Support trackers form magnet links

[arestov]

Magnet links may have trackers list, but they do no have "length" prop as usual ".torrent" files, so I gues this code may cause bugs

https://github.com/feross/bittorrent-tracker/blob/master/index.js#L395

self._torrentLength = torrent.length

example of magnet link with trackers
magnet:?xt=urn:btih:2b545d70644ade8ccaedca8a20c9253616fc0644&dn=RJD2+-+The+Colossus&tr=udp%3A%2F%2Ftracker.openbittorrent.com%3A80&tr=udp%3A%2F%2Ftracker.publicbt.com%3A80&tr=udp%3A%2F%2Ftracker.istole.it%3A6969&tr=udp%3A%2F%2Ftracker-ccc.de%3A6969&tr=udp%3A%2F%2Fopen.demonii.com%3A1337

[feross]

It looks like this code was actually working, even though you're right that torrentLength could be undefined. It just means that the tracker server was receiving some garbage (probably negative number) as the number of bytes left in the torrent.

I added code to explicitly handle this case, and exposed the torrentLength property so users can set it explicitly once they know the size.

Thanks for reporting this issue!

[arestov]

Thank for fast response :)

[feross]

Forgot to mention that I published this fix as 0.7.0.