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bencode.py
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bencode.py
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#!/usr/bin/env python3
def parse_blist(bdata):
blist = []
if bdata[0:1] == b'l':
bdata = bdata[1:]
while bdata[0:1] != b'' and bdata[0:1] != b'e':
parse_func = btype_dict.get(bdata[0:1], parse_bstring)
elem, bdata = parse_func(bdata)
blist.append(elem)
return blist, bdata[1:]
def parse_bdict(bdata):
bdict = {}
if bdata[0:1] == b'd':
bdata = bdata[1:]
while bdata[0:1] != b'' and bdata[0:1] != b'e':
parse_func = btype_dict.get(bdata[0:1], parse_bstring)
key, bdata = parse_func(bdata)
if bdata[0:1] == '' or bdata[0:1] == 'e':
value = None
else:
parse_func = btype_dict.get(bdata[0:1], parse_bstring)
value, bdata = parse_func(bdata)
if key in bdict:
raise KeyError("Multiple keys in bencoded dictionary")
bdict[key] = value
return bdict, bdata[1:]
def parse_bint(bdata):
end_pos = bdata.index(ord('e'))
num_str = bdata[1:end_pos]
bdata = bdata[end_pos + 1:]
return int(num_str), bdata
def parse_bstring(bdata):
delim_pos = bdata.index(ord(':'))
length = bdata[0:delim_pos]
length = int(length)
delim_pos += 1
bstring = bdata[delim_pos:delim_pos + length]
bdata = bdata[delim_pos + length:]
if len(bstring) != length:
raise ValueError("Incorrect bencoded string length")
return bstring, bdata
def decode(bdata):
return parse_blist(bdata)[0]
btype_dict = {
b'd': parse_bdict,
b'l': parse_blist,
b'i': parse_bint
}