code: func certificatesFromFile(file string) ([]*x509.Certificate, error) {
  	if len(file) == 0 {
  		return nil, errors.New("error reading certificates from an empty filename")
  	}
  	pemBlock, err := ioutil.ReadFile(file)
  	if err != nil {
  		return nil, err
  	}
  	certs, err := CertsFromPEM(pemBlock)
  	if err != nil {
  		return nil, fmt.Errorf("error reading %s: %s", file, err)
  	}
  	return certs, nil
  }
docs: // certificatesFromFile returns the x509.Certificates contained in the given PEM-encoded file.
  // Returns an error if the file could not be read, a certificate could not be parsed, or if the file does not contain any certificates