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:
._ 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.
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
import io.kaitai.struct.ByteBufferKaitaiStream;
import io.kaitai.struct.KaitaiStruct;
import io.kaitai.struct.KaitaiStream;
import java.io.IOException;
import java.util.Map;
import java.util.HashMap;
import java.util.ArrayList;
import io.kaitai.struct.ConsistencyError;
import java.util.Objects;
import java.util.List;
/**
* 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 <a href="http://kaiser-edv.de/documents/AppleSingle_AppleDouble.pdf">Source</a>
*/
public class AppleSingleDouble extends KaitaiStruct.ReadWrite {
public static AppleSingleDouble fromFile(String fileName) throws IOException {
return new AppleSingleDouble(new ByteBufferKaitaiStream(fileName));
}
public enum FileType {
APPLE_SINGLE(333312),
APPLE_DOUBLE(333319);
private final long id;
FileType(long id) { this.id = id; }
public long id() { return id; }
private static final Map<Long, FileType> byId = new HashMap<Long, FileType>(2);
static {
for (FileType e : FileType.values())
byId.put(e.id(), e);
}
public static FileType byId(long id) { return byId.get(id); }
}
public AppleSingleDouble() {
this(null, null, null);
}
public AppleSingleDouble(KaitaiStream _io) {
this(_io, null, null);
}
public AppleSingleDouble(KaitaiStream _io, KaitaiStruct.ReadWrite _parent) {
this(_io, _parent, null);
}
public AppleSingleDouble(KaitaiStream _io, KaitaiStruct.ReadWrite _parent, AppleSingleDouble _root) {
super(_io);
this._parent = _parent;
this._root = _root == null ? this : _root;
}
public void _read() {
this.magic = FileType.byId(this._io.readU4be());
this.version = this._io.readU4be();
this.reserved = this._io.readBytes(16);
this.numEntries = this._io.readU2be();
this.entries = new ArrayList<Entry>();
for (int i = 0; i < numEntries(); i++) {
Entry _t_entries = new Entry(this._io, this, _root);
try {
_t_entries._read();
} finally {
this.entries.add(_t_entries);
}
}
_dirty = false;
}
public void _fetchInstances() {
for (int i = 0; i < this.entries.size(); i++) {
this.entries.get(((Number) (i)).intValue())._fetchInstances();
}
}
public void _write_Seq() {
_assertNotDirty();
this._io.writeU4be(((Number) (this.magic.id())).longValue());
this._io.writeU4be(this.version);
this._io.writeBytes(this.reserved);
this._io.writeU2be(this.numEntries);
for (int i = 0; i < this.entries.size(); i++) {
this.entries.get(((Number) (i)).intValue())._write_Seq(this._io);
}
}
public void _check() {
if (this.reserved.length != 16)
throw new ConsistencyError("reserved", 16, this.reserved.length);
if (this.entries.size() != numEntries())
throw new ConsistencyError("entries", numEntries(), this.entries.size());
for (int i = 0; i < this.entries.size(); i++) {
if (!Objects.equals(this.entries.get(((Number) (i)).intValue())._root(), _root()))
throw new ConsistencyError("entries", _root(), this.entries.get(((Number) (i)).intValue())._root());
if (!Objects.equals(this.entries.get(((Number) (i)).intValue())._parent(), this))
throw new ConsistencyError("entries", this, this.entries.get(((Number) (i)).intValue())._parent());
}
_dirty = false;
}
public static class Entry extends KaitaiStruct.ReadWrite {
public static Entry fromFile(String fileName) throws IOException {
return new Entry(new ByteBufferKaitaiStream(fileName));
}
public enum Types {
DATA_FORK(1),
RESOURCE_FORK(2),
REAL_NAME(3),
COMMENT(4),
ICON_BW(5),
ICON_COLOR(6),
FILE_DATES_INFO(8),
FINDER_INFO(9),
MACINTOSH_FILE_INFO(10),
PRODOS_FILE_INFO(11),
MSDOS_FILE_INFO(12),
