AppleSingle / AppleDouble: C# 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:

var data = AppleSingleDouble.FromFile("path/to/local/file.apple_single_double");

Or parse structure from a byte array:

byte[] someArray = new byte[] { ... };
var data = new AppleSingleDouble(new KaitaiStream(someArray));

After that, one can get various attributes from the structure by accessing properties like:

data.Reserved // => Must be all 0.

C# source code to parse AppleSingle / AppleDouble

AppleSingleDouble.cs

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

using System.Collections.Generic;

namespace Kaitai
{

    /// <summary>
    /// 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 &quot;data fork&quot; in Apple
    ///   terminology), and the attributes (AKA &quot;resource fork&quot;).
    /// * AppleDouble means that two files will be created: a normal file
    ///   that keeps the data (&quot;data fork&quot;) is kept separately from an
    ///   auxiliary file that contains attributes (&quot;resource fork&quot;), 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.
    /// </summary>
    /// <remarks>
    /// Reference: <a href="http://kaiser-edv.de/documents/AppleSingle_AppleDouble.pdf">Source</a>
    /// </remarks>
    public partial class AppleSingleDouble : KaitaiStruct
    {
        public static AppleSingleDouble FromFile(string fileName)
        {
            return new AppleSingleDouble(new KaitaiStream(fileName));
        }


        public enum FileType
        {
            AppleSingle = 333312,
            AppleDouble = 333319,
        }
        public AppleSingleDouble(KaitaiStream p__io, KaitaiStruct p__parent = null, AppleSingleDouble p__root = null) : base(p__io)
        {
            m_parent = p__parent;
            m_root = p__root ?? this;
            _read();
        }
        private void _read()
        {
            _magic = ((FileType) m_io.ReadU4be());
            _version = m_io.ReadU4be();
            _reserved = m_io.ReadBytes(16);
            _numEntries = m_io.ReadU2be();
            _entries = new List<Entry>((int) (NumEntries));
            for (var i = 0; i < NumEntries; i++)
            {
                _entries.Add(new Entry(m_io, this, m_root));
            }
        }
        public partial class Entry : KaitaiStruct
        {
            public static Entry FromFile(string fileName)
            {
                return new Entry(new KaitaiStream(fileName));
            }


            public enum Types
            {
                DataFork = 1,
                ResourceFork = 2,
                RealName = 3,
                Comment = 4,
                IconBw = 5,
                IconColor = 6,
                FileDatesInfo = 8,
                FinderInfo = 9,
                MacintoshFileInfo = 10,
                ProdosFileInfo = 11,
                MsdosFileInfo = 12,
                AfpShortName = 13,
                AfpFileInfo = 14,
                AfpDirectoryId = 15,
            }
            public Entry(KaitaiStream p__io, AppleSingleDouble p__parent = null, AppleSingleDouble p__root = null) : base(p__io)
            {
                m_parent = p__parent;
                m_root = p__root;
                f_body = false;
                _read();
            }
            private void _read()
            {
                _type = ((Types) m_io.ReadU4be());
                _ofsBody = m_io.ReadU4be();
                _lenBody = m_io.ReadU4be();
            }
            private bool f_body;
            private object _body;
            public object Body
            {
                get
                {
                    if (f_body)
                        return _body;
                    long _pos = m_io.Pos;
                    m_io.Seek(OfsBody);
                    switch (Type) {
                    case Types.FinderInfo: {
                        __raw_body = m_io.ReadBytes(LenBody);
                        var io___raw_body = new KaitaiStream(__raw_body);
                        _body = new FinderInfo(io___raw_body, this, m_root);
                        break;
                    }
                    default: {
                        _body = m_io.ReadBytes(LenBody);
                        break;
                    }
                    }
                    m_io.Seek(_pos);
                    f_body = true;
                    return _body;
                }
            }
            private Types _type;
            private uint _ofsBody;
            private uint _lenBody;
            private AppleSingleDouble m_root;
            private AppleSingleDouble m_parent;
            private byte[] __raw_body;
            public Types Type { get { return _type; } }
            public uint OfsBody { get { return _ofsBody; } }
            public uint LenBody { get { return _lenBody; } }
            public AppleSingleDouble M_Root { get { return m_root; } }
            public AppleSingleDouble M_Parent { get { return m_parent; } }
            public byte[] M_RawBody { get { return __raw_body; } }
        }

