Description

cl-bencode is a Common Lisp bencode library. Bencode is the encoding used by BitTorrent.

Features

cl-bencode supports all four different types of bencode values.

• byte strings as strings or byte vectors
• integers as integers
• lists as lists
• and dictionaries as hashtables

It's proven capable of roundtripping several torrents found in the wild.

String encoding

The bencode specification does not deal with character encodings. cl-bencode uses flexi-streams' external-formats for character encoding. The default is UTF-8. See http://weitz.de/flexi-streams/#external-formats

Binary strings

The parameter *binary-dictionary-keys* can be used to avoid decoding byte string values of dictionaries with a given key. The default value will leave the "pieces" entry of a torrent "info" dictionary intact when decoding the meta-info dictionary.

Example

BENCODE> (with-open-file (stream "/tmp/torrent"
                                 :element-type '(unsigned-byte 8))
           (decode stream))
#<HASH-TABLE :TEST EQUAL :COUNT 4 {CB06069}>
BENCODE> (gethash "announce-list" *)
(("http://tracker.openbittorrent.com/announce")
 ("udp://tracker.openbittorrent.com:80/announce"))
T
BENCODE> (type-of (gethash "pieces" (gethash "info" **)))
(SIMPLE-ARRAY (UNSIGNED-BYTE 8) (420660))
BENCODE> (equalp (ironclad:digest-sequence :sha1 (encode *** nil))
                 (ironclad:digest-file :sha1 "/tmp/torrent"))
T
BENCODE> 

Todo

• Tests
• Documentation
• Error handling