func googleAddr(c *icmp.PacketConn, protocol int) (net.Addr, error) { const host = "www.google.com" ips, err := net.LookupIP(host) if err != nil { return nil, err } netaddr := func(ip net.IP) (net.Addr, error) { switch c.LocalAddr().(type) { case *net.UDPAddr: return &net.UDPAddr{IP: ip}, nil case *net.IPAddr: return &net.IPAddr{IP: ip}, nil default: return nil, errors.New("neither UDPAddr nor IPAddr") } } for _, ip := range ips { switch protocol { case iana.ProtocolICMP: if ip.To4() != nil { return netaddr(ip) } case iana.ProtocolIPv6ICMP: if ip.To16() != nil && ip.To4() == nil { return netaddr(ip) } } } return nil, errors.New("no A or AAAA record") }