Wrapper for redirecting stdin/stdout of a shell command to a pseudo-terminal

ptywrap.c

/*
 * \brief       Wrapper for redirecting stdin/stdout to a pseudo-terminal
 * \author      Albert Ou <aou@eecs.berkeley.edu>
 * \copyright   BSD 2-Clause License
 */

#define _XOPEN_SOURCE (600)
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <signal.h>

#include <unistd.h>
#include <fcntl.h>
#include <poll.h>
#include <sys/wait.h>
#include <termios.h>

int main(int argc, char **argv)
{
	const char *errmsg;
	const char *name;
	int pty, pts;
	pid_t pid;
	sigset_t set;
	struct termios tios;

	if (argc < 2) {
		fprintf(stderr, "usage: %s [command]\n", argv[0]);
		return EXIT_FAILURE;
	}

	errno = 0;
	errmsg = NULL;
	if ((pty = posix_openpt(O_RDWR | O_NOCTTY)) < 0) {
		errmsg = "posix_openpt";
		goto exit;
	}
	if (grantpt(pty)) {
		errmsg = "grantpt";
		goto close;
	}
	if (unlockpt(pty)) {
		errmsg = "unlockpt";
		goto close;
	}

	name = ptsname(pty);
	if ((pts = open(name, O_RDWR | O_NOCTTY)) < 0) {
		errmsg = "open";
		goto close;
	}
	close(pts);
	puts(name);

	/* Poll until HUP condition vanishes, which should
	   indicate that the slave device has been reopened */
	for (;;) {
		struct pollfd fds;
		fds.fd = pty;
		fds.events = POLLHUP;
		if (poll(&fds, 1, 0) < 0) {
			errmsg = "poll";
			goto close;
		}
		if (!(fds.revents & POLLHUP))
			break;
		usleep(100);
	}
	if (tcgetattr(pty, &tios)) {
		errmsg = "tcgetattr";
		goto close;
	}
	tios.c_lflag &= ~(ICANON | ECHO | ISIG);
	if (tcsetattr(pty, TCSANOW, &tios)) {
		errmsg = "tcsetattr";
		goto close;
	}

	if ((pid = fork()) < 0) {
		errmsg = "fork";
		goto close;
	}
	if (pid == 0) {
		if ((dup2(pty, STDIN_FILENO) < 0) ||
		    (dup2(pty, STDOUT_FILENO) < 0)) {
			errmsg = "dup2";
			goto close;
		}
		execvp(argv[1], argv + 1);
		errmsg = "execvp";
		goto close;
	}

	sigemptyset(&set);
	sigaddset(&set, SIGINT);
	sigaddset(&set, SIGTERM);
	sigaddset(&set, SIGCHLD);
	sigprocmask(SIG_BLOCK, &set, NULL);
	for (;;) {
		int signo;
		sigwait(&set, &signo);
		if (signo == SIGCHLD) {
			int status;
			waitpid(pid, &status, WNOHANG);
			if (WIFEXITED(status))
				break;
		} else {
			kill(pid, SIGTERM);
			break;
		}
	}

close:
	close(pty);
exit:
	if (errno)
		perror(errmsg);
	return errno;
}