lznt1

A safe, pure-Rust, no_std implementation of the LZNT1 compression algorithm.

LZNT1 is the standard compression algorithm used by the Windows NT kernel, notably in NTFS filesystem compression, Active Directory replication, and various Windows API functions (RtlCompressBuffer). This crate allows you to read and write LZNT1 streams on any platform without linking to system libraries.

✨ Features

• Pure Rust: No C dependencies or bindings.
• Safe: Enforced via #![forbid(unsafe_code)].
• no_std Compatible: only requires the alloc crate.
• Robust: Extensively fuzz-tested to ensure resilience against malformed inputs.
• Simple API: Straightforward compress and decompress functions operating on byte slices and vectors.

📦 Installation

Add this to your Cargo.toml:

[dependencies]
lznt1 = "0.1.0" # Use the latest version

🚀 Usage

Decompression

use lznt1::decompress;

fn main() -> Result<(), lznt1::DecompressionError> {
    // Example: "Hello world" compressed
    let compressed_data = [
        0x0c, 0xb0, 0x00, 
        b'H', b'e', b'l', b'l', b'o', b' ', b'w', b'o',
        0x00, 
        b'r', b'l', b'd',
    ];

    let mut buffer = Vec::new();
    decompress(&compressed_data, &mut buffer)?;

    assert_eq!(buffer, b"Hello world");
    Ok(())
}

Compression

use lznt1::compress;

fn main() {
    let input = b"The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.";
    let mut compressed_output = Vec::new();

    compress(input, &mut compressed_output);

    println!("Original size: {}", input.len());
    println!("Compressed size: {}", compressed_output.len());
}

🛠️ Technical Details

LZNT1 works by splitting data into 4KB chunks. Each chunk is stored either:

1. Compressed: A header (0xB000 + size) followed by LZ77 sequences (literals and offset/length tuples).
2. Uncompressed: A header (0x3000 + size) followed by raw data (used when compression doesn't save space).

This implementation handles the adaptive window splitting logic and the "Tag Group" format (1 tag byte per 8 items) defined by the algorithm.

🧪 Testing & Fuzzing

This crate prioritizes correctness and safety.

• Unit Tests: Comprehensive suite covering edge cases, boundary conditions, and RLE patterns.
• Fuzzing: Integration with cargo-fuzz to verify that the decompressor never panics or crashes, even on malicious/random input.
• Benchmarks: Performance tracked via criterion.

To run the tests:

cargo test

To run benchmarks:

cargo bench

⚖️ License

This project is licensed under the MIT License.