Distributing Content with BitTorrent
Pages: 1, 2, 3

Using Other People's Trackers

Yes, that's right, you can jump onto other people's trackers instead of relying on one of your own! You can share your documents without having either a web server or a tracker. Suppose I want to use the postgresql.org tracker: all I need to do is download one of their latest postgresql torrents and read the first couple of lines to identify the tracker URL:

$ wget http://bt.postgresql.org/postgresql-8.0.1.zip.torrent
$ cat bt.postgresql.org:6969 | less

In this case, the URL turns out to be http//bt.postgresql.org:6969/announce. I can reannounce the tracker of my existing torrent by using the torrent utility btreannounce (btreannounce.py).

Here's the general format:

btreannounce url torrent [ torrent ... ]

I can choose this tracker for my torrent with:

$ btreannounce http://bt.postgresql.org:6969/announce \
	pg_live.1.3.3-SRAA.iso.torrent

The postgresql.org tracker will now manage all subsequent connections to the pg_live ISO. You can review the tracker's statistics by using your browser and going to http://bt.postrgresql.org:6969. (Some sites list only the md5 checksum without naming the file, but you can compare it with the checksum generated by your own tracker).

It's good etiquette to request permission for using other people's trackers. You can prevent other people from using your tracker--as postgresql.org does, by the way--by telling bttrack to track only those torrents of which it has copies in a user-defined directory. For example, if I place a copy of the pg_live torrent file in a directory where bttrack can see it, it will limit the tracker to file sharing for just pg_live. That's the purpose of the --show_names and --allowed_dir switches:

$ bttrack --port 8099 --show_names 1 --allowed_dir ~/mytorrents \
	--dfile downloadinfo.txt

Another advantage of using this particular invocation is the detailed report that the tracker supplies.

• tracker version: 3.4.2
• server time: 2005-03-29 14:36 UTC

info hash	torrent name	size	complete	down- loading	down- loaded	trans- ferred
4e98ea442573f5b88685 37e970fd3ce6321e9e81	pg_live.1.3.3-SRAA.iso	382MiB	2	0	0	0B
	1 files	382MiB	1/2	0/0	0/0	0B

• Info hash: SHA1 hash of the "info" section of the meta info (*.torrent)
• Complete: number of connected clients with the complete file (total: unique IPs/total connections)
• Downloading: number of connected clients still downloading (total: unique IPs/total connections)
• Downloaded: reported complete downloads (total: current/all)
• Transferred: torrent size * total downloaded (does not include partial transfers)

Conclusion

I always seem to be ending articles when I say this, but ... I've only just scratched the surface of what you can do. I guess you'll just have to play with it to learn more. I recommend reading the man pages for apt-get, wget, cat, btmakemetafile, bttrack, bittorrent-downloader, and btreannounce.

Have fun.

Robert Bernier is the PostgreSQL business intelligence analyst for SRA America, a subsidiary of Software Research America (SRA).

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