pager.c

/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* util/ss/pager.c - create a "more" running out of a file descriptor */
/*
 * Copyright 1987, 1988 by MIT Student Information Processing Board
 *
 * For copyright information, see copyright.h.
 */

#include "ss_internal.h"
#include "copyright.h"
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/file.h>
#include <signal.h>

static char MORE[] = "more";
extern char *_ss_pager_name;

/*
 * this needs a *lot* of work....
 *
 * run in same process
 * handle SIGINT sensibly
 * allow finer control -- put-page-break-here
 */
void ss_page_stdin(void);

#ifndef NO_FORK
int ss_pager_create(void)
{
    int filedes[2];

    if (pipe(filedes) != 0)
        return(-1);

    switch((int) fork()) {
    case -1:
        return(-1);
    case 0:
        /*
         * Child; dup read half to 0, close all but 0, 1, and 2
         */
        if (dup2(filedes[0], 0) == -1)
            exit(1);
        ss_page_stdin();
    default:
        /*
         * Parent:  close "read" side of pipe, return
         * "write" side.
         */
        (void) close(filedes[0]);
        set_cloexec_fd(filedes[1]);
        return(filedes[1]);
    }
}
#else /* don't fork */
int ss_pager_create(void)
{
    int fd;
    fd = open("/dev/tty", O_WRONLY, 0);
    if (fd >= 0)
        set_cloexec_fd(fd);
    return fd;
}
#endif

void ss_page_stdin(void)
{
    int i;
#ifdef POSIX_SIGNALS
    struct sigaction sa;
    sigset_t mask;
#endif
    for (i = 3; i < 32; i++)
        (void) close(i);
#ifdef POSIX_SIGNALS
    sa.sa_handler = SIG_DFL;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(SIGINT, &sa, (struct sigaction *)0);
#else
    (void) signal(SIGINT, SIG_DFL);
#endif
    {
#ifdef POSIX_SIGNALS
        sigemptyset(&mask);
        sigaddset(&mask, SIGINT);
        sigprocmask(SIG_UNBLOCK, &mask, (sigset_t *)0);
#else
        int mask = sigblock(0);
        mask &= ~sigmask(SIGINT);
        sigsetmask(mask);
#endif
    }
    if (_ss_pager_name == (char *)NULL) {
        if ((_ss_pager_name = getenv("PAGER")) == (char *)NULL)
            _ss_pager_name = MORE;
    }
    (void) execlp(_ss_pager_name, _ss_pager_name, (char *) NULL);
    {
        /* minimal recovery if pager program isn't found */
        char buf[80];
        int n;
        while ((n = read(0, buf, 80)) > 0)
            write(1, buf, (unsigned) n);
    }
    exit(errno);
}