I am strange that "Async" module doesn't work well

I want to

1. Download a image file, then


2. Upload the image file to Google Drive

---

var async = require('async');
var fileToUpload = require('./FileToUpload.js');

var fu;

async.waterfall([
    function (callback) {
        /*** At first, download image file ***/
        fu = new fileToUpload.FileToUpload('http://ift.tt/1Cnna84');
        callback(null, fu);
    },
    function (arg, callback) {
        /*** Secondary, upload the image file to Google Drive ***/
        arg.uploadToGoogleDrive();
        callback(null, 'done');
    }
]);

• There is no error, and


• the response from Google is that the file upload succeeded.


• In Google Drive, there is the new file


• but the data is broken so that I can't open the image.

In addition, download and upload separately, there is no problem. I can open the uploaded image in Google Drive.