nowinch.c

/* Copyright 2016-2017 random832@fastmail.com
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE. */

#define _XOPEN_SOURCE 600
#define _BSD_SOURCE /* for cfmakeraw */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <signal.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/ioctl.h>

/* Simple tool to relay data between a pty and the tty it is run on.
 * This version deliberately does not handle SIGWINCH or propagate window
 * resizes, though it does set the initial size of the window before running
 * the subprocess. */

int ptyfd;
struct termios tio;
struct winsize ws;

int ptyproc(const char *path, char * const *argv) {
    pid_t pid;
    int ptyfd = posix_openpt(O_RDWR|O_NOCTTY);
    if(ptyfd < 0) {
        perror("openpt");
        exit(1);
    }
    if(grantpt(ptyfd) < 0) {
        perror("grantpt");
        exit(1);
    }
    if(unlockpt(ptyfd) < 0) {
        perror("unlockpt");
        exit(1);
    }
    pid = fork();
    if(pid < 0) {
        perror("fork");
        exit(1);
    } else if(pid == 0) {
        char *fn = ptsname(ptyfd);
        int fd = open(fn, O_RDWR);
	pid = setsid();
        if(fd < 0) {
            perror(fn);
            exit(1);
        }
	if(ioctl(fd, TIOCSCTTY)) {
		perror("sctty");
		exit(1);
	}
	tcsetattr(fd, 0, &tio);
	ioctl(fd, TIOCSWINSZ, &ws);
        close(0); close(1); close(2);
        dup(fd); dup(fd); dup(fd); close(fd);
	execvp(path, argv);
	perror(path);
	_exit(errno == ENOENT ? 127 : 126);
    } else {
	return ptyfd;
    }
}

void
do_input(void) {
    char buf;
    int n = read(0, &buf, 1);
    if(n > 0) {
        switch(buf) {
            case 0x1d: // ^]
                exit(1);
                break;
            default:
                write(ptyfd, &buf, n);
                break;
        }
    } else if(n < 0) {
        perror("write pty");
        exit(1);
    } else {
        return;
    }
}

int eof;

void
do_output(void) {
    char buf[512];
    ssize_t n;
    n = read(ptyfd, buf, sizeof buf);
    if(n > 0) {
        eof = 0;
        write(1, &buf, n);
    } else if(n < 0) {
        if(errno == EIO)
            /* Can happen on normal subprocess exit */
            exit(0);
        write(2, "\r\n", 2);
        perror("read pty");
        write(2, "\r\n", 2);
        exit(1);
    } else {
        exit(0);
    }
}

char *shellpath = "/bin/sh";
char *shellargv[] = { "sh", 0 };

void
do_cleanup(void) {
    tcsetattr(0, 0, &tio);
}

void
sigexit(int sig) {
    do_cleanup();
    signal(sig, SIG_DFL);
    raise(sig);
}

int main(int argc, char **argv) {
    pid_t pid;
    if(tcgetattr(0, &tio) < 0) {
        perror("gtty");
        exit(1);
    }
    ioctl(0, TIOCGWINSZ, &ws);
    char *pprog = argv[1] ? argv[1] : shellpath;
    char **pargs = argv[1] ? argv+1 : shellargv;
    ptyfd = ptyproc(pprog, pargs);
    struct termios tio2 = tio;
    cfmakeraw(&tio2);

    /* Don't expect to receive any signals normally since the outer terminal is
     * in raw mode, but at least make an effort to clean up if killed. */
    signal(SIGABRT, sigexit);
    signal(SIGTERM, sigexit);
    signal(SIGQUIT, sigexit);
    atexit(do_cleanup);

    tcsetattr(0, 0, &tio2);

    for(;;) {
        fd_set in_fds;
        struct timeval tv;
        FD_ZERO(&in_fds);
        FD_SET(0, &in_fds);
        FD_SET(ptyfd, &in_fds);
        tv.tv_sec = 1;
        tv.tv_usec = 0;
        int sr = select(ptyfd+1, &in_fds, 0, 0, &tv);
        if(sr > 0) {
            if(FD_ISSET(0, &in_fds)) {
                do_input();
            }
            if(FD_ISSET(ptyfd, &in_fds)) {
                do_output();
            }
        }
    }
}