WIP: Kaitai Struct definition for .xz file format

xz.ksy

# This definition is incomplete, several fiels are hardcoded.
# See https://github.com/kaitai-io/kaitai_struct_formats/issues/719

meta:
  id: xz
  title: XZ compressed file
  file-extension: xz
  xref:
    forensicswiki: xz
    justsolve: XZ
    mime: application/x-xz
    pronom: fmt/1098
    wikidata: Q162839
  license: CC0-1.0
  endian: le
  imports:
    - /common/vlq_base128_le
doc: |
  XZ single-file archive format compressed using LZMA.
  XZ files typically have a .xz file extension.
  They're often produced or consumed with xz-utils suite of software.
  LZMA (and hence XZ) usually achieves higher compression ratios,
  at the expense of slower compression & decompression.
doc-ref:
  - https://tukaani.org/xz/xz-file-format-1.2.1.txt
  - https://tukaani.org/xz/xz-file-format.txt
seq:
  - id: header
    type: header
  - id: block
    type: block  # FIXME A stream can have 0 - many blocks
  - id: index
    type: index
  - id: footer
    type: footer
enums:
  filters:
    0x03:
      id: delta
    0x04:
      id: x86_bcj
    0x05:
      id: powerpc_be
    0x06:
      id: ia64
    0x07:
      id: arm
    0x08:
      id: arm_thumb
    0x09:
      id: sparc
    0x0a:
      id: arm64
    0x0b:
      id: risc_v
    0x21:
      id: lzma2

  stream_checks:
    0:
      id: none
    1:
      id: crc32
    4:
      id: crc64
    10:
      id: sha256
types:
  check_none:
    doc: This type is intentionally left blank
  check_crc32:
    seq:
      - id: value
        type: u4
  check_crc64:
    seq:
      - id: value
        type: u8
  check_sha256:
    seq:
      - id: value
        size: 32
  header:
    seq:
      - id: magic
        contents: [0xfd, 0x37, 0x7a, 0x58, 0x5a, 0x00]
      - id: flags
        type: stream_flags
      - id: crc32
        type: u4
  stream_flags:
    seq:
      - id: reserved1
        type: u1
      - id: reserved2
        type: b4
      - id: check
        type: b4
        enum: stream_checks
  block:
    seq:
      - id: header
        type: block_header
      - id: compressed_data
        size: 8  # FIXME
      - id: padding
        size: 0  # FIXME
      - id: check
        type:
          switch-on: _root.header.flags.check
          cases:
            'stream_checks::none': check_none
            'stream_checks::crc32': check_crc32
            'stream_checks::crc64': check_crc64
            'stream_checks::sha256': check_sha256
  block_header:
    seq:
      - id: len_header_encoded
        type: u1
      - id: has_len_uncompressed
        type: b1
      - id: has_len_compressed
        type: b1
      - id: reserved
        type: b4
      - id: num_filters_encoded
        type: b2
      - id: len_compressed
        type: vlq_base128_le
        if: has_len_uncompressed
      - id: len_uncompressed
        type: vlq_base128_le
        if: has_len_compressed
      - id: filter_flags
        type: block_filter_flag
        repeat: expr
        repeat-expr: num_filters
      - id: padding
        size: 9  # FIXME Calculate so that header length matchs len_header
      - id: crc32
        type: u4
    instances:
        len_header:
          value: (len_header_encoded + 1) * 4
        num_filters:
          value: num_filters_encoded + 1
  block_filter_flag:
    seq:
      - id: id
        type: vlq_base128_le
      - id: len_properties
        type: vlq_base128_le
      - id: properties
        size: len_properties.value
    instances:
      type:
        value: id.value
        enum: filters
  index:
    seq:
      - id: index_indicator
        contents: [0]
      - id: num_records
        type: vlq_base128_le
      - id: records
        type: index_record
        repeat: expr
        repeat-expr: num_records.value
      - id: padding
        size: (4 - (_io.pos % 4)) % 4
      - id: crc32
        type: u4
  index_record:
    seq:
      - id: len_unpadded
        type: vlq_base128_le
      - id: len_uncompressed
        type: vlq_base128_le
  footer:
    seq:
      - id: crc32
        type: u4
      - id: backward_size_raw
        type: u4
      - id: flags
        type: stream_flags
      - id: magic
        contents: [0x59, 0x5a]
    instances:
      backward_size:
        value: (backward_size_raw + 1) * 4

File used during development generated by echo foo | xz > foo.xz. The uncompressed data is 4 bytes, including a final newline.