WIP: MAC-based implementation of maccopy network-unix.c in network-info Haskell package

network-unix.c

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

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

#ifdef __linux__
#   include <netpacket/packet.h>
#else
#   include <sys/socket.h>
#   include <net/if.h>
#   ifndef __GNU__
#      include <net/if_dl.h>
#      ifndef __sun
#         define AF_PACKET AF_LINK
#      endif
#   endif
#   ifdef __sun
#      include <net/if_arp.h>
#      include <unistd.h>
#      include <stropts.h>
#      include <sys/sockio.h>
#   endif
#endif

#ifdef __FreeBSD__
#   include <net/pfvar.h>
#endif

#include "network.h"
#include "common.h"


#if defined(AF_PACKET) || defined(__sun)
void maccopy(unsigned char *dst, struct sockaddr *addr)
{
#ifdef __sun
    // SOURCE DERIVED FROM: http://www.pauliesworld.org/project/getmac.c
    int sock;
    if ((sock=socket(AF_INET,SOCK_DGRAM,0)) > -1) {
        struct arpreq arpreq;
        memset(&arpreq, 0, sizeof (struct arpreq));
        arpreq.arp_pa = *addr;
        if (ioctl(sock,SIOCGARP,(char*)&arpreq) == 0) {
            close (sock);
            memcpy(dst, (unsigned char *)arpreq.arp_ha.sa_data, MAC_SIZE);
        } else {
            memset(dst, 255, MAC_SIZE);
        }
    } else {
        memset(dst, 255, MAC_SIZE);
    }
#elif defined(__linux__)
    /* TODO check that sll_halen is equal to 6 (MAC_SIZE) */
    memcpy(dst, ((struct sockaddr_ll *)addr)->sll_addr, MAC_SIZE);
#else
    /* TODO check that sdl_alen is equal to 6 (MAC_SIZE) */
    struct sockaddr_dl *sdl = (struct sockaddr_dl *)addr;
    memcpy(dst, sdl->sdl_data + sdl->sdl_nlen, MAC_SIZE);
#endif
}
#endif

struct network_interface *add_interface(struct network_interface *ns, const wchar_t *name, int max_ns)
{
    int i;
    for (i = 0; i < max_ns; i++) {
        if (wcsempty(ns[i].name)) {
            wszcopy(ns[i].name, name, NAME_SIZE);
            return &ns[i];
        } else if (wcscmp(ns[i].name, name) == 0) {
            return &ns[i];
        }
    }
    return NULL;
}

int count_interfaces(struct network_interface *ns, int max_ns)
{
    int i;
    for (i = 0; i < max_ns; i++) {
        if (wcsempty(ns[i].name)) {
            break;
        }
    }
    return i;
}

int c_get_network_interfaces(struct network_interface *ns, int max_ns)
{
    struct network_interface *n;
    struct ifaddrs *ifaddr, *ifa;
    struct sockaddr *addr;
    wchar_t name[NAME_SIZE];
    int family, error;

    error = getifaddrs(&ifaddr);
    if (error != 0) {
        /* TODO printing the error to stderr is not a very nice thing for
         * TODO a library to do, but i've never seen this happen and its
         * TODO probably better than failing silently. */
        perror("getifaddrs");
        return 0;
    }

    memset(ns, 0, sizeof(struct network_interface) * max_ns);

    for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
        /* check we actually have an address in this item */
        addr = ifa->ifa_addr;
        if (addr == NULL)
            continue;

        /* convert the interface name to wide characters */
        mbswszcopy(name, ifa->ifa_name, NAME_SIZE);

        /* lookup or add a new interface with the given name */
        n = add_interface(ns, name, max_ns);

        /* extract the address from this item */
        family = addr->sa_family;
        if (family == AF_INET) {
            ipv4copy(&n->ip_address, addr);
#ifdef __sun
            if ((ifa->ifa_flags && IFF_LOOPBACK) == 0) {
                maccopy(n->mac_address, addr);
            }
#endif
        } else if (family == AF_INET6) {
            ipv6copy(&n->ip6_address, addr);
#ifdef __sun
            if ((ifa->ifa_flags && IFF_LOOPBACK) == 0) {
                maccopy(n->mac_address, addr);
            }
#endif
#ifdef AF_PACKET
        } else if (family == AF_PACKET) {
            maccopy(n->mac_address, addr);
#endif
        }
    }

    freeifaddrs(ifaddr);
    return count_interfaces(ns, max_ns);
}

Bam! It builds.

IFF_LOOPBACK lines should be == 0. Condition is inverted.

/*
 * Test getifaddrs behavior.
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <net/if.h>
#include <unistd.h>
#include <stropts.h>
#include <sys/sockio.h>
#include <strings.h>
#include <net/if_arp.h>

int
main(int argc, const char *argv[])
{
        struct ifaddrs *ifa, *oif;
        struct arpreq arp;

        if (getifaddrs(&ifa) != 0) {
                perror("getifaddrs");
                return (1);
        }   

        oif = ifa;
        while (ifa != NULL) {
                int sock, i;

                printf("%s: [%d]\n", ifa->ifa_name, ifa->ifa_addr->sa_family);
                if (ifa->ifa_flags & IFF_LOOPBACK) {
                        ifa = ifa->ifa_next;
                        continue;
                }   

                sock = socket(ifa->ifa_addr->sa_family, SOCK_DGRAM, 0); 
                if (sock < 0) {
                        perror("socket");
                        freeifaddrs(oif);
                        return (1);
                }   

                bzero(&arp, sizeof (struct arpreq));
                arp.arp_pa = *ifa->ifa_addr;
                if (ioctl(sock, SIOCGARP, (void *)&arp) != 0) {
                        perror("ioctl");
                        return (1);
                }   

                for (i = 0; i < 6; i++) {
                        printf("%02x%s", (unsigned char)arp.arp_ha.sa_data[i],
                            i != 5 ? ":" : "");
                }   
                printf("\n");
                ifa = ifa->ifa_next;
        }   

        freeifaddrs(oif);

        return (0);
}

Use #elif in maccopy instead of #endif because otherwise linux code will clobber.

Thank you @rmustacc for identifying the bugs and finding a working implementation.

@rmustacc your implementation works like a charm,

Mine compiles with the elif and if condition changes, but still yields zeroes for MAC address. I'll have to review your implementation in more detail to see what mine is missing.