poweroff_guard/poweroff_guard.c

/*
 * poweroff_guard - Simple yet effective guardian to prevent accidentally
 * powering off the wrong system because let's face it, you're stupid.
 *
 * Copyright (c) 2022 anna <owo AT fef.moe>.
 * See the end of this file for license terms.
 */

#define _POSIX_C_SOURCE 200112L

#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>

#ifndef POWEROFF_PATH
#define POWEROFF_PATH "/sbin/poweroff"
#endif
#ifndef COUNTDOWN_SECS
#define COUNTDOWN_SECS 10
#endif

#define red(s) "\x1b[1;91m" s "\x1b[0m" /* bright red */
#define cyn(s) "\x1b[1;96m" s "\x1b[0m" /* bright cyan */
#define wht(s) "\x1b[1;97m" s "\x1b[0m" /* bright white */

enum confirm_match {
	CONFIRM_MATCH_UPPERCASE,	/* exact match ("YES") */
	CONFIRM_MATCH_LOWERCASE,	/* case-insensitive match */
	CONFIRM_MATCH_NONE,		/* no match */
};

/* read and evaluate confirmation answer from stdin */
static enum confirm_match get_confirmation(void);
/* count down from COUNTDOWN_SECS and do the actual poweroff afterwards */
static void poweroff_with_countdown(void);
/* do the actual poweroff, without countdown */
static void do_poweroff(void);
/* call perror(message) and then exit(status) */
static void perror_and_exit(int status, const char *message);

static char hostname[HOST_NAME_MAX];

int main(void)
{
	/* behave like regular poweroff if we're not running in a tty */
	if (!isatty(STDOUT_FILENO))
		do_poweroff();

	int err = gethostname(hostname, sizeof(hostname));
	if (err) {
		perror("Could not determine hostname");
		strncpy(hostname, "this host", sizeof(hostname));
	}

	puts(red("\n########  ATTENTION, DIPSHIT  ########\n"));
	printf("You are about to shut down " cyn("%s") "!\n", hostname);
	puts("Are you really sure about this?");
	printf("Type " wht("yes") " in UPPERCASE and press enter to confirm: ");
	fflush(stdout);

	int try = 0;
again:
	switch (get_confirmation()) {
	case CONFIRM_MATCH_UPPERCASE:
		poweroff_with_countdown();
		break;
	case CONFIRM_MATCH_LOWERCASE:
		if (try++ == 0) {
			printf("I said " wht("UPPERCASE") " you idiot, try again: ");
			fflush(stdout);
			goto again; /* it's very important to piss off Dijkstra */
		} else {
			puts("Go fuck yourself");
			return 0;
		}
	case CONFIRM_MATCH_NONE:
		puts("That's what I thought.");
		return 0;
	}
}

static char buf[5];

static enum confirm_match get_confirmation(void)
{
	char *input = fgets(buf, sizeof(buf), stdin);
	if (!input) {
		if (feof(stdin)) {
			/* user probably pressed CTRL+D, print
			 * a line break to make it look nicer */
			printf("\n");
			return CONFIRM_MATCH_NONE;
		} else {
			perror_and_exit(1, "Reading stdin failed");
		}
	}

	/* if, for some reason, the input came from a pipe rather than typing
	 * on the keyboard (cat, echo, etc), the newline might be missing */
	char *newline = strchr(input, '\n');
	if (newline)
		*newline = '\0';
	else
		printf("\n");

	if (!strcmp(input, "YES"))
		return CONFIRM_MATCH_UPPERCASE;
	if (!strcasecmp(input, "yes"))
		return CONFIRM_MATCH_LOWERCASE;
	return CONFIRM_MATCH_NONE;
}

static void poweroff_with_countdown(void)
{
#if COUNTDOWN_SECS > 0
	printf("Alright, shutting down in ");
	for (int i = COUNTDOWN_SECS; i > 0; i--) {
		printf(wht("%d") "\n", i);
		fflush(stdout);
		sleep(1);
	}
#else
	puts("Alright, shutting down " wht("NOW"));
#endif

	do_poweroff();
}

static void do_poweroff(void)
{
	execl(POWEROFF_PATH, POWEROFF_PATH, NULL);
	perror_and_exit(2, "exec() failed");
}

static void perror_and_exit(int status, const char *message)
{
	if (!message)
		message = "poweroff_guard";
	perror(message);
	exit(status);
}

/*
 * LICENSE TERMS
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */