commands/truncate/truncate.c
/*
 * Copyright (c) 2000 Sheldon Hearn <sheldonh@FreeBSD.org>.
 * All rights reserved.
 *
 * 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 AUTHOR 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 AUTHOR 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.
 *
 */

#include <sys/stat.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static off_t	parselength(char *, off_t *);
static void	usage(void);

static int	no_create;
static int	do_relative;
static int	do_refer;
static int	got_size;

int
main(int argc, char **argv)
{
	struct stat	sb;
	mode_t	omode;
	off_t	oflow, rsize, sz, tsize;
	int	ch, error, fd, oflags;
	char   *fname, *rname;

	rsize = tsize = 0;
	error = 0;
	rname = NULL;
	while ((ch = getopt(argc, argv, "cr:s:")) != -1)
		switch (ch) {
		case 'c':
			no_create = 1;
			break;
		case 'r':
			do_refer = 1;
			rname = optarg;
			break;
		case 's':
			if (parselength(optarg, &sz) == -1) {
				fprintf(stderr,
				    "invalid size argument `%s'", optarg);
				   exit(EXIT_FAILURE);
				  }
			if (*optarg == '+' || *optarg == '-')
				do_relative = 1;
			got_size = 1;
			break;
		default:
			usage();
			/* NOTREACHED */
		}

	argv += optind;
	argc -= optind;

	/*
	 * Exactly one of do_refer or got_size must be specified.  Since
	 * do_relative implies got_size, do_relative and do_refer are
	 * also mutually exclusive.  See usage() for allowed invocations.
	 */
	if (do_refer + got_size != 1 || argc < 1)
		usage();
	if (do_refer) {
		if (stat(rname, &sb) == -1) {
			fprintf(stderr, "%s", rname);
			exit(EXIT_FAILURE);
		}
		tsize = sb.st_size;
	} else if (do_relative)
		rsize = sz;
	else
		tsize = sz;

	if (no_create)
		oflags = O_WRONLY;
	else
		oflags = O_WRONLY | O_CREAT;
	omode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;

	while ((fname = *argv++) != NULL) {
		if ((fd = open(fname, oflags, omode)) == -1) {
			if (errno != ENOENT) {
				perror(fname);
				error++;
			}
			continue;
		}
		if (do_relative) {
			if (fstat(fd, &sb) == -1) {
				perror(fname);
				error++;
				continue;
			}
			oflow = sb.st_size + rsize;
			if (oflow < (sb.st_size + rsize)) {
				errno = EFBIG;
				perror(fname);
				error++;
				continue;
			}
			tsize = oflow;
		}
		if (tsize < 0)
			tsize = 0;

		if (ftruncate(fd, tsize) == -1) {
			perror(fname);
			error++;
			continue;
		}

		close(fd);
	}

	return error ? EXIT_FAILURE : EXIT_SUCCESS;
}

/*
 * Return the numeric value of a string given in the form [+-][0-9]+[GMK]
 * or -1 on format error or overflow.
 */
static off_t
parselength(char *ls, off_t *sz)
{
	off_t	length, oflow;
	int	lsign;

	length = 0;
	lsign = 1;

	switch (*ls) {
	case '-':
		lsign = -1;
	case '+':
		ls++;
	}

#define	ASSIGN_CHK_OFLOW(x, y)	if (x < y) return -1; y = x
	/*
	 * Calculate the value of the decimal digit string, failing
	 * on overflow.
	 */
	while (isdigit(*ls)) {
		oflow = length * 10 + *ls++ - '0';
		ASSIGN_CHK_OFLOW(oflow, length);
	}

	switch (*ls) {
	case 'G':
	case 'g':
		oflow = length * 1024;
		ASSIGN_CHK_OFLOW(oflow, length);
	case 'M':
	case 'm':
		oflow = length * 1024;
		ASSIGN_CHK_OFLOW(oflow, length);
	case 'K':
	case 'k':
		if (ls[1] != '\0')
			return -1;
		oflow = length * 1024;
		ASSIGN_CHK_OFLOW(oflow, length);
	case '\0':
		break;
	default:
		return -1;
	}

	*sz = length * lsign;
	return 0;
}

static void
usage(void)
{
	fprintf(stderr, "%s\n%s\n",
	    "usage: truncate [-c] -s [+|-]size[K|k|M|m|G|g] file ...",
	    "       truncate [-c] -r rfile file ...");
	exit(EXIT_FAILURE);
}
