Comment by carson

I will second this. At the bottom of this article there is a reference the article I wrote a while ago when Amazon released this feature. I was planing on doing multipart uploading at that time using the FileReader but there was a bug in the way S3 did CORS so I didn't want to continue until that was fixed. They fixed it and I never came back to it. Maybe be a good time to try it again. Resuming a partial upload seemed like a good win to me.