LzfseSharp 0.0.1

LzfseSharp

A C# port of Apple's LZFSE (Lempel-Ziv Finite State Entropy) compression algorithm. This library provides decoding-only functionality for decompressing LZFSE-compressed data.

What is LZFSE?

LZFSE is a Lempel-Ziv style data compression algorithm using Finite State Entropy coding, introduced by Apple with OS X 10.11 and iOS 9. It targets similar compression ratios to DEFLATE but with significantly higher compression and decompression speeds.

Features

• Supports all LZFSE block types:
  • LZFSE compressed blocks (V1 and V2 with FSE encoding)
  • LZVN compressed blocks (simpler algorithm for small data)
  • Uncompressed blocks

Installation

dotnet add package LzfseSharp

Usage

Basic Decompression

using LzfseSharp;

// Read compressed data
byte[] compressedData = File.ReadAllBytes("data.lzfse");

// Allocate buffer for decompressed output
// You need to know the uncompressed size beforehand
byte[] decompressedData = new byte[uncompressedSize];

// Decompress
int bytesWritten = LzfseDecoder.Decompress(
    decompressedData,
    compressedData
);

if (bytesWritten == 0)
{
    Console.WriteLine("Decompression failed!");
}
else
{
    Console.WriteLine($"Decompressed {bytesWritten} bytes");
}

Working with Streams

using LzfseSharp;

using var inputStream = File.OpenRead("data.lzfse");
using var outputStream = File.OpenWrite("data.bin");

// Read compressed data
byte[] compressed = new byte[inputStream.Length];
inputStream.Read(compressed, 0, compressed.Length);

// Decompress
byte[] decompressed = new byte[uncompressedSize];
int bytesWritten = LzfseDecoder.Decompress(decompressed, compressed);

// Write decompressed data
if (bytesWritten > 0)
{
    outputStream.Write(decompressed, 0, bytesWritten);
}

LZFSE Format Overview

LZFSE uses a block-based structure where each block has a magic number identifier:

The decoder automatically detects and handles all block types.

Limitations

• Decode-only: This library only supports decompression. For compression, use the original C library or platform-specific APIs on Apple platforms.
• No streaming API: Currently requires the entire compressed data in memory. Streaming support may be added in future versions.
• Buffer size: You must allocate the output buffer with the correct uncompressed size beforehand.

License

This project is licensed under the BSD 3-Clause License - the same license as Apple's original LZFSE implementation. See the LICENSE file for details.

References

• Apple Compression Framework Documentation
• LZFSE GitHub Repository