AFP_SHORT_NAME(13),
AFP_FILE_INFO(14),
AFP_DIRECTORY_ID(15);
private final long id;
Types(long id) { this.id = id; }
public long id() { return id; }
private static final Map<Long, Types> byId = new HashMap<Long, Types>(14);
static {
for (Types e : Types.values())
byId.put(e.id(), e);
}
public static Types byId(long id) { return byId.get(id); }
}
public Entry() {
this(null, null, null);
}
public Entry(KaitaiStream _io) {
this(_io, null, null);
}
public Entry(KaitaiStream _io, AppleSingleDouble _parent) {
this(_io, _parent, null);
}
public Entry(KaitaiStream _io, AppleSingleDouble _parent, AppleSingleDouble _root) {
super(_io);
this._parent = _parent;
this._root = _root;
}
public void _read() {
this.type = Types.byId(this._io.readU4be());
this.ofsBody = this._io.readU4be();
this.lenBody = this._io.readU4be();
_dirty = false;
}
public void _fetchInstances() {
body();
if (this.body != null) {
{
Types on = type();
if (on != null) {
switch (type()) {
case FINDER_INFO: {
((FinderInfo) (this.body))._fetchInstances();
break;
}
default: {
break;
}
}
} else {
}
}
}
}
public void _write_Seq() {
_assertNotDirty();
_shouldWriteBody = _enabledBody;
this._io.writeU4be(((Number) (this.type.id())).longValue());
this._io.writeU4be(this.ofsBody);
this._io.writeU4be(this.lenBody);
}
public void _check() {
if (_enabledBody) {
{
Types on = type();
if (on != null) {
switch (type()) {
case FINDER_INFO: {
if (!Objects.equals(((AppleSingleDouble.FinderInfo) (this.body))._root(), _root()))
throw new ConsistencyError("body", _root(), ((AppleSingleDouble.FinderInfo) (this.body))._root());
if (!Objects.equals(((AppleSingleDouble.FinderInfo) (this.body))._parent(), this))
throw new ConsistencyError("body", this, ((AppleSingleDouble.FinderInfo) (this.body))._parent());
break;
}
default: {
if (((byte[]) (this.body)).length != lenBody())
throw new ConsistencyError("body", lenBody(), ((byte[]) (this.body)).length);
break;
}
}
} else {
if (((byte[]) (this.body)).length != lenBody())
throw new ConsistencyError("body", lenBody(), ((byte[]) (this.body)).length);
}
}
}
_dirty = false;
}
private Object body;
private boolean _shouldWriteBody = false;
private boolean _enabledBody = true;
public Object body() {
if (_shouldWriteBody)
_writeBody();
if (this.body != null)
return this.body;
if (!_enabledBody)
return null;
long _pos = this._io.pos();
this._io.seek(ofsBody());
{
Types on = type();
if (on != null) {
switch (type()) {
case FINDER_INFO: {
this._raw_body = this._io.readBytes(lenBody());
KaitaiStream _io__raw_body = new ByteBufferKaitaiStream(this._raw_body);
this.body = new FinderInfo(_io__raw_body, this, _root);
((FinderInfo) (this.body))._read();
break;
}
default: {
this.body = this._io.readBytes(lenBody());
break;
}
}
} else {
this.body = this._io.readBytes(lenBody());
}
}
this._io.seek(_pos);
return this.body;
}
public void setBody(Object _v) { _dirty = true; body = _v; }
public void setBody_Enabled(boolean _v) { _dirty = true; _enabledBody = _v; }
private void _writeBody() {
_shouldWriteBody = false;
long _pos = this._io.pos();
this._io.seek(ofsBody());
{
Types on = type();
if (on != null) {
switch (type()) {
case FINDER_INFO: {
final KaitaiStream _io__raw_body = new ByteBufferKaitaiStream(lenBody());
this._io.addChildStream(_io__raw_body);
{
long _pos2 = this._io.pos();
this._io.seek(this._io.pos() + (lenBody()));
final Entry _this = this;
_io__raw_body.setWriteBackHandler(new KaitaiStream.WriteBackHandler(_pos2) {
@Override
protected void write(KaitaiStream parent) {
_this._raw_body = _io__raw_body.toByteArray();
if (((byte[]) (_this._raw_body)).length != lenBody())
