Recover data from Apple backup files

unbak.py

#!/usr/bin/env python3

# See https://www.downtowndougbrown.com/2013/06/legacy-apple-backup-file-format-on-floppy-disks/

import os
import pathlib
import struct
import sys

f = open(sys.argv[1], 'rb')

magic, disk_n, n_disks, _, _, volume_name, _, size = struct.unpack_from('>xx4sHHII32pII', f.read(0x200))
assert magic == b'CMWL'

# Skip boot blocks
f.read(0x400)

size -= 0x600

while size:
    magic, _, _, _, filename, part_n, folder_flags, valid, created, modified, data_length, resource_length, data_length_this_disk, resource_length_this_disk, path_length = struct.unpack_from('>xx4sHII32pHBB34xIIIIIIH', f.read(0x70))
    assert magic == b'RLDW'
    is_folder = folder_flags & (1<<7) != 0
    full_path = f.read(path_length)
    data_fork = f.read(data_length_this_disk)
    resource_fork = f.read(resource_length_this_disk)
    total_size = 0x70 + path_length + data_length_this_disk + resource_length_this_disk
    padding = 0x200 - (total_size % 0x200) if (total_size % 0x200) else 0
    f.read(padding)
    size -= total_size + padding

    nix_path = pathlib.Path(*full_path.decode('macroman').split(':'))
    if len(nix_path.parts) > 1:
        os.makedirs(nix_path if is_folder else nix_path.parent, exist_ok=True)

    print("writing to{} {}, part {}, df={} rf={}".format(" folder" if is_folder else "", nix_path, part_n, len(data_fork), len(resource_fork)))

    open_flags = 'ab' if part_n > 1 else 'wb'

    if not is_folder:
        with open(nix_path, open_flags) as of:
            of.write(data_fork)

    if resource_fork:
        with open(nix_path.joinpath('..namedfork', 'rsrc'), open_flags) as of:
            of.write(resource_fork)