Take advantage of Chromium reason code for why dev tools connection was aborted

[njx]

Chromium has added a reason code that explains why the remote debugging connection was closed. We could take advantage of this to let the user know that the live development connection was terminated because the user opened Web Inspector in the browser.

https://chromiumcodereview.appspot.com/10947037/

[pthiess]

Reviewed - assigned to Glenn

[DennisKehrig]

To me this seems to be an internal Chromium API.

Looking at http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/api/debugger.json?view=markup, the "method" parameter of the "onEvent" event refers to the Remote Debugging Protocol, i.e. internally it seems "onEvent" is triggered whenever a debugger triggers one of the events that we can actually observe.

Though the current Inspector.json doesn't mention any "onDetach" event either, I tested the following in LiveDevelopment/Inspector.js without any luck:

function _onConnect() {
    $exports.triggerHandler("connect");
    exports.Debugger.enable();
    $(exports.Debugger).on("onDetach", function () {
        console.log("onDetach", arguments);
    });
    $(exports.Debugger).on("detach", function () {
        console.log("detach", arguments);
    });
}

[gruehle]

The onDetach event was added very recently to chromium, and it's not yet available in the version we have bundled with CEF. Our next CEF drop will move us up to Chromium 24, but I'm not sure if it is a version that includes this API.

[DennisKehrig]

Is that at all relevant? As far as the shell is concerned, the live preview connection is just another websocket connection. The Chrome browser we connect to has to support this feature, i.e. has to tell us that it's about to close the socket because the user opened the developer tools in the browser.

Or am I missing something?

[gruehle]

Right, my mistake. I was recently playing around with Live Development connections to Brackets, which would require a new CEF. For Live Development connections from Brackets to a browser, we just need a browser that supports those events.

It looks like the new "onDetach" event was added to the debugger API for Chrome Extensions (http://developer.chrome.com/extensions/debugger.html), but I don't see it in Inspector.json. We may need to contact someone on the chrome devtools team for details.

[DennisKehrig]

Oh, strike most of my comment, I misread your last paragraph. Yes, I agree.

[DennisKehrig]

The following works in a Chrome extension (background script):

chrome.debugger.onDetach.addListener(function() {
    console.log("onDetach", arguments);
});

Chrome version is 22.0.1229.94, the only argument is the source that was detached, the reason argument is not yet passed.

However, the above is only called when a debugger was attached via the same API:

chrome.tabs.onActivated.addListener(function(activeInfo) {
    chrome.debugger.attach({ tabId: activeInfo.tabId }, "1.0");
});

Attaching a debugger in this way prevents Brackets from connecting via the remote debugging protocol. So to take advantage of this we would need to find a way to communicate with a Chrome extension, and tunnel all our inspector stuff through that Chrome extension. Or find an official way to use the Chrome extension API externally, which I doubt is possible.

[DennisKehrig]

I contacted the team with the information Glenn provided me with. Thanks, Glenn!

[DennisKehrig]

Thanks to Pavel Feldman we're going to be able to pull this off! Awesome!

[gruehle]

Great news! How will it work?

[DennisKehrig]

There'll be an event shortly before the socket connection is closed:
https://chromiumcodereview.appspot.com/11361034/
https://bugs.webkit.org/show_bug.cgi?id=100948

[DennisKehrig]

The above pull request includes information on how to start implementing this feature.