I'm using angular-file-upload library which uses multipart/formdata content type for file uploading. When I tried to simulate network error on the demo page by simply unplugging network cable I saw progress bar stopped and started from the current upload state after reconnecting cable. Does it mean that multipart/formdata request automatically works without reloading whole file again?
How client side knows what parts of file already loaded to server when it resumes upload?
Actually, my objective is to provide upload with possibility to resume, limit speed and size.
OK, resume after reconnect was not multipart's merit it was browsers' smart behavior. Answer is here