What does this addon-sdk implementation expect as param to access addon filesystem?

Question

I'm messing around with trigger.io's browser extensions framework. It's using addon-sdk when creating .xpi's for Firefox. The tidbit in question is from a main JS file which wraps the API for later use elsewhere by the extension developers. Relevant bit:

var data = require("self").data;
// other stuff
var apiImpl = {
  // other APIs here
  file: {
    string: function (b, c, a) {
      c(data.load(b.uri.substring(data.url("").length)))
    }
  }
}

It looks like data.load() expects a string like resource://rabblerabble-at-jetpack/f/data/src/a.json.

What's with the b.uri.substring(data.url("").length))? What's the point of that? I had to go digging to figure out why I had to send

forge.file.string({uri:'resource://rabblerabble-at-jetpack/f/data/src/a.json'}, function(data) {
  toLog(data);
}, function(e) {toError(e)});

Instead of simply sending the string as the first param.

I have a feeling it's expecting some commonly-used object which you can call a .uri() on but if that's the case I've no idea what it is.

Answer 1

It looks like data.load() expects a string like resource://rabblerabble-at-jetpack/f/data/src/a.json.

data.url("") returns resource://rabblerabble-at-jetpack/f/data/. So

b.uri.substring(data.url("").length) returns src/a.json, which is what data.load() expects.

The self module has a uri property. So maybe the forge.file.string() is structured like that so that it can accept self as a parameter. That's my best guess without being able to see all the code.