I need a way to convert .torrents into magnet links. Would like a way to do so in python. Are there any libraries that already do this?
You can do this with the bencode module, extracted from BitTorrent.
To show you an example, I downloaded a torrent ISO of Ubuntu from here:
http://releases.ubuntu.com/12.04/ubuntu-12.04.1-desktop-i386.iso.torrent
Then, you can parse it in Python like this:
>>> import bencode
>>> torrent = open('ubuntu-12.04.1-desktop-i386.iso.torrent', 'r').read()
>>> metadata = bencode.bdecode(torrent)
A magnet hash is calculated from only the "info" section of the torrent metadata and then encoded in base32, like this:
>>> hashcontents = bencode.bencode(metadata['info'])
>>> import hashlib
>>> digest = hashlib.sha1(hashcontents).digest()
>>> import base64
>>> b32hash = base64.b32encode(digest)
>>> b32hash
'CT76LXJDDCH5LS2TUHKH6EUJ3NYKX4Y6'
You can verify that this is correct by looking here and you will see the magnet link is:
magnet:?xt=urn:btih:CT76LXJDDCH5LS2TUHKH6EUJ3NYKX4Y6
If you want to fill in some extra parameters to the magnet URI:
>>> params = {'xt': 'urn:btih:%s' % b32hash,
... 'dn': metadata['info']['name'],
... 'tr': metadata['announce'],
... 'xl': metadata['info']['length']}
>>> import urllib
>>> paramstr = urllib.urlencode(params)
>>> magneturi = 'magnet:?%s' % paramstr
>>> magneturi
'magnet:?dn=ubuntu-12.04.1-desktop-i386.iso&tr=http%3A%2F%2Ftorrent.ubuntu.com%3A6969%2Fannounce&xl=729067520&xt=urn%3Abtih%3ACT76LXJDDCH5LS2TUHKH6EUJ3NYKX4Y6'