Help me create a Firefox extension (Javascript XPCOM Component)

Question

I've been looking at different tutorials and I know I'm close but I'm getting lost in implementation details because some of them are a little bit dated and a few things have changed since Firefox 3. I have already written the javascript for the firefox extension, now I need to make it into an XPCOM component.

This is the functionality that I need: My Javascript file is simple, I have two functions startServer() and stopServer. I need to run startServer() when the browser starts and stopServer() when firefox quits.

Edit:

I've updated my code with a working solution (thanks to Neil). The following is in MyExtension/components/myextension.js.

Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
const CI = Components.interfaces, CC = Components.classes, CR = Components.results;

// class declaration
function MyExtension() {}

MyExtension.prototype = {
    classDescription: "My Firefox Extension",
    classID:          Components.ID("{xxxx-xxxx-xxx-xxxxx}"),
    contractID:       "@example.com/MyExtension;1",
    QueryInterface: XPCOMUtils.generateQI([CI.nsIObserver]),

    // add to category manager
    _xpcom_categories: [{
        category: "profile-after-change"
    }],

    // start socket server
    startServer: function () { /* socket initialization code */ },

    // stop socket server
    stopServer: function () { /* stop server */ },


    observe: function(aSubject, aTopic, aData) 
    {
        var obs = CC["@mozilla.org/observer-service;1"].getService(CI.nsIObserverService);

        switch (aTopic) 
        {
            case "quit-application":
                this.stopServer();
                obs.removeObserver(this, "quit-application");
                break;
            case "profile-after-change":
                this.startServer();
                obs.addObserver(this, "quit-application", false);
                break;
            default:
                throw Components.Exception("Unknown topic: " + aTopic);
        }
    }
};

var components = [MyExtension];

function NSGetModule(compMgr, fileSpec) {
    return XPCOMUtils.generateModule(components);
}

Neil · Accepted Answer · 2011-01-29 17:10:55Z

5

As far as I can tell, all of your code goes into your component.

You need a JavaScript object that represents your component and register it with the component registrar. (It can be a new object or you can multitask an existing object.) The way this is done depends on whether you're targetting Firefox 3.x or Firefox 4.

You need to register for the profile-after-change notification using the category manager. The way this is done also depends on whether you're targetting Firefox 3, Firefox 3.5/6 or Firefox 4.

When the profile-after-change notification fires, your component is then created and the observe method is called. This is where you start your server and also ask to observe the quit-application notification. Note that this also calls the observe method, so it has to check which notification it's getting.

function myExt() {}
myExt.prototype = {
  observe: function(aSubject, aTopic, aData) {
    switch (aTopic) {
      case "quit-application":
        stopServer();
        obs.removeObserver(this, "quit-application");
        break;
      case "profile-after-change":
        startServer();
        obs.addObserver(this, "quit-application", false);
        break;
    }
  }
};

answered Jan 29, 2011 at 17:10

Neil

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10 Comments

David Over a year ago

I've updated my code with my changes so far. The component is registered in compreg.dat but the observe: function doesn't get called.

Neil Over a year ago

So, does compreg.dat have entries for you component under all of a) [COMPONENTS] b) [CLASSIDS] c) [CONTRACTIDS] d) [CATEGORIES]?

David Over a year ago

Yes, I finally got it working by not using the XPCOMUtils module for the query interface and XPCOM registration. I had to write a lot more code but I'm still curious as to why it wouldn't work when I used the module.

Neil Over a year ago

Thanks for that update, it's made me realise that your QueryInterface was advertising the wrong interface, you need to advertise nsIObserver as (one of) your interface(s).

David Over a year ago

Thanks for catching that. That was my problem.

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