Class: Omnizip::Parity::Models::FileDescriptionPacket

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

Overview

PAR2 File Description packet

Contains metadata about a protected file including hashes and filename.

Body structure:

  • file_id (16 bytes): MD5 hash identifying the file
  • file_hash (16 bytes): MD5 hash of complete file content
  • file_hash_16k (16 bytes): MD5 hash of first 16KB
  • length (8 bytes, Q<): File size in bytes
  • filename (variable): Null-terminated filename, padded to multiple of 4

Constant Summary collapse

PACKET_TYPE =

Packet type identifier

"PAR 2.0\x00FileDesc"

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) ⇒ FileDescriptionPacket

Initialize file description packet

Parameters:

  • attributes (Hash) —

    Packet attributes



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# File 'lib/omnizip/parity/models/file_description_packet.rb', line 38

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

Instance Method Details

#basename ⇒ String

Get basename of file

Returns:

  • (String) —

    File basename



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# File 'lib/omnizip/parity/models/file_description_packet.rb', line 125

def basename
  File.basename(filename)
end

#build_body ⇒ String

Build body data from attributes

Constructs binary body data with proper padding

Returns:

  • (String) —

    Binary body data



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# File 'lib/omnizip/parity/models/file_description_packet.rb', line 91

def build_body
  data = +""

  # Validate file_id, file_hash, file_hash_16k are 16 bytes
  [file_id, file_hash, file_hash_16k].each_with_index do |hash, idx|
    field_name = %w[file_id file_hash file_hash_16k][idx]
    if hash.bytesize != 16
      raise ArgumentError,
            "#{field_name} must be 16 bytes, got #{hash.bytesize}"
    end
  end

  # Write hashes
  data << file_id
  data << file_hash
  data << file_hash_16k

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

  # Write filename (null-terminated, padded to multiple of 4)
  data << filename
  data << "\x00"

  # Add padding to make total length multiple of 4
  padding = (4 - ((filename.bytesize + 1) % 4)) % 4
  data << ("\x00" * padding) if padding.positive?

  self.body_data = data
end

#parse_body ⇒ Object

Parse body data into attributes

Body format:

  • file_id: 16 bytes
  • file_hash: 16 bytes
  • file_hash_16k: 16 bytes
  • length: 8 bytes (Q<)
  • filename: null-terminated, padded to multiple of 4


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# File 'lib/omnizip/parity/models/file_description_packet.rb', line 51

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

  # Validate minimum size (16+16+16+8 = 56 bytes minimum)
  if body_data.bytesize < 56
    warn "FileDescriptionPacket body too short: #{body_data.bytesize} bytes"
    return
  end

  pos = 0

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

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

  # Read file_hash_16k (16 bytes)
  self.file_hash_16k = body_data[pos, 16]
  pos += 16

  # Read length (8 bytes, little-endian unsigned 64-bit)
  length_data = body_data[pos, 8]
  return if length_data.nil? || length_data.bytesize < 8

  self.length = length_data.unpack1("Q<")
  pos += 8

  # Read filename (null-terminated, remaining bytes)
  filename_data = body_data[pos..]
  self.filename = filename_data&.unpack1("Z*") || ""
end