Compressed Macintosh resource data, as stored in resources with the "compressed" attribute.
Resource decompression is not documented by Apple. It is mostly used internally in System 7, some of Apple's own applications (such as ResEdit), and also by some third-party applications. Later versions of Classic Mac OS make less use of resource compression, but still support it fully for backwards compatibility. Carbon in Mac OS X no longer supports resource compression in any way.
The data of all compressed resources starts with a common header,
followed by the compressed data.
The data is decompressed using code in a 'dcmp' resource.
Some decompressors used by Apple are included in the System file,
but applications can also include custom decompressors.
The header of the compressed data indicates the ID of the 'dcmp' resource used to decompress the data,
along with some parameters for the decompressor.
This page hosts a formal specification of Compressed Macintosh resource 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
use strict;
use warnings;
use IO::KaitaiStruct 0.009_000;
use BytesWithIo;
########################################################################
package CompressedResource;
our @ISA = 'IO::KaitaiStruct::Struct';
sub from_file {
my ($class, $filename) = @_;
my $fd;
open($fd, '<', $filename) or return undef;
binmode($fd);
return new($class, IO::KaitaiStruct::Stream->new($fd));
}
sub new {
my ($class, $_io, $_parent, $_root) = @_;
my $self = IO::KaitaiStruct::Struct->new($_io);
bless $self, $class;
$self->{_parent} = $_parent;
$self->{_root} = $_root || $self;;
$self->_read();
return $self;
}
sub _read {
my ($self) = @_;
$self->{header} = CompressedResource::Header->new($self->{_io}, $self, $self->{_root});
$self->{compressed_data} = $self->{_io}->read_bytes_full();
}
sub header {
my ($self) = @_;
return $self->{header};
}
sub compressed_data {
my ($self) = @_;
return $self->{compressed_data};
}
########################################################################
package CompressedResource::Header;
our @ISA = 'IO::KaitaiStruct::Struct';
sub from_file {
my ($class, $filename) = @_;
my $fd;
open($fd, '<', $filename) or return undef;
binmode($fd);
return new($class, IO::KaitaiStruct::Stream->new($fd));
}
sub new {
my ($class, $_io, $_parent, $_root) = @_;
my $self = IO::KaitaiStruct::Struct->new($_io);
bless $self, $class;
$self->{_parent} = $_parent;
$self->{_root} = $_root || $self;;
$self->_read();
return $self;
}
sub _read {
my ($self) = @_;
$self->{common_part} = CompressedResource::Header::CommonPart->new($self->{_io}, $self, $self->{_root});
$self->{_raw_type_specific_part_raw_with_io} = $self->{_io}->read_bytes(($self->common_part()->len_header() - 12));
my $io__raw_type_specific_part_raw_with_io = IO::KaitaiStruct::Stream->new($self->{_raw_type_specific_part_raw_with_io});
$self->{type_specific_part_raw_with_io} = BytesWithIo->new($io__raw_type_specific_part_raw_with_io);
}
sub type_specific_part_raw {
my ($self) = @_;
return $self->{type_specific_part_raw} if ($self->{type_specific_part_raw});
$self->{type_specific_part_raw} = $self->type_specific_part_raw_with_io()->data();
return $self->{type_specific_part_raw};
}
sub type_specific_part {
my ($self) = @_;
return $self->{type_specific_part} if ($self->{type_specific_part});
my $io = $self->type_specific_part_raw_with_io()->_io();
my $_pos = $io->pos();
$io->seek(0);
my $_on = $self->common_part()->header_type();
if ($_on == 8) {
$self->{type_specific_part} = CompressedResource::Header::TypeSpecificPartType8->new($io, $self, $self->{_root});
}
elsif ($_on == 9) {
$self->{type_specific_part} = CompressedResource::Header::TypeSpecificPartType9->new($io, $self, $self->{_root});
}
$io->seek($_pos);
return $self->{type_specific_part};
}
sub common_part {
my ($self) = @_;
return $self->{common_part};
}
sub type_specific_part_raw_with_io {
my ($self) = @_;
return $self->{type_specific_part_raw_with_io};
}
sub _raw_type_specific_part_raw_with_io {
