diff options
Diffstat (limited to 'contrib/file/is_tar.c')
-rw-r--r-- | contrib/file/is_tar.c | 101 |
1 files changed, 101 insertions, 0 deletions
diff --git a/contrib/file/is_tar.c b/contrib/file/is_tar.c new file mode 100644 index 0000000..6c5b61c --- /dev/null +++ b/contrib/file/is_tar.c @@ -0,0 +1,101 @@ +/* + * is_tar() -- figure out whether file is a tar archive. + * + * Stolen (by the author!) from the public domain tar program: + * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu). + * + * @(#)list.c 1.18 9/23/86 Public Domain - gnu + * $Id: is_tar.c,v 1.13 2000/08/05 17:36:48 christos Exp $ + * + * Comments changed and some code/comments reformatted + * for file command by Ian Darwin. