code: func DecodeCompactBytes(b []byte) ([]byte, []byte, error) {
  	b, n, err := DecodeVarint(b)
  	if err != nil {
  		return nil, nil, errors.Trace(err)
  	}
  	if int64(len(b)) < n {
  		return nil, nil, errors.Errorf("insufficient bytes to decode value, expected length: %v", n)
  	}
  	return b[n:], b[:n], nil
  }
docs: // DecodeCompactBytes decodes bytes which is encoded by EncodeCompactBytes before.