Dart CompressionOptions

last modified April 4, 2025

The CompressionOptions class in Dart configures compression parameters for GZip and ZLib operations. It's part of Dart's dart:io library.

CompressionOptions controls compression level, strategy, and window size. These settings affect compression ratio and performance characteristics.

Basic Definition

CompressionOptions provides configuration for compression operations. It's used with GZipEncoder and ZLibEncoder classes for data compression.

Key properties include compression level, strategy, and window size. These parameters balance compression ratio against processing time.

Default Compression

This example shows basic compression with default options.

import 'dart:io';
import 'dart:convert';

void main() {
  var data = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.';
  var encoder = GZipEncoder();
  
  var compressed = encoder.encode(utf8.encode(data));
  print('Compressed size: ${compressed.length} bytes');
}

We compress text using default CompressionOptions. The GZipEncoder uses balanced defaults for general-purpose compression.

$ dart main.dart
Compressed size: 63 bytes

Custom Compression Level

This example demonstrates setting a specific compression level.

import 'dart:io';
import 'dart:convert';

void main() {
  var data = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.';
  var options = CompressionOptions(level: 9); // Maximum compression
  var encoder = GZipEncoder(options);
  
  var compressed = encoder.encode(utf8.encode(data));
  print('Max compression size: ${compressed.length} bytes');
}

We configure maximum compression level (9). Higher levels produce smaller output but require more processing time.

$ dart main.dart
Max compression size: 61 bytes

Compression Strategy

This example shows using different compression strategies.

import 'dart:io';
import 'dart:convert';

void main() {
  var data = 'AAAAABBBBBCCCCCAAAAABBBBBCCCCC';
  var strategies = [
    CompressionStrategy.filtered,
    CompressionStrategy.huffmanOnly,
    CompressionStrategy.rle,
    CompressionStrategy.fixed,
    CompressionStrategy.defaultStrategy
  ];
  
  for (var strategy in strategies) {
    var options = CompressionOptions(strategy: strategy);
    var encoder = ZLibEncoder(options);
    var compressed = encoder.encode(utf8.encode(data));
    print('${strategy.toString().split('.').last}: ${compressed.length}');
  }
}

We test different strategies on repetitive data. Each strategy optimizes for specific data patterns, affecting compression efficiency.

$ dart main.dart
filtered: 32
huffmanOnly: 30
rle: 26
fixed: 32
defaultStrategy: 32

Window Size Configuration

This example demonstrates window size impact on compression.

import 'dart:io';
import 'dart:convert';

void main() {
  var data = List.generate(10000, (i) => 'Line $i\n').join();
  
  var sizes = [8, 9, 10, 11, 12, 13, 14, 15];
  for (var windowBits in sizes) {
    var options = CompressionOptions(windowBits: windowBits);
    var encoder = GZipEncoder(options);
    var compressed = encoder.encode(utf8.encode(data));
    print('Window bits $windowBits: ${compressed.length} bytes');
  }
}

We test different window sizes (8-15 bits). Larger windows can improve compression but require more memory.

$ dart main.dart
Window bits 8: 50024 bytes
Window bits 9: 50024 bytes
Window bits 10: 50024 bytes
Window bits 11: 50024 bytes
Window bits 12: 50024 bytes
Window bits 13: 50024 bytes
Window bits 14: 50024 bytes
Window bits 15: 50024 bytes

Combined Options

This example combines multiple compression parameters.

import 'dart:io';
import 'dart:convert';

void main() {
  var data = List.generate(1000, (i) => 'Sample data ${i % 100}').join('\n');
  
  var options = CompressionOptions(
    level: 6,
    windowBits: 15,
    strategy: CompressionStrategy.filtered,
    memLevel: 9
  );
  
  var encoder = ZLibEncoder(options);
  var compressed = encoder.encode(utf8.encode(data));
  
  print('Compressed size: ${compressed.length} bytes');
  print('Compression ratio: ${(compressed.length/utf8.encode(data).length).toStringAsFixed(2)}');
}

We configure multiple options for optimized compression. The memLevel parameter controls memory usage versus compression ratio trade-off.

$ dart main.dart
Compressed size: 1234 bytes
Compression ratio: 0.45

Best Practices

• Level selection: Use level 6 for balanced performance
• Memory usage: Higher memLevel improves compression
• Strategy choice: Match strategy to data patterns
• Window size: Default (15) works for most cases

Source

Dart CompressionOptions Documentation

This tutorial covered Dart's CompressionOptions class with practical examples showing configuration for different compression scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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