.lzh file format of LHA (AKA LHarc) by Yoshizaki Haruyasu: format specification

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

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.

Block diagram

Format specification in Kaitai Struct YAML

meta:
  id: lzh
  endian: le
  application: LHA (AKA LHarc) by Yoshizaki Haruyasu
  file-extension: lzh
  license: CC0-1.0
doc: |
  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.
seq:
  - id: entries
    type: record
    repeat: eos
types:
  record:
    seq:
      - id: header_len
        type: u1
      - id: file_record
        type: file_record
        if: header_len > 0
  file_record:
    seq:
      - id: header
        size: _parent.header_len - 1
        type: header
      - id: file_uncompr_crc16
        type: u2
        if: header.header1.lha_level == 0
      - id: body
        size: header.header1.file_size_compr
  header:
    seq:
      - id: header1
        type: header1
        doc: >
          Level-neutral header, same for all LHA levels. Subsequent
          fields order and meaning varies, based on LHA level
          specified in this header.
      - id: filename_len
        type: u1
        if: header1.lha_level == 0
      - id: filename
        type: str
        size: filename_len
        encoding: ASCII
        if: header1.lha_level == 0
      - id: file_uncompr_crc16
        type: u2
        if: header1.lha_level == 2
      - id: os
        type: u1
        if: header1.lha_level == 2
      - id: ext_header_size
        type: u2
        if: header1.lha_level == 2
  header1:
    seq:
      - id: header_checksum
        type: u1
      - id: method_id
        type: str
        size: 5
        encoding: ASCII
      - id: file_size_compr
        type: u4
        doc: Compressed file size
      - id: file_size_uncompr
        type: u4
        doc: Uncompressed file size
      - id: file_timestamp
        type: u4
        doc: Original file date/time
      - id: attr
        type: u1
        doc: File or directory attribute
      - id: lha_level
        type: u1