d.idx += int64(w)
		n += w
	}
	if d.idx >= d.length {
		extraBytes := d.idx - d.length
		n -= int(extraBytes)
		if n < 0 {
			n = 0
		}
		err = io.EOF
	}
	return
}

func (d *DummyDataGen) Seek(offset int64, whence int) (int64, error) {
	switch whence {
	case io.SeekStart:
		if offset < 0 {
			return 0, errors.New("Invalid offset")
		}
		d.idx = offset
	case io.SeekCurrent:
		if d.idx+offset < 0 {