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("@(#)$File: is_tar.c,v 1.29 2007/10/17 19:33:31 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 static const char *tartype[] = {
  57         "tar archive",
  58         "POSIX tar archive",
  59         "POSIX tar archive (GNU)",
  60 };
  61
  62 protected int
  63 file_is_tar(struct magic_set *ms, const unsigned char *buf, size_t nbytes)
  64 {
  65         /*
  66          * Do the tar test first, because if the first file in the tar
  67          * archive starts with a dot, we can confuse it with an nroff file.
  68          */
  69         int tar = is_tar(buf, nbytes);
  70         int mime = ms->flags & MAGIC_MIME;
  71
  72         if (tar < 1 || tar > 3)
  73                 return 0;
  74
  75         if (mime == MAGIC_MIME_ENCODING)
  76                 return 0;
  77
  78         if (file_printf(ms, mime ? "application/x-tar" :
  79             tartype[tar - 1]) == -1)
  80                 return -1;
  81         return 1;
  82 }
  83
  84 /*
  85  * Return
  86  *      0 if the checksum is bad (i.e., probably not a tar archive),
  87  *      1 for old UNIX tar file,
  88  *      2 for Unix Std (POSIX) tar file.
  89  */
  90 private int
  91 is_tar(const unsigned char *buf, size_t nbytes)
  92 {
  93         const union record *header = (const union record *)(const void *)buf;
  94         int     i;
  95         int     sum, recsum;
  96         const char      *p;
  97
  98         if (nbytes < sizeof(union record))
  99                 return 0;
 100
 101         recsum = from_oct(8,  header->header.chksum);
 102
 103         sum = 0;
 104         p = header->charptr;
 105         for (i = sizeof(union record); --i >= 0;) {
 106                 /*
 107                  * We cannot use unsigned char here because of old compilers,
 108                  * e.g. V7.
 109                  */
 110                 sum += 0xFF & *p++;
 111         }
 112
 113         /* Adjust checksum to count the "chksum" field as blanks. */
 114         for (i = sizeof(header->header.chksum); --i >= 0;)
 115                 sum -= 0xFF & header->header.chksum[i];
 116         sum += ' '* sizeof header->header.chksum;
 117
 118         if (sum != recsum)
 119                 return 0;       /* Not a tar archive */
 120
 121         if (strcmp(header->header.magic, GNUTMAGIC) == 0)
 122                 return 3;               /* GNU Unix Standard tar archive */
 123         if (strcmp(header->header.magic, TMAGIC) == 0)
 124                 return 2;               /* Unix Standard tar archive */
 125
 126         return 1;                       /* Old fashioned tar archive */
 127 }
 128
 129
 130 /*
 131  * Quick and dirty octal conversion.
 132  *
 133  * Result is -1 if the field is invalid (all blank, or nonoctal).
 134  */
 135 private int
 136 from_oct(int digs, const char *where)
 137 {
 138         int     value;
 139
 140         while (isspace((unsigned char)*where)) {        /* Skip spaces */
 141                 where++;
 142                 if (--digs <= 0)
 143                         return -1;              /* All blank field */
 144         }
 145         value = 0;
 146         while (digs > 0 && isodigit(*where)) {  /* Scan til nonoctal */
 147                 value = (value << 3) | (*where++ - '0');
 148                 --digs;
 149         }
 150
 151         if (digs > 0 && *where && !isspace((unsigned char)*where))
 152                 return -1;                      /* Ended on non-space/nul */
 153
 154         return value;
 155 }