OpenWrt – Rev 4

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/*
 * Based on code found at https://dev.openwrt.org/ticket/4876 .
 * Extended by Jo-Philipp Wich <jo@mein.io> for use in OpenWrt.
 *
 * You may use this program under the terms of the GPLv2 license.
 */

#include <string.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>


static void abort_query(int sig)
{
        exit(1);
}

static void show_usage(void)
{
        printf("Usage:\n");
        printf("        resolveip -h\n");
        printf("        resolveip [-t timeout] hostname\n");
        printf("        resolveip -4 [-t timeout] hostname\n");
        printf("        resolveip -6 [-t timeout] hostname\n");
        exit(255);
}

int main(int argc, char **argv)
{
        int timeout = 3;
        int opt;
        char ipaddr[INET6_ADDRSTRLEN];
        void *addr;
        struct addrinfo *res, *rp;
        struct sigaction sa = { .sa_handler = &abort_query };
        struct addrinfo hints = {
                .ai_family   = AF_UNSPEC,
                .ai_socktype = SOCK_STREAM,
                .ai_protocol = IPPROTO_TCP,
                .ai_flags    = 0
        };

        while ((opt = getopt(argc, argv, "46t:h")) > -1)
        {
                switch ((char)opt)
                {
                        case '4':
                                hints.ai_family = AF_INET;
                                break;

                        case '6':
                                hints.ai_family = AF_INET6;
                                break;

                        case 't':
                                timeout = atoi(optarg);
                                if (timeout <= 0)
                                        show_usage();
                                break;

                        case 'h':
                                show_usage();
                                break;
                }
        }

        if (!argv[optind])
                show_usage();

        sigaction(SIGALRM, &sa, NULL);
        alarm(timeout);

        if (getaddrinfo(argv[optind], NULL, &hints, &res))
                exit(2);

        for (rp = res; rp != NULL; rp = rp->ai_next)
        {
                addr = (rp->ai_family == AF_INET)
                        ? (void *)&((struct sockaddr_in *)rp->ai_addr)->sin_addr
                        : (void *)&((struct sockaddr_in6 *)rp->ai_addr)->sin6_addr
                ;

                if (!inet_ntop(rp->ai_family, addr, ipaddr, INET6_ADDRSTRLEN - 1))
                        exit(3);

                printf("%s\n", ipaddr);
        }

        freeaddrinfo(res);
        exit(0);
}