tty/test_tty_functions.c

#include <termios.h>
#include <signal.h>
#include <ctype.h>
#include "tty_functions.h"              /* Declarations of ttySetCbreak()
                                           and ttySetRaw() */
#include "tlpi_hdr.h"

static struct termios userTermios;
                        /* Terminal settings as defined by user */

static void             /* General handler: restore tty settings and exit */
handler(int sig)
{
    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &userTermios) == -1)
        errExit("tcsetattr");
    _exit(EXIT_SUCCESS);
}

static void             /* Handler for SIGTSTP */
tstpHandler(int sig)
{
    struct termios ourTermios;          /* To save our tty settings */
    sigset_t tstpMask, prevMask;
    struct sigaction sa;
    int savedErrno;

    savedErrno = errno;                 /* We might change 'errno' here */

    /* Save current terminal settings, restore terminal to
       state at time of program startup */

    if (tcgetattr(STDIN_FILENO, &ourTermios) == -1)
        errExit("tcgetattr");
    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &userTermios) == -1)
        errExit("tcsetattr");

    /* Set the disposition of SIGTSTP to the default, raise the signal
       once more, and then unblock it so that we actually stop */

    if (signal(SIGTSTP, SIG_DFL) == SIG_ERR)
        errExit("signal");
    raise(SIGTSTP);

    sigemptyset(&tstpMask);
    sigaddset(&tstpMask, SIGTSTP);
    if (sigprocmask(SIG_UNBLOCK, &tstpMask, &prevMask) == -1)
        errExit("sigprocmask");

    /* Execution resumes here after SIGCONT */

    if (sigprocmask(SIG_SETMASK, &prevMask, NULL) == -1)
        errExit("sigprocmask");         /* Reblock SIGTSTP */

    sigemptyset(&sa.sa_mask);           /* Reestablish handler */
    sa.sa_flags = SA_RESTART;
    sa.sa_handler = tstpHandler;
    if (sigaction(SIGTSTP, &sa, NULL) == -1)
        errExit("sigaction");

    /* The user may have changed the terminal settings while we were
       stopped; save the settings so we can restore them later */

    if (tcgetattr(STDIN_FILENO, &userTermios) == -1)
        errExit("tcgetattr");

    /* Restore our terminal settings */

    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &ourTermios) == -1)
        errExit("tcsetattr");

    errno = savedErrno;
}

int
main(int argc, char *argv[])
{
    char ch;
    struct sigaction sa, prev;
    ssize_t n;

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;

    if (argc > 1) {                     /* Use cbreak mode */
        if (ttySetCbreak(STDIN_FILENO, &userTermios) == -1)
            errExit("ttySetCbreak");

        /* Terminal special characters can generate signals in cbreak
           mode. Catch them so that we can adjust the terminal mode.
           We establish handlers only if the signals are not being ignored. */

        sa.sa_handler = handler;

        if (sigaction(SIGQUIT, NULL, &prev) == -1)
            errExit("sigaction");
        if (prev.sa_handler != SIG_IGN)
            if (sigaction(SIGQUIT, &sa, NULL) == -1)
                errExit("sigaction");

        if (sigaction(SIGINT, NULL, &prev) == -1)
            errExit("sigaction");
        if (prev.sa_handler != SIG_IGN)
            if (sigaction(SIGINT, &sa, NULL) == -1)
                errExit("sigaction");

        sa.sa_handler = tstpHandler;

        if (sigaction(SIGTSTP, NULL, &prev) == -1)
            errExit("sigaction");
        if (prev.sa_handler != SIG_IGN)
            if (sigaction(SIGTSTP, &sa, NULL) == -1)
                errExit("sigaction");
    } else {                            /* Use raw mode */
        if (ttySetRaw(STDIN_FILENO, &userTermios) == -1)
            errExit("ttySetRaw");
    }

    sa.sa_handler = handler;
    if (sigaction(SIGTERM, &sa, NULL) == -1)
        errExit("sigaction");

    setbuf(stdout, NULL);               /* Disable stdout buffering */

    for (;;) {                          /* Read and echo stdin */
        n = read(STDIN_FILENO, &ch, 1);
        if (n == -1) {
            errMsg("read");
            break;
        }

        if (n == 0)                     /* Can occur after terminal disconnect */
            break;

        if (isalpha((unsigned char) ch))        /* Letters --> lowercase */
            putchar(tolower((unsigned char) ch));
        else if (ch == '\n' || ch == '\r')
            putchar(ch);
        else if (iscntrl((unsigned char) ch))
            printf("^%c", ch ^ 64);     /* Echo Control-A as ^A, etc. */
        else
            putchar('*');               /* All other chars as '*' */

        if (ch == 'q')                  /* Quit loop */
            break;
    }

    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &userTermios) == -1)
        errExit("tcsetattr");
    exit(EXIT_SUCCESS);
}