Lzip.Lib 1.1.141

Lzip.Lib

Pure-managed lzip (LZMA1) codec for .NET -- a fast, AOT/trim-friendly compressor and decompressor for the lzip container format, including multi-member files that are decoded in parallel. Output is read by the reference lzip binary. No external lzip binary required.

1.0 shipped the decoder; 1.1 adds the encoder (LZMA1 + lzip member framing + -b-style member splitting).

Install

dotnet add package Lzip.Lib

Usage

using SharpAstro.Lzip;

// From a byte array:
byte[] data = LzipDecoder.Decompress(File.ReadAllBytes("catalog.lz"));

// From a stream:
using var stream = File.OpenRead("catalog.lz");
byte[] fromStream = LzipDecoder.Decompress(stream);

// As a read-only MemoryStream (decoded whole before it returns; the input is not disposed):
using var file = File.OpenRead("catalog.lz");
using var decompressed = LzipDecoder.DecompressToStream(file);

Every member is checked against its trailer as the reference lzip checks it (the CRC32 of the data, the data size and the member size), and corrupt input of any kind throws InvalidDataException.

Multi-member lzip files (e.g. produced by lzip -b) are detected and decoded across cores automatically.

Compressing

using SharpAstro.Lzip;

// Best ratio (approximates `lzip -9`), single member:
byte[] lz = LzipEncoder.Compress(File.ReadAllBytes("catalog.json"));

// Choose a level (0..9) and split into independent members for parallel decode (like `lzip -b`):
byte[] chunked = LzipEncoder.Compress(data, new LzipOptions { Level = 9, MemberSize = 2 << 20 });

// Stream in / stream out:
using var input = File.OpenRead("catalog.json");
using var output = File.Create("catalog.json.lz");
LzipEncoder.Compress(input, output);

LzipOptions.Level (0..9) selects lzip's dictionary size and match-length limit; DictionarySize and MatchLenLimit override them; MemberSize (uncompressed bytes per member, 0 = single) enables -b-style splitting. The output is standard lzip -- verified against the reference lzip -t/-d.

Format notes

Each lzip member is a 6-byte header ("LZIP" magic + version + coded dictionary size) followed by an LZMA1 stream (fixed properties lc=3, lp=0, pb=2) and a 20-byte trailer (CRC32 of the uncompressed data + uncompressed size + member size). A multi-member file is simply independent members concatenated.

Attribution

The LZMA1 compression core (src/Lzip.Lib/Lzma/) is vendored from the public-domain 7-Zip LZMA SDK by Igor Pavlov (https://www.7-zip.org/sdk.html). The only edits vs upstream are a #nullable disable header and making the namespace-level types internal so Lzip.Lib's public API stays SharpAstro.Lzip.*. The decoder and the lzip container framing (LzipDecoder, LzipEncoder, LzipFraming) are original code. The lzip format itself was created by Antonio Diaz Diaz; this library was validated for compatibility against the reference lzip binary but contains no lzip (GPL) source.

License

MIT -- see LICENSE. The vendored LZMA SDK is public domain.