Module: Omnizip::Formats::SevenZip::EncodedHeader

Includes:
Constants
Defined in:
lib/omnizip/formats/seven_zip/encoded_header.rb

Overview

Handles 7-Zip encoded headers

7-Zip can compress the Next Header metadata with LZMA2 to save space. This module provides functionality to encode and decode headers.

Constant Summary

Constants included from Constants

Constants::MAJOR_VERSION, Constants::MAX_NUM_BONDS, Constants::MAX_NUM_CODERS, Constants::MAX_NUM_PACK_STREAMS, Constants::MINOR_VERSION, Constants::SIGNATURE, Constants::SIGNATURE_SIZE, Constants::START_HEADER_SIZE

Class Method Summary collapse

Class Method Details

.compress_header(header_data) ⇒ String

Compress header data with LZMA2

Parameters:

  • header_data (String) —

    Uncompressed header

Returns:

  • (String) —

    Compressed header



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# File 'lib/omnizip/formats/seven_zip/encoded_header.rb', line 68

def compress_header(header_data)
  # Use 7-Zip SDK LZMA2 encoder for 7-Zip format
  encoder = Omnizip::Implementations::SevenZip::LZMA2::Encoder.new(
    dict_size: 4096, # Small dictionary for headers
    lc: 3,
    lp: 0,
    pb: 2,
    standalone: false, # No property byte
  )

  encoder.encode(header_data)
end

.encode(header_data) ⇒ String

Encode next header with LZMA2 compression

Parameters:

  • header_data (String) —

    Uncompressed header data

Returns:

  • (String) —

    Encoded header property with compressed data



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# File 'lib/omnizip/formats/seven_zip/encoded_header.rb', line 19

def encode(header_data)
  # Compress header with LZMA2
  compressed = compress_header(header_data)

  # Build encoded header property
  encoded = String.new(encoding: "BINARY")
  encoded << [PropertyId::ENCODED_HEADER].pack("C")

  # Write pack info for compressed header
  encoded << [PropertyId::PACK_INFO].pack("C")
  encoded << encode_uint64(0)  # Pack position
  encoded << encode_uint64(1)  # Number of pack streams

  # Write size
  encoded << [PropertyId::SIZE].pack("C")
  encoded << encode_uint64(compressed.bytesize)

  encoded << [PropertyId::K_END].pack("C")

  # Write coder info (LZMA2)
  encoded << [PropertyId::UNPACK_INFO].pack("C")
  encoded << [PropertyId::FOLDER].pack("C")
  encoded << encode_uint64(1)  # Number of folders
  encoded << [0].pack("C")     # External flag (0 = inline)

  # Number of coders
  encoded << encode_uint64(1)

  # Coder info for LZMA2
  # Method ID: LZMA2 = 0x21
  encoded << [1].pack("C") # Main byte (1 byte for ID, no properties)
  encoded << [0x21].pack("C") # LZMA2 method ID

  # Unpack size
  encoded << [PropertyId::CODERS_UNPACK_SIZE].pack("C")
  encoded << encode_uint64(header_data.bytesize)

  encoded << [PropertyId::K_END].pack("C")

  # Append compressed data
  encoded << compressed

  encoded
end

.encode_uint64(value) ⇒ String

Encode unsigned 64-bit integer in 7-Zip variable-length format

Parameters:

  • value (Integer) —

    Value to encode

Returns:

  • (String) —

    Encoded bytes



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# File 'lib/omnizip/formats/seven_zip/encoded_header.rb', line 85

def encode_uint64(value)
  return [value].pack("C") if value < 0x80

  result = String.new(encoding: "BINARY")
  shift = 0

  loop do
    byte = value & 0x7F
    value >>= 7

    if value.zero?
      result << [byte].pack("C")
      break
    else
      result << [byte | 0x80].pack("C")
    end

    shift += 7
  end

  result
end