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.

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).

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

• 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.

• 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!