Function createZlibHandle

lib/internal/streams/iter/transform.js:166–199

* Create a bare Zlib handle (gzip, gunzip, deflate, inflate). * @returns {{ handle: object, writeState: Uint32Array, chunkSize: number }}

(mode, options, processCallback, onError)

 * @returns {{ handle: object, writeState: Uint32Array, chunkSize: number }}
 */
function createZlibHandle(mode, options, processCallback, onError) {
  // Validate all options before creating the native handle to avoid
  // "close before init" assertion if validation throws.
  const chunkSize = validateChunkSize(options);
  const windowBits = checkRangesOrGetDefault(
    options.windowBits, 'options.windowBits',
    Z_MIN_WINDOWBITS, Z_MAX_WINDOWBITS, Z_DEFAULT_WINDOWBITS);
  // Default compression level 4 (not Z_DEFAULT_COMPRESSION which maps to
  // level 6). Level 4 is ~1.5x faster with only ~5-10% worse compression
  // ratio - the sweet spot for streaming and HTTP content-encoding.
  const level = checkRangesOrGetDefault(
    options.level, 'options.level',
    Z_MIN_LEVEL, Z_MAX_LEVEL, 4);
  // memLevel 9 uses ~128KB more memory than 8 but provides faster hash
  // lookups during compression. Negligible memory cost for the speed gain.
  const memLevel = checkRangesOrGetDefault(
    options.memLevel, 'options.memLevel',
    Z_MIN_MEMLEVEL, Z_MAX_MEMLEVEL, 9);
  const strategy = checkRangesOrGetDefault(
    options.strategy, 'options.strategy',
    Z_DEFAULT_STRATEGY, Z_FIXED, Z_DEFAULT_STRATEGY);
  const dictionary = validateDictionary(options.dictionary);

  const handle = new binding.Zlib(mode);
  const writeState = new Uint32Array(2);

  handle.onerror = onError;
  handle.init(
    windowBits, level, memLevel, strategy,
    writeState, processCallback, dictionary,
  );

  return { __proto__: null, handle, writeState, chunkSize };
}

/**
 * Create a bare Brotli handle.