throw new ConsistencyError("raw(body)", lenBody(), ((byte[]) (_this._raw_body)).length);
parent.writeBytes(((byte[]) (((byte[]) (_this._raw_body)))));
}
});
}
((FinderInfo) (this.body))._write_Seq(_io__raw_body);
break;
}
default: {
this._io.writeBytes(((byte[]) (((byte[]) (this.body)))));
break;
}
}
} else {
this._io.writeBytes(((byte[]) (((byte[]) (this.body)))));
}
}
this._io.seek(_pos);
}
private Types type;
private long ofsBody;
private long lenBody;
private AppleSingleDouble _root;
private AppleSingleDouble _parent;
private byte[] _raw_body;
public Types type() { return type; }
public void setType(Types _v) { _dirty = true; type = _v; }
public long ofsBody() { return ofsBody; }
public void setOfsBody(long _v) { _dirty = true; ofsBody = _v; }
public long lenBody() { return lenBody; }
public void setLenBody(long _v) { _dirty = true; lenBody = _v; }
public AppleSingleDouble _root() { return _root; }
public void set_root(AppleSingleDouble _v) { _dirty = true; _root = _v; }
public AppleSingleDouble _parent() { return _parent; }
public void set_parent(AppleSingleDouble _v) { _dirty = true; _parent = _v; }
public byte[] _raw_body() { return _raw_body; }
public void set_raw_Body(byte[] _v) { _dirty = true; _raw_body = _v; }
}
/**
* Information specific to Finder
* @see "older Inside Macintosh, Volume II page 84 or Volume IV page 104."
*/
public static class FinderInfo extends KaitaiStruct.ReadWrite {
public static FinderInfo fromFile(String fileName) throws IOException {
return new FinderInfo(new ByteBufferKaitaiStream(fileName));
}
public FinderInfo() {
this(null, null, null);
}
public FinderInfo(KaitaiStream _io) {
this(_io, null, null);
}
public FinderInfo(KaitaiStream _io, AppleSingleDouble.Entry _parent) {
this(_io, _parent, null);
}
public FinderInfo(KaitaiStream _io, AppleSingleDouble.Entry _parent, AppleSingleDouble _root) {
super(_io);
this._parent = _parent;
this._root = _root;
}
public void _read() {
this.fileType = this._io.readBytes(4);
this.fileCreator = this._io.readBytes(4);
this.flags = this._io.readU2be();
this.location = new Point(this._io, this, _root);
this.location._read();
this.folderId = this._io.readU2be();
_dirty = false;
}
public void _fetchInstances() {
this.location._fetchInstances();
}
public void _write_Seq() {
_assertNotDirty();
this._io.writeBytes(this.fileType);
this._io.writeBytes(this.fileCreator);
this._io.writeU2be(this.flags);
this.location._write_Seq(this._io);
this._io.writeU2be(this.folderId);
}
public void _check() {
if (this.fileType.length != 4)
throw new ConsistencyError("file_type", 4, this.fileType.length);
if (this.fileCreator.length != 4)
throw new ConsistencyError("file_creator", 4, this.fileCreator.length);
if (!Objects.equals(this.location._root(), _root()))
throw new ConsistencyError("location", _root(), this.location._root());
if (!Objects.equals(this.location._parent(), this))
throw new ConsistencyError("location", this, this.location._parent());
_dirty = false;
}
private byte[] fileType;
private byte[] fileCreator;
private int flags;
private Point location;
private int folderId;
private AppleSingleDouble _root;
private AppleSingleDouble.Entry _parent;
public byte[] fileType() { return fileType; }
public void setFileType(byte[] _v) { _dirty = true; fileType = _v; }
public byte[] fileCreator() { return fileCreator; }
public void setFileCreator(byte[] _v) { _dirty = true; fileCreator = _v; }
public int flags() { return flags; }
public void setFlags(int _v) { _dirty = true; flags = _v; }
/**
* File icon's coordinates when displaying this folder.
