code: func (m *Mocker) Sign(ctx context.Context, in string, sigf string) error {
  	buf, err := ioutil.ReadFile(in)
  	if err != nil {
  		return err
  	}
  	sum := sha256.New()
  	_, _ = sum.Write(buf)
  	hexsum := fmt.Sprintf("%X", sum.Sum(nil))
  	return ioutil.WriteFile(sigf, []byte(hexsum), 0644)
  }
docs: // Sign writes the hashsum to the given file