serialsh.m

#include <unistd.h>
#include <termios.h>

#import <sys/event.h>
#import <Foundation/Foundation.h>

int kq = 0;
pid_t pd = 0;

int pipe_shin[2] = { 0 };
int pipe_shout[2] = { 0 };

#define spawn_shin pipe_shin[1]
#define main_sherr pipe_shout[1]

int attribs(int fd, speed_t baudrate)
{
    struct termios tty;

    memset(&tty, 0x0, sizeof(tty));

    if (tcgetattr(fd, &tty) != 0) return -1;

    cfsetispeed(&tty, baudrate);
    cfsetospeed(&tty, baudrate);

    tty.c_cflag &= ~CRTSCTS;
    tty.c_cflag |= (CLOCAL | CREAD);
    tty.c_iflag |= (IGNPAR);
    tty.c_iflag &= ~(IXON | IXOFF | INLCR | IGNCR);
    tty.c_oflag &= ~OPOST;

    tty.c_cflag &= ~CSIZE;
    tty.c_cflag |= CS8;
    tty.c_cflag &= ~PARENB;
    tty.c_iflag &= ~INPCK;
    tty.c_cflag &= ~CSTOPB;
    tty.c_iflag |= INPCK;

    tty.c_cc[VMIN] = 0;
    tty.c_cc[VTIME] = 5;

    tty.c_lflag &= ~(ICANON | ECHO | ISIG | IEXTEN);

    if (tcsetattr(fd, TCSANOW, &tty) != 0) return -1;

    return 0;
}

void spawnproc(void) {
    struct kevent ke;

    if (pd == 0) {
        if ((pd = fork()) == 0) {
            dup2(pipe_shin[0], STDIN_FILENO);

            dup2(main_sherr, STDOUT_FILENO);
            dup2(main_sherr, STDERR_FILENO);

            char *args[] = { "createpty", "-q", "/dev/null", "login", NULL };

            execve("/usr/bin/script", args, NULL);

            exit(0);
        }

        EV_SET(&ke, pd, EVFILT_PROC, EV_ADD, NOTE_EXIT, 0, NULL);
        kevent(kq, (const struct kevent *)&ke, 1, NULL, 0, NULL);
    }
}

int main(void) {
    int fd = 0;
    char buf[0x400];
    struct kevent ke;

    if (fork() != 0) return 0;

    /* it will works the same if you open /dev/uart.debug-console */
    if ((fd = open("/dev/tty.debug-console", O_RDWR | O_NOCTTY | O_SYNC | O_NONBLOCK)) < 0) return 0;

    assert(attribs(fd, B115200) != -1);

    dprintf(fd, "\r\n[serialsh]: hello from the userland!\r\n\n");

    pipe(pipe_shin);
    pipe(pipe_shout);

    dup2(pipe_shout[0], STDIN_FILENO);

    dup2(spawn_shin, STDOUT_FILENO);
    dup2(spawn_shin, STDERR_FILENO);

    if ((kq = kqueue()) == -1) {
        dprintf(fd, "\r\n[serialsh]: error during initialization!\r\n\n");
        close(fd);
        return -1;
    }

    EV_SET(&ke, fd, EVFILT_READ, EV_ADD, 0, 5, 0);
    kevent(kq, &ke, 1, NULL, 0, NULL);

    EV_SET(&ke, 0, EVFILT_READ, EV_ADD, 0, 5, 0);
    kevent(kq, &ke, 1, NULL, 0, NULL);

    spawnproc();

    for (;;) {
        memset(&ke, 0x0, sizeof(ke));

        if (kevent(kq, NULL, 0, &ke, 1, NULL) == 0) continue;

        if (ke.ident == fd) {
            ssize_t rd = read(fd, buf, sizeof(buf));
            write(STDOUT_FILENO, buf, rd);
        } else if (ke.ident) {
            if ((ke.filter == EVFILT_PROC) && (ke.ident == pd)) {
                waitpid(pd, NULL, 0);
                pd = 0;
                spawnproc();
            }
        } else {
            ssize_t rd = read(STDIN_FILENO, buf, sizeof(buf));
            write(fd, buf, rd);
        }
    }

    return 0;
}