Compressed resource data in 'dcmp' (2) format,
as stored in compressed resources with header type 9 and decompressor ID 2.
The 'dcmp' (2) decompressor resource is included in the System file of System 7.0 and later.
This compression format is used for a few compressed resources in System 7.0's files
(such as the System file).
This decompressor is also included with and used by some other Apple applications,
such as ResEdit.
(Note: ResEdit includes the 'dcmp' (2) resource,
but none of its resources actually use this decompressor.)
This compression format is based on simple dictionary coding, where each byte in the compressed data expands to two bytes, based on a lookup table (either included in the compressed data or provided by the decompressor). An alternative "tagged" compression format is also supported, which allows using two-byte literals in addition to single-byte table references, at the cost of requiring an extra "tag" byte every 16 output bytes, to differentiate literals and table references.
This page hosts a formal specification of Compressed Macintosh resource data, Apple `'dcmp' (2)` format using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for Python generated by Kaitai Struct depends on the Python runtime library. You have to install it before you can parse data.
The Python runtime library can be installed from PyPI:
python3 -m pip install kaitaistructParse a local file and get structure in memory:
data = Dcmp2.from_file("path/to/local/file.bin")
Or parse structure from a bytes:
from kaitaistruct import KaitaiStream, BytesIO
raw = b"\x00\x01\x02..."
data = Dcmp2(KaitaiStream(BytesIO(raw)))
After that, one can get various attributes from the structure by invoking getter methods like:
data.custom_lookup_table # => The custom lookup table to be used instead of the default lookup table.
data.header_parameters # => The parsed decompressor-specific parameters from the compressed resource header.
# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
# type: ignore
import kaitaistruct
from kaitaistruct import KaitaiStruct, KaitaiStream, BytesIO
import bytes_with_io
if getattr(kaitaistruct, 'API_VERSION', (0, 9)) < (0, 11):
raise Exception("Incompatible Kaitai Struct Python API: 0.11 or later is required, but you have %s" % (kaitaistruct.__version__))
class Dcmp2(KaitaiStruct):
"""Compressed resource data in `'dcmp' (2)` format,
as stored in compressed resources with header type `9` and decompressor ID `2`.
The `'dcmp' (2)` decompressor resource is included in the System file of System 7.0 and later.
This compression format is used for a few compressed resources in System 7.0's files
(such as the System file).
This decompressor is also included with and used by some other Apple applications,
such as ResEdit.
(Note: ResEdit includes the `'dcmp' (2)` resource,
but none of its resources actually use this decompressor.)
This compression format is based on simple dictionary coding,
where each byte in the compressed data expands to two bytes,
based on a lookup table
(either included in the compressed data or provided by the decompressor).
An alternative "tagged" compression format is also supported,
which allows using two-byte literals in addition to single-byte table references,
at the cost of requiring an extra "tag" byte every 16 output bytes,
to differentiate literals and table references.
.. seealso::
Source - https://github.com/dgelessus/python-rsrcfork/blob/f891a6e/src/rsrcfork/compress/dcmp2.py
"""
def __init__(self, len_decompressed, header_parameters_with_io, _io, _parent=None, _root=None):
super(Dcmp2, self).__init__(_io)
self._parent = _parent
self._root = _root or self
self.len_decompressed = len_decompressed
self.header_parameters_with_io = header_parameters_with_io
self._read()
def _read(self):
if self.header_parameters.flags.has_custom_lookup_table:
pass
self.custom_lookup_table = []
for i in range(self.header_parameters.num_custom_lookup_table_entries):
self.custom_lookup_table.append(self._io.read_bytes(2))
_on = self.header_parameters.flags.tagged
if _on == True:
pass
self._raw_data = self._io.read_bytes((self._io.size() - self._io.pos()) - (1 if self.is_len_decompressed_odd else 0))
_io__raw_data = KaitaiStream(BytesIO(self._raw_data))
self.data = Dcmp2.TaggedData(_io__raw_data, self, self._root)
else:
pass
self._raw_data = self._io.read_bytes((self._io.size() - self._io.pos()) - (1 if self.is_len_decompressed_odd else 0))
_io__raw_data = KaitaiStream(BytesIO(self._raw_data))
self.data = Dcmp2.UntaggedData(_io__raw_data, self, self._root)
if self.is_len_decompressed_odd:
pass
self.last_byte = self._io.read_bytes(1)
def _fetch_instances(self):
pass
if self.header_parameters.flags.has_custom_lookup_table:
pass
for i in range(len(self.custom_lookup_table)):
pass
_on = self.header_parameters.flags.tagged
if _on == True:
pass
self.data._fetch_instances()
else:
pass
self.data._fetch_instances()
if self.is_len_decompressed_odd:
pass
_ = self.header_parameters
if hasattr(self, '_m_header_parameters'):
pass
self._m_header_parameters._fetch_instances()
class HeaderParameters(KaitaiStruct):
"""Decompressor-specific parameters for this compression format,
as stored in the compressed resource header.
