Find out the path to the addon folder in the Thunderbird API

Question

I am modifying an addon for thunderbird and found the path to the addon hardcoded in one of the javascript files. This seemed sloppy to me and I thought that it had to be possible to find out this path programmatically. However, after much googeling, I still can't find an answer to that question.

Do you know how I can find out the path to the folder (containing the install.rdf) of a Thunderbird addon?

Answer 1

You can use the AddonManager API for that:

Components.utils.import("resource://gre/modules/AddonManager.jsm");

AddonManager.getAddonByID("foo@example.com", function(addon)
{
  var uri = addon.getResourceURI("install.rdf");
  if (uri instanceof Components.interfaces.nsIFileURL)
  {
    var file = uri.file;
    alert(file.parent.path);
  }
});

For reference: Addon, nsIFileURL, nsIFile.

The assumption in the code above is that the extension is unpacked upon installation, your predecessor probably added <em:unpack>true</em:unpack> to install.rdf. Normally this flag shouldn't be specified, leaving the extension packed on disk is better for performance. If you simply need to read a file from your extension you can use XMLHttpRequest for that without requiring that it is a physical file on disk:

Components.utils.import("resource://gre/modules/AddonManager.jsm");

AddonManager.getAddonByID("foo@example.com", function(addon)
{
  var uri = addon.getResourceURI("example.txt");
  var request = new XMLHttpRequest("GET", uri.spec);
  request.addEventListener("load", function()
  {
    alert(request.responseText);
  }, false);
  request.send();
});