How to identify requests originating from the `hiddenDOMWindow`?

Question

What event-listeners can I use to identify requests originating from the hiddenDOMWindow (or an iframe within it) in a firefox-addon? I need to do this BEFORE the request has been sent, in the "http-on-modify-request" event, for example.

What I've tried:

• register for the global "http-on-modify-request"; but I can't distinguish the source window
• add listener to the hiddenDOMWindow itself; but I can't find any before-load-event
• add listener to the hiddenDOMWindow.document; no before-load-event
• add listener to the created hiddenDOMWindow.document.iframe; no before-load-event

Answer 1

First, you need to get a DOMWindow from an nsIChannel:

function getDOMWindowFromChannel(ch) {
    var wp;
    try {
        if (ch.loadGroup && ch.loadGroup.groupObserver) {
            wp = ch.loadGroup.groupObserver.
                 QueryInterface(Ci.nsIWebProgress);
        }
    } catch (ex) {}
    try {
        if (!wp) {
            wp = ch.notificationCallbacks.
                 getInterface(Ci.nsIWebProgress);
        }
    }
    catch (ex) {}
    try {
        if (wp) {
            return wp.DOMWindow || null;
        }
    }
    catch (ex) {}
    return null;
}

Now that you got a DOMWindow, you need to find the top level window for that DOMWindow, which is not really intuitive:

function getToplevelWindow(win) {
    try {
        return win.QueryInterface(Ci.nsIInterfaceRequestor).
               getInterface(Ci.nsIWebNavigation).
               QueryInterface(Ci.nsIDocShell).
               treeOwner.
               QueryInterface(Ci.nsIInterfaceRequestor).
               getInterface(Ci.nsIXULWindow).
               docShell.
               contentViewer.DOMDocument.defaultView;
    }
    catch (ex) {
        // Likely already a top-level window.
        return win;
    }
}

Now, lets craft and install the observer, bringing all together:

function observe(channel, topic, data) {

    if (!(channel instanceof Ci.nsIChannel)) {
        return;
    }
    var win = getDOMWindowFromChannel(channel);
    if (!win) {
        return;
    }
    var topWin = getToplevelWindow(win);
    if (topWin.location.href.indexOf("chrome://browser/content/hiddenWindow") != 0) {
        return;
    }
    // do stuff, e.g.
    console.log(topWin.location.href);
}

Services.obs.addObserver(observe, "http-on-modify-request", false);

It should be noted that not all requests are nsIChannel and not all nsIChannel actually have a DOMWindow or real loadGroup associated (e.g. background requests), hence all those try catch blocks.

Also, don't forget to remove the observer again at some point, which I skipped. ;)

And lastly, here is some code to actually test this (I ran the whole thing as a Scratchpad on an about:newtab tab, which happens to have chrome privileges just like add-ons):

var hw = Services.appShell.hiddenDOMWindow;
var iframe = hw.document.createElement("iframe");
hw.document.documentElement.appendChild(iframe);
var r = iframe.contentWindow.XMLHttpRequest();
r.open("GET", "http://example.org/");
r.send();