockets, only chrome apps can. There are 2 possible solutions on my mind:
As a workaround, I could perhaps write a small chrome app. The Qt application would talk to the chrome extension via the chrome app (chrome apps support sockets). But I think this method is clumsy and not quite elegant.
On the other hand, I have read about socket.io.
The idea is: The chrome extension talks via http requests with socket.io, and socket.io talks via sockets with my desktop app. Is this a possible solution?
What I also tried, is to directly connect to the local server with the following code. In my Qt server application, I see that there is a new connection. But I can not get a response at all (either my Qt code is wrong or it is because extensions can not listen to sockets?)
var xhr = new XMLHttpRequest();
xhr.open("GET", "http://localhost:12345", true);
xhr.onreadystatechange = function() {
if (xhr.readyState == 4) {
alert('This is the response from the server: '+ xhr.responseText );
}

Answer 1

as you already know extensions can not create direct connections:
Google Chrome Socket API in extensions
possible solution
maybe your QT application could serve a websocket and you should be able to communicate with that from Javascript:
http://www.html5rocks.com/en/tutorials/websockets/basics/
if you are unable to serve websockets from inside the QT application, another approach could be create a "bridge" a little script that could serve a websocket to your JavaScript and pass the messages from/to the QT application
you will find plenty of examples on websockets, the easy way to get into this could be creating a little server using node.js to play with it stackabuse.com/node-js-websocket-examples-with-socket-io/
oh! and do a search for "websocket same origin policy"
Example of an extension using websockets (that will be useful for debugging): chrome.google.com/webstore/detail/simple-websocket-client/pfdhoblngboilpfeibdedpjgfnlcodoo?hl=en
hope this helps