DotnetPackaging.Formats.Dmg.MachO

Dotnet.Dmg

Pure .NET tooling to craft macOS DMG images without external macOS tooling.

Highlights

• Build ISO9660 layouts with Rock Ridge entries in memory and wrap them into UDIF DMGs
• Dual compression support: UDBZ (bzip2) and UDZO (zlib) - 100% managed code via SharpCompress
• Minimal Mach-O ad-hoc signer to stamp executables and dylibs during packaging
• CLI helper to turn a published folder into a .app bundle inside a DMG, including Info.plist and PkgInfo
• Targets .NET 10; no native dependencies or platform-specific tooling required
• Structurally compatible with industry-standard DMGs (verified against Parcel output)

Quick start

1. Publish your app for macOS:

   dotnet publish -c Release -r osx-arm64 -p:PublishSingleFile=true -p:SelfContained=true -o ./publish
   

2. Build the DMG (app name is optional; defaults to the input folder name with .app appended):

   dotnet run --project Dotnet.Dmg.App -- ./publish ./MyApp.dmg MyGreatApp
   

   The tool uses bzip2 compression by default for optimal file size.

3. Mount MyApp.dmg on macOS to verify the bundle layout and ad-hoc signatures.

Projects

• Dotnet.Dmg.App: Console entry point that wires the builders together and emits the final DMG from a publish folder.
• Dotnet.Dmg.Iso: ISO9660 + Rock Ridge builder with directory, file, and symlink support.
• Dotnet.Dmg.Udif: UDIF writer that produces compressed DMG streams from an ISO image.
• Dotnet.Dmg.MachO: Lightweight Mach-O parser and ad-hoc code signer used by the CLI.
• Dotnet.Dmg.Tests: xUnit test suite covering the core libraries.

NuGet packaging

• Shared package metadata (authors, license, repo URL, tags, README) lives in Directory.Build.props and is picked up by every packable project.
• The root README.md is packed into the generated .nupkg files via PackageReadmeFile.
• Build packages locally with dotnet pack -c Release; Dotnet.Dmg.Tests is excluded via IsPackable=false.

Features

Compression

• UDBZ (bzip2): Default compression, better ratios (~4% smaller than zlib)
• UDZO (zlib): Alternative compression, faster but larger output
• Both implemented as 100% managed code (no P/Invoke or native dependencies)

Programmatic Usage

using Dotnet.Dmg.Udif;

var writer = new UdifWriter 
{ 
    CompressionType = CompressionType.Bzip2  // or CompressionType.Zlib
};
writer.Create(isoStream, dmgStream);

Known gaps

• Large file support is limited by the ISO builder using 32-bit lengths (roughly 2 GB per entry)
• Only Rock Ridge extensions are emitted; Joliet and El Torito are not implemented
• DMG signing of the container itself is not implemented; only ad-hoc signing of Mach-O binaries occurs
• Optional metadata (checksums, size info) not yet implemented

Contributing

• Run dotnet test to validate changes.
• Open issues or PRs with ideas for better compression, real code signing, or broader ISO support.