GZipCodec({int level: ZLibOption.DEFAULT_LEVEL, int windowBits: ZLibOption.DEFAULT_WINDOW_BITS, int memLevel: ZLibOption.DEFAULT_MEM_LEVEL, int strategy: ZLibOption.STRATEGY_DEFAULT, List<int> dictionary: null, bool raw: false, bool gzip: true })

Source 

GZipCodec(
    {this.level: ZLibOption.DEFAULT_LEVEL,
    this.windowBits: ZLibOption.DEFAULT_WINDOW_BITS,
    this.memLevel: ZLibOption.DEFAULT_MEM_LEVEL,
    this.strategy: ZLibOption.STRATEGY_DEFAULT,
    this.dictionary: null,
    this.raw: false,
    this.gzip: true}) {
  _validateZLibeLevel(level);
  _validateZLibMemLevel(memLevel);
  _validateZLibStrategy(strategy);
  _validateZLibWindowBits(windowBits);
}