code: func newFileReader(ctx context.Context, driver storagedriver.StorageDriver, path string, size int64) (*fileReader, error) {
  	return &fileReader{
  		ctx:    ctx,
  		driver: driver,
  		path:   path,
  		size:   size,
  	}, nil
  }
docs: // newFileReader initializes a file reader for the remote file. The reader
  // takes on the size and path that must be determined externally with a stat
  // call. The reader operates optimistically, assuming that the file is already
  // there.