Class: Omnizip::Parity::Models::IfscPacket

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

Overview

PAR2 IFSC (Input File Slice Checksum) packet

Contains checksums for individual data blocks of a file. One IFSC packet contains checksums for ALL blocks of a file.

Body structure:

  • file_id (16 bytes): File identifier
  • For each block:
    • block_hash (16 bytes): MD5 hash of block data
    • block_crc32 (4 bytes, L<): CRC32 of block data

Constant Summary collapse

PACKET_TYPE =

Packet type identifier

"PAR 2.0\x00IFSC\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) ⇒ IfscPacket

Initialize IFSC packet

Parameters:

  • attributes (Hash) —

    Packet attributes



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# File 'lib/omnizip/parity/models/ifsc_packet.rb', line 32

def initialize(**attributes)
  super
  self.type = PACKET_TYPE
  self.block_hashes = [] if block_hashes.nil?
  self.block_crc32s = [] if block_crc32s.nil?
end

Instance Method Details

#build_body ⇒ String

Build body data from attributes

Constructs binary body data

Returns:

  • (String) —

    Binary body data



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# File 'lib/omnizip/parity/models/ifsc_packet.rb', line 79

def build_body
  data = +""

  # Validate file_id is 16 bytes
  if file_id.bytesize != 16
    raise ArgumentError,
          "file_id must be 16 bytes, got #{file_id.bytesize}"
  end

  # Write file_id
  data << file_id

  # Write all blocks
  block_hashes.each_with_index do |block_hash, i|
    # Validate block_hash is 16 bytes
    if block_hash.bytesize != 16
      raise ArgumentError,
            "block_hash must be 16 bytes, got #{block_hash.bytesize}"
    end

    # Write block_hash
    data << block_hash

    # Write block_crc32 (4 bytes, little-endian)
    data << [block_crc32s[i]].pack("L<")
  end

  self.body_data = data
end

#parse_body ⇒ Object

Parse body data into attributes

Body format:

  • file_id: 16 bytes
  • For each block:
    • block_hash: 16 bytes
    • block_crc32: 4 bytes (L<)


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

def parse_body
  return if body_data.nil? || body_data.empty?
  return if body_data.bytesize < 16

  pos = 0

  # Read file_id (16 bytes)
  self.file_id = body_data[pos, 16]
  pos += 16

  # Read all blocks (each is 16 bytes hash + 4 bytes CRC = 20 bytes)
  self.block_hashes = []
  self.block_crc32s = []

  while pos + 20 <= body_data.bytesize
    # Read block_hash (16 bytes)
    block_hash = body_data[pos, 16]
    pos += 16

    # Read block_crc32 (4 bytes, little-endian unsigned 32-bit)
    block_crc32 = body_data[pos, 4].unpack1("L<")
    pos += 4

    block_hashes << block_hash
    block_crc32s << block_crc32
  end
end