"""
def __init__(self, _io, _parent=None, _root=None):
super(Dcmp2.HeaderParameters, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.unknown = self._io.read_u2be()
self.num_custom_lookup_table_entries_m1 = self._io.read_u1()
self.flags = Dcmp2.HeaderParameters.Flags(self._io, self, self._root)
def _fetch_instances(self):
pass
self.flags._fetch_instances()
class Flags(KaitaiStruct):
"""Flags for the decompressor,
as stored in the decompressor-specific parameters.
"""
def __init__(self, _io, _parent=None, _root=None):
super(Dcmp2.HeaderParameters.Flags, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.reserved = self._io.read_bits_int_be(6)
self.tagged = self._io.read_bits_int_be(1) != 0
self.has_custom_lookup_table = self._io.read_bits_int_be(1) != 0
def _fetch_instances(self):
pass
_ = self.as_int
if hasattr(self, '_m_as_int'):
pass
@property
def as_int(self):
"""The flags as a packed integer,
as they are stored in the data.
"""
if hasattr(self, '_m_as_int'):
return self._m_as_int
_pos = self._io.pos()
self._io.seek(0)
self._m_as_int = self._io.read_u1()
self._io.seek(_pos)
return getattr(self, '_m_as_int', None)
@property
def num_custom_lookup_table_entries(self):
"""The number of entries in the custom lookup table.
Only used if a custom lookup table is present.
"""
if hasattr(self, '_m_num_custom_lookup_table_entries'):
return self._m_num_custom_lookup_table_entries
if self.flags.has_custom_lookup_table:
pass
self._m_num_custom_lookup_table_entries = self.num_custom_lookup_table_entries_m1 + 1
return getattr(self, '_m_num_custom_lookup_table_entries', None)
class TaggedData(KaitaiStruct):
"""Compressed data in the "tagged" variant of the format.
"""
def __init__(self, _io, _parent=None, _root=None):
super(Dcmp2.TaggedData, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.chunks = []
i = 0
while not self._io.is_eof():
self.chunks.append(Dcmp2.TaggedData.Chunk(self._io, self, self._root))
i += 1
def _fetch_instances(self):
pass
for i in range(len(self.chunks)):
pass
self.chunks[i]._fetch_instances()
class Chunk(KaitaiStruct):
"""A single tagged chunk of compressed data.
Each chunk expands to 16 bytes of decompressed data.
In compressed form,
the chunks have a variable length
(between 9 and 17 bytes)
depending on the value of the tag byte.
"""
def __init__(self, _io, _parent=None, _root=None):
super(Dcmp2.TaggedData.Chunk, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.tag = []
for i in range(8):
self.tag.append(self._io.read_bits_int_be(1) != 0)
self.units = []
i = 0
while True:
_on = self.tag[i]
if _on == True:
pass
_ = self._io.read_u1()
self.units.append(_)
else:
pass
_ = self._io.read_bytes((1 if self.tag[i] else 2))
self.units.append(_)
if ((i >= 7) or (self._io.is_eof())) :
break
i += 1
def _fetch_instances(self):
pass
for i in range(len(self.tag)):
pass
for i in range(len(self.units)):
pass
_on = self.tag[i]
if _on == True:
pass
else:
pass
class UntaggedData(KaitaiStruct):
"""Compressed data in the "untagged" variant of the format.
