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/* $OpenBSD: is_tar.c,v 1.9 2009/04/24 18:54:34 chl 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 "file.h"
#include "magic.h"
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include "tar.h"
#ifndef lint
FILE_RCSID("@(#)$Id: is_tar.c,v 1.9 2009/04/24 18:54:34 chl 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 */
static const char tartype[][32] = {
"tar archive",
"POSIX tar archive",
"POSIX tar archive (GNU)",
};
protected int
file_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.
*/
int tar = is_tar(buf, nbytes);
int mime = ms->flags & MAGIC_MIME;
if (tar < 1 || tar > 3)
return 0;
if (mime == MAGIC_MIME_ENCODING)
return 0;
if (file_printf(ms, mime ? "application/x-tar" :
tartype[tar - 1]) == -1)
return -1;
return 1;
}
/*
* 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.
*/
private int
is_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 int
from_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;
}
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