Documentation for Hasher
Module
torrentfile.
hasher
Piece/File Hashers for Bittorrent meta file contents.
Hasher
— Piece hasher for Bittorrent V1 files.HasherV2
— Calculate the root hash and piece layers for file contents.HasherHybrid
— Calculate hashes for Hybrid torrentfile.
merkle_root
(
blocks
)
— Calculate the merkle root for a seq of sha256 hash digests.
Piece/File Hashers for Bittorrent meta file contents.
Hasher
Piece hasher for Bittorrent V1 files.
Takes a sorted list of all file paths, calculates sha1 hash for fixed size pieces of file data from each file seemlessly until the last piece which may be smaller than others.
Parameters
paths : list
List of files.
piece_length : int
Size of chuncks to split the data into.
total : int
Sum of all files in file list.
__init__(self, paths, piece_length)
special
Generate hashes of piece length data from filelist contents.
Source code in torrentfile\hasher.py
def __init__(self, paths, piece_length):
"""Generate hashes of piece length data from filelist contents."""
self.piece_length = piece_length
self.paths = paths
self.total = sum([os.path.getsize(i) for i in self.paths])
self.index = 0
self.current = open(self.paths[0], "rb")
logging.debug(
"Hashing v1 torrent file. Size: %s Piece Length: %s",
humanize_bytes(self.total),
humanize_bytes(self.piece_length),
)
__iter__(self)
special
Iterate through feed pieces.
Returns
self : iterator
Iterator for leaves/hash pieces.
Source code in torrentfile\hasher.py
def __iter__(self):
"""Iterate through feed pieces.
Returns
-------
self : `iterator`
Iterator for leaves/hash pieces.
"""
return self
__next__(self)
special
Generate piece-length pieces of data from input file list.
Source code in torrentfile\hasher.py
def __next__(self):
"""Generate piece-length pieces of data from input file list."""
while True:
piece = bytearray(self.piece_length)
size = self.current.readinto(piece)
if size == 0:
if not self.next_file():
raise StopIteration
elif size < self.piece_length:
return self._handle_partial(piece[:size])
else:
return sha1(piece).digest() # nosec
next_file(self)
Seemlessly transition to next file in file list.
Source code in torrentfile\hasher.py
def next_file(self):
"""Seemlessly transition to next file in file list."""
self.index += 1
if self.index < len(self.paths):
self.current.close()
self.current = open(self.paths[self.index], "rb")
return True
return False
HasherHybrid
Calculate hashes for Hybrid torrentfile.
Uses sha1 and sha256 hashes for each version # nosec of the Bittorrent protocols meta files respectively.
Parameters
path : str
path to target file.
piece_length : int
piece length for data chunks.
__init__(self, path, piece_length)
special
Construct Hasher class instances for each file in torrent.
Source code in torrentfile\hasher.py
def __init__(self, path, piece_length):
"""Construct Hasher class instances for each file in torrent."""
self.path = path
self.piece_length = piece_length
self.pieces = []
self.layer_hashes = []
self.piece_layer = None
self.root = None
self.padding_piece = None
self.padding_file = None
self.amount = piece_length // BLOCK_SIZE
logging.debug(
"Hashing partial Hybrid torrent file. Piece Length: %s Path: %s",
humanize_bytes(self.piece_length),
str(self.path),
)
with open(path, "rb") as data:
self._process_file(data)
calculate_root(self)
Calculate the root hash for opened file.
Source code in torrentfile\hasher.py
def calculate_root(self):
"""Calculate the root hash for opened file."""
self.piece_layer = b"".join(self.layer_hashes)
if len(self.layer_hashes) > 1:
pad_piece = merkle_root([bytes(32) for _ in range(self.amount)])
next_pow_two = 1 << (len(self.layer_hashes) - 1).bit_length()
remainder = next_pow_two - len(self.layer_hashes)
self.layer_hashes += [pad_piece for _ in range(remainder)]
self.root = merkle_root(self.layer_hashes)
HasherV2
Calculate the root hash and piece layers for file contents.
Iterates over 16KiB blocks of data from given file, hashes the data, then creates a hash tree from the individual block hashes until size of hashed data equals the piece-length. Then continues the hash tree until root hash is calculated.
Parameters
path : str
Path to file.
piece_length : int
Size of layer hashes pieces.
__init__(self, path, piece_length)
special
Calculate and store hash information for specific file.
Source code in torrentfile\hasher.py
def __init__(self, path, piece_length):
"""Calculate and store hash information for specific file."""
self.path = path
self.root = None
self.piece_layer = None
self.layer_hashes = []
self.piece_length = piece_length
self.num_blocks = piece_length // BLOCK_SIZE
logging.debug(
"Hashing partial v2 torrent file. Piece Length: %s Path: %s",
humanize_bytes(self.piece_length),
str(self.path),
)
with open(self.path, "rb") as fd:
self.process_file(fd)
process_file(self, fd)
Calculate hashes over 16KiB chuncks of file content.
Parameters
fd : str
Opened file in read mode.
Source code in torrentfile\hasher.py
def process_file(self, fd):
"""Calculate hashes over 16KiB chuncks of file content.
Parameters
----------
fd : `str`
Opened file in read mode.
"""
while True:
total = 0
blocks = []
leaf = bytearray(BLOCK_SIZE)
# generate leaves of merkle tree
for _ in range(self.num_blocks):
size = fd.readinto(leaf)
total += size
if not size:
break
blocks.append(sha256(leaf[:size]).digest())
# blocks is empty mean eof
if not blocks:
break
if len(blocks) != self.num_blocks:
# when size of file doesn't fill the last block
if not self.layer_hashes:
# when the there is only one block for file
next_pow_2 = 1 << int(math.log2(total) + 1)
remaining = ((next_pow_2 - total) // BLOCK_SIZE) + 1
else:
# when the file contains multiple pieces
remaining = self.num_blocks - size
# pad the the rest with zeroes to fill remaining space.
padding = [bytes(HASH_SIZE) for _ in range(remaining)]
blocks.extend(padding)
# calculate the root hash for the merkle tree up to piece-length
layer_hash = merkle_root(blocks)
self.layer_hashes.append(layer_hash)
self._calculate_root()
merkle_root(blocks)
Calculate the merkle root for a seq of sha256 hash digests.
Source code in torrentfile\hasher.py
def merkle_root(blocks):
"""Calculate the merkle root for a seq of sha256 hash digests."""
while len(blocks) > 1:
blocks = [sha256(x + y).digest() for x, y in zip(*[iter(blocks)] * 2)]
return blocks[0]