bytesSent property
Bytes the store has acknowledged. Present on UploadEvent.progress.
Google's own count, not this package's. A resumable upload PUTs one chunk at a time and answers each with the range it now holds, and this is that range — so the number is what Play says it has, arriving when Play says it. It cannot run ahead of the socket, and it stops arriving when the transfer stops, which is the property the whole signal exists for: a tick driven by a timer turns at the same rate whether the connection is moving or dead, and that is exactly the failure this is meant to make visible.
Absolute, never a count from the start of this run. A resumable upload that resumes picks up at the offset the store already holds, and reading the number off the wire is what makes the first line after a resume report that offset instead of a jump from zero.
One line per chunk, and a chunk is 1 MiB — so a 68 MB bundle produces about sixty-eight of these, which is tens and not thousands.
Implementation
final int? bytesSent;