is_tar.c 4.3 KB

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  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. #include "file.h"
  40. #include "magic.h"
  41. #include <string.h>
  42. #include <ctype.h>
  43. #include <sys/types.h>
  44. #include "tar.h"
  45. #ifndef lint
  46. FILE_RCSID("@(#)$Id: is_tar.c,v 1.25 2004/09/11 19:15:57 christos Exp $")
  47. #endif
  48. #define isodigit(c) ( ((c) >= '0') && ((c) <= '7') )
  49. private int is_tar(const unsigned char *, size_t);
  50. private int from_oct(int, const char *); /* Decode octal number */
  51. protected int
  52. file_is_tar(struct magic_set *ms, const unsigned char *buf, size_t nbytes)
  53. {
  54. /*
  55. * Do the tar test first, because if the first file in the tar
  56. * archive starts with a dot, we can confuse it with an nroff file.
  57. */
  58. switch (is_tar(buf, nbytes)) {
  59. case 1:
  60. if (file_printf(ms, (ms->flags & MAGIC_MIME) ?
  61. "application/x-tar" : "tar archive") == -1)
  62. return -1;
  63. return 1;
  64. case 2:
  65. if (file_printf(ms, (ms->flags & MAGIC_MIME) ?
  66. "application/x-tar, POSIX" : "POSIX tar archive") == -1)
  67. return -1;
  68. return 1;
  69. default:
  70. return 0;
  71. }
  72. }
  73. /*
  74. * Return
  75. * 0 if the checksum is bad (i.e., probably not a tar archive),
  76. * 1 for old UNIX tar file,
  77. * 2 for Unix Std (POSIX) tar file.
  78. */
  79. private int
  80. is_tar(const unsigned char *buf, size_t nbytes)
  81. {
  82. const union record *header = (const union record *)(const void *)buf;
  83. int i;
  84. int sum, recsum;
  85. const char *p;
  86. if (nbytes < sizeof(union record))
  87. return 0;
  88. recsum = from_oct(8, header->header.chksum);
  89. sum = 0;
  90. p = header->charptr;
  91. for (i = sizeof(union record); --i >= 0;) {
  92. /*
  93. * We cannot use unsigned char here because of old compilers,
  94. * e.g. V7.
  95. */
  96. sum += 0xFF & *p++;
  97. }
  98. /* Adjust checksum to count the "chksum" field as blanks. */
  99. for (i = sizeof(header->header.chksum); --i >= 0;)
  100. sum -= 0xFF & header->header.chksum[i];
  101. sum += ' '* sizeof header->header.chksum;
  102. if (sum != recsum)
  103. return 0; /* Not a tar archive */
  104. if (0==strcmp(header->header.magic, TMAGIC))
  105. return 2; /* Unix Standard tar archive */
  106. return 1; /* Old fashioned tar archive */
  107. }
  108. /*
  109. * Quick and dirty octal conversion.
  110. *
  111. * Result is -1 if the field is invalid (all blank, or nonoctal).
  112. */
  113. private int
  114. from_oct(int digs, const char *where)
  115. {
  116. int value;
  117. while (isspace((unsigned char)*where)) { /* Skip spaces */
  118. where++;
  119. if (--digs <= 0)
  120. return -1; /* All blank field */
  121. }
  122. value = 0;
  123. while (digs > 0 && isodigit(*where)) { /* Scan til nonoctal */
  124. value = (value << 3) | (*where++ - '0');
  125. --digs;
  126. }
  127. if (digs > 0 && *where && !isspace((unsigned char)*where))
  128. return -1; /* Ended on non-space/nul */
  129. return value;
  130. }