Regression: File.downloaded becomes negative once the first piece is fully downloaded

[corwin-of-amber]

What version of WebTorrent?
0.102.4

What operating system and Node.js version?
macOS 10.13.6
Node.js 10.0.0

What browser and version? (if using WebTorrent in the browser)

What did you expect to happen?
File.download property should always be a nonnegative integer.

What actually happened?
After the first piece (_startPiece) of the file has finished downloaded, the file's offset is subtracted from the downloaded size, causing it to be a (sometimes quite large) negative.
This occurs in file.js, line 46 (https://github.com/webtorrent/webtorrent/blob/master/lib/file.js#L46), as of revision 6fbef8e.

I noticed the negative values after upgrading from version 0.98.24, which did not have this issue.

[corwin-of-amber]

I was able to patch the problem by replacing - this.offset with - (this.offset % pieceLength). I am not 100% sure that this is how pieces work in a torrent so I leave it to your judgement.

[KayleePop]

Is this where it happened? #1479

[corwin-of-amber]

@KayleePop Yes, this seems so. I think the author of that push request only considered the case where there is only one large file and that this file starts at the first piece of the torrent. When there are multiple videos, for instance, and the video starts at a high-index piece (e.g. 1000), it does not make sense to initialize the size to pieceLength - this.offset.

[G-Ray]

I'm affected. @DiegoRBaquero what about you ?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[corwin-of-amber]

Any news about this? Seems like a pretty simple fix.
It will be so sad if WebTorrent becomes abandoned...

[DiegoRBaquero]

I'll review a PR if you a willing to take on this :)

[corwin-of-amber]

Sure, you got it.