Class: Omnizip::Formats::XzImpl::IndexEncoder

Inherits:
Object
  • Object
show all
Includes:
Omnizip::Formats::XzConst
Defined in:
lib/omnizip/formats/xz_impl/index_encoder.rb

Overview

XZ Index encoder Stores positions and sizes of all blocks in the stream

Constant Summary

Constants included from Omnizip::Formats::XzConst

Omnizip::Formats::XzConst::BACKWARD_SIZE_MAX, Omnizip::Formats::XzConst::BACKWARD_SIZE_MIN, Omnizip::Formats::XzConst::BLOCK_HEADER_SIZE_MAX, Omnizip::Formats::XzConst::BLOCK_HEADER_SIZE_MIN, Omnizip::Formats::XzConst::CHECK_CRC32, Omnizip::Formats::XzConst::CHECK_CRC64, Omnizip::Formats::XzConst::CHECK_NONE, Omnizip::Formats::XzConst::CHECK_SHA256, Omnizip::Formats::XzConst::FILTERS_MAX, Omnizip::Formats::XzConst::FILTER_LZMA2, Omnizip::Formats::XzConst::FOOTER_MAGIC, Omnizip::Formats::XzConst::INDEX_INDICATOR, Omnizip::Formats::XzConst::MAGIC, Omnizip::Formats::XzConst::STREAM_FLAGS_SIZE, Omnizip::Formats::XzConst::STREAM_FOOTER_SIZE, Omnizip::Formats::XzConst::STREAM_HEADER_SIZE, Omnizip::Formats::XzConst::VLI_BYTES_MAX, Omnizip::Formats::XzConst::VLI_UNKNOWN

Instance Method Summary collapse

Constructor Details

#initialize ⇒ IndexEncoder

Returns a new instance of IndexEncoder.



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# File 'lib/omnizip/formats/xz_impl/index_encoder.rb', line 14

def initialize
  @records = []
end

Instance Method Details

#add_record(unpadded_size, uncompressed_size) ⇒ Object

Add a block record to the index

Parameters:

  • unpadded_size (Integer) —

    Block size without padding

  • uncompressed_size (Integer) —

    Uncompressed size of the block



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# File 'lib/omnizip/formats/xz_impl/index_encoder.rb', line 21

def add_record(unpadded_size, uncompressed_size)
  @records << {
    unpadded: unpadded_size,
    uncompressed: uncompressed_size,
  }
end

#encode ⇒ Object

Encode the complete index Returns the encoded index as a binary string



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# File 'lib/omnizip/formats/xz_impl/index_encoder.rb', line 30

def encode
  output = StringIO.new
  output.set_encoding(Encoding::BINARY)

  # Index Indicator (0x00)
  output.write("\x00")

  # Number of Records
  output.write(encode_vli(@records.size))

  # Encode each record
  @records.each do |record|
    # Unpadded Size
    output.write(encode_vli(record[:unpadded]))

    # Uncompressed Size
    output.write(encode_vli(record[:uncompressed]))
  end

  # Add padding to make index multiple of 4 bytes (including CRC32)
  # CRITICAL: Capture index_data before writing padding (StringIO#string returns a reference!)
  index_data = output.string.dup # Make a copy to avoid reference
  padding = calculate_padding(index_data.bytesize) # Pad to multiple of 4
  output.write("\x00" * padding) if padding.positive?

  # Calculate and write CRC32
  crc = Zlib.crc32(index_data + ("\x00" * padding))
  output.write([crc].pack("V"))

  output.string
end

#size ⇒ Object

Get the size of the encoded index (for backward size)



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# File 'lib/omnizip/formats/xz_impl/index_encoder.rb', line 63

def size
  # Calculate without actually encoding
  size = 1 # Index Indicator
  size += vli_size(@records.size)

  @records.each do |record|
    size += vli_size(record[:unpadded])
    size += vli_size(record[:uncompressed])
  end

  # Add CRC32
  size += 4

  # Round up to multiple of 4
  ((size + 3) / 4) * 4
end