udif

Cross-platform Rust library for Apple DMG disk images (aka Universal Disk Image Format)

Read, write, and manipulate Apple DMG files on any platform.

Full LZFSE support — works with modern macOS disk images that other libraries can't read.

Why udif?

udif is the only cross-platform Rust crate that can both read AND write DMGs with modern compression.

Feature	udif	dmgwiz	apple-dmg	dmg-oxide
Read	✓	✓	✓	✓
Write	✓	❌	❌	✓
LZFSE	✓	✓	❌	❌
XZ	✓	❌	❌	❌
Bzip2	✓	✓	❌	❌
Zlib	✓	✓	✓	✓
Checksum	✓	❌	❌	❌

Example: A typical macOS Kernel Debug Kit DMG uses 100% LZFSE compression. Only udif and dmgwiz can read it — but only udif can write new DMGs with LZFSE.

Features


List partitions	Parse DMG structure, show partition table
Extract data	Decompress partitions to raw disk images
Create DMG	Build DMG files with multiple compression options
Checksum verification	CRC32 integrity validation on read and write
Cross-platform	Works on Windows, Linux, and macOS

Compression Support

Format	Read	Write	Description
LZFSE			Apple's native compression
XZ			XZ (LZMA2) compression
Zlib			Best compatibility
Bzip2			Better ratio, slower
Raw			No compression

Quick Start

Read DMG

use udif::DmgArchive;

// Open and list partitions
let mut archive = DmgArchive::open("image.dmg")?;
for p in archive.partitions() {
    println!("{}: {} bytes", p.name, p.size);
}

// Extract main HFS+/APFS partition
let data = archive.extract_main_partition()?;
std::fs::write("disk.raw", &data)?;

Create DMG

use udif::{DmgBuilder, CompressionMethod};

let disk_data = std::fs::read("disk.raw")?;

DmgBuilder::new()
    .compression(CompressionMethod::Zlib)
    .add_partition("Macintosh HD", disk_data)
    .build("output.dmg")?;

Checksum Verification

By default, checksums are verified when opening a DMG. To skip verification (e.g., for corrupted files):

use udif::{DmgArchive, DmgReaderOptions};

// Default: checksums verified
let archive = DmgArchive::open("image.dmg")?;

// Skip verification for corrupted/legacy files
let options = DmgReaderOptions { verify_checksums: false };
let archive = DmgArchive::open_with_options("image.dmg", options)?;

Documentation


Format Specification	DMG binary format details
CLI Tool	Command-line tool usage
Implementation Notes	Tricky parts and gotchas

Example Output

$ udif-tool info Kernel_Debug_Kit.dmg

DMG Information: Kernel_Debug_Kit.dmg
============================================================

Header:
  Version:          4
  Sector count:     2351263
  Data fork length: 1023271318 bytes
  Segment:          1/1

Size:
  Uncompressed:     1203845632 bytes (1148.08 MB)
  Compressed:       1023271318 bytes (975.87 MB)
  Compression:      15.0%

Partitions:         7

Block types used:
  LZFSE:            988 blocks

$ udif-tool list Kernel_Debug_Kit.dmg

Partitions in Kernel_Debug_Kit.dmg:
================================================================================
  ID       Sectors          Size     Ratio  Name
--------------------------------------------------------------------------------
  -1             1         512 B     89.6%  Protective Master Boot Record (MBR : 0)
   0             1         512 B     78.9%  GPT Header (Primary GPT Header : 1)
   1            32      16.00 KB     98.7%  GPT Partition Data (Primary GPT Table : 2)
   2       2089050    1020.04 MB      4.3%  Untitled 1 (Apple_HFSX : 3)
   3        262144     128.00 MB    100.0%   (Apple_Free : 4)

Alternatives

Crate	Read	Write	LZFSE	XZ	Bzip2	Zlib	Checksum	Encrypted	Notes
udif	✓	✓	✓	✓	✓	✓	✓	❌	Full featured
dmgwiz	✓	❌	✓	❌	✓	✓	❌	✓	Read-only
apple-dmg	✓	❌	❌	❌	❌	✓	❌	❌	Zlib only
dmg-oxide	✓	✓	❌	❌	❌	✓	❌	❌	Zlib only
dmg	✓	✓	✓	✓	✓	✓	✓	✓	macOS only (hdiutil)

Choose udif if you need:

Write/create DMG support AND modern compression (LZFSE/XZ)
Cross-platform support (Windows, Linux, macOS)
XZ compression (no other cross-platform crate supports it)
Ensure integrity (no other cross-platform crate have checksum generation / validation)

Choose dmgwiz if you need:

Encrypted DMG support (we don't have this yet)
Read-only access is sufficient

See Comparison for detailed analysis.

Next Steps

Encrypted DMG support — FileVault / AES-128 / AES-256 encrypted disk images
ADC compression — Apple Data Compression for legacy DMGs
Streaming decompression — decompress partitions without buffering entire output
Parallel block decompression — decompress blocks across multiple threads
LZFSE write optimization — tunable compression levels for LZFSE output
APFS partition detection — identify APFS containers within DMGs
Partition resizing — create DMGs with custom partition layouts
Progress callbacks — report compression/decompression progress for UI integration

License

MIT

udif 0.3.0