live-bootstrap/steps-guix/loopback-bind-127001/files/loopback-bind-127001.c

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <sys/socket.h>

int main(void) {
    int fd;
    struct ifreq ifr;
    struct sockaddr_in addr;

    fd = socket(AF_INET, SOCK_DGRAM, 0);
    if (fd < 0) {
        perror("socket");
        return 1;
    }

    memset(&ifr, 0, sizeof(ifr));
    memset(&addr, 0, sizeof(addr));

    addr.sin_family = AF_INET;
    if (inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr) != 1) {
        perror("inet_pton");
        close(fd);
        return 1;
    }

    strncpy(ifr.ifr_name, "lo", IFNAMSIZ - 1);
    memcpy(&ifr.ifr_addr, &addr, sizeof(addr));
    if (ioctl(fd, SIOCSIFADDR, &ifr) < 0) {
        perror("ioctl(SIOCSIFADDR)");
        close(fd);
        return 1;
    }

    if (ioctl(fd, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        close(fd);
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(fd, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        close(fd);
        return 1;
    }

    close(fd);
    return 0;
}