/* vi: set sw=4 ts=4: */
/*
 * Stripped down version of net-tools for busybox.
 *
 * Author: Ignacio Garcia Perez (iggarpe at gmail dot com)
 *
 * License: GPLv2 or later, see LICENSE file in this tarball.
 *
 * There are some differences from the standard net-tools slattach:
 *
 * - The -l option is not supported.
 *
 * - The -F options allows disabling of RTS/CTS flow control.
 */

#include "libbb.h"
#include "libiproute/utils.h" /* invarg() */

struct globals {
        int handle;
        int saved_disc;
        struct termios saved_state;
};
#define G (*(struct globals*)&bb_common_bufsiz1)
#define handle       (G.handle      )
#define saved_disc   (G.saved_disc  )
#define saved_state  (G.saved_state )
#define INIT_G() do { } while (0)


/*
 * Save tty state and line discipline
 *
 * It is fine here to bail out on errors, since we haven modified anything yet
 */
static void save_state(void)
{
        /* Save line status */
        if (tcgetattr(handle, &saved_state) < 0)
                bb_perror_msg_and_die("get state");

        /* Save line discipline */
        xioctl(handle, TIOCGETD, &saved_disc);
}

static int set_termios_state_or_warn(struct termios *state)
{
        int ret;

        ret = tcsetattr(handle, TCSANOW, state);
        if (ret < 0) {
                bb_perror_msg("set state");
                return 1; /* used as exitcode */
        }
        return 0;
}

/*
 * Restore state and line discipline for ALL managed ttys
 *
 * Restoring ALL managed ttys is the only way to have a single
 * hangup delay.
 *
 * Go on after errors: we want to restore as many controlled ttys
 * as possible.
 */
static void restore_state_and_exit(int exitcode) NORETURN;
static void restore_state_and_exit(int exitcode)
{
        struct termios state;

        /* Restore line discipline */
        if (ioctl_or_warn(handle, TIOCSETD, &saved_disc) < 0) {
                exitcode = 1;
        }

        /* Hangup */
        memcpy(&state, &saved_state, sizeof(state));
        cfsetispeed(&state, B0);
        cfsetospeed(&state, B0);
        if (set_termios_state_or_warn(&state))
                exitcode = 1;
        sleep(1);

        /* Restore line status */
        if (set_termios_state_or_warn(&saved_state))
                exit(EXIT_FAILURE);
        if (ENABLE_FEATURE_CLEAN_UP)
                close(handle);

        exit(exitcode);
}

/*
 * Set tty state, line discipline and encapsulation
 */
static void set_state(struct termios *state, int encap)
{
        int disc;

        /* Set line status */
        if (set_termios_state_or_warn(state))
                goto bad;
        /* Set line discliple (N_SLIP always) */
        disc = N_SLIP;
        if (ioctl_or_warn(handle, TIOCSETD, &disc) < 0) {
                goto bad;
        }

        /* Set encapsulation (SLIP, CSLIP, etc) */
        if (ioctl_or_warn(handle, SIOCSIFENCAP, &encap) < 0) {
 bad:
                restore_state_and_exit(EXIT_FAILURE);
        }
}

static void sig_handler(int signo UNUSED_PARAM)
{
        restore_state_and_exit(EXIT_SUCCESS);
}

int slattach_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int slattach_main(int argc UNUSED_PARAM, char **argv)
{
        /* Line discipline code table */
        static const char proto_names[] ALIGN1 =
                "slip\0"        /* 0 */
                "cslip\0"       /* 1 */
                "slip6\0"       /* 2 */
                "cslip6\0"      /* 3 */
                "adaptive\0"    /* 8 */
                ;

        int i, encap, opt;
        struct termios state;
        const char *proto = "cslip";
        const char *extcmd;                             /* Command to execute after hangup */
        const char *baud_str;
        int baud_code = -1;                             /* Line baud rate (system code) */

        enum {
                OPT_p_proto  = 1 << 0,
                OPT_s_baud   = 1 << 1,
                OPT_c_extcmd = 1 << 2,
                OPT_e_quit   = 1 << 3,
                OPT_h_watch  = 1 << 4,
                OPT_m_nonraw = 1 << 5,
                OPT_L_local  = 1 << 6,
                OPT_F_noflow = 1 << 7
        };

        INIT_G();

        /* Parse command line options */
        opt = getopt32(argv, "p:s:c:ehmLF", &proto, &baud_str, &extcmd);
        /*argc -= optind;*/
        argv += optind;

        if (!*argv)
                bb_show_usage();

        encap = index_in_strings(proto_names, proto);

        if (encap < 0)
                invarg(proto, "protocol");
        if (encap > 3)
                encap = 8;

        /* We want to know if the baud rate is valid before we start touching the ttys */
        if (opt & OPT_s_baud) {
                baud_code = tty_value_to_baud(xatoi(baud_str));
                if (baud_code < 0)
                        invarg(baud_str, "baud rate");
        }

        /* Trap signals in order to restore tty states upon exit */
        if (!(opt & OPT_e_quit)) {
                bb_signals(0
                        + (1 << SIGHUP)
                        + (1 << SIGINT)
                        + (1 << SIGQUIT)
                        + (1 << SIGTERM)
                        , sig_handler);
        }

        /* Open tty */
        handle = open(*argv, O_RDWR | O_NDELAY);
        if (handle < 0) {
                char *buf = concat_path_file("/dev", *argv);
                handle = xopen(buf, O_RDWR | O_NDELAY);
                /* maybe if (ENABLE_FEATURE_CLEAN_UP) ?? */
                free(buf);
        }

        /* Save current tty state */
        save_state();

        /* Configure tty */
        memcpy(&state, &saved_state, sizeof(state));
        if (!(opt & OPT_m_nonraw)) { /* raw not suppressed */
                memset(&state.c_cc, 0, sizeof(state.c_cc));
                state.c_cc[VMIN] = 1;
                state.c_iflag = IGNBRK | IGNPAR;
                state.c_oflag = 0;
                state.c_lflag = 0;
                state.c_cflag = CS8 | HUPCL | CREAD
                              | ((opt & OPT_L_local) ? CLOCAL : 0)
                              | ((opt & OPT_F_noflow) ? 0 : CRTSCTS);
                cfsetispeed(&state, cfgetispeed(&saved_state));
                cfsetospeed(&state, cfgetospeed(&saved_state));
        }

        if (opt & OPT_s_baud) {
                cfsetispeed(&state, baud_code);
                cfsetospeed(&state, baud_code);
        }

        set_state(&state, encap);

        /* Exit now if option -e was passed */
        if (opt & OPT_e_quit)
                return 0;

        /* If we're not requested to watch, just keep descriptor open
         * until we are killed */
        if (!(opt & OPT_h_watch))
                while (1)
                        sleep(24*60*60);

        /* Watch line for hangup */
        while (1) {
                if (ioctl(handle, TIOCMGET, &i) < 0 || !(i & TIOCM_CAR))
                        goto no_carrier;
                sleep(15);
        }

 no_carrier:

        /* Execute command on hangup */
        if (opt & OPT_c_extcmd)
                system(extcmd);

        /* Restore states and exit */
        restore_state_and_exit(EXIT_SUCCESS);
}