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Turn's BitTorrent Java library (tracker and client)
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README.md

Ttorrent, a Java implementation of the BitTorrent protocol

Description

Ttorrent is a pure-Java implementation of the BitTorrent protocol, providing a BitTorrent tracker, a BitTorrent client and the related Torrent metainfo files creation and parsing capabilities. It is designed to be embedded into larger applications, but its components can also be used as standalone programs.

Ttorrent supports the following BEPs (BitTorrent enhancement proposals):

  • BEP#0003: The BitTorrent protocol specification
    This is the base official protocol specification, which Ttorrent implements fully.
  • BEP#0012: Multi-tracker metadata extension
    Full support for the announce-list meta-info key providing a tiered tracker list.
  • BEP#0015: UDP Tracker Protocol for BitTorrent
    The UDP tracker protocol is fully supported in the BitTorrent client to make announce requests to UDP trackers. UDP tracker support itself is planned.
  • BEP#0020: Peer ID conventions
    Ttorrent uses TO as the client identification string, and currently uses the -T00042- client ID prefix.
  • BEP#0023: Tracker Returns Compact Peer Lists
    Compact peer lists are supported in both the client and the tracker. Currently the tracker only supports sending back compact peer lists to an announce request.

History

This tool suite was implemented as part of Turn's (http://www.turn.com) release distribution and deployment system and is used to distribute new build tarballs to a large number of machines inside a datacenter as efficiently as possible. At the time this project was started, few Java implementations of the BitTorrent protocol existed and unfortunately none of them fit our needs:

  • Vuze's, which is very hard to extract from their codebase, and thus complex to re-integrate into another application;
  • torrent4j, which is largely incomplete and not usable;
  • Snark's, which is old, and unfortunately unstable;
  • bitext, which was also unfortunately unstable, and extremely slow.

This implementation aims at providing a down-to-earth, simple to use library. No fancy protocol extensions are implemented here: just the basics that allows for the exchange and distribution of files through the BitTorrent protocol.

Although the write performance of the BitTorrent client is currently quite poor (~10MB/sec/connected peer), it has been measured that the distribution of a 150MB file to thousands of machines across several datacenters took no more than 30 seconds, with very little network overhead for the initial seeder (only 125% of the original file size uploaded by the initial seeder).

How to use

As standalone programs

The client, tracker and torrent file manipulation utilities will all present a usage message on the console when invoked with the -h command-line flag.

As a library

Thanks to Anatoli Vladev for the code examples in #16.

Client code

// First, instantiate the Client object.
Client client = new Client(
  // This is the interface the client will listen on (you might need something
  // else than localhost here).
  InetAddress.getLocalHost(),

  // Load the torrent from the torrent file and use the given
  // output directory. Partials downloads are automatically recovered.
  SharedTorrent.fromFile(
    new File("/path/to/your.torrent"),
    new File("/path/to/output/directory")));

// At this point, can you either call download() to download the torrent and
// stop immediately after...
client.download();

// Or call client.share(...) with a seed time in seconds:
// client.share(3600);
// Which would seed the torrent for an hour after the download is complete.

// At any time you can call client.stop() to interrupt the download.

// When you're done, call client.finish() to close everything up:
client.finish();

Tracker code

// First, instantiate a Tracker object with the port you want it to listen on.
// The default tracker port recommended by the BitTorrent protocol is 6969.
Tracker tracker = new Tracker(new InetSocketAddress(6969));

// Then, for each torrent you wish to announce on this tracker, simply created
// a TrackedTorrent object and pass it to the tracker.announce() method:
FilenameFilter filter = new FilenameFilter() {
  @Override
  public boolean accept(File dir, String name) {
    return name.endsWith(".torrent");
  }
};

for (File f : new File("/path/to/torrent/files").listFiles(filter)) {
  tracker.announce(TrackedTorrent.load(f));
}

// Once done, you just have to start the tracker's main operation loop:
tracker.start();

// You can stop the tracker when you're done with:
tracker.stop();

License

This BitTorrent library is distributed under the terms of the Apache Software License version 2.0. See COPYING file for more details.

Authors and contributors

  • Maxime Petazzoni <mpetazzoni@turn.com> (Platform Engineer at Turn, Inc)
    Original author, main developer and maintainer
  • David Giffin <david@etsy.com>
    Contributed parallel hashing and multi-file torrent support.
  • Thomas Zink <thomas.zink@uni-konstanz.de>
    Fixed a piece length computation issue when the total torrent size is an exact multiple of the piece size.
  • Johan Parent <parent_johan@yahoo.com>
    Fixed a bug in unfresh peer collection and issues on download completion on Windows platforms.
  • Dmitriy Dumanskiy
    Contributed the switch from Ant to Maven.
  • Alexey Ptashniy
    Fixed an integer overflow in the calculation of a torrent's full size.

Caveats

  • Client write performance is a bit poor, mainly due to a (too?) simple piece caching algorithm.
  • End-game can be slow if the peer selected to retrieve the last piece from doesn't upload fast enough (or at all). An end-game scenario should be implemented.

Contributions are welcome in all areas, even more so for these few points above!

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