contrib/file-4/src/is_tar.c

   1 /*
   2  * Copyright (c) Ian F. Darwin 1986-1995.
   3  * Software written by Ian F. Darwin and others;
   4  * maintained 1995-present by Christos Zoulas and others.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice immediately at the beginning of the file, without modification,
  11  *    this list of conditions, and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
  20  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  */
  28 /*
  29  * is_tar() -- figure out whether file is a tar archive.
  30  *
  31  * Stolen (by the author!) from the public domain tar program:
  32  * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
  33  *
  34  * @(#)list.c 1.18 9/23/86 Public Domain - gnu
  35  *
  36  * Comments changed and some code/comments reformatted
  37  * for file command by Ian Darwin.
  38  */
  39
  40 #include "file.h"
  41 #include "magic.h"
  42 #include <string.h>
  43 #include <ctype.h>
  44 #include <sys/types.h>
  45 #include "tar.h"
  46
  47 #ifndef lint
  48 FILE_RCSID("@(#)$Id: is_tar.c,v 1.25 2004/09/11 19:15:57 christos Exp $")
  49 #endif
  50
  51 #define isodigit(c)     ( ((c) >= '0') && ((c) <= '7') )
  52
  53 private int is_tar(const unsigned char *, size_t);
  54 private int from_oct(int, const char *);        /* Decode octal number */
  55
  56 protected int
  57 file_is_tar(struct magic_set *ms, const unsigned char *buf, size_t nbytes)
  58 {
  59         /*
  60          * Do the tar test first, because if the first file in the tar
  61          * archive starts with a dot, we can confuse it with an nroff file.
  62          */
  63         switch (is_tar(buf, nbytes)) {
  64         case 1:
  65                 if (file_printf(ms, (ms->flags & MAGIC_MIME) ?
  66                     "application/x-tar" : "tar archive") == -1)
  67                         return -1;
  68                 return 1;
  69         case 2:
  70                 if (file_printf(ms, (ms->flags & MAGIC_MIME) ?
  71                     "application/x-tar, POSIX" : "POSIX tar archive") == -1)
  72                         return -1;
  73                 return 1;
  74         default:
  75                 return 0;
  76         }
  77 }
  78
  79 /*
  80  * Return
  81  *      0 if the checksum is bad (i.e., probably not a tar archive),
  82  *      1 for old UNIX tar file,
  83  *      2 for Unix Std (POSIX) tar file.
  84  */
  85 private int
  86 is_tar(const unsigned char *buf, size_t nbytes)
  87 {
  88         const union record *header = (const union record *)(const void *)buf;
  89         int     i;
  90         int     sum, recsum;
  91         const char      *p;
  92
  93         if (nbytes < sizeof(union record))
  94                 return 0;
  95
  96         recsum = from_oct(8,  header->header.chksum);
  97
  98         sum = 0;
  99         p = header->charptr;
 100         for (i = sizeof(union record); --i >= 0;) {
 101                 /*
 102                  * We cannot use unsigned char here because of old compilers,
 103                  * e.g. V7.
 104                  */
 105                 sum += 0xFF & *p++;
 106         }
 107
 108         /* Adjust checksum to count the "chksum" field as blanks. */
 109         for (i = sizeof(header->header.chksum); --i >= 0;)
 110                 sum -= 0xFF & header->header.chksum[i];
 111         sum += ' '* sizeof header->header.chksum;
 112
 113         if (sum != recsum)
 114                 return 0;       /* Not a tar archive */
 115
 116         if (0==strcmp(header->header.magic, TMAGIC))
 117                 return 2;               /* Unix Standard tar archive */
 118
 119         return 1;                       /* Old fashioned tar archive */
 120 }
 121
 122
 123 /*
 124  * Quick and dirty octal conversion.
 125  *
 126  * Result is -1 if the field is invalid (all blank, or nonoctal).
 127  */
 128 private int
 129 from_oct(int digs, const char *where)
 130 {
 131         int     value;
 132
 133         while (isspace((unsigned char)*where)) {        /* Skip spaces */
 134                 where++;
 135                 if (--digs <= 0)
 136                         return -1;              /* All blank field */
 137         }
 138         value = 0;
 139         while (digs > 0 && isodigit(*where)) {  /* Scan til nonoctal */
 140                 value = (value << 3) | (*where++ - '0');
 141                 --digs;
 142         }
 143
 144         if (digs > 0 && *where && !isspace((unsigned char)*where))
 145                 return -1;                      /* Ended on non-space/nul */
 146
 147         return value;
 148 }