pty_spawn.c

#define _XOPEN_SOURCE 600
#define _BSD_SOURCE

#include <unistd.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/select.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <assert.h>
#include <string.h>

int main(int argc, char** argv) {
        int pmd, rc, sfd;
        char *name;
        pid_t child;

        /* open an unused pseudoterminal master device */
        pmd = posix_openpt(O_RDWR);
        assert(pmd != -1);

        /* grant access to the slave pseudoterminal */
        rc = grantpt(pmd);
        assert(rc != -1);

        /* unlock the slave pseudoterminal device corresponding
           to the master pseudoterminal referred */
        rc = unlockpt(pmd);
        assert(rc != -1);

        /* get the slave pseudoterminal device name */
        name = ptsname(pmd);
        assert(name != NULL);
        printf("Slave side name %s\n", name);

        /* open the slave side */
        sfd = open(name, O_RDWR);
        assert(sfd != -1);

        child = fork();
        assert(child != -1);

        if (child == 0) {
                /* child process */
                struct termios os, ns;

                /* close the master side */
                close(pmd);

                /* save old settings */
                rc = tcgetattr(sfd, &os);

                /* set raw mode (input available character by character,
                   echoing disabled, all special processing disabled */
                ns = os;
                cfmakeraw(&ns);
                /* apply the change now */
                tcsetattr(sfd, TCSANOW, &ns);

                /* sanity check */
                rc = isatty(sfd);
                assert(rc == 1);

                /* close stdin, stdout and stderr of the current terminal
                   they will come from the slave side */
                close(0);
                close(1);
                close(2);

                /* pseudoterminal becomes stdin, stdout, stderr */
                dup(sfd);
                dup(sfd);
                dup(sfd);

                /* original file descriptor can be closed */
                close(sfd);

                /* make this process the new session leader */
                setsid();

                /* set the slave side to be the controlling terminal */
                rc = ioctl(0, TIOCSCTTY, 1);
                assert(rc != -1);

                { /* execute the child */
                        char** cargv;
                        int i;
                        cargv = (char**)malloc(argc * sizeof(char*));
                        assert(cargv != NULL);
                        for (i = 1; i < argc; ++i) {
                                cargv[i - 1] = strdup(argv[i]);
                        }
                        cargv[i - 1] = NULL;
                        rc = execvp(cargv[0], cargv);
                }
        }
        else {
                /* master process */
                fd_set fi;
                char buf[128];

                /* close the slave side */
                close(sfd);

                while (1) {
                        /* wait on stdin and the master side */
                        FD_ZERO(&fi);
                        FD_SET(0, &fi);
                        FD_SET(pmd, &fi);
                        rc = select(pmd + 1, &fi, NULL, NULL, NULL);
                        assert(rc != -1);
                        if(FD_ISSET(0, &fi)) {
                                /* data on stdin */
                                rc  = read(0, buf, sizeof(buf));
                                if (rc > 0) {
                                        /* write it on the master side */
                                        write(pmd, buf, rc);
                                }
                                else {
                                        if (rc < 0) {
                                                fprintf(stderr, "Error reading on stdin\n");
                                                assert(0);
                                        }
                                }
                        }
                        if(FD_ISSET(pmd, &fi)) {
                                /* data on the master side */
                                rc = read(pmd, buf, sizeof(buf));
                                if (rc > 0) {
                                        /* write to stdout */
                                        write(1, buf, rc);
                                }
                                else {
                                        if (rc < 0) {
                                                if (errno == EIO) {
                                                        /* child died */
                                                        break;
                                                }
                                                fprintf(stderr, "Error reading on master\n");
                                        }
                                }
                        }
                }
        }
        fprintf(stderr, "Done.\n");
        return rc;
}