Security: getnameinfo

   error = getnameinfo(sa, salen, addr, sizeof(addr),
       NULL, 0, NI_NAMEREQD);
   if (error == 0) {
           /* could be malicious PTR record */
           memset(&hints, 0, sizeof(hints));
           hints.ai_socktype = SOCK_DGRAM; /*dummy*/
           hints.ai_flags = AI_NUMERICHOST;
           if (getaddrinfo(addr, "0", &hints, &res) == 0) {
                   /* malicious PTR record */
                   freeaddrinfo(res);
                   printf("bogus PTR record\n");
                   return -1;
           }
           /* addr is FQDN as a result of PTR lookup */
   } else {
           /* addr is numeric string */
           error = getnameinfo(sa, salen, addr, sizeof(addr),
               NULL, 0, NI_NUMERICHOST);
   }