machfs/README.md

This is a library for creating and inspecting HFS-format disk images. Mac-specific concepts like resource forks and type/creator codes are first-class citizens.

Python interface

The Python API is simple. The contents of a Volume or a Folder are accessed using the index operator []. While working on a filesystem, its entire high-level contents are stored in memory as a Python object.

from machfs import Volume, Folder, File

v = Volume()

v['Folder'] = Folder()

v['Folder']['File'] = File()
v['Folder']['File'].data = b'Hello from Python!\r'
v['Folder']['File'].rsrc = b'' # Use the macresources library to work with resource forks
v['Folder']['File'].type = b'TEXT'
v['Folder']['File'].creator = b'TTXT' # Teach Text/SimpleText

with open('FloppyImage.dsk', 'wb') as f:
    flat = v.write(
        size=1440*1024, # "High Density" floppy
        align=512, # Allocation block alignment modulus (2048 for CDs)
        desktopdb=True, # Create a dummy Desktop Database to prevent a rebuild on boot
        bootable=True, # This requires a folder with a ZSYS and a FNDR file
        startapp=('Folder','File'), # Path (as tuple) to an app to open at boot
    )
    f.write(flat)

with open('FloppyImage.dsk', 'rb') as f:
    flat = f.read()
    v = Volume()
    v.read(flat) # And you can read an image back!

Command-line interface

This package also installs the MakeHFS and DumpHFS utilities, for working with folders on your native filesystem. Briefly, resource forks are stored in Rez-formatted .rdump files, and type and creator codes are stored in 8-byte .idump files. Admittedly this method of storage is not pretty, but it exposes changes to resource files without requiring Mac-specific software. For example, Git can track the addition and removal of resources. Files with a TEXT type are assumed to be UTF-8 encoded with Unix-style (LF) line endings, and are converted to Mac OS Roman encoding with Mac-style (CR) line endings.

Both commands have a --help argument to display their options.

Why?

I want an automated, reproducible way to compile legacy MacOS software. Without any current operating system fully supporting HFS, libhfs/hfsutils (a C library and command-line wrapper) is the most capable implementation. The implementor chose to emulate POSIX I/O on a fake "mounted" filesystem. While this is important for machines with very limited RAM, the maintenance of consistent HFS data structures across incremental operations is a complicated task requiring a large amount of low-level code. Frequent I/O to the real filesystem also occurs. Current machines have memory and cycles to burn, so an in-memory implementation in a high-level programming language seemed like a reasonable tradeoff. As a result, machfs has nearly an order of magnitude fewer lines than libhfs, and is more maintainable, at a nearly negligible cost in performance.