Gzip is a popular and standard single-file archiving format. It essentially provides a container that stores original file name, timestamp and a few other things (like optional comment), basic CRCs, etc, and a file compressed by a chosen compression algorithm.
As of 2019, there is actually only one working solution for compression algorithms, so it's typically raw DEFLATE stream (without zlib header) in all gzipped files.
This page hosts a formal specification of .gz file format 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 = Gzip.from_file("path/to/local/file.gz")
Or parse structure from a bytes:
from kaitaistruct import KaitaiStream, BytesIO
raw = b"\x00\x01\x02..."
data = Gzip(KaitaiStream(BytesIO(raw)))
After that, one can get various attributes from the structure by invoking getter methods like:
data.compression_method # => Compression method used to compress file body. In practice, only
one method is widely used: 8 = deflate.
# 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
from enum import Enum
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 Gzip(KaitaiStruct):
"""Gzip is a popular and standard single-file archiving format. It
essentially provides a container that stores original file name,
timestamp and a few other things (like optional comment), basic
CRCs, etc, and a file compressed by a chosen compression algorithm.
As of 2019, there is actually only one working solution for
compression algorithms, so it's typically raw DEFLATE stream
(without zlib header) in all gzipped files.
.. seealso::
Source - https://www.rfc-editor.org/rfc/rfc1952
"""
class CompressionMethods(Enum):
deflate = 8
class Oses(Enum):
fat = 0
amiga = 1
vms = 2
unix = 3
vm_cms = 4
atari_tos = 5
hpfs = 6
macintosh = 7
z_system = 8
cp_m = 9
tops_20 = 10
ntfs = 11
qdos = 12
acorn_riscos = 13
unknown = 255
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(2)
if not self.magic == b"\x1F\x8B":
raise kaitaistruct.ValidationNotEqualError(b"\x1F\x8B", self.magic, self._io, u"/seq/0")
self.compression_method = KaitaiStream.resolve_enum(Gzip.CompressionMethods, self._io.read_u1())
self.flags = Gzip.Flags(self._io, self, self._root)
self.mod_time = self._io.read_u4le()
_on = self.compression_method
if _on == Gzip.CompressionMethods.deflate:
self.extra_flags = Gzip.ExtraFlagsDeflate(self._io, self, self._root)
self.os = KaitaiStream.resolve_enum(Gzip.Oses, self._io.read_u1())
if self.flags.has_extra:
self.extras = Gzip.Extras(self._io, self, self._root)
if self.flags.has_name:
self.name = self._io.read_bytes_term(0, False, True, True)
if self.flags.has_comment:
self.comment = self._io.read_bytes_term(0, False, True, True)
if self.flags.has_header_crc:
self.header_crc16 = self._io.read_u2le()
self.body = self._io.read_bytes(((self._io.size() - self._io.pos()) - 8))
self.body_crc32 = self._io.read_u4le()
self.len_uncompressed = self._io.read_u4le()
class Flags(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.reserved1 = self._io.read_bits_int_be(3)
self.has_comment = self._io.read_bits_int_be(1) != 0
self.has_name = self._io.read_bits_int_be(1) != 0
self.has_extra = self._io.read_bits_int_be(1) != 0
self.has_header_crc = self._io.read_bits_int_be(1) != 0
self.is_text = self._io.read_bits_int_be(1) != 0
class ExtraFlagsDeflate(KaitaiStruct):
class CompressionStrengths(Enum):
best = 2
fast = 4
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.compression_strength = KaitaiStream.resolve_enum(Gzip.ExtraFlagsDeflate.CompressionStrengths, self._io.read_u1())
class Subfields(KaitaiStruct):
"""Container for many subfields, constrained by size of stream.
"""
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.entries = []
i = 0
while not self._io.is_eof():
self.entries.append(Gzip.Subfield(self._io, self, self._root))
i += 1
class Subfield(KaitaiStruct):
"""Every subfield follows typical [TLV scheme](https://en.wikipedia.org/wiki/Type-length-value):
* `id` serves role of "T"ype
* `len_data` serves role of "L"ength
* `data` serves role of "V"alue
This way it's possible to for arbitrary parser to skip over
subfields it does not support.
"""
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.id = self._io.read_u2le()
self.len_data = self._io.read_u2le()
self.data = self._io.read_bytes(self.len_data)
class Extras(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.len_subfields = self._io.read_u2le()
self._raw_subfields = self._io.read_bytes(self.len_subfields)
_io__raw_subfields = KaitaiStream(BytesIO(self._raw_subfields))
self.subfields = Gzip.Subfields(_io__raw_subfields, self, self._root)