Just Zstd

A pure Dart implementation of the Zstandard (RFC 8878) decompression algorithm.

This package provides a lightweight, dependency-free decoder for Zstandard (zstd) compressed data, making it suitable for environments where native or FFI-based Zstandard implementations are unavailable or difficult to integrate (such as certain Flutter web scenarios or isolated Dart scripts).

It was originally built for the just_tiled package to decompress TMX map layers.

Features

• Pure Dart implementation (no dart:ffi or native extensions required)
• Supports decoding Zstandard frames and blocks
• Handles both raw and compressed blocks

Getting started

Add just_zstd to your pubspec.yaml:

dependencies:
  just_zstd: ^1.0.0

Usage

import 'dart:typed_data';
import 'package:just_zstd/just_zstd.dart';

void main() {
  // A hypothetical compressed buffer (e.g., loaded from a file or network)
  final compressedData = Uint8List.fromList([
    0x28, 0xB5, 0x2F, 0xFD, // Magic Number (little-endian: 0xFD2FB528)
    0x00,                   // Frame Header Descriptor
    0x00,                   // Block Header (last block, raw, size 0)
  ]);

  try {
    const decoder = ZstdDecoder();
    
    // Decode directly into a Uint8List
    final decompressedData = decoder.decodeBytes(compressedData);
    
    print('Decoded ${decompressedData.length} bytes.');
  } on FormatException catch (e) {
    print('Invalid Zstandard data: $e');
  }
}

Limitations

Currently, this is a simplified decoder designed primarily for the specific compression profiles used by tools like the Tiled Map Editor. While it successfully decodes many Zstandard frames, it may not yet fully support all advanced features of the complete Zstandard specification (such as complex dictionary decompression).