Example Super Server

struct service {
    char    *sv_name;
    char    sv_useTCP;
    int     sv_sock;
    int     (*sv_func)(int);
};

struct service svent[] = {
    { "echo", TCP_SERV, NOSOCK, TCPechod },
    { "chargen", TCP_SERV, NOSOCK, TCPchargend },
    { "daytime", TCP_SERV, NOSOCK, TCPdaytimed },
    { "time", TCP_SERV, NOSOCK, TCPtimed },
    { 0, 0, 0, 0 },
};

int main(int argc, char *argv[])
{
    struct service  *psv,       /* service table pointer    */
            *fd2sv[NOFILE];     /* map fd to service pointer    */
    int     fd, nfds;
    fd_set  afds, rfds;         /* readable file descriptors    */

    nfds = 0;
    FD_ZERO(&afds);
    for (psv = &svent[0]; psv->sv_name; ++psv) {
        if (psv->sv_useTCP)
            psv->sv_sock = passiveTCP(psv->sv_name, QLEN);
        else
            psv->sv_sock = passiveUDP(psv->sv_name);
        fd2sv[psv->sv_sock] = psv;
        nfds = MAX(psv->sv_sock+1, nfds);
        FD_SET(psv->sv_sock, &afds);
    }
    (void) signal(SIGCHLD, reaper);

    while (1) {
        memcpy(&rfds, &afds, sizeof(rfds));
        if (select(nfds, &rfds, (fd_set *)0, (fd_set *)0,
            (struct timeval *)0) < 0) {
            if (errno == EINTR) continue;
            errexit("select error: %s\n", strerror(errno));
        }
        for (fd=0; fd<nfds; ++fd) {
            if (FD_ISSET(fd, &rfds)) {
                psv = fd2sv[fd];
                if (psv->sv_useTCP) doTCP(psv);
                else psv->sv_func(psv->sv_sock);
            }
        }
    }
}

/*------------------------------------------------------------------------
 * doTCP - handle a TCP service connection request
 *------------------------------------------------------------------------
 */
void doTCP(struct service *psv)
{
    struct sockaddr_in fsin;    /* the request from address     */
    int     alen;               /* from-address length      */
    int     fd, ssock;

    alen = sizeof(fsin);
    ssock = accept(psv->sv_sock, (struct sockaddr *)&fsin, &alen);
    if (ssock < 0)
        errexit("accept: %s\n", strerror(errno));
    switch (fork()) {
    case 0: 
        break;
    case -1:
        errexit("fork: %s\n", strerror(errno));
    default:
        (void) close(ssock);
        return;     /* parent */
    }
    /* child */

    for (fd = NOFILE; fd >= 0; --fd)
        if (fd != ssock) (void) close(fd);

    exit(psv->sv_func(ssock));
}

/*------------------------------------------------------------------------
 * reaper - clean up zombie children
 *------------------------------------------------------------------------
 */
void reaper(int sig)
{
    int     status;

    while (wait3(&status, WNOHANG, (struct rusage *)0) >= 0)
            /* empty */;
}