AppleSingle / AppleDouble: Ruby parsing library

AppleSingle and AppleDouble files are used by certain Mac applications (e.g. Finder) to store Mac-specific file attributes on filesystems that do not support that.

Syntactically, both formats are the same, the only difference is how they are being used:

  • AppleSingle means that only one file will be created on external filesystem that will hold both the data (AKA "data fork" in Apple terminology), and the attributes (AKA "resource fork").
  • AppleDouble means that two files will be created: a normal file that keeps the data ("data fork") is kept separately from an auxiliary file that contains attributes ("resource fork"), which is kept with the same name, but starting with an extra dot and underscore ._ to keep it hidden.

In modern practice (Mac OS X), Finder only uses AppleDouble to keep compatibility with other OSes, as virtually nobody outside of Mac understands how to access data in AppleSingle container.

This page hosts a formal specification of AppleSingle / AppleDouble using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Parse a local file and get structure in memory:

data = AppleSingleDouble.from_file("path/to/local/file.AppleSingle / AppleDouble")

Or parse structure from a string of bytes:

bytes = "\x00\x01\x02..."
data = AppleSingleDouble.new(Kaitai::Struct::Stream.new(bytes))

After that, one can get various attributes from the structure by invoking getter methods like:

data.reserved # => Must be all 0.

Ruby source code to parse AppleSingle / AppleDouble

apple_single_double.rb

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

require 'kaitai/struct/struct'

unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.7')
  raise "Incompatible Kaitai Struct Ruby API: 0.7 or later is required, but you have #{Kaitai::Struct::VERSION}"
end


##
# AppleSingle and AppleDouble files are used by certain Mac
# applications (e.g. Finder) to store Mac-specific file attributes on
# filesystems that do not support that.
# 
# Syntactically, both formats are the same, the only difference is how
# they are being used:
# 
# * AppleSingle means that only one file will be created on external
#   filesystem that will hold both the data (AKA "data fork" in Apple
#   terminology), and the attributes (AKA "resource fork").
# * AppleDouble means that two files will be created: a normal file
#   that keeps the data ("data fork") is kept separately from an
#   auxiliary file that contains attributes ("resource fork"), which
#   is kept with the same name, but starting with an extra dot and
#   underscore `._` to keep it hidden.
# 
# In modern practice (Mac OS X), Finder only uses AppleDouble to keep
# compatibility with other OSes, as virtually nobody outside of Mac
# understands how to access data in AppleSingle container.
# @see http://kaiser-edv.de/documents/AppleSingle_AppleDouble.pdf Source
class AppleSingleDouble < Kaitai::Struct::Struct

  FILE_TYPE = {
    333312 => :file_type_apple_single,
    333319 => :file_type_apple_double,
  }
  I__FILE_TYPE = FILE_TYPE.invert
  def initialize(_io, _parent = nil, _root = self)
    super(_io, _parent, _root)
    _read
  end

  def _read
    @magic = Kaitai::Struct::Stream::resolve_enum(FILE_TYPE, @_io.read_u4be)
    @version = @_io.read_u4be
    @reserved = @_io.read_bytes(16)
    @num_entries = @_io.read_u2be
    @entries = Array.new(num_entries)
    (num_entries).times { |i|
      @entries[i] = Entry.new(@_io, self, @_root)
    }
    self
  end
  class Entry < Kaitai::Struct::Struct

    TYPES = {
      1 => :types_data_fork,
      2 => :types_resource_fork,
      3 => :types_real_name,
      4 => :types_comment,
      5 => :types_icon_bw,
      6 => :types_icon_color,
      8 => :types_file_dates_info,
      9 => :types_finder_info,
      10 => :types_macintosh_file_info,
      11 => :types_prodos_file_info,
      12 => :types_msdos_file_info,
      13 => :types_afp_short_name,
      14 => :types_afp_file_info,
      15 => :types_afp_directory_id,
    }
    I__TYPES = TYPES.invert
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @type = Kaitai::Struct::Stream::resolve_enum(TYPES, @_io.read_u4be)
      @ofs_body = @_io.read_u4be
      @len_body = @_io.read_u4be
      self
    end
    def body
      return @body unless @body.nil?
      _pos = @_io.pos
      @_io.seek(ofs_body)
      case type
      when :types_finder_info
        @_raw_body = @_io.read_bytes(len_body)
        io = Kaitai::Struct::Stream.new(@_raw_body)
        @body = FinderInfo.new(io, self, @_root)
      else
        @body = @_io.read_bytes(len_body)
      end
      @_io.seek(_pos)
      @body
    end
    attr_reader :type
    attr_reader :ofs_body
    attr_reader :len_body
    attr_reader :_raw_body
  end

  ##
  # Information specific to Finder
  # @see '' older Inside Macintosh, Volume II page 84 or Volume IV page 104.
  class FinderInfo < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @file_type = @_io.read_bytes(4)
      @file_creator = @_io.read_bytes(4)
      @flags = @_io.read_u2be
      @location = Point.new(@_io, self, @_root)
      @folder_id = @_io.read_u2be
      self
    end
    attr_reader :file_type
    attr_reader :file_creator
    attr_reader :flags

    ##
    # File icon's coordinates when displaying this folder.
    attr_reader :location

    ##
    # File folder ID (=window).
    attr_reader :folder_id
  end

  ##
  # Specifies 2D coordinate in QuickDraw grid.
  class Point < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @x = @_io.read_u2be
      @y = @_io.read_u2be
      self
    end
    attr_reader :x
    attr_reader :y
  end
  attr_reader :magic
  attr_reader :version

  ##
  # Must be all 0.
  attr_reader :reserved
  attr_reader :num_entries
  attr_reader :entries
end