.lzh file format of LHA (AKA LHarc) by Yoshizaki Haruyasu: Python parsing library

LHA (LHarc, LZH) is a file format used by a popular freeware eponymous archiver, created in 1988 by Haruyasu Yoshizaki. Over the years, many ports and implementations were developed, sporting many extensions to original 1988 LZH.

File format is pretty simple and essentially consists of a stream of records.

Application

LHA (AKA LHarc) by Yoshizaki Haruyasu

File extension

lzh

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of .lzh file format of LHA (AKA LHarc) by Yoshizaki Haruyasu using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Runtime 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 kaitaistruct

Code

Parse a local file and get structure in memory:

data = Lzh.from_file("path/to/local/file.lzh")

Or parse structure from a bytes:

from kaitaistruct import KaitaiStream, BytesIO

raw = b"\x00\x01\x02..."
data = Lzh(KaitaiStream(BytesIO(raw)))

After that, one can get various attributes from the structure by invoking getter methods like:

data.entries # => get entries

Python source code to parse .lzh file format of LHA (AKA LHarc) by Yoshizaki Haruyasu

lzh.py

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

from pkg_resources import parse_version
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO


if parse_version(kaitaistruct.__version__) < parse_version('0.9'):
    raise Exception("Incompatible Kaitai Struct Python API: 0.9 or later is required, but you have %s" % (kaitaistruct.__version__))

import dos_datetime
class Lzh(KaitaiStruct):
    """LHA (LHarc, LZH) is a file format used by a popular freeware
    eponymous archiver, created in 1988 by Haruyasu Yoshizaki. Over the
    years, many ports and implementations were developed, sporting many
    extensions to original 1988 LZH.
    
    File format is pretty simple and essentially consists of a stream of
    records.
    """
    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(Lzh.Record(self._io, self, self._root))
            i += 1


    class Record(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.header_len = self._io.read_u1()
            if self.header_len > 0:
                self.file_record = Lzh.FileRecord(self._io, self, self._root)



    class FileRecord(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._raw_header = self._io.read_bytes((self._parent.header_len - 1))
            _io__raw_header = KaitaiStream(BytesIO(self._raw_header))
            self.header = Lzh.Header(_io__raw_header, self, self._root)
            if self.header.header1.lha_level == 0:
                self.file_uncompr_crc16 = self._io.read_u2le()

            self.body = self._io.read_bytes(self.header.header1.file_size_compr)


    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.header1 = Lzh.Header1(self._io, self, self._root)
            if self.header1.lha_level == 0:
                self.filename_len = self._io.read_u1()

            if self.header1.lha_level == 0:
                self.filename = (self._io.read_bytes(self.filename_len)).decode(u"ASCII")

            if self.header1.lha_level == 2:
                self.file_uncompr_crc16 = self._io.read_u2le()

            if self.header1.lha_level == 2:
                self.os = self._io.read_u1()

            if self.header1.lha_level == 2:
                self.ext_header_size = self._io.read_u2le()



    class Header1(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.header_checksum = self._io.read_u1()
            self.method_id = (self._io.read_bytes(5)).decode(u"ASCII")
            self.file_size_compr = self._io.read_u4le()
            self.file_size_uncompr = self._io.read_u4le()
            self._raw_file_timestamp = self._io.read_bytes(4)
            _io__raw_file_timestamp = KaitaiStream(BytesIO(self._raw_file_timestamp))
            self.file_timestamp = dos_datetime.DosDatetime(_io__raw_file_timestamp)
            self.attr = self._io.read_u1()
            self.lha_level = self._io.read_u1()