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Modify Torrent file using Python2
# This is a Python2 file to modify torrent file
# take a look at main() which at the bottom
# copy from:
# it only supports Python2, hope someone help to translate to PY3
# -- deals with bencoding
# Written by Joe Salisbury <>
# You are free to use this code in anyway you see fit, on the basis
# that if it is used, modified, or distributed, proper accreditation
# of the original author remains.
""" This module deals with the encoding and decoding of bencoded data.
decode() and encode() are the major functions available, to decode
and encode data. """
# Note: Bencoding specification:
import types
def collapse(data):
""" Given an homogenous list, returns the items of that list
concatenated together. """
return reduce(lambda x, y: x + y, data)
def stringlength(string, index = 0):
""" Given a bencoded expression, starting with a string, returns
the length of the string. """
colon = string.find(":", index) # Find the colon, ending the number.
except ValueError:
raise BencodeError("Decode", "Malformed expression", data)
# Return a list of the number characters.
num = [a for a in string[index:colon] if a.isdigit() ]
n = int(collapse(num)) # Collapse them, and turn them into an int.
# Return the length of the number, colon, and the string length.
return len(num) + 1 + n
def walk(exp, index = 1):
""" Given a compound bencoded expression, as a string, returns
the index of the end of the first dict, or list.
Start at an index of 1, to avoid the start of the actual list. """
# The expression starts with an integer.
if exp[index] == "i":
# Find the end of the integer, then, keep walking.
endchar = exp.find("e", index)
return walk(exp, endchar + 1)
# The expression starts with a string.
elif exp[index].isdigit():
# Skip to the end of the string, keep walking.
strlength = stringlength(exp, index)
return walk(exp, index + strlength)
# The expression starts with a list or dict.
elif exp[index] == "l" or exp[index] == "d":
# Walk through to the end of the sub, then keep going.
endsub = walk(exp[index:], 1)
return walk(exp, index + endsub)
# The expression is a lone 'e', so we're at the end of the list.
elif exp[index] == "e":
index += 1 # Jump one, to include it, then return the index.
return index
def inflate(exp):
""" Given a compound bencoded expression, as a string, returns the
individual data types within the string as items in a list.
Note, that lists and dicts will come out not inflated. """
# Base case, for an empty expression.
if exp == "":
return []
# The expression starts with an integer.
if ben_type(exp) == int:
# Take the integer, and inflate the rest.
end = exp.find("e") # The end of the integer.
x = exp[:end + 1]
xs = inflate(exp[end + 1:])
# The expression starts with a string.
elif ben_type(exp) == str:
# Take the string, and inflate the rest.
strlength = stringlength(exp) # The end of the string.
x = exp[:strlength]
xs = inflate(exp[strlength:])
# The expression starts with a dict, or a list.
# We can treat both the same way.
elif ben_type(exp) == list or ben_type(exp) == dict:
# Take the sub type, and inflate the rest.
end = walk(exp) # Find the end of the data type
x = exp[:end]
xs = inflate(exp[end:])
# Returns the first item, with the inflated rest of the list.
return [x] + xs
def ben_type(exp):
""" Given a bencoded expression, returns what type it is. """
if exp[0] == "i":
return int
elif exp[0].isdigit():
return str
elif exp[0] == "l":
return list
elif exp[0] == "d":
return dict
def check_type(exp, datatype):
""" Given an expression, and a datatype, checks the two against
each other. """
assert type(exp) == datatype
except AssertionError:
raise BencodeError("Encode", "Malformed expression", exp)
def check_ben_type(exp, datatype):
""" Given a bencoded expression, and a datatype, checks the two
against each other. """
assert ben_type(exp) == datatype
except AssertionError:
raise BencodeError("Decode", "Malformed expression", exp)
class BencodeError(Exception):
""" Raised if an error occurs encoding or decoding. """
def __init__(self, mode, value, data):
""" Takes information of the error. """
assert mode in ["Encode", "Decode"]
self.mode = mode
self.value = value = data
def __str__(self):
""" Pretty-prints the information. """
return repr(self.mode + ": " + self.value + " : " + str(
def encode_int(data):
""" Given an integer, returns a bencoded string of that integer. """
check_type(data, int)
return "i" + str(data) + "e"
def decode_int(data):
""" Given a bencoded string of a integer, returns the integer. """
check_ben_type(data, int)