        /// <summary>
        /// Information specific to Finder
        /// </summary>
        /// <remarks>
        /// Reference: older Inside Macintosh, Volume II page 84 or Volume IV page 104.
        /// </remarks>
        public partial class FinderInfo : KaitaiStruct
        {
            public static FinderInfo FromFile(string fileName)
            {
                return new FinderInfo(new KaitaiStream(fileName));
            }

            public FinderInfo(KaitaiStream p__io, AppleSingleDouble.Entry p__parent = null, AppleSingleDouble p__root = null) : base(p__io)
            {
                m_parent = p__parent;
                m_root = p__root;
                _read();
            }
            private void _read()
            {
                _fileType = m_io.ReadBytes(4);
                _fileCreator = m_io.ReadBytes(4);
                _flags = m_io.ReadU2be();
                _location = new Point(m_io, this, m_root);
                _folderId = m_io.ReadU2be();
            }
            private byte[] _fileType;
            private byte[] _fileCreator;
            private ushort _flags;
            private Point _location;
            private ushort _folderId;
            private AppleSingleDouble m_root;
            private AppleSingleDouble.Entry m_parent;
            public byte[] FileType { get { return _fileType; } }
            public byte[] FileCreator { get { return _fileCreator; } }
            public ushort Flags { get { return _flags; } }

            /// <summary>
            /// File icon's coordinates when displaying this folder.
            /// </summary>
            public Point Location { get { return _location; } }

            /// <summary>
            /// File folder ID (=window).
            /// </summary>
            public ushort FolderId { get { return _folderId; } }
            public AppleSingleDouble M_Root { get { return m_root; } }
            public AppleSingleDouble.Entry M_Parent { get { return m_parent; } }
        }

        /// <summary>
        /// Specifies 2D coordinate in QuickDraw grid.
        /// </summary>
        public partial class Point : KaitaiStruct
        {
            public static Point FromFile(string fileName)
            {
                return new Point(new KaitaiStream(fileName));
            }

            public Point(KaitaiStream p__io, AppleSingleDouble.FinderInfo p__parent = null, AppleSingleDouble p__root = null) : base(p__io)
            {
                m_parent = p__parent;
                m_root = p__root;
                _read();
            }
            private void _read()
            {
                _x = m_io.ReadU2be();
                _y = m_io.ReadU2be();
            }
            private ushort _x;
            private ushort _y;
            private AppleSingleDouble m_root;
            private AppleSingleDouble.FinderInfo m_parent;
            public ushort X { get { return _x; } }
            public ushort Y { get { return _y; } }
            public AppleSingleDouble M_Root { get { return m_root; } }
            public AppleSingleDouble.FinderInfo M_Parent { get { return m_parent; } }
        }
        private FileType _magic;
        private uint _version;
        private byte[] _reserved;
        private ushort _numEntries;
        private List<Entry> _entries;
        private AppleSingleDouble m_root;
        private KaitaiStruct m_parent;
        public FileType Magic { get { return _magic; } }
        public uint Version { get { return _version; } }

        /// <summary>
        /// Must be all 0.
        /// </summary>
        public byte[] Reserved { get { return _reserved; } }
        public ushort NumEntries { get { return _numEntries; } }
        public List<Entry> Entries { get { return _entries; } }
        public AppleSingleDouble M_Root { get { return m_root; } }
        public KaitaiStruct M_Parent { get { return m_parent; } }
    }
}