my ($self) = @_;
return $self->{_raw_type_specific_part_raw_with_io};
}
########################################################################
package CompressedResource::Header::CommonPart;
our @ISA = 'IO::KaitaiStruct::Struct';
sub from_file {
my ($class, $filename) = @_;
my $fd;
open($fd, '<', $filename) or return undef;
binmode($fd);
return new($class, IO::KaitaiStruct::Stream->new($fd));
}
sub new {
my ($class, $_io, $_parent, $_root) = @_;
my $self = IO::KaitaiStruct::Struct->new($_io);
bless $self, $class;
$self->{_parent} = $_parent;
$self->{_root} = $_root || $self;;
$self->_read();
return $self;
}
sub _read {
my ($self) = @_;
$self->{magic} = $self->{_io}->read_bytes(4);
$self->{len_header} = $self->{_io}->read_u2be();
$self->{header_type} = $self->{_io}->read_u1();
$self->{unknown} = $self->{_io}->read_u1();
$self->{len_decompressed} = $self->{_io}->read_u4be();
}
sub magic {
my ($self) = @_;
return $self->{magic};
}
sub len_header {
my ($self) = @_;
return $self->{len_header};
}
sub header_type {
my ($self) = @_;
return $self->{header_type};
}
sub unknown {
my ($self) = @_;
return $self->{unknown};
}
sub len_decompressed {
my ($self) = @_;
return $self->{len_decompressed};
}
########################################################################
package CompressedResource::Header::TypeSpecificPartType8;
our @ISA = 'IO::KaitaiStruct::Struct';
sub from_file {
my ($class, $filename) = @_;
my $fd;
open($fd, '<', $filename) or return undef;
binmode($fd);
return new($class, IO::KaitaiStruct::Stream->new($fd));
}
sub new {
my ($class, $_io, $_parent, $_root) = @_;
my $self = IO::KaitaiStruct::Struct->new($_io);
bless $self, $class;
$self->{_parent} = $_parent;
$self->{_root} = $_root || $self;;
$self->_read();
return $self;
}
sub _read {
my ($self) = @_;
$self->{working_buffer_fractional_size} = $self->{_io}->read_u1();
$self->{expansion_buffer_size} = $self->{_io}->read_u1();
$self->{decompressor_id} = $self->{_io}->read_s2be();
$self->{reserved} = $self->{_io}->read_u2be();
}
sub working_buffer_fractional_size {
my ($self) = @_;
return $self->{working_buffer_fractional_size};
}
sub expansion_buffer_size {
my ($self) = @_;
return $self->{expansion_buffer_size};
}
sub decompressor_id {
my ($self) = @_;
return $self->{decompressor_id};
}
sub reserved {
my ($self) = @_;
return $self->{reserved};
}
########################################################################
package CompressedResource::Header::TypeSpecificPartType9;
our @ISA = 'IO::KaitaiStruct::Struct';
sub from_file {
my ($class, $filename) = @_;
my $fd;
open($fd, '<', $filename) or return undef;
binmode($fd);
return new($class, IO::KaitaiStruct::Stream->new($fd));
}
sub new {
my ($class, $_io, $_parent, $_root) = @_;
my $self = IO::KaitaiStruct::Struct->new($_io);
bless $self, $class;
$self->{_parent} = $_parent;
$self->{_root} = $_root || $self;;
$self->_read();
return $self;
}
sub _read {
my ($self) = @_;
$self->{decompressor_id} = $self->{_io}->read_s2be();
$self->{_raw_decompressor_specific_parameters_with_io} = $self->{_io}->read_bytes(4);
my $io__raw_decompressor_specific_parameters_with_io = IO::KaitaiStruct::Stream->new($self->{_raw_decompressor_specific_parameters_with_io});
$self->{decompressor_specific_parameters_with_io} = BytesWithIo->new($io__raw_decompressor_specific_parameters_with_io);
}
sub decompressor_specific_parameters {
my ($self) = @_;
return $self->{decompressor_specific_parameters} if ($self->{decompressor_specific_parameters});
$self->{decompressor_specific_parameters} = $self->decompressor_specific_parameters_with_io()->data();
return $self->{decompressor_specific_parameters};
}
sub decompressor_id {
my ($self) = @_;
return $self->{decompressor_id};
}
sub decompressor_specific_parameters_with_io {
my ($self) = @_;
return $self->{decompressor_specific_parameters_with_io};
}
sub _raw_decompressor_specific_parameters_with_io {
my ($self) = @_;
return $self->{_raw_decompressor_specific_parameters_with_io};
}
1;