ipv6

static int tcp_open_socket(unsigned short port, const char *bindaddr,
                           const char *ifname)
{
    int fd = -1, n, af, opt;
    struct sockaddr_in si;
    struct sockaddr_in6 si6;
    struct sockaddr *sa;
    socklen_t sa_len;
    void *dst;

    if (index(bindaddr, ':')) {
        af = AF_INET6;

        memset(&si6, 0, sizeof(si6));
        si6.sin6_family = af;
        si6.sin6_port = htons(port);

        dst = &si6.sin6_addr.s6_addr;
        sa = (struct sockaddr *)&si6;
        sa_len = sizeof(si6);
    } else {
        af = AF_INET;

        si.sin_family = af;
        si.sin_port = htons(port);
        memset(&si.sin_zero, 0, sizeof(si.sin_zero));

        dst = &si.sin_addr.s_addr;
        sa = (struct sockaddr *)&si;
        sa_len = sizeof(si);
    }

    n = inet_pton(af, bindaddr, dst);
    if (n <= 0) {
        logprintf(STDERR_FILENO, "Could not parse the bind address '%s'\n",
                  bindaddr);
        return -1;
    }

    if (af == AF_INET6) {
        if (IN6_IS_ADDR_LINKLOCAL(&si6.sin6_addr)) {
            if (!ifname) {
                logprintf(STDERR_FILENO,
                          "Missing interface name for link local address\n");
                return -1;
            }
            n = if_nametoindex(ifname);
            if (!n) {
                logprintf(STDERR_FILENO,
                          "Could not convert interface name '%s' to "
                          "index: %s\n",
                          ifname, strerror(errno));
                return -1;
            }
            si6.sin6_scope_id = n;
        }
    }

    fd = socket(af, SOCK_STREAM, 0);
    if (fd < 0) {
        logprintf(STDERR_FILENO, "Could not open TCP socket\n");
        return -1;
    }

    opt = 1;
    n = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
    if (n < 0) {
        logprintf(STDERR_FILENO,
                  "Could not set socket option SO_REUSEADDR: %s\n",
                  strerror(errno));
        goto error;
    }

    n = bind(fd, sa, sa_len);
    if (n < 0) {
        logprintf(STDERR_FILENO, "Could not open TCP socket: %s\n",
                  strerror(errno));
        goto error;
    }

    n = listen(fd, 1);
    if (n < 0) {
        logprintf(STDERR_FILENO, "Cannot listen on TCP socket: %s\n",
                  strerror(errno));
        goto error;
    }

    return fd;

error:
    close(fd);

    return -1;
}