Annotation of src/usr.bin/file/is_tar.c, Revision 1.6
1.6 ! deraadt 1: /* $OpenBSD: is_tar.c,v 1.5 2002/02/19 19:39:38 millert Exp $ */
1.3 millert 2:
1.1 deraadt 3: /*
4: * is_tar() -- figure out whether file is a tar archive.
5: *
6: * Stolen (by the author!) from the public domain tar program:
7: * Pubic Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
8: *
9: * @(#)list.c 1.18 9/23/86 Public Domain - gnu
10: *
11: * Comments changed and some code/comments reformatted
12: * for file command by Ian Darwin.
13: */
14:
15: #include <string.h>
16: #include <ctype.h>
17: #include <sys/types.h>
18: #include "tar.h"
1.6 ! deraadt 19: #include "file.h"
1.1 deraadt 20:
21: #define isodigit(c) ( ((c) >= '0') && ((c) <= '7') )
22:
1.3 millert 23: static int from_oct(int, char*); /* Decode octal number */
1.1 deraadt 24:
25: /*
26: * Return
27: * 0 if the checksum is bad (i.e., probably not a tar archive),
28: * 1 for old UNIX tar file,
29: * 2 for Unix Std (POSIX) tar file.
30: */
31: int
32: is_tar(buf, nbytes)
33: unsigned char *buf;
34: int nbytes;
35: {
1.4 mpech 36: union record *header = (union record *)buf;
37: int i;
38: int sum, recsum;
39: char *p;
1.1 deraadt 40:
41: if (nbytes < sizeof(union record))
42: return 0;
43:
44: recsum = from_oct(8, header->header.chksum);
45:
46: sum = 0;
47: p = header->charptr;
48: for (i = sizeof(union record); --i >= 0;) {
49: /*
50: * We can't use unsigned char here because of old compilers,
51: * e.g. V7.
52: */
53: sum += 0xFF & *p++;
54: }
55:
56: /* Adjust checksum to count the "chksum" field as blanks. */
57: for (i = sizeof(header->header.chksum); --i >= 0;)
58: sum -= 0xFF & header->header.chksum[i];
59: sum += ' '* sizeof header->header.chksum;
60:
61: if (sum != recsum)
62: return 0; /* Not a tar archive */
63:
64: if (0==strcmp(header->header.magic, TMAGIC))
65: return 2; /* Unix Standard tar archive */
66:
67: return 1; /* Old fashioned tar archive */
68: }
69:
70:
71: /*
72: * Quick and dirty octal conversion.
73: *
74: * Result is -1 if the field is invalid (all blank, or nonoctal).
75: */
1.3 millert 76: static int
1.1 deraadt 77: from_oct(digs, where)
1.4 mpech 78: int digs;
79: char *where;
1.1 deraadt 80: {
1.4 mpech 81: int value;
1.1 deraadt 82:
83: while (isspace(*where)) { /* Skip spaces */
84: where++;
85: if (--digs <= 0)
86: return -1; /* All blank field */
87: }
88: value = 0;
89: while (digs > 0 && isodigit(*where)) { /* Scan til nonoctal */
90: value = (value << 3) | (*where++ - '0');
91: --digs;
92: }
93:
94: if (digs > 0 && *where && !isspace(*where))
95: return -1; /* Ended on non-space/nul */
96:
97: return value;
98: }