Class: Omnizip::Formats::XzImpl::StreamFooter

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

Overview

XZ Stream Footer encoder Based on XZ Utils stream_flags_encoder.c

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 Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(backward_size:, check_type: CHECK_CRC64) ⇒ StreamFooter

Returns a new instance of StreamFooter.



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# File 'lib/omnizip/formats/xz_impl/stream_footer.rb', line 15

def initialize(backward_size:, check_type: CHECK_CRC64)
  @check_type = check_type
  @backward_size = backward_size
end

Instance Attribute Details

#backward_size ⇒ Object (readonly)

Returns the value of attribute backward_size.



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# File 'lib/omnizip/formats/xz_impl/stream_footer.rb', line 13

def backward_size
  @backward_size
end

#check_type ⇒ Object (readonly)

Returns the value of attribute check_type.



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# File 'lib/omnizip/formats/xz_impl/stream_footer.rb', line 13

def check_type
  @check_type
end

Instance Method Details

#encode ⇒ Object

Encode stream footer (12 bytes total) Format:

- CRC32 (4 bytes): CRC32 of backward size + stream flags
- Backward Size (4 bytes): Size of Index in 4-byte multiples
- Stream Flags (2 bytes): version + check type
- Footer Magic (2 bytes): 59 5A


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# File 'lib/omnizip/formats/xz_impl/stream_footer.rb', line 26

def encode
  output = String.new(encoding: Encoding::BINARY)

  # Validate backward size
  unless valid_backward_size?
    raise ArgumentError, "Invalid backward size: #{@backward_size}"
  end

  # Encode backward size (stored as (bytes / 4) - 1)
  backward_encoded = (@backward_size / 4) - 1
  backward_bytes = [backward_encoded].pack("V") # Little-endian uint32

  # Encode stream flags
  flags = encode_stream_flags

  # Calculate CRC32 of backward size + flags
  crc_data = backward_bytes + flags
  crc = Zlib.crc32(crc_data)

  # Write CRC32
  output << [crc].pack("V")

  # Write backward size
  output << backward_bytes

  # Write stream flags
  output << flags

  # Write footer magic
  output << FOOTER_MAGIC.pack("C*")

  output
end