Crate cpt 

Compact Pro

Rust library to read compressed files created by Compact Pro

Usage

This crate offers the high-level functions probe and verify to check if a reader is a (valid) Archive.

use cpt::Fork;
use std::io::Read;

let mut archive = cpt::Archive::open("sample-files/FRED.CPT")
                               .unwrap();

assert_eq!(archive.iter().unwrap().count(), 7);

for entry in archive.iter().unwrap() {
  let Ok(entry) = entry else {continue};
  let Some(file) = entry.as_file() else {continue;};

  if file.name == "Freddie Manual" {
    let mut reader = archive.open_entry(&entry, Fork::Data).unwrap();
    let mut buffer = vec![0u8; file.data_uncompressed_size as usize];
    reader.read_exact(&mut buffer).unwrap();

    // … do something with extracted data …
  }
}

Limitiations

The crate has not been tested with multi-volume archives, or encrypted entries.

File Format

Note: This section was copied from https://code.google.com/archive/p/theunarchiver/wikis/CompactProSpecs.wiki for proper table rendering

Archive header

The only magic number for a Compact Pro file is that the first byte is “0x01”. All types larger than one byte in size are stored in big-endian order, as expected from a Mac format.

Offset	Size	Meaning
0	1	File identifier, 0x01
1	1	Volume number (meaning not entirely clear, is 0x01 for single-volume archives)
2	2	Cross-volume magic number (meaning not entirely clear)
4	4	Offset to file headers from beginning of file

The offset points to a second part of the archive header, followed by file and directory headers. The second part is:

Offset	Size	Meaning
0	4	CRC-32 of the header
4	2	Total number of files and directories
6	1	Comment length
7	N	Comment with the length indicated above

Next come as many file or directory headers as indicated by the header.

File header

Offset	Size	Meaning
0	1	Name length and type flag. The highest bit of this field is zero for a file entry.
1	N	File name with the length indicated above
N+1	1	Volume number (meaning not entirely clear)
N+2	4	Offset to file data from beginning of file
N+2	4	Offset to file data
N+6	4	Mac OS file type
N+10	4	Mac OS file creator
N+14	4	Creation date in classic Mac OS format (seconds since 1904)
N+18	4	Modification date in classic Mac OS format (seconds since 1904)
N+22	2	Mac OS Finder flags
N+24	4	Uncompressed file data CRC. This is calculated for the concaternation of the resource and data forks.
N+28	2	File flags (see below)
N+30	4	Resource fork uncompressed length
N+34	4	Data fork uncompressed length
N+38	4	Resource fork compressed length
N+42	4	Data fork compressed length

The flags field contains at least the following bits:

Bit	Meaning
0	File is encrypted (the algorithm for this is unknown)
1	Resource fork uses LZH compression
2	Data fork uses LZH compression

Directory header

Offset	Size	Meaning
0	1	Name length and type flag. The highest bit of this field is one for a directory entry.
1	N	Directory name with the length indicated above
N+1	2	Total number of files and directory in this directory, counting files in sub-directories

The directory structure can be entirely inferred from the entry count field.

Algorithms

Files are compressed using either just an RLE algorithm, or RLE followed by an LZSS and Huffman based algorithm, depending on bits 1 and 2 of the flags as described above. The resource and data forks are compressed separately even though the CRC is calculated for their combination. The resource fork appears first in the file, followed by the data fork. Thus the offset to the resource fork is the same as the “Offset to file data” field, while the offset to the data fork is “Offset to file data” plus “Resource fork compressed length”.

The algorithms are described on these pages:

• Rle8182Algorithm - An RLE encoding
• CompactProLzhAlgorithm - An LZSS+Huffman encoding

Testing

The test “suite” uses sample files from https://sembiance.com/fileFormatSamples/archive/compactPro/ and can be downloaded using wget:

wget --directory-prefix=sample-files --no-clobber --recursive --no-parent --no-host-directories --cut-dirs 3 https://sembiance.com/fileFormatSamples/archive/compactPro/

After the files have been downloaded just run cargo test as usual:

cargo test

Re-exports

pub use error::Error;

pub use structs::Entry;

pub use structs::Flags;

pub use macintosh_utils::chrono;

pub use macintosh_utils::fourcc;

Modules

error

structs

On-disk structures of CPT files

Macros

fourcc

Structs

Archive

A structure representing a CPT archive

FourCC

A four-character code

Enums

Fork

Identifies either of the two forks that can be used to store data on classic Macintosh file systems

Functions

probe

Detect if the given reader is a CPT archive

verify

Verify the structure and checksums of the given reader