CLI torrent

'''
Usage:
  torrent.py [options] <file> [--url_list <url>...]
  torrent.py -h | --help

  -t, --tracker <url>     Tracker address
  [default: udp://tracker.openbittorrent.com:80/announce]
  -u, --url_list <url>    GetRight webseeds
  -p, --min_pieces <min>  [default: 1]
  -P, --max_pieces <max>  [default: 0]
  -l, --min_length <min>  [default: 16]
  -L, --max_length <max>  [default: 0]
  -h, --help              Help file

  The lengths need to be a multiple of 16 since that is the smallest
  unit torrent transports.

  This is my hack at Robert Nitsch's code to get a command line
  torrenter that I can use. I've added webseed support, docopt,
  progress, and some piece/length control.

http://www.robertnitsch.de/projects:py3createtorrent
'''
from py3bencode import bencode
from docopt import docopt
import os, hashlib, sys, requests

def auto_length(length, min_p, max_p, min_l, max_l):
    assert length > 0
    piece_length = 2**((length.bit_length()+8)//2)
    pieces = length / piece_length
    assert min_p >= 1
    while pieces < min_p:
        piece_length /= 2
        pieces *= 2
    if max_p > 0:
        while pieces > max_p:
            piece_length *= 2
            pieces /= 2
    assert min_l >= 16384
    assert min_l % 16384 == 0
    assert max_l % 16384 == 0
    if piece_length < min_l:
        piece_length = min_l
    if max_l > 0 and piece_length > max_l:
        piece_length = max_l
    return piece_length

def torrent_dict(announce, file, url_list, min_p, max_p, min_l, max_l):
    name = os.path.basename(file)
    length = os.path.getsize(file)
    piece_length = auto_length(length, min_p, max_p, min_l, max_l)
    pieces = bytearray()
    num = length // piece_length + 1
    with open(file, 'rb') as f:
        i = 0
        print('Hashing ... ')
        for piece in iter((lambda:f.read(piece_length)),b''):
            pieces += hashlib.sha1(piece).digest()
            i += 1
            sys.stdout.write('\r{}/{}'.format(i,num))
    d = {
        'announce': announce,
        'info':
        {
            'name': name,
            'length': length,
            'piece length': piece_length,
            'pieces': pieces
        }
    }
    if url_list:
        if len(url_list) is 1:
            d['url-list'] = url_list[0]
        else:
            d['url-list'] = url_list
    return d

def torrent_bencode(a, f, u, p, P, l, L):
    return bencode(torrent_dict(a, f, u, p, P, l, L))

def write_torrent(a, f, u, p=1, P=0, l=16384, L=0):
    with open(f + '.torrent', 'wb') as file:
        file.write(bencode(torrent_dict(a, f, u, p, P, l, L)))

def try_int(s, default):
    try:
        i = int(s)
    except ValueError:
        print('[warning] pieces and length must be integers, using default values')
        i = default
    return i

def try_file(f):
    if os.path.isfile(f):
        return os.path.abspath(f)
    else:
        sys.exit("[error] '{}' isn't a file".format(f))

def try_url(u):
    try:
        r = requests.head(u.strip())
        r.raise_for_status()
    except Exception as e:
        print("[warning] url '{}' had an error: {}".format(u, e))

if __name__ == '__main__':
    arguments = docopt(__doc__)
    announce = arguments['--tracker']
    file = try_file(arguments['<file>'])
    url_list = arguments['--url_list']
    min_p = try_int(arguments['--min_pieces'], 1)
    max_p = try_int(arguments['--max_pieces'], 0)
    min_l = try_int(arguments['--min_length'], 16) * 1024
    max_l = try_int(arguments['--max_length'], 0) * 1024
    write_torrent(announce, file, url_list, min_p, max_p, min_l, max_l)