Class: Omnizip::Parity::Models::MainPacket

Inherits:
Packet
  • Object
show all
Defined in:
lib/omnizip/parity/models/main_packet.rb

Overview

PAR2 Main packet

Contains recovery set metadata including block size and file IDs.

Body structure:

  • block_size (8 bytes, Q<): Size of each data block
  • file_ids (16 bytes each): List of file IDs in the recovery set

Note: In current Par2Creator implementation, the body includes additional fields after block_size that are not part of the standard PAR2 spec. This model follows the actual PAR2 spec.

Constant Summary collapse

PACKET_TYPE =

Packet type identifier

"PAR 2.0\x00Main\x00\x00\x00\x00"

Constants inherited from Packet

Packet::PACKET_SIGNATURE

Instance Attribute Summary

Attributes inherited from Packet

#body_data

Instance Method Summary collapse

Methods inherited from Packet

#calculate_hash, #packet_type, read_from, #valid_hash?, #write_to

Constructor Details

#initialize(**attributes) ⇒ MainPacket

Initialize main packet

Parameters:

  • attributes (Hash) —

    Packet attributes



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# File 'lib/omnizip/parity/models/main_packet.rb', line 30

def initialize(**attributes)
  super
  self.type = PACKET_TYPE
end

Instance Method Details

#build_body ⇒ String

Build body data from attributes

Constructs binary body data from block_size and file_ids

Returns:

  • (String) —

    Binary body data



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# File 'lib/omnizip/parity/models/main_packet.rb', line 90

def build_body
  data = +""

  # Write block_size (8 bytes, little-endian)
  data << [block_size].pack("Q<")

  # Write file IDs (16 bytes each)
  file_ids.each do |file_id|
    # Ensure file_id is exactly 16 bytes
    if file_id.bytesize != 16
      raise ArgumentError,
            "File ID must be 16 bytes, got #{file_id.bytesize}"
    end
    data << file_id
  end

  self.body_data = data
end

#file_count ⇒ Integer

Get number of files in recovery set

Returns:

  • (Integer) —

    File count



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# File 'lib/omnizip/parity/models/main_packet.rb', line 112

def file_count
  file_ids.size
end

#includes_file?(file_id) ⇒ Boolean

Check if packet contains specific file ID

Parameters:

  • file_id (String) —

    16-byte file ID to check

Returns:

  • (Boolean) —

    true if file ID is present



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# File 'lib/omnizip/parity/models/main_packet.rb', line 120

def includes_file?(file_id)
  file_ids.include?(file_id)
end

#parse_body ⇒ Object

Parse body data into attributes

Body format (PAR2 spec):

  • block_size: 8 bytes (Q<)
  • file_ids: 16 bytes each, until end of body

par2cmdline variant also includes:

  • file_count: 4 bytes (L<) after block_size
  • then file_ids: 16 bytes each

This method detects which format is used.



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# File 'lib/omnizip/parity/models/main_packet.rb', line 46

def parse_body
  return if body_data.nil? || body_data.empty?

  pos = 0

  # Read block_size (8 bytes, little-endian unsigned 64-bit)
  self.block_size = body_data[pos, 8].unpack1("Q<")
  pos += 8

  # Detect format: check if next 4 bytes are a file_count
  remaining = body_data.bytesize - pos

  if remaining >= 4
    # Try to read potential file_count
    potential_count = body_data[pos, 4].unpack1("L<")
    expected_size = potential_count * 16

    # Check if this looks like par2cmdline format:
    # - Remaining bytes should be: 4 (count) + count * 16 (file_ids)
    # - Count should be reasonable (> 0, < 10000 for sanity)
    if remaining == (4 + expected_size) &&
        potential_count.positive? &&
        potential_count < 10_000
      # par2cmdline format detected
      pos += 4 # Skip the file_count field
    end
  end

  # Read file IDs (16 bytes each) until end of body
  self.file_ids = []
  while pos < body_data.bytesize
    file_id = body_data[pos, 16]
    break if file_id.nil? || file_id.bytesize < 16

    file_ids << file_id
    pos += 16
  end
end