Unsit

Open classic StuffIt archives on macOS, with a drag-and-drop app or the unsit command-line tool. Files keep their data forks, resource forks, type and creator codes, Finder flags, and modification dates.

Unsit supports classic SIT! / rLau containers with stored and method-13 compression. StuffIt 5 containers, StuffIt X (.sitx), encrypted forks, and other compression methods are outside its current scope.

macOS app

Download Unsit for macOS. Choose the Apple silicon (arm64) or Intel (x86_64) DMG, open it, and drag Unsit.app to Applications. The app requires macOS 12 or later.

Drop one or more .sit files into Unsit, or use File → Open Archives. Each archive gets a fresh output folder beside the original. Use Save To to choose another destination, then Open Folder to see the recovered files in Finder. Existing archives and extracted files are preserved.

If you close the window, choose Window → Show Unsit (⌘0) or click Unsit in the Dock to reopen it. Your extraction queue and results remain available.

When damage is detected, the app says Unsit recovered N files despite archive damage, with complete, partial, and failed counts. It credits files recovered beyond damaged records and makes their recovery folders visible in Finder. Details explains problems; Stop stops the current extraction and queued work while keeping files already recovered. The app uses the same extractor as the CLI and does not require an installed command-line tool.

Unsit → Check for Updates checks GitHub releases. Stable release builds also check automatically; choose every six hours, daily, or weekly, or turn checks off. Unsit verifies the download before opening its installer. Finish extracting, quit the app, and drag the new copy into Applications. See updates.

Build the app with the Xcode command-line tools and Swift 5.7 or later:

make app
open dist/Unsit.app

The app requires macOS 12 or later. make universal builds an app and CLI with both Apple silicon and Intel slices. Packaging produces an installer DMG, app ZIP, CLI archive, source archive, and update/checksum manifests in dist/. Local snapshots use ad hoc signing. Public release packaging requires Developer ID signing and Apple notarization. See builds and releases for installation and verification, and RELEASE.md for the maintainer runbook.

Command line

The CLI targets macOS 11 or later:

swift build -c release --product unsit
.build/release/unsit archive.sit recovered-files
.build/release/unsit --list archive.sit

unsit [options] <archive.sit> [output-directory]

  -l, --list        List contents without extracting
  -o, --output DIR  Extract into DIR
  -q, --quiet       Only warnings/errors during extraction
      --json        Extraction report on stdout, warnings on stderr
      --no-verify   Skip fork CRC checks, retain structural checks
      --self-test   Run built-in table/CRC checks
      --version     Show version
  -h, --help        Show help
      --           End options; remaining tokens are paths

Without an output directory, the CLI creates a folder named after the archive in the current directory. Unlike the app, it uses the requested destination directly; conflicting members are skipped. --list --quiet still prints the requested list. Exit status is 0 for success, 1 for incomplete restoration or validation, and 2 for invalid arguments.

Recovery and integrity

Unsit validates entry headers, fork lengths, and CRC-16/ARC checksums. Damage to one member does not automatically stop later recoverable members. A valid fork can survive damage to the other fork, and safe decoder prefixes are retained.

Incomplete members use NAME.partial-HEADER_OFFSET. After a lost header makes folder placement uncertain, identifiable files go into unsit-recovery-HEADER_OFFSET/NAME. These names distinguish damaged bytes and uncertain placement from fully restored members. Warnings and a nonzero exit status remain available even in quiet mode.

Damage is reported as possible bitrot, with the number of files Unsit saved; this does not claim to determine the cause or reconstruct missing bytes. An unsupported method, a skipped count check, or a disk/metadata error is reported as a warning without being called bitrot. Counts describe files Unsit identified; unreadable archive regions can contain additional members it cannot count.

In a local compatibility comparison, the updated extractor recovered 1,095 members versus 290 from the initial implementation. All 290 earlier members' data forks, resource forks, and file metadata were preserved; 805 additional members were recovered. Of the new total, 56 members remain explicitly partial. These are measured recovery results, not a promise that damaged bytes can be repaired. See verification and its limits.

Output uses native macOS forks and descriptor-based filesystem operations. Existing files are preserved, symlink traversal is rejected, and members are published atomically after their forks and metadata have been attempted. Folder modification dates are restored after their children. APFS is recommended for retaining native Mac metadata.

Default resource limits are 256 MiB input, 64 MiB per decoded fork, 512 MiB decoded output, 100,000 records, 128 nested folders, and 1 MiB of recovery scanning. The CLI provides --max-input-bytes, --max-fork-bytes, --max-total-bytes, --max-members, --max-depth, and --max-recovery-bytes overrides. See extraction behavior for the full contract.

Development and verification

swift test
make check
python3 scripts/verify-method13.py --binary .build/debug/unsit

The native suite covers malformed archives, both forks, every preset codebook, dynamic Huffman tables, filesystem confinement, interrupted writes, resource limits, dates, CLI actions, and the app's helper workflow. Synthetic fixtures have frozen expected bytes or hashes. No private archive or network connection is required. A custom swift test --scratch-path DIR uses the executable built beside that test bundle; UNSIT_TEST_BINARY explicitly selects another executable.

The package contains the unsit and UnsitApp executable targets plus the UnsitDesktop helper/updater library and shared UnsitReport schema. For development without packaging:

swift build
swift run --skip-build UnsitApp

Contributing · Security reporting · Container format · Method 13 · Localization · Changelog

License

Current source is licensed under MIT. The method-13 implementation was replaced with new Swift code using a canonical range decoder and bounded output history. Fixed numeric codebooks are maintained separately as interoperability data, with their provenance and reference notices retained in third-party notices. No GPL or LGPL implementation is bundled or linked by the app or CLI. Historical revisions retain their original licensing provenance.