code: func (p *Packet) String() string {
  	// If there are no headers, print "unsupported protocol".
  	if len(p.Headers) == 0 {
  		return fmt.Sprintf("%s unsupported protocol %d", p.Time, int(p.Type))
  	}
  	return fmt.Sprintf("%s %s", p.Time, p.headerString(p.Headers))
  }
docs: // String prints a one-line representation of the packet header.
  // The output is suitable for use in a tcpdump program.