# Find the end constant of the integer. It may not exist, which would lead
# to an error being raised.
end = data.index("e")
except ValueError:
raise BencodeError("Decode", "Cannot find end of integer expression", data)
t = data[1:end] # Remove the substring we want.
# Check for leading zeros, which are not allowed.
if len(t) > 1 and t[0] == "0":
raise BencodeError("Decode", "Malformed expression, leading zeros", data)
return int(t) # Return an integer.
def encode_str(data):
""" Given a string, returns a bencoded string of that string. """
check_type(data, str)
# Return the length of the string, the colon, and the string itself.
return str(len(data)) + ":" + data
def decode_str(data):
""" Given a bencoded string, returns the decoded string. """
check_ben_type(data, str)
# We want everything past the first colon.
colon = data.find(":")
except ValueError:
raise BencodeError("Decode", "Badly formed expression", data)
# Up to the end of the data.
strlength = stringlength(data)
# The subsection of the data we want.
return data[colon + 1:strlength]
def encode_list(data):
""" Given a list, returns a bencoded list. """
check_type(data, list)
# Special case of an empty list.
if data == []:
return "le"
# Encode each item in the list.
temp = [encode(item) for item in data]
# Add list annotation, and collapse the list.
return "l" + collapse(temp) + "e"
def decode_list(data):
""" Given a bencoded list, return the unencoded list. """
check_ben_type(data, list)
# Special case of an empty list.
if data == "le":
return []
# Remove list annotation, and inflate the l.
temp = inflate(data[1:-1])
# Decode each item in the list.
return [decode(item) for item in temp]
def encode_dict(data):
""" Given a dictionary, return the bencoded dictionary. """
check_type(data, dict)
# Special case of an empty dictionary.
if data == {}:
return "de"
# Encode each key and value for each key in the dictionary.
temp = [encode_str(key) + encode(data[key]) for key in sorted(data.keys())]
# Add dict annotation, and collapse the dictionary.
return "d" + collapse(temp) + "e"
def decode_dict(data):
""" Given a bencoded dictionary, return the dictionary. """
check_ben_type(data, dict)
# Special case of an empty dictionary.
if data == "de":
return {}
# Remove dictionary annotation
data = data[1:-1]
temp = {}
terms = inflate(data)
# For every key value pair in the terms list, decode the key,
# and add it to the dictionary, with its decoded value
count = 0
while count != len(terms):
temp[decode_str(terms[count])] = decode(terms[count + 1])
count += 2
return temp
# Dictionaries of the data type, and the function to use
encode_functions = { int : encode_int ,
str : encode_str ,
list : encode_list ,
dict : encode_dict }
decode_functions = { int : decode_int ,
str : decode_str ,
list : decode_list ,
dict : decode_dict }
def encode(data):
""" Dispatches data to appropriate encode function. """
return encode_functions[type(data)](data)
except KeyError:
raise BencodeError("Encode", "Unknown data type", data)
def decode(data):
""" Dispatches data to appropriate decode function. """
return decode_functions[ben_type(data)](data)
except KeyError:
raise BencodeError("Decode", "Unknown data type", data)
def main():
import sys
tdata = open(sys.argv[1],"rb").read()
data = decode(tdata)
data["announce"] = ""
data["info"]["source"] = "qiushichao"
if data["info"].get("private"):
del data["info"]["private"]
newdata = encode(data)
with open(sys.argv[1], "wb") as torrent_file:
print("Modify Success!")
if __name__=="__main__":
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