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bencode.py

# Written by Petru Paler, Uoti Urpala, Ross Cohen and John Hoffman
# see LICENSE.txt for license information

from types import IntType, LongType, StringType, ListType, TupleType, DictType
try:
    from types import BooleanType
except ImportError:
    BooleanType = IntType
from cStringIO import StringIO

def decode_int(x, f):
    f += 1
    newf = x.index('e', f)
    n = long(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):
    colon = x.index(':', f)
    try:
        n = int(x[f:colon])
    except (OverflowError, ValueError):
        n = long(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):
    r, f = [], f+1
    while x[f] != 'e':
        v, f = decode_func[x[f]](x, f)
        r.append(v)
    return (r, f + 1)

def decode_dict(x, f):
    r, f = {}, f+1
    lastkey = None
    while x[f] != 'e':
        k, f = decode_string(x, f)
        if lastkey >= k:
            raise ValueError
        lastkey = k
        r[k], f = decode_func[x[f]](x, f)
    return (r, f + 1)

decode_func = {}
decode_func['l'] = decode_list
decode_func['d'] = decode_dict
decode_func['i'] = decode_int
decode_func['0'] = decode_string
decode_func['1'] = decode_string
decode_func['2'] = decode_string
decode_func['3'] = decode_string
decode_func['4'] = decode_string
decode_func['5'] = decode_string
decode_func['6'] = decode_string
decode_func['7'] = decode_string
decode_func['8'] = decode_string
decode_func['9'] = decode_string
  
def bdecode(x):
    try:
        r, l = decode_func[x[0]](x, 0)
    except (IndexError, KeyError):
        raise ValueError
    if l != len(x):
        raise ValueError
    return r

def test_bdecode():
    try:
        bdecode('0:0:')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('ie')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('i341foo382e')
        assert 0
    except ValueError:
        pass
    assert bdecode('i4e') == 4L
    assert bdecode('i0e') == 0L
    assert bdecode('i123456789e') == 123456789L
    assert bdecode('i-10e') == -10L
    try:
        bdecode('i-0e')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('i123')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('i6easd')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('35208734823ljdahflajhdf')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('2:abfdjslhfld')
        assert 0
    except ValueError:
        pass
    assert bdecode('0:') == ''
    assert bdecode('3:abc') == 'abc'
    assert bdecode('10:1234567890') == '1234567890'
    try:
        bdecode('02:xy')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('l')
        assert 0
    except ValueError:
        pass
    assert bdecode('le') == []
    try:
        bdecode('leanfdldjfh')
        assert 0
    except ValueError:
        pass
    assert bdecode('l0:0:0:e') == ['', '', '']
    try:
        bdecode('relwjhrlewjh')
        assert 0
    except ValueError:
        pass
    assert bdecode('li1ei2ei3ee') == [1, 2, 3]
    assert bdecode('l3:asd2:xye') == ['asd', 'xy']
    assert bdecode('ll5:Alice3:Bobeli2ei3eee') == [['Alice', 'Bob'], [2, 3]]
    try:
        bdecode('d')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('defoobar')
        assert 0
    except ValueError:
        pass
    assert bdecode('de') == {}
    assert bdecode('d3:agei25e4:eyes4:bluee') == {'age': 25, 'eyes': 'blue'}
    assert bdecode('d8:spam.mp3d6:author5:Alice6:lengthi100000eee') == {'spam.mp3': {'author': 'Alice', 'length': 100000}}
    try:
        bdecode('d3:fooe')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('di1e0:e')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('d1:b0:1:a0:e')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('d1:a0:1:a0:e')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('i03e')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('l01:ae')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('9999:x')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('l0:')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('d0:0:')
        assert 0
    except ValueError:
        pass
    try:
        bdecode('d0:')
        assert 0
    except ValueError:
        pass

bencached_marker = []

class Bencached:
    def __init__(self, s):
        self.marker = bencached_marker
        self.bencoded = s

BencachedType = type(Bencached('')) # insufficient, but good as a filter

def encode_bencached(x,r):
    assert x.marker == bencached_marker
    r.append(x.bencoded)

def encode_int(x,r):
    r.extend(('i',str(x),'e'))

def encode_string(x,r):    
    r.extend((str(len(x)),':',x))

def encode_list(x,r):    
        r.append('l')
        for e in x:
            encode_func[type(e)](e, r)
        r.append('e')

def encode_dict(x,r):
    r.append('d')
    ilist = x.items()
    ilist.sort()
    for k,v in ilist:
        r.extend((str(len(k)),':',k))
        encode_func[type(v)](v, r)
    r.append('e')

encode_func = {}
encode_func[BencachedType] = encode_bencached
encode_func[IntType] = encode_int
encode_func[LongType] = encode_int
encode_func[BooleanType] = encode_int
encode_func[StringType] = encode_string
encode_func[ListType] = encode_list
encode_func[TupleType] = encode_list
encode_func[DictType] = encode_dict
    
def bencode(x):
    r = []
    try:
        encode_func[type(x)](x, r)
    except:
        print "*** error *** could not encode type %s (value: %s)" % (t, x)
        assert 0
    return ''.join(r)

def test_bencode():
    assert bencode(4) == 'i4e'
    assert bencode(0) == 'i0e'
    assert bencode(-10) == 'i-10e'
    assert bencode(12345678901234567890L) == 'i12345678901234567890e'
    assert bencode('') == '0:'
    assert bencode('abc') == '3:abc'
    assert bencode('1234567890') == '10:1234567890'
    assert bencode([]) == 'le'
    assert bencode([1, 2, 3]) == 'li1ei2ei3ee'
    assert bencode([['Alice', 'Bob'], [2, 3]]) == 'll5:Alice3:Bobeli2ei3eee'
    assert bencode({}) == 'de'
    assert bencode({'age': 25, 'eyes': 'blue'}) == 'd3:agei25e4:eyes4:bluee'
    assert bencode({'spam.mp3': {'author': 'Alice', 'length': 100000}}) == 'd8:spam.mp3d6:author5:Alice6:lengthi100000eee'
    try:
        bencode({1: 'foo'})
        assert 0
    except AssertionError:
        pass

  
try:
    import psyco
    psyco.bind(bdecode)
    psyco.bind(bencode)
except ImportError:
    pass

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