ZstdNet

ZstdNet is a wrapper of Zstd native library for .NET languages. The following features are implemented:

• Compression and decompression of byte arrays
• Dictionary generation from a collection of samples

Streaming APIs are not implemented.

Take a look on library reference or unit tests to explore its behavior in different situations.

Zstd

Zstd, short for Zstandard, is a new lossless compression algorithm, which provides both good compression ratio and speed for your standard compression needs. "Standard" translates into everyday situations which neither look for highest possible ratio (which LZMA and ZPAQ cover) nor extreme speeds (which LZ4 covers). Zstandard is licensed under BSD 3-Clause License.

Zstd is developed by Yann Collet and the source is available at: https://github.com/Cyan4973/zstd

The motivation for development, the algorithm used and its properties are explained in the blog post that introduces the library: http://fastcompression.blogspot.com/2015/01/zstd-stronger-compression-algorithm.html

The benefits of the dictionary mode are described here: http://fastcompression.blogspot.ru/2016/02/compressing-small-data.html

Reference

Requirements

ZstdNet requires Zstdlib >= v1.0.0. Both 32-bit and 64-bit versions are supported. The corresponding DLLs (compiled from v1.2.0 using Visual C++) are included in this repository.

Exceptions

The wrapper throws ZstdException in case of malformed data or an error inside Zstdlib. If the given destination buffer is too small, InsufficientMemoryException is thrown.

Compressor class

Allocates buffers for performing compression. Instances of this class are not thread-safe.

• new Compressor()

  new Compressor(CompressionOptions options)

  Constructors allow to specify compression options. Otherwise, default values for CompressionOptions will be used. Options will be exposed in Options read-only field.

  Note that Compressor class implements IDisposable. If you use a lot of instances of this class, it's recommended to call Dispose to avoid loading on the finalizer thread. For example:

  using (var compressor = new Compressor()) {
      compressedData = compressor.Wrap(sourceData);
  }

• byte[] Wrap(byte[] src)

  byte[] Wrap(ArraySegment<byte> src)

  int Wrap(byte[] src, byte[] dst, int offset)

  int Wrap(ArraySegment<byte> src, byte[] dst, int offset)

  These methods compress data and save it in a new buffer or an existing one (in such case a length of saved data will be returned).

• static int GetCompressBound(int size)

  Returns required destination buffer size for source data of size size.

CompressionOptions class

Stores compression options and "digested" (for compression) information from a compression dictionary, if present. Instances of this class are thread-safe. They can be shared across threads to avoid performance and memory overhead.

• new CompressionOptions(byte[] dict, int compressionLevel = DefaultCompressionLevel)

  new CompressionOptions(int compressionLevel)

  Options:

  • byte[] dict — compression dictionary. It can be read from a file or generated with DictBuilder class. Default is null (no dictionary).
  • int compressionLevel — compression level. Should be in range from 1 to CompressionOptions.MaxCompressionLevel (currently 22). Default is CompressionOptions.DefaultCompressionLevel (currently 3).

  Specified options will be exposed in read-only fields.

  Note that CompressionOptions class implements IDisposable. If you use a lot of instances of this class, it's recommended to call Dispose to avoid loading on the finalizer thread. For example:

  using (var options = new CompressionOptions(dict, compressionLevel: 5))
  using (var compressor = new Compressor(options)) {
  	  compressedData = compressor.Wrap(sourceData);
  }

Decompressor class

Allocates buffers for performing decompression. Instances of this class are not thread-safe.

• new Decompressor()

  new Decompressor(DecompressionOptions options)

  Constructors allow to specify decompression options. Otherwise, default values for DecompressionOptions will be used. Options will be exposed in Options read-only field.

  Note that Decompressor class implements IDisposable. If you use a lot of instances of this class, it's recommended to call Dispose to avoid loading on the finalizer thread. For example:

  using (var decompressor = new Decompressor()) {
      decompressedData = decompressor.Unwrap(compressedData);
  }

• byte[] Unwrap(byte[] src, size_t maxDecompressedSize = size_t.MaxValue)

  byte[] Unwrap(ArraySegment<byte> src, size_t maxDecompressedSize = size_t.MaxValue)

  int Unwrap(byte[] src, byte[] dst, int offset)

  int Unwrap(ArraySegment<byte> src, byte[] dst, int offset, bool bufferSizePrecheck = true)

  These methods decompress data and save it in a new buffer or an existing one (in such case a length of saved data will be returned).

  Data can be saved to a new buffer only if a field with decompressed data size is present in compressed data. You can limit size of the new buffer with maxDecompressedSize parameter (it's necessary to do this on untrusted data).

  If bufferSizePrecheck flag is set and the decompressed field length is specified, size of the destination buffer will be checked before actual decompression.

  Note that if this field is malformed (and is less than actual decompressed data size), Zstdlib still doesn't allow a buffer overflow to happen during decompression.

• static ulong GetDecompressedSize(byte[] src)

  Reads a field with decompressed data size in compressed data.

DecompressionOptions class

Stores decompression options and "digested" (for decompression) information from a compression dictionary, if present. Instances of this class are thread-safe. They can be shared across threads to avoid performance and memory overhead.

• new DecompressionOptions(byte[] dict)

  Options:

  • byte[] dict — compression dictionary. It can be read from a file or generated with DictBuilder class. Default is null (no dictionary).

  Specified options will be exposed in read-only fields.

  Note that CompressionOptions class implements IDisposable. If you use a lot of instances of this class, it's recommended to call Dispose to avoid loading on the finalizer thread. For example:

  using (var options = new DecompressionOptions(dict))
  using (var decompressor = new Decompressor(options)) {
  	  decompressedData = decompressor.Unwrap(compressedData);
  }

DictBuilder static class

• static byte[] TrainFromBuffer(ICollection<byte[]> samples, int dictCapacity = DefaultDictCapacity)

  Generate a compression dictionary from a collection of samples.

  Options:

  • int dictCapacity — maximal dictionary size in bytes. Default is DictBuilder.DefaultDictCapacity, currently 110 KiB (the default in zstd utility).

Wrapper Authors

Copyright (c) 2016-2017 SKB Kontur

ZstdNet is distributed under BSD 3-Clause License.