"""
def __init__(self, _io, _parent=None, _root=None):
super(Dcmp2.UntaggedData, self).__init__(_io)
self._parent = _parent
self._root = _root
self._read()
def _read(self):
self.table_references = []
i = 0
while not self._io.is_eof():
self.table_references.append(self._io.read_u1())
i += 1
def _fetch_instances(self):
pass
for i in range(len(self.table_references)):
pass
@property
def default_lookup_table(self):
"""The default lookup table,
which is used if no custom lookup table is included with the compressed data.
"""
if hasattr(self, '_m_default_lookup_table'):
return self._m_default_lookup_table
self._m_default_lookup_table = [b"\x00\x00", b"\x00\x08", b"\x4E\xBA", b"\x20\x6E", b"\x4E\x75", b"\x00\x0C", b"\x00\x04", b"\x70\x00", b"\x00\x10", b"\x00\x02", b"\x48\x6E", b"\xFF\xFC", b"\x60\x00", b"\x00\x01", b"\x48\xE7", b"\x2F\x2E", b"\x4E\x56", b"\x00\x06", b"\x4E\x5E", b"\x2F\x00", b"\x61\x00", b"\xFF\xF8", b"\x2F\x0B", b"\xFF\xFF", b"\x00\x14", b"\x00\x0A", b"\x00\x18", b"\x20\x5F", b"\x00\x0E", b"\x20\x50", b"\x3F\x3C", b"\xFF\xF4", b"\x4C\xEE", b"\x30\x2E", b"\x67\x00", b"\x4C\xDF", b"\x26\x6E", b"\x00\x12", b"\x00\x1C", b"\x42\x67", b"\xFF\xF0", b"\x30\x3C", b"\x2F\x0C", b"\x00\x03", b"\x4E\xD0", b"\x00\x20", b"\x70\x01", b"\x00\x16", b"\x2D\x40", b"\x48\xC0", b"\x20\x78", b"\x72\x00", b"\x58\x8F", b"\x66\x00", b"\x4F\xEF", b"\x42\xA7", b"\x67\x06", b"\xFF\xFA", b"\x55\x8F", b"\x28\x6E", b"\x3F\x00", b"\xFF\xFE", b"\x2F\x3C", b"\x67\x04", b"\x59\x8F", b"\x20\x6B", b"\x00\x24", b"\x20\x1F", b"\x41\xFA", b"\x81\xE1", b"\x66\x04", b"\x67\x08", b"\x00\x1A", b"\x4E\xB9", b"\x50\x8F", b"\x20\x2E", b"\x00\x07", b"\x4E\xB0", b"\xFF\xF2", b"\x3D\x40", b"\x00\x1E", b"\x20\x68", b"\x66\x06", b"\xFF\xF6", b"\x4E\xF9", b"\x08\x00", b"\x0C\x40", b"\x3D\x7C", b"\xFF\xEC", b"\x00\x05", b"\x20\x3C", b"\xFF\xE8", b"\xDE\xFC", b"\x4A\x2E", b"\x00\x30", b"\x00\x28", b"\x2F\x08", b"\x20\x0B", b"\x60\x02", b"\x42\x6E", b"\x2D\x48", b"\x20\x53", b"\x20\x40", b"\x18\x00", b"\x60\x04", b"\x41\xEE", b"\x2F\x28", b"\x2F\x01", b"\x67\x0A", b"\x48\x40", b"\x20\x07", b"\x66\x08", b"\x01\x18", b"\x2F\x07", b"\x30\x28", b"\x3F\x2E", b"\x30\x2B", b"\x22\x6E", b"\x2F\x2B", b"\x00\x2C", b"\x67\x0C", b"\x22\x5F", b"\x60\x06", b"\x00\xFF", b"\x30\x07", b"\xFF\xEE", b"\x53\x40", b"\x00\x40", b"\xFF\xE4", b"\x4A\x40", b"\x66\x0A", b"\x00\x0F", b"\x4E\xAD", b"\x70\xFF", b"\x22\xD8", b"\x48\x6B", b"\x00\x22", b"\x20\x4B", b"\x67\x0E", b"\x4A\xAE", b"\x4E\x90", b"\xFF\xE0", b"\xFF\xC0", b"\x00\x2A", b"\x27\x40", b"\x67\x02", b"\x51\xC8", b"\x02\xB6", b"\x48\x7A", b"\x22\x78", b"\xB0\x6E", b"\xFF\xE6", b"\x00\x09", b"\x32\x2E", b"\x3E\x00", b"\x48\x41", b"\xFF\xEA", b"\x43\xEE", b"\x4E\x71", b"\x74\x00", b"\x2F\x2C", b"\x20\x6C", b"\x00\x3C", b"\x00\x26", b"\x00\x50", b"\x18\x80", b"\x30\x1F", b"\x22\x00", b"\x66\x0C", b"\xFF\xDA", b"\x00\x38", b"\x66\x02", b"\x30\x2C", b"\x20\x0C", b"\x2D\x6E", b"\x42\x40", b"\xFF\xE2", b"\xA9\xF0", b"\xFF\x00", b"\x37\x7C", b"\xE5\x80", b"\xFF\xDC", b"\x48\x68", b"\x59\x4F", b"\x00\x34", b"\x3E\x1F", b"\x60\x08", b"\x2F\x06", b"\xFF\xDE", b"\x60\x0A", b"\x70\x02", b"\x00\x32", b"\xFF\xCC", b"\x00\x80", b"\x22\x51", b"\x10\x1F", b"\x31\x7C", b"\xA0\x29", b"\xFF\xD8", b"\x52\x40", b"\x01\x00", b"\x67\x10", b"\xA0\x23", b"\xFF\xCE", b"\xFF\xD4", b"\x20\x06", b"\x48\x78", b"\x00\x2E", b"\x50\x4F", b"\x43\xFA", b"\x67\x12", b"\x76\x00", b"\x41\xE8", b"\x4A\x6E", b"\x20\xD9", b"\x00\x5A", b"\x7F\xFF", b"\x51\xCA", b"\x00\x5C", b"\x2E\x00", b"\x02\x40", b"\x48\xC7", b"\x67\x14", b"\x0C\x80", b"\x2E\x9F", b"\xFF\xD6", b"\x80\x00", b"\x10\x00", b"\x48\x42", b"\x4A\x6B", b"\xFF\xD2", b"\x00\x48", b"\x4A\x47", b"\x4E\xD1", b"\x20\x6F", b"\x00\x41", b"\x60\x0C", b"\x2A\x78", b"\x42\x2E", b"\x32\x00", b"\x65\x74", b"\x67\x16", b"\x00\x44", b"\x48\x6D", b"\x20\x08", b"\x48\x6C", b"\x0B\x7C", b"\x26\x40", b"\x04\x00", b"\x00\x68", b"\x20\x6D", b"\x00\x0D", b"\x2A\x40", b"\x00\x0B", b"\x00\x3E", b"\x02\x20"]
return getattr(self, '_m_default_lookup_table', None)
@property
def header_parameters(self):
"""The parsed decompressor-specific parameters from the compressed resource header.
"""
if hasattr(self, '_m_header_parameters'):
return self._m_header_parameters
io = self.header_parameters_with_io._io
_pos = io.pos()
io.seek(0)
self._m_header_parameters = Dcmp2.HeaderParameters(io, self, self._root)
io.seek(_pos)
return getattr(self, '_m_header_parameters', None)
@property
def is_len_decompressed_odd(self):
"""Whether the length of the decompressed data is odd.
This affects the meaning of the last byte of the compressed data.
"""
if hasattr(self, '_m_is_len_decompressed_odd'):
return self._m_is_len_decompressed_odd
self._m_is_len_decompressed_odd = self.len_decompressed % 2 != 0
return getattr(self, '_m_is_len_decompressed_odd', None)
@property
def lookup_table(self):
"""The lookup table to be used for this compressed data.
"""
if hasattr(self, '_m_lookup_table'):
return self._m_lookup_table
self._m_lookup_table = (self.custom_lookup_table if self.header_parameters.flags.has_custom_lookup_table else self.default_lookup_table)
return getattr(self, '_m_lookup_table', None)