/* * 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 "file.h"#include "magic.h"#include <string.h>#include <ctype.h>#include <sys/types.h>#include "tar.h"#ifndef lintFILE_RCSID("@(#)$File: is_tar.c,v 1.27 2007/01/12 17:38:28 christos Exp $")#endif#define	isodigit(c)	( ((c) >= '0') && ((c) <= '7') )private int is_tar(const unsigned char *, size_t);private int from_oct(int, const char *);	/* Decode octal number */protected intfile_is_tar(struct magic_set *ms, const unsigned char *buf, size_t nbytes){	/*	 * Do the tar test first, because if the first file in the tar	 * archive starts with a dot, we can confuse it with an nroff file.	 */	switch (is_tar(buf, nbytes)) {	case 1:	        if (file_printf(ms, (ms->flags & MAGIC_MIME) ?		    "application/x-tar" : "tar archive") == -1)			return -1;		return 1;	case 2:		if (file_printf(ms, (ms->flags & MAGIC_MIME) ?		    "application/x-tar, POSIX" : "POSIX tar archive") == -1)			return -1;		return 1;	case 3:		if (file_printf(ms, (ms->flags & MAGIC_MIME) ?		    "application/x-tar, POSIX (GNU)" :		    "POSIX tar archive (GNU)") == -1)			return -1;		return 1;	default:		return 0;	}}/* * 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. */private intis_tar(const unsigned char *buf, size_t nbytes){	const union record *header = (const union record *)(const void *)buf;	int	i;	int	sum, recsum;	const char	*p;	if (nbytes < sizeof(union record))		return 0;	recsum = from_oct(8,  header->header.chksum);	sum = 0;	p = header->charptr;	for (i = sizeof(union record); --i >= 0;) {		/*		 * We cannot use unsigned char here because of old compilers,		 * e.g. V7.		 */		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 */}/* * Quick and dirty octal conversion. * * Result is -1 if the field is invalid (all blank, or nonoctal). */private intfrom_oct(int digs, const char *where){	int	value;	while (isspace((unsigned char)*where)) {	/* Skip spaces */		where++;		if (--digs <= 0)			return -1;		/* All blank field */	}	value = 0;	while (digs > 0 && isodigit(*where)) {	/* Scan til nonoctal */		value = (value << 3) | (*where++ - '0');		--digs;	}	if (digs > 0 && *where && !isspace((unsigned char)*where))		return -1;			/* Ended on non-space/nul */	return value;}