code: function FileReadStream(path, options) {
    stream.Stream.call(this);
    this.readable = true;
  
    if(!options) {
      options = {};
    }
  
    this._destroyed = false;
    this._streamEnded = false;
    this._fd = null;
    this._fileName = undefined;
    this._highWaterMark = options.highWaterMark || bufferSize;
    this._offset = 0;
    this._paused = undefined;
    this._allocator = options.allocator;
    this._fileName = path;
  
    this._md5hash = null;
    this._md5sum = undefined;
  
    if (options.calcContentMd5) {
      this._md5hash = new Md5Wrapper().createMd5Hash();
    }
  
    this._open();
  }
docs: File read stream
  1. Calculate md5
  2. Track reading offset
  3. Work with customize memory allocator
  4. Buffer data from stream.
  @param {object} options stream.Readable options