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# The contents of this file are subject to the BitTorrent Open Source License
# Version 1.1 (the License). You may not copy or use this file, in either
# source code or executable form, except in compliance with the License. You
# may obtain a copy of the License at http://www.bittorrent.com/license/.
#
# Software distributed under the License is distributed on an AS IS basis,
# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
# for the specific language governing rights and limitations under the
# License.
# Written by Petru Paler
# Modified by Julien (jvoisin) Voisin
'''
A quick (and also nice) lib to bencode/bdecode torrent files
'''
import types
class BTFailure(Exception):
'''Custom Exception'''
pass
class Bencached(object):
'''Custom type : cached string'''
__slots__ = ['bencoded']
def __init__(self, string):
self.bencoded = string
def decode_int(x, f):
'''decode an int'''
f += 1
newf = x.index('e', f)
n = int(x[f:newf])
if x[f] == '-':
if x[f + 1] == '0':
raise ValueError
elif x[f] == '0' and newf != f + 1:
raise ValueError
return (n, newf + 1)
def decode_string(x, f):
'''decode a string'''
colon = x.index(':', f)
n = int(x[f:colon])
if x[f] == '0' and colon != f + 1:
raise ValueError
colon += 1
return (x[colon:colon + n], colon + n)
def decode_list(x, f):
'''decode a list'''
result = []
f += 1
while x[f] != 'e':
v, f = DECODE_FUNC[x[f]](x, f)
result.append(v)
return (result, f + 1)
def decode_dict(x, f):
'''decode a dict'''
result = {}
f += 1
while x[f] != 'e':
k, f = decode_string(x, f)
result[k], f = DECODE_FUNC[x[f]](x, f)
return (result, f + 1)
def encode_bool(x, r):
'''bencode a boolean'''
if x:
encode_int(1, r)
else:
encode_int(0, r)
def encode_int(x, r):
'''bencode an integer/float'''
r.extend(('i', str(x), 'e'))
def encode_list(x, r):
'''bencode a list/tuple'''
r.append('l')
[ENCODE_FUNC[type(item)](item, r) for item in x]
r.append('e')
def encode_dict(x, result):
'''bencode a dict'''
result.append('d')
ilist = x.items()
ilist.sort()
for k, v in ilist:
result.extend((str(len(k)), ':', k))
ENCODE_FUNC[type(v)](v, result)
result.append('e')
DECODE_FUNC = {}
DECODE_FUNC.update(dict([(str(x), decode_string) for x in xrange(9)]))
DECODE_FUNC['l'] = decode_list
DECODE_FUNC['d'] = decode_dict
DECODE_FUNC['i'] = decode_int
ENCODE_FUNC = {}
ENCODE_FUNC[Bencached] = lambda x, r: r.append(x.bencoded)
ENCODE_FUNC[types.IntType] = encode_int
ENCODE_FUNC[types.LongType] = encode_int
ENCODE_FUNC[types.StringType] = lambda x, r: r.extend((str(len(x)), ':', x))
ENCODE_FUNC[types.ListType] = encode_list
ENCODE_FUNC[types.TupleType] = encode_list
ENCODE_FUNC[types.DictType] = encode_dict
ENCODE_FUNC[types.BooleanType] = encode_bool
def bencode(string):
'''bencode $string'''
table = []
ENCODE_FUNC[type(string)](string, table)
return ''.join(table)
def bdecode(string):
'''decode $string'''
try:
result, lenght = DECODE_FUNC[string[0]](string, 0)
except (IndexError, KeyError, ValueError):
raise BTFailure('Not a valid bencoded string')
if lenght != len(string):
raise BTFailure('Invalid bencoded value (data after valid prefix)')
return result
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