Jun 05, 2010

Getting rid of dead bittorrent trackers for rtorrent by scrubbing .torrent files

If you're downloading stuff off the 'net via bt like me, then TPB is probably quite a familiar place to you.

Ever since the '09 trial there were a problems with TPB trackers (tracker.thepiratebay.org) - the name gets inserted into every .torrent yet it points to 127.0.0.1.
Lately, TPB offshot, tracker.openbittorrent.com suffers from the same problem and actually there's a lot of other trackers in .torrent files that point either at 0.0.0.0 or 127.0.0.1 these days.
As I use rtorrent, I have an issue with this - rtorrent seem pretty dumb when it comes to tracker filtering so it queries all of them on a round-robin basis, without checking where it's name points to or if it's down for the whole app uptime, and queries take quite a lot of time to timeout, so that means at least two-minute delay in starting download (as there's TPB trackers first), plus it breaks a lot of other things like manual tracker-cycling ("t" key), since it seem to prefer only top-tier trackers and these are 100% down.
Now the problem with http to localhost can be solved with the firewall, of course, although it's an ugly solution, and 0.0.0.0 seem to fail pretty fast by itself, but stateless udp is still a problem.
Another way to tackle the issue is probably just to use a client that is capable of filtering the trackers by ip address, but that probably means some heavy-duty stuff like azureus or vanilla bittorrent which I've found pretty buggy and also surprisingly heavy in the past.

So the easiest generic solution (which will, of course, work for rtorrent) I've found is just to process the .torrent files before feeding them to the leecher app. Since I'm downloading these via firefox exclusively, and there I use FlashGot (not the standard "open with" interface since I also use it to download large files on remote machine w/o firefox, and afaik it's just not the way "open with" works) to drop them into an torrent bin via script, it's actually a matter of updating the link-receiving script.

Bencode is not a mystery, plus it's pure-py implementation is actually the reference one, since it's a part of original python bittorrent client, so all I basically had to do is to rip bencode.py from it and paste the relevant part into the script.
The right way might've been to add dependency on the whole bittorrent client, but it's an overkill for such a simple task plus the api itself seem to be purely internal and probably a subject to change with client releases anyway.

So, to the script itself...

# URL checker
def trak_check(trak):
    if not trak: return False
    try: ip = gethostbyname(urlparse(trak).netloc.split(':', 1)[0])
    except gaierror: return True # prehaps it will resolve later on
    else: return ip not in ('127.0.0.1', '0.0.0.0')

# Actual processing
torrent = bdecode(torrent)
for tier in list(torrent['announce-list']):
    for trak in list(tier):
        if not trak_check(trak):
            tier.remove(trak)
            # print >>sys.stderr, 'Dropped:', trak
    if not tier: torrent['announce-list'].remove(tier)
# print >>sys.stderr, 'Result:', torrent['announce-list']
if not trak_check(torrent['announce']):
    torrent['announce'] = torrent['announce-list'][0][0]
torrent = bencode(torrent)
That, plus the simple "fetch-dump" part, if needed.
No magic of any kind, just a plain "announce-list" and "announce" urls check, dropping each only if it resolves to that bogus placeholder IPs.

I've wanted to make it as light as possible so no logging or optparse/argparse stuff I tend cram everywhere I can, and the extra and heavy imports like urllib/urllib2 are conditional as well. The only dependency is python (>=2.6) itself.

Basic use-case is one of these:

% brecode.py < /path/to/file.torrent > /path/to/proccessed.torrent
% brecode.py http://tpb.org/torrents/myfile.torrent > /path/to/proccessed.torrent
% brecode.py http://tpb.org/torrents/myfile.torrent\
    -r http://tpb.org/ -c "...some cookies..." -d /path/to/torrents-bin/

All the extra headers like cookies and referer are optional, so is the destination path (dir, basename is generated from URL). My use-case in FlashGot is this: "[URL] -r [REFERER] -c [COOKIE] -d /mnt/p2p/bt/torrents"

And there's the script itself.

Quick, dirty and inconclusive testing showed almost 100 KB/s -> 600 KB/s increase on several different (two successive tests on the same file even with clean session are obviously wrong) popular and unrelated .torrent files.
That's pretty inspiring. Guess now I can waste even more time on the TV-era crap than before, oh joy ;)
Member of The Internet Defense League