Is it possible to migrate preferences from a Firefox XUL addon to an SDK addon? - firefox

Question

I'm down to the (hopefully) last hurdle in the process of migrating our extension from XUL to Firefox SDK, but I've got one last sticking point:
Preferences.
There are a number of preferences set that simply MUST be migrated when the SDK version of the addon is installed over the top of the XUL addon. These preferences are not exposed to the end user for various reasons. The preference namespacing between the two architectures are completely different. For example -
A "version_number" preference in XUL is named arbitrarily by the developer, and appears as such in about:config :
my.preference.name
However, in SDK, they are scoped to the extension in question:
extensions.[extension ID].my.preference.name
Can preferences from XUL addons be migrated for re-use inside SDK addons? If so, how?

Answer 1

While it didn't seem possible to read from preferences outside the SDK addon's namespace, it WAS possible to write into the EXPECTED namespace in the old XUL extension. The solution we came up with was to publish a small, final point release of the old XUL addon with a small bit of extra logic responsible for carrying out this migration before we publish the new SDK version to AMO.
Here's a pseudocode representation of our approach:
ContentScript.js
function initNewFFInstallation() {
...
if (checkIsUpgrade()) {
var keys = getPrefKeys()
migratePrefs(keys);
}
}
Utils.js - acts as a bridge to expose Overlay functionality to the content script
Util.prototype.getPrefsBranch = function() {
return Components.classes["#mozilla.org/preferences-service;1"].
getService(Components.interfaces.nsIPrefService).
getBranch("my.prefs.ns.");
}
Util.prototype.getV2PrefsBranch = function() {
return Components.classes["#mozilla.org/preferences-service;1"].
getService(Components.interfaces.nsIPrefService).
getBranch("extensions.[SDK_ADDON_ID].");
}
Util.prototype.setBoolPref = function(key, val) {
this.getPrefsBranch().setBoolPref(key, val);
this.getPrefsBranch().setBoolPref(key, val);
}
Util.prototype.setCharPref = function(key, val) {
this.getPrefsBranch().setCharPref (key, val);
this.getV2PrefsBranch().setCharPref (key, val);
}
//copies all the preferences over
Util.prototype.migratePrefs = function(boolPrefKeys, charPrefKeys) {
boolPrefKeys.each(function (key) {
this.getV2PrefsBranch().setBoolPref(key, this.getPrefsBranch().getBoolPref(key));
});
charPrefKeys.forEach(function (key) {
this.getV2PrefsBranch().setCharPref(key, this.getPrefsBranch().getCharPref(key));
});
}
Then in our scriptcompiler.js, which actually injects the scripts onto the page, the util methods are hooked onto the SafeWindow object.
injectScript: function(script, unsafeContentWin) {
var safeWin=new XPCNativeWrapper(unsafeContentWin);
var sandbox=new Components.utils.Sandbox(safeWin, {"sandboxPrototype":safeWin});
sandbox.window=safeWin;
sandbox.document=sandbox.window.document;
sandbox.unsafeWindow=unsafeContentWin;
var util = new Util();
//...other APIs
sandbox.migratePreferences=app_gmCompiler.hitch(util , "migratePreferences");
try {
Components.utils.evalInSandbox("(function(){"+script+"})()", sandbox);
} catch (e) {
}
}