*/
public Point location() { return location; }
public void setLocation(Point _v) { _dirty = true; location = _v; }
/**
* File folder ID (=window).
*/
public int folderId() { return folderId; }
public void setFolderId(int _v) { _dirty = true; folderId = _v; }
public AppleSingleDouble _root() { return _root; }
public void set_root(AppleSingleDouble _v) { _dirty = true; _root = _v; }
public AppleSingleDouble.Entry _parent() { return _parent; }
public void set_parent(AppleSingleDouble.Entry _v) { _dirty = true; _parent = _v; }
}
/**
* Specifies 2D coordinate in QuickDraw grid.
*/
public static class Point extends KaitaiStruct.ReadWrite {
public static Point fromFile(String fileName) throws IOException {
return new Point(new ByteBufferKaitaiStream(fileName));
}
public Point() {
this(null, null, null);
}
public Point(KaitaiStream _io) {
this(_io, null, null);
}
public Point(KaitaiStream _io, AppleSingleDouble.FinderInfo _parent) {
this(_io, _parent, null);
}
public Point(KaitaiStream _io, AppleSingleDouble.FinderInfo _parent, AppleSingleDouble _root) {
super(_io);
this._parent = _parent;
this._root = _root;
}
public void _read() {
this.x = this._io.readU2be();
this.y = this._io.readU2be();
_dirty = false;
}
public void _fetchInstances() {
}
public void _write_Seq() {
_assertNotDirty();
this._io.writeU2be(this.x);
this._io.writeU2be(this.y);
}
public void _check() {
_dirty = false;
}
private int x;
private int y;
private AppleSingleDouble _root;
private AppleSingleDouble.FinderInfo _parent;
public int x() { return x; }
public void setX(int _v) { _dirty = true; x = _v; }
public int y() { return y; }
public void setY(int _v) { _dirty = true; y = _v; }
public AppleSingleDouble _root() { return _root; }
public void set_root(AppleSingleDouble _v) { _dirty = true; _root = _v; }
public AppleSingleDouble.FinderInfo _parent() { return _parent; }
public void set_parent(AppleSingleDouble.FinderInfo _v) { _dirty = true; _parent = _v; }
}
private FileType magic;
private long version;
private byte[] reserved;
private int numEntries;
private List<Entry> entries;
private AppleSingleDouble _root;
private KaitaiStruct.ReadWrite _parent;
public FileType magic() { return magic; }
public void setMagic(FileType _v) { _dirty = true; magic = _v; }
public long version() { return version; }
public void setVersion(long _v) { _dirty = true; version = _v; }
/**
* Must be all 0.
*/
public byte[] reserved() { return reserved; }
public void setReserved(byte[] _v) { _dirty = true; reserved = _v; }
public int numEntries() { return numEntries; }
public void setNumEntries(int _v) { _dirty = true; numEntries = _v; }
public List<Entry> entries() { return entries; }
public void setEntries(List<Entry> _v) { _dirty = true; entries = _v; }
public AppleSingleDouble _root() { return _root; }
public void set_root(AppleSingleDouble _v) { _dirty = true; _root = _v; }
public KaitaiStruct.ReadWrite _parent() { return _parent; }
public void set_parent(KaitaiStruct.ReadWrite _v) { _dirty = true; _parent = _v; }
}