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")
}
