unwraps a url from shorteners. assumes request is available.

unwrapUrl.js

var unwrapUrl = function(input, callback) {
  var options = {};
  if (typeof(input) === 'string') {
    options.url = input;
  } else if (typeof(input) === 'object') {
    options = input;
  }

  options._attempts = options._attempts || 0;
  options.maxAttempts = options.maxAttempts || 5;

  if (options._attempts > options.maxAttempts) {
    if (callback) {
      callback(new Error('Exceeded max redirect follow attempts (' + options.maxAttempts + ')'));
      return;
    }
  }

  request({
    url: options.url,
    followRedirect: false
  }, function(err, response) {

    if (err) {
      var newErr = new Error("Error following redirects: " + err.message);
      newErr.innerError = err;

      if (callback) callback(newErr);
    } else {

      if (response.headers.location) {

        unwrapUrl({
          url: response.headers.location,
          _attempts: options._attempts + 1,
          maxAttempts: options.maxAttempts
        }, callback);

      } else {
        if (callback) callback(null, options.url);
      }

    }

  });
};