zisofs is a compression format for files on ISO9660 file system. It has limited support across operating systems, mainly Linux kernel. Typically a directory tree is first preprocessed by mkzftree (from the zisofs-tools package before being turned into an ISO9660 image by mkisofs, genisoimage or similar tool. The data is zlib compressed.
The specification here describes the structure of a file that has been preprocessed by mkzftree, not of a full ISO9660 ziso. Data is not decompressed, as blocks with length 0 have a special meaning. Decompression and deconstruction of this data should be done outside of Kaitai Struct.
This page hosts a formal specification of zisofs using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for Python generated by Kaitai Struct depends on the Python runtime library. You have to install it before you can parse data.
The Python runtime library can be installed from PyPI:
python3 -m pip install kaitaistructParse a local file and get structure in memory:
data = Zisofs.from_file("path/to/local/file.bin")
Or parse structure from a bytes:
from kaitaistruct import KaitaiStream, BytesIO
raw = b"\x00\x01\x02..."
data = Zisofs(KaitaiStream(BytesIO(raw)))
After that, one can get various attributes from the structure by invoking getter methods like:
data.block_pointers # => The final pointer (`block_pointers[header.num_blocks]`) indicates the end
of the last block. Typically this is also the end of the file data.
# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO
if getattr(kaitaistruct, 'API_VERSION', (0, 9)) < (0, 9):
raise Exception("Incompatible Kaitai Struct Python API: 0.9 or later is required, but you have %s" % (kaitaistruct.__version__))
class Zisofs(KaitaiStruct):
"""zisofs is a compression format for files on ISO9660 file system. It has
limited support across operating systems, mainly Linux kernel. Typically a
directory tree is first preprocessed by mkzftree (from the zisofs-tools
package before being turned into an ISO9660 image by mkisofs, genisoimage
or similar tool. The data is zlib compressed.
The specification here describes the structure of a file that has been
preprocessed by mkzftree, not of a full ISO9660 ziso. Data is not
decompressed, as blocks with length 0 have a special meaning. Decompression
and deconstruction of this data should be done outside of Kaitai Struct.
.. seealso::
Source - https://web.archive.org/web/20200612093441/https://dev.lovelyhq.com/libburnia/web/-/wikis/zisofs
"""
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self._raw_header = self._io.read_bytes(16)
_io__raw_header = KaitaiStream(BytesIO(self._raw_header))
self.header = Zisofs.Header(_io__raw_header, self, self._root)
self.block_pointers = []
for i in range((self.header.num_blocks + 1)):
self.block_pointers.append(self._io.read_u4le())
class Header(KaitaiStruct):
def __init__(self, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self._read()
def _read(self):
self.magic = self._io.read_bytes(8)
if not self.magic == b"\x37\xE4\x53\x96\xC9\xDB\xD6\x07":
raise kaitaistruct.ValidationNotEqualError(b"\x37\xE4\x53\x96\xC9\xDB\xD6\x07", self.magic, self._io, u"/types/header/seq/0")
self.uncompressed_size = self._io.read_u4le()
self.len_header = self._io.read_u1()
if not self.len_header == 4:
raise kaitaistruct.ValidationNotEqualError(4, self.len_header, self._io, u"/types/header/seq/2")
self.block_size_log2 = self._io.read_u1()
if not ((self.block_size_log2 == 15) or (self.block_size_log2 == 16) or (self.block_size_log2 == 17)) :
raise kaitaistruct.ValidationNotAnyOfError(self.block_size_log2, self._io, u"/types/header/seq/3")
self.reserved = self._io.read_bytes(2)
if not self.reserved == b"\x00\x00":
raise kaitaistruct.ValidationNotEqualError(b"\x00\x00", self.reserved, self._io, u"/types/header/seq/4")
@property
def block_size(self):
if hasattr(self, '_m_block_size'):
return self._m_block_size
self._m_block_size = (1 << self.block_size_log2)
return getattr(self, '_m_block_size', None)
@property
def num_blocks(self):
"""ceil(uncompressed_size / block_size)."""
if hasattr(self, '_m_num_blocks'):
return self._m_num_blocks
self._m_num_blocks = (self.uncompressed_size // self.block_size + (1 if (self.uncompressed_size % self.block_size) != 0 else 0))
return getattr(self, '_m_num_blocks', None)
class Block(KaitaiStruct):
def __init__(self, ofs_start, ofs_end, _io, _parent=None, _root=None):
self._io = _io
self._parent = _parent
self._root = _root if _root else self
self.ofs_start = ofs_start
self.ofs_end = ofs_end
self._read()
def _read(self):
pass
@property
def len_data(self):
if hasattr(self, '_m_len_data'):
return self._m_len_data
self._m_len_data = (self.ofs_end - self.ofs_start)
return getattr(self, '_m_len_data', None)
@property
def data(self):
if hasattr(self, '_m_data'):
return self._m_data
io = self._root._io
_pos = io.pos()
io.seek(self.ofs_start)
self._m_data = io.read_bytes(self.len_data)
io.seek(_pos)
return getattr(self, '_m_data', None)
@property
def blocks(self):
if hasattr(self, '_m_blocks'):
return self._m_blocks
self._m_blocks = []
for i in range(self.header.num_blocks):
self._m_blocks.append(Zisofs.Block(self.block_pointers[i], self.block_pointers[(i + 1)], self._io, self, self._root))
return getattr(self, '_m_blocks', None)