/*
 * getifaddr.c — retourne l'adresse IPv4 d'une interface réseau par son nom
 *
 * Usage : ifaddr <interface>
 * Exemple : ifaddr eth0
 *           ifaddr enp3s0
 *
 * Dépendances : POSIX, getifaddrs(3)
 * Compile : gcc -o ifaddr getifaddr.c
 *
 * Paul Schneider — reconstitué depuis pazof/myovh-zone
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ifaddrs.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(int argc, char *argv[])
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <interface>\n", argv[0]);
        return EXIT_FAILURE;
    }

    const char *ifname = argv[1];
    struct ifaddrs *ifaddr_list = NULL;

    if (getifaddrs(&ifaddr_list) == -1) {
        perror("getifaddrs");
        return EXIT_FAILURE;
    }

    int found = 0;
    for (struct ifaddrs *ifa = ifaddr_list; ifa != NULL; ifa = ifa->ifa_next) {
        /* On cherche uniquement IPv4 (AF_INET) */
        if (ifa->ifa_addr == NULL)
            continue;
        if (ifa->ifa_addr->sa_family != AF_INET)
            continue;
        if (strcmp(ifa->ifa_name, ifname) != 0)
            continue;

        char buf[INET_ADDRSTRLEN];
        struct sockaddr_in *sa = (struct sockaddr_in *)ifa->ifa_addr;

        if (inet_ntop(AF_INET, &sa->sin_addr, buf, sizeof(buf)) == NULL) {
            perror("inet_ntop");
            freeifaddrs(ifaddr_list);
            return EXIT_FAILURE;
        }

        printf("%s\n", buf);
        found = 1;
        break;
    }

    freeifaddrs(ifaddr_list);

    if (!found) {
        fprintf(stderr, "ifaddr: interface '%s' not found or has no IPv4 address\n", ifname);
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}