code: func AppendIPv4(dst []byte, ip net.IP) []byte {
  	ip = ip.To4()
  	if ip == nil {
  		return append(dst, "non-v4 ip passed to AppendIPv4"...)
  	}
  
  	dst = AppendUint(dst, int(ip[0]))
  	for i := 1; i < 4; i++ {
  		dst = append(dst, '.')
  		dst = AppendUint(dst, int(ip[i]))
  	}
  	return dst
  }
docs: // AppendIPv4 appends string representation of the given ip v4 to dst
  // and returns the extended dst.