Class: Omnizip::Formats::XzImpl::BlockHeader

Inherits:
Object
  • Object
show all
Defined in:
lib/omnizip/formats/xz_impl/block_header.rb

Overview

XZ block header

Block header contains:

  • Header size (1 byte) - size in 4-byte blocks
  • Block flags (1 byte)
  • Compressed size (variable, optional)
  • Uncompressed size (variable, optional)
  • Filter flags (variable)
  • Padding to 4-byte boundary
  • CRC32 (4 bytes)

Constant Summary collapse

FILTER_LZMA2 =

Filter IDs

0x21

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(options = {}) ⇒ BlockHeader

Initialize block header

Parameters:

  • options (Hash) (defaults to: {}) —

    Header options



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 25

def initialize(options = {})
  @compressed_size = options[:compressed_size]
  @uncompressed_size = options[:uncompressed_size]
  @filters = options[:filters] || [{ id: FILTER_LZMA2 }]
end

Instance Attribute Details

#compressed_size ⇒ Object (readonly)

Returns the value of attribute compressed_size.



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 20

def compressed_size
  @compressed_size
end

#filters ⇒ Object (readonly)

Returns the value of attribute filters.



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 20

def filters
  @filters
end

#uncompressed_size ⇒ Object (readonly)

Returns the value of attribute uncompressed_size.



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 20

def uncompressed_size
  @uncompressed_size
end

Class Method Details

.decode(io) ⇒ BlockHeader

Decode block header from stream

Parameters:

  • io (IO) —

    Input stream

Returns:



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 81

def self.decode(io)
  header_size_blocks = io.read(1).unpack1("C")
  return nil if header_size_blocks.nil? || header_size_blocks.zero?

  header_size_bytes = header_size_blocks * 4

  # Read rest of header (excluding size byte and CRC32)
  header_data_size = header_size_bytes - 1 - 4
  header_data = io.read(header_data_size)

  # Read and verify CRC32
  crc32_expected = io.read(4).unpack1("V")
  full_header = [header_size_blocks].pack("C") + header_data
  crc32_actual = Zlib.crc32(full_header)

  unless crc32_expected == crc32_actual
    raise Error, "XZ block header CRC32 mismatch"
  end

  # Parse header data
  flags = header_data.unpack1("C")
  offset = 1

  options = {}

  # Read compressed size if present
  if flags.anybits?(0x40)
    options[:compressed_size], bytes_read =
      decode_multibyte_integer(header_data[offset..])
    offset += bytes_read
  end

  # Read uncompressed size if present
  if flags.anybits?(0x80)
    options[:uncompressed_size], bytes_read =
      decode_multibyte_integer(header_data[offset..])
    offset += bytes_read
  end

  # Parse filters
  filter_count = (flags & 0x03) + 1
  options[:filters] = []

  filter_count.times do
    filter, bytes_read = decode_filter(header_data[offset..])
    options[:filters] << filter
    offset += bytes_read
  end

  new(options)
end

.decode_filter(data) ⇒ Array<Hash, Integer>

Decode filter

Parameters:

  • data (String) —

    Data to decode

Returns:

  • (Array<Hash, Integer>) —

    Filter and bytes consumed



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 193

def self.decode_filter(data)
  filter_id, offset = decode_multibyte_integer(data)

  props_size, bytes_read = decode_multibyte_integer(data[offset..])
  offset += bytes_read

  props = data[offset, props_size]
  offset += props_size

  filter = { id: filter_id }
  filter[:properties] = props unless props.empty?

  [filter, offset]
end

.decode_multibyte_integer(data) ⇒ Array<Integer, Integer>

Decode multibyte integer

Parameters:

  • data (String) —

    Data to decode

Returns:

  • (Array<Integer, Integer>) —

    Value and bytes consumed



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 155

def self.decode_multibyte_integer(data)
  value = 0
  shift = 0
  offset = 0

  loop do
    byte = data[offset].unpack1("C")
    value |= (byte & 0x7F) << shift
    offset += 1
    break if byte.nobits?(0x80)

    shift += 7
  end

  [value, offset]
end

Instance Method Details

#encode ⇒ String

Encode block header to bytes

Returns:

  • (String) —

    Encoded header



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# File 'lib/omnizip/formats/xz_impl/block_header.rb', line 34

def encode
  # Block flags byte
  flags = 0
  flags |= 0x40 if @compressed_size
  flags |= 0x80 if @uncompressed_size

  # Number of filters (0 = 1 filter, 3 = 4 filters)
  filter_count = [@filters.size - 1, 3].min
  flags |= filter_count

  data = [flags].pack("C")

  # Add sizes if present (encoded as multibyte integers)
  if @compressed_size
    data << encode_multibyte_integer(@compressed_size)
  end

  if @uncompressed_size
    data << encode_multibyte_integer(@uncompressed_size)
  end

  # Add filter properties
  @filters.each do |filter|
    data << encode_filter(filter)
  end

  # Calculate header size (including size byte and CRC32)
  # Round up to 4-byte blocks
  header_size_bytes = 1 + data.bytesize + 4
  header_size_blocks = (header_size_bytes + 3) / 4

  # Add padding
  padding_size = (header_size_blocks * 4) - header_size_bytes
  data << ("\0" * padding_size) if padding_size.positive?

  # Prepend header size
  full_header = [header_size_blocks].pack("C") + data

  # Append CRC32
  crc32 = Zlib.crc32(full_header)
  full_header + [crc32].pack("V")
end