Class: Cabriolet::Decompressors::MSZIP

Inherits:
Base
  • Object
show all
Defined in:
lib/cabriolet/decompressors/mszip.rb

Overview

MSZIP handles MSZIP (deflate) compressed data Based on RFC 1951 and libmspack implementation

Constant Summary collapse

FRAME_SIZE =

MSZIP frame size (32KB sliding window)

32_768
LITERAL_MAXSYMBOLS =

Huffman tree constants

288
LITERAL_TABLEBITS = 
9
DISTANCE_MAXSYMBOLS = 
32
DISTANCE_TABLEBITS = 
6
LIT_LENGTHS =

Match lengths for literal codes 257-285

[
  3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27,
  31, 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258
].freeze
DIST_OFFSETS =

Match offsets for distance codes 0-29

[
  1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 257, 385,
  513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 8193, 12_289, 16_385, 24_577
].freeze
LIT_EXTRABITS =

Extra bits for literal codes 257-285

[
  0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2,
  2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0
].freeze
DIST_EXTRABITS =

Extra bits for distance codes 0-29

[
  0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6,
  6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13
].freeze
BITLEN_ORDER =

Order of bit length code lengths

[
  16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
].freeze

Instance Attribute Summary

Attributes inherited from Base

#buffer_size, #input, #io_system, #output

Instance Method Summary collapse

Methods inherited from Base

#free

Constructor Details

#initialize(io_system, input, output, buffer_size, fix_mszip: false) ⇒ MSZIP

Initialize MSZIP decompressor

Parameters:



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# File 'lib/cabriolet/decompressors/mszip.rb', line 53

def initialize(io_system, input, output, buffer_size, fix_mszip: false)
  super(io_system, input, output, buffer_size)
  @fix_mszip = fix_mszip

  # Initialize sliding window
  @window = "\0" * FRAME_SIZE
  @window_posn = 0
  @bytes_output = 0

  # Initialize bitstream
  @bitstream = Binary::Bitstream.new(io_system, input, buffer_size)

  # Initialize Huffman trees
  @literal_lengths = Array.new(LITERAL_MAXSYMBOLS, 0)
  @distance_lengths = Array.new(DISTANCE_MAXSYMBOLS, 0)
  @literal_tree = nil
  @distance_tree = nil
end

Instance Method Details

#decompress(bytes) ⇒ Integer

Decompress MSZIP data

Parameters:

  • bytes (Integer) —

    Number of bytes to decompress

Returns:

  • (Integer) —

    Number of bytes decompressed



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# File 'lib/cabriolet/decompressors/mszip.rb', line 76

def decompress(bytes)
  total_written = 0

  while bytes.positive?
    # Read 'CK' signature
    read_signature

    # Reset window state for new block
    @window_posn = 0
    @bytes_output = 0

    # Inflate the block
    begin
      inflate_block
    rescue DecompressionError
      raise unless @fix_mszip

      # In repair mode, pad with zeros
      (@bytes_output...FRAME_SIZE).each do |i|
        @window.setbyte(i, 0)
      end
      @bytes_output = FRAME_SIZE
    end

    # Write output
    write_amount = [bytes, @bytes_output].min
    io_system.write(output, @window[0, write_amount])
    total_written += write_amount
    bytes -= write_amount
  end

  total_written
end