[[!comment format=mdwn
 username="joey"
 subject="""comment 1"""
 date="2017-11-14T19:19:30Z"
 content="""
It indeed would be possible for `copy --to` to check the actual file
size when the key does not have a known size, and use that for progress.
I don't know how hard it would be.

Note that, even if that were done, there's no guarantee that a given remote
will update progress information, and if it doesn't, --json-progress
won't result in any. So your code certianly needs to handle that case.
"""]]
