MACs for Macs

macForInterface.c

/* Write at result the hardware (MAC) address of the network interface name.
   Return -1 on failure or 0 on success.
*/
static int macForInterface(const char *name, struct sockaddr *result)
#ifdef __APPLE__
{
    int failed = -1;
    struct ifaddrs *ifap = NULL;
    if (0 == getifaddrs(&ifap)) {
        struct ifaddrs *p = ifap;
        for (p = ifap; p; p = p->ifa_next) {
            const int match =
                p->ifa_addr &&
                p->ifa_addr->sa_family == AF_LINK &&
                0 == strcmp(name, p->ifa_name);
            if (match) {
                struct sockaddr_dl *const sadl =
                    (struct sockaddr_dl *)p->ifa_addr;
                result->sa_len = sadl->sdl_alen;
                result->sa_family = p->ifa_addr->sa_family;
                memcpy(result->sa_data, LLADDR(sadl), result->sa_len);
                failed = 0;
                break;
            }
        }
        freeifaddrs(ifap);
    }
    return failed;
}
#else
{
    int fd;
    struct ifreq ifr;
    if ((fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) return -1;
    strcpy(ifr.ifr_name, name);
    if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) return -1;
    *result = ifr.ifr_hwaddr;
    if (close(fd) < 0) return -1;
    return 0;
}
#endif