Local Network interface 얻기

man if_tcp
http://www.scit.wlv.ac.uk/cgi-bin/mansec?7P+if_tcp

소스코드
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <arpa/inet.h>

#define inaddrr(x) (*(struct in_addr *) &ifr->x[sizeof sa.sin_port])
#define IFRSIZE ((int)(size * sizeof (struct ifreq)))

static int get_addr(int sock, char * ifname, struct sockaddr * ifaddr)
{
        struct ifreq *ifr;
        struct ifreq ifrr;
        struct sockaddr_in sa;

        ifr = &ifrr;

        ifrr.ifr_addr.sa_family = AF_INET;

        strncpy(ifrr.ifr_name, ifname, sizeof(ifrr.ifr_name));

        if (ioctl(sock, SIOCGIFADDR, ifr) < 0) {
                printf("No %s interface.\n", ifname);
                return -1;
        }

        *ifaddr = ifrr.ifr_addr;
        printf("Address for %s: %s\n", ifname, inet_ntoa(inaddrr(ifr_addr.sa_data)));
        return 0;
}

int main(void)
{
        unsigned char *u;
        int sockfd, size = 1;
        struct ifreq *ifr;
        struct ifconf ifc;
        struct sockaddr_in sa;


        if (0 > (sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP))) {
                fprintf(stderr, "Cannot open socket.\n");
                exit(EXIT_FAILURE);
        }

        ifc.ifc_len = IFRSIZE;
        ifc.ifc_req = NULL;

        do {
                ++size;
                /* realloc buffer size until no overflow occurs */
                if (NULL == (ifc.ifc_req = realloc(ifc.ifc_req, IFRSIZE))) {
                        fprintf(stderr, "Out of memory.\n");
                        exit(EXIT_FAILURE);
                }
                ifc.ifc_len = IFRSIZE;
                if (ioctl(sockfd, SIOCGIFCONF, &ifc)) {
                        perror("ioctl SIOCFIFCONF");
                        exit(EXIT_FAILURE);
                }
        } while (IFRSIZE <= ifc.ifc_len);

        /* this is an alternate way to get info... */
        {
                struct sockaddr ifa;
                get_addr(sockfd, "ppp0", &ifa);
        }

        ifr = ifc.ifc_req;
        for (;(char *) ifr < (char *) ifc.ifc_req + ifc.ifc_len; ++ifr) {

                if (ifr->ifr_addr.sa_data == (ifr+1)->ifr_addr.sa_data) {
                        continue; /* duplicate, skip it */
                }

                if (ioctl(sockfd, SIOCGIFFLAGS, ifr)) {
                        continue; /* failed to get flags, skip it */
                }

                printf("Interface: %s\n", ifr->ifr_name);
                printf("IP Address: %s\n", inet_ntoa(inaddrr(ifr_addr.sa_data)));

                /*
                This won't work on HP-UX 10.20 as there's no SIOCGIFHWADDR ioctl. You'll
                need to use DLPI or the NETSTAT ioctl on /dev/lan0, etc (and you'll need
                to be root to use the NETSTAT ioctl. Also this is deprecated and doesn't
                work on 11.00).

                On Digital Unix you can use the SIOCRPHYSADDR ioctl according to an old
                utility I have. Also on SGI I think you need to use a raw socket, e.g. s
                = socket(PF_RAW, SOCK_RAW, RAWPROTO_SNOOP)

                Dave

                From: David Peter <dave.peter@eu.citrix.com>
                */

                if (0 == ioctl(sockfd, SIOCGIFHWADDR, ifr)) {

                        /* Select which hardware types to process.
                        *
                        * See list in system include file included from
                        * /usr/include/net/if_arp.h (For example, on
                        * Linux see file /usr/include/linux/if_arp.h to
                        * get the list.)
                        */
                        switch (ifr->ifr_hwaddr.sa_family) {
                                default:
                                printf("\n");
                                continue;
                                case ARPHRD_NETROM: case ARPHRD_ETHER: case ARPHRD_PPP:
                                case ARPHRD_EETHER: case ARPHRD_IEEE802: break;
                        }

                        u = (unsigned char *) &ifr->ifr_addr.sa_data;

                        if (u[0] + u[1] + u[2] + u[3] + u[4] + u[5]) {
                                printf("HW Address: %2.2x.%2.2x.%2.2x.%2.2x.%2.2x.%2.2x\n",
                                u[0], u[1], u[2], u[3], u[4], u[5]);
                        }
                }

                if (0 == ioctl(sockfd, SIOCGIFNETMASK, ifr) &&
                strcmp("255.255.255.255", inet_ntoa(inaddrr(ifr_addr.sa_data)))) {
                        printf("Netmask: %s\n", inet_ntoa(inaddrr(ifr_addr.sa_data)));
                }

                if (ifr->ifr_flags & IFF_BROADCAST) {
                        if (0 == ioctl(sockfd, SIOCGIFBRDADDR, ifr) &&
                                strcmp("0.0.0.0", inet_ntoa(inaddrr(ifr_addr.sa_data)))) {
                                printf("Broadcast: %s\n", inet_ntoa(inaddrr(ifr_addr.sa_data)));
                        }
                }

                if (0 == ioctl(sockfd, SIOCGIFMTU, ifr)) {
                        printf("MTU: %u\n", ifr->ifr_mtu);
                }

                if (0 == ioctl(sockfd, SIOCGIFMETRIC, ifr)) {
                        printf("Metric: %u\n", ifr->ifr_metric);
                }
                printf("\n");
        }

        close(sockfd);
        return EXIT_SUCCESS;
}