/* showif.c : PUBLIC DOMAIN - Jon Mayo - August 22, 2006
 * - You may remove any comments you wish, modify this code any way you wish,
 *   and distribute any way you wish.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * Updated: June 1, 2011 */

/* finds all network interfaces and shows a little information about them.
 * some operating systems list interfaces multiple times because of different
 * flags, modes, etc. if you want to use this code you should be aware that
 * duplicate interfaces is a possibility */

#include <stdio.h>
#include <stdlib.h>

/* Old way */
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <net/if.h>
#include <netdb.h>

static void show_interface(int fd, const char *name)
{
	int family;
	struct ifreq ifreq;
	char host[128];
	memset(&ifreq, 0, sizeof ifreq);
	strncpy(ifreq.ifr_name, name, IFNAMSIZ);

	if (ioctl(fd, SIOCGIFADDR, &ifreq) != 0) {
		perror(name);
		return; /* ignore */
	}

	switch (family = ifreq.ifr_addr.sa_family) {
	case AF_UNSPEC:
		return; /* ignore */
	case AF_INET:
	case AF_INET6:
		getnameinfo(&ifreq.ifr_addr, sizeof(ifreq.ifr_addr),
			host, sizeof(host), 0, 0, NI_NUMERICHOST);
		break;
	default:
		sprintf(host, "unknown (family: %d)", family);
	}

	printf("%-24s%s\n", name, host);
}

static void list_interfaces(int fd, void (*show)(int fd, const char *name))
{
	struct ifreq *ifreq;
	struct ifconf ifconf;
	char buf[16384];
	int i;
	size_t len;

	ifconf.ifc_len = sizeof buf;
	ifconf.ifc_buf = buf;

	if (ioctl(fd, SIOCGIFCONF, &ifconf) != 0) {
		perror("ioctl(SIOCGIFCONF)");
		exit(EXIT_FAILURE);
	}

	ifreq = ifconf.ifc_req;

	for (i = 0; i < ifconf.ifc_len;) {
		/* some systems have ifr_addr.sa_len and adjust the length that
		 * way, but not mine. weird */
#ifndef linux
		len = IFNAMSIZ + ifreq->ifr_addr.sa_len;
#else
		len = sizeof * ifreq;
#endif

		if (show) {
			show(fd, ifreq->ifr_name);
		} else {
			printf("%s\n", ifreq->ifr_name);
		}

		ifreq = (struct ifreq*)((char*)ifreq + len);
		i += len;
	}
}

/* IPv4 only, but works with old systems */
void show_all_interfaces_old(void)
{
	int fd;
	const int family = AF_INET;

	fd = socket(family, SOCK_DGRAM, 0);

	if (fd < 0) {
		perror("socket()");
		exit(EXIT_FAILURE);
	}

	list_interfaces(fd, show_interface);
	close(fd);
}

/** New way **/

#include <sys/types.h>
#include <ifaddrs.h>

void show_all_interfaces_new(void)
{
	struct ifaddrs *a, *curr;
	char host[128];

	if (getifaddrs(&a)) {
		perror("getifaddrs()");
		return;
	}

	for (curr = a; curr; curr = curr->ifa_next) {
		size_t addr_len;
		switch (curr->ifa_addr->sa_family) {
		default:
			continue;
		case AF_INET:
			addr_len = sizeof(struct sockaddr_in);
			break;
		case AF_INET6:
			addr_len = sizeof(struct sockaddr_in6);
			break;
		}
		getnameinfo(curr->ifa_addr, addr_len, host, sizeof(host),
			0, 0, NI_NUMERICHOST);
		printf("%-24s%s\n", curr->ifa_name, host);
	}

	freeifaddrs(a);
}

int main()
{
	fprintf(stderr, "OLD:\n");
	show_all_interfaces_old();
	fprintf(stderr, "NEW:\n");
	show_all_interfaces_new();
	return EXIT_SUCCESS;
}