1 Introduction
3 History
4 Legal
Version: 0.2

bencode: BitTorrent Bencode Decoding in Scheme

Neil Van Dyke

License: LGPL 3   Web: http://www.neilvandyke.org/bencode-scheme/

 (require (planet neil/bencode:1:1))

1 Introduction

The bencode library is for parsing the bencoding format of the BitTorrent network protocol into basic Scheme data types (and currently PLT-specific byte strings). This is useful for inspecting .torrent files, and might later be used in the implementation of a BitTorrent client or protocol analyzer.

The format interpretation is based on the undated BitTorrent protocol documentation Web page as viewed on 2005-04-17. The mapping from those bencoding types to Scheme types is:

For example, a parse of a certain real-world .torrent file:

  (unbencode (open-input-file "debian.torrent"))
    (#"announce"      . #"http://cdimage.debian.org:6969/announce")
    (#"comment"       . #"Debian CD from cdimage.debian.org")
    (#"creation date" . 1105009474)
     (#"length"       . 600158208)
     (#"name"         . #"debian-30r4-i386-binary-1.iso")
     (#"piece length" . 524288)
     (#"pieces"          ...large byte string...))))

bencode.scm is currently specific to PLT 299/3xx, due to the need for byte I/O and some representation for byte sequences. Otherwise, the code has been written to require only R5RS, SRFI-6, and SRFI-23.


(unbencode-single port)  any/c
  port : any/c

Parses a single bencoding object (and any child objects, in the case of a list or dictionary) from input port port and yields the Scheme representation.

(unbencode port)  any/c
  port : any/c

Yields a list of the Scheme representations of all bencoding objects parsed from input port port.

3 History

4 Legal

Copyright (c) 2005-2009 Neil Van Dyke. This program is Free Software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License (LGPL 3), or (at your option) any later version. This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. See http://www.gnu.org/licenses/ for details. For other licenses and consulting, please contact the author.