file/is_tar.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
   7  * Reserved.  This file contains Original Code and/or Modifications of
   8  * Original Code as defined in and that are subject to the Apple Public
   9  * Source License Version 1.1 (the "License").  You may not use this file
  10  * except in compliance with the License.  Please obtain a copy of the
  11  * License at http://www.apple.com/publicsource and read it before using
  12  * this file.
  13  *
  14  * The Original Code and all software distributed under the License are
  15  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  16  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  17  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE OR NON- INFRINGEMENT.  Please see the
  19  * License for the specific language governing rights and limitations
  20  * under the License.
  21  *
  22  * @APPLE_LICENSE_HEADER_END@
  23  */
  24 /*      $OpenBSD: is_tar.c,v 1.3 1997/02/09 23:58:27 millert Exp $      */
  25
  26 /*
  27  * is_tar() -- figure out whether file is a tar archive.
  28  *
  29  * Stolen (by the author!) from the public domain tar program:
  30  * Pubic Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
  31  *
  32  * @(#)list.c 1.18 9/23/86 Public Domain - gnu
  33  *
  34  * Comments changed and some code/comments reformatted
  35  * for file command by Ian Darwin.
  36  */
  37
  38 #include <string.h>
  39 #include <ctype.h>
  40 #include <sys/types.h>
  41 #include "tar.h"
  42
  43 #define isodigit(c)     ( ((c) >= '0') && ((c) <= '7') )
  44
  45 #if     defined(__STDC__) || defined(__cplusplus)
  46 static int from_oct(int, char*);        /* Decode octal number */
  47 #else
  48 static int from_oct();
  49 #endif
  50
  51 /*
  52  * Return
  53  *      0 if the checksum is bad (i.e., probably not a tar archive),
  54  *      1 for old UNIX tar file,
  55  *      2 for Unix Std (POSIX) tar file.
  56  */
  57 int
  58 is_tar(buf, nbytes)
  59 unsigned char *buf;
  60 int nbytes;
  61 {
  62         register union record *header = (union record *)buf;
  63         register int    i;
  64         register int    sum, recsum;
  65         register char   *p;
  66
  67         if (nbytes < sizeof(union record))
  68                 return 0;
  69
  70         recsum = from_oct(8,  header->header.chksum);
  71
  72         sum = 0;
  73         p = header->charptr;
  74         for (i = sizeof(union record); --i >= 0;) {
  75                 /*
  76                  * We can't use unsigned char here because of old compilers,
  77                  * e.g. V7.
  78                  */
  79                 sum += 0xFF & *p++;
  80         }
  81
  82         /* Adjust checksum to count the "chksum" field as blanks. */
  83         for (i = sizeof(header->header.chksum); --i >= 0;)
  84                 sum -= 0xFF & header->header.chksum[i];
  85         sum += ' '* sizeof header->header.chksum;
  86
  87         if (sum != recsum)
  88                 return 0;       /* Not a tar archive */
  89
  90         if (0==strcmp(header->header.magic, TMAGIC))
  91                 return 2;               /* Unix Standard tar archive */
  92
  93         return 1;                       /* Old fashioned tar archive */
  94 }
  95
  96
  97 /*
  98  * Quick and dirty octal conversion.
  99  *
 100  * Result is -1 if the field is invalid (all blank, or nonoctal).
 101  */
 102 static int
 103 from_oct(digs, where)
 104         register int    digs;
 105         register char   *where;
 106 {
 107         register int    value;
 108
 109         while (isspace(*where)) {               /* Skip spaces */
 110                 where++;
 111                 if (--digs <= 0)
 112                         return -1;              /* All blank field */
 113         }
 114         value = 0;
 115         while (digs > 0 && isodigit(*where)) {  /* Scan til nonoctal */
 116                 value = (value << 3) | (*where++ - '0');
 117                 --digs;
 118         }
 119
 120         if (digs > 0 && *where && !isspace(*where))
 121                 return -1;                      /* Ended on non-space/nul */
 122
 123         return value;
 124 }