mcast_join函数

#include    <errno.h>
#include    <string.h>
#include    <net/if.h>
#include    <netinet/in.h>

#define     SA      struct sockaddr 

int family_to_level(int);

int mcast_join(int sockfd, const SA *grp, socklen_t grplen,
    const char *ifname, u_int ifindex) 
{
#ifdef MCAST_JOIN_GROUP
    struct group_req req;
    if (ifindex > 0) {
        req.gr_interface = ifindex;
    } else if (ifname != NULL) {
        if ( (req.gr_interface = if_nametoindex(ifname)) == 0) {
            errno = ENXIO;    /* i/f name not found */
            return (-1);
        }
    } else {
        req.gr_interface = 0;
    }
    if (grplen > sizeof(req.gr_group)) {
        errno = EINVAL;
        return -1;
    }
    memcpy(&req.gr_group, grp, grplen);
    return (setsockopt(sockfd, family_to_level(grp->sa_family),
            MCAST_JOIN_GROUP, &req, sizeof(req)));
#else
    switch (grp->sa_family) {
        case AF_INET: {
            struct ip_mreq    mreq;
            struct ifreq    ifreq;

            memcpy(&mreq.imr_multiaddr,
               &((const struct sockaddr_in *) grp)->sin_addr,
               sizeof(struct in_addr));

            if (ifindex > 0) {
                if (if_indextoname(ifindex, ifreq.ifr_name) == NULL) {
                    errno = ENXIO;    /* i/f index not found */
                    return(-1);
                }
                goto doioctl;
            } else if (ifname != NULL) {
                strncpy(ifreq.ifr_name, ifname, IFNAMSIZ);
                doioctl:
                if (ioctl(sockfd, SIOCGIFADDR, &ifreq) < 0) {
                    return(-1);
                }
                memcpy(&mreq.imr_interface,
                   &((struct sockaddr_in *) &ifreq.ifr_addr)->sin_addr,
                   sizeof(struct in_addr));
            } else {
                mreq.imr_interface.s_addr = htonl(INADDR_ANY);
            }

            return(setsockopt(sockfd, IPPROTO_IP, 
                IP_ADD_MEMBERSHIP,&mreq, sizeof(mreq)));
        }
#ifdef    IPV6
#ifndef    IPV6_JOIN_GROUP        /* APIv0 compatibility */
#define    IPV6_JOIN_GROUP        IPV6_ADD_MEMBERSHIP
#endif
        case AF_INET6: {
            struct ipv6_mreq  mreq6;

            memcpy(&mreq6.ipv6mr_multiaddr,
               &((const struct sockaddr_in6 *) grp)->sin6_addr,
               sizeof(struct in6_addr));

            if (ifindex > 0) {
                mreq6.ipv6mr_interface = ifindex;
            } else if (ifname != NULL) {
                if ( (mreq6.ipv6mr_interface = 
                if_nametoindex(ifname)) == 0) {
                    errno = ENXIO;    /* i/f name not found */
                    return(-1);
                }
            } else {
                mreq6.ipv6mr_interface = 0;
            }

            return(setsockopt(sockfd, IPPROTO_IPV6, 
                IPV6_JOIN_GROUP,&mreq6, sizeof(mreq6)));
        }
#endif
        default: {
            errno = EAFNOSUPPORT;
            return(-1);
        }
    }
#endif
}

#include    <netinet/in.h>
#include    <sys/socket.h>

int family_to_level(int family)
{
    switch (family) {
        case AF_INET: {
            return (IPPROTO_IP);
        }
#ifdef    IPV6
        case AF_INET6: {
            return (IPPROTO_IPV6);
        }
#endif
        default: {
            return (-1);
        }
    }
}