/*	$OpenBSD: is_tar.c,v 1.10 2009/10/27 23:59:37 deraadt Exp $ */
/*
 * Copyright (c) Ian F. Darwin 1986-1995.
 * Software written by Ian F. Darwin and others;
 * maintained 1995-present by Christos Zoulas and others.
 *
 * 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 immediately at the beginning of the file, without modification,
 *    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.
 */
/*
 * is_tar () -- figure out whether file is a tar archive.
 *
 * Stolen (by the author!) from the public domain tar program:
 * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
 *
 * @ (#)list.c 1.18 9/23/86 Public Domain - gnu
 *
 * Comments changed and some code/comments reformatted
 * for file command by Ian Darwin.
 */
#include <r_userconf.h>

#if !USE_LIB_MAGIC

#include <r_util.h>
#include "file.h"
#include "tar.h"

static const char tartype[][32] = {
	"tar archive",
	"POSIX tar archive",
	"POSIX tar archive (GNU)",
};

/*
 * Quick and dirty octal conversion.
 *
 * Result is -1 if the field is invalid (all blank, or nonoctal).
 */
#define isodigit(c) (((c) >= '0') && ((c) <= '7'))
static int from_oct(int digs, const char *where) {
	int value = 0;
	while (isspace ((ut8)*where)) { /* Skip spaces */
		where++;
		if (--digs <= 0) {
			return -1; /* All blank field */
		}
	}
	while (digs > 0 && isodigit (*where)) { /* Scan til nonoctal */
		value = (value << 3) | (*where++ - '0');
		--digs;
	}
	if (digs > 0 && *where && !isspace ((ut8)*where)) {
		return -1; /* Ended on non-space/nul */
	}
	return value;
}

/*
 * Return
 *	0 if the checksum is bad (i.e., probably not a tar archive),
 *	1 for old UNIX tar file,
 *	2 for Unix Std (POSIX) tar file,
 *	3 for GNU tar file.
 */
static int is_tar(const ut8 *buf, size_t nbytes) {
	const union record *const header = (const union record *) (const void *)buf;

	if (nbytes < sizeof (union record)) {
		return 0;
	}

	const int recsum = from_oct (8, header->header.chksum);

	int i, sum = 0;
	const char *p = header->charptr;
	for (i = sizeof (union record); --i >= 0;) {
		// Keep this int-compatible for old compilers.
		sum += 0xFF & *p++;
	}

	/* Adjust checksum to count the "chksum" field as blanks. */
	for (i = sizeof header->header.chksum; --i >= 0;) {
		sum -= 0xFF & header->header.chksum[i];
	}
	sum += ' ' * sizeof header->header.chksum;
	if (sum != recsum) {
		return 0; /* Not a tar archive */
	}
	if (strcmp (header->header.magic, GNUTMAGIC) == 0) {
		return 3; /* GNU Unix Standard tar archive */
	}
	if (strcmp (header->header.magic, TMAGIC) == 0) {
		return 2; /* Unix Standard tar archive */
	}
	return 1; /* Old fashioned tar archive */
}

int __magic_file_is_tar(RMagic *ms, const ut8 *buf, size_t nbytes) {
	// Check tar first so dotfiles are not mistaken for nroff.
	const int tar = is_tar (buf, nbytes);
	const int mime = ms->flags & R_MAGIC_MIME;

	if (tar < 1 || tar > 3) {
		return 0;
	}
	if (mime == R_MAGIC_MIME_ENCODING) {
		return 0;
	}
	if (__magic_file_printf (ms, mime? "application/x-tar": tartype[tar - 1]) == -1) {
		return -1;
	}
	return 1;
}
#endif
