/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2026.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU Lesser General Public License as published   *
* by the Free Software Foundation, either version 3 or (at your option)   *
* any later version. This program is distributed without any warranty.    *
* See the files COPYING.lgpl-v3 and COPYING.gpl-v3 for details.           *
\*************************************************************************/

#include <fcntl.h>
#include <termios.h>
#include <sys/ioctl.h>
#include "pty_master_open.h"
#include "pty_fork.h"                   /* Declares ptyFork() */
#include "tlpi_hdr.h"

#define MAX_SNAME 1000

pid_t
ptyFork(int *masterFd, char *slaveName, size_t snLen,
        const struct termios *slaveTermios, const struct winsize *slaveWS)
{
    int mfd, slaveFd, savedErrno;
    pid_t childPid;
    char slname[MAX_SNAME];

    mfd = ptyMasterOpen(slname, MAX_SNAME);
    if (mfd == -1)
        return -1;

    if (slaveName != NULL) {            /* Return slave name to caller */
        if (strlen(slname) < snLen) {
            strncpy(slaveName, slname, snLen);

        } else {                        /* 'slaveName' was too small */
            close(mfd);
            errno = EOVERFLOW;
            return -1;
        }
    }

    childPid = fork();

    if (childPid == -1) {               /* fork() failed */
        savedErrno = errno;             /* close() might change 'errno' */
        close(mfd);                     /* Don't leak file descriptors */
        errno = savedErrno;
        return -1;
    }

    if (childPid != 0) {                /* Parent */
        *masterFd = mfd;                /* Only parent gets master fd */
        return childPid;                /* Like parent of fork() */
    }

    /* Child falls through to here */

    if (setsid() == -1)                 /* Start a new session */
        err_exit("ptyFork:setsid");

    close(mfd);                         /* Not needed in child */

    slaveFd = open(slname, O_RDWR);     /* Becomes controlling tty */
    if (slaveFd == -1)
        err_exit("ptyFork:open-slave");

#ifdef TIOCSCTTY                        /* Acquire controlling tty on BSD */
    if (ioctl(slaveFd, TIOCSCTTY, 0) == -1)
        err_exit("ptyFork:ioctl-TIOCSCTTY");
#endif

    if (slaveTermios != NULL)           /* Set slave tty attributes */
        if (tcsetattr(slaveFd, TCSANOW, slaveTermios) == -1)
            err_exit("ptyFork:tcsetattr");

    if (slaveWS != NULL)                /* Set slave tty window size */
        if (ioctl(slaveFd, TIOCSWINSZ, slaveWS) == -1)
            err_exit("ptyFork:ioctl-TIOCSWINSZ");

    /* Duplicate pty slave to be child's stdin, stdout, and stderr */

    if (dup2(slaveFd, STDIN_FILENO) != STDIN_FILENO)
        err_exit("ptyFork:dup2-STDIN_FILENO");
    if (dup2(slaveFd, STDOUT_FILENO) != STDOUT_FILENO)
        err_exit("ptyFork:dup2-STDOUT_FILENO");
    if (dup2(slaveFd, STDERR_FILENO) != STDERR_FILENO)
        err_exit("ptyFork:dup2-STDERR_FILENO");

    if (slaveFd > STDERR_FILENO)        /* Safety check */
        close(slaveFd);                 /* No longer need this fd */

    return 0;                           /* Like child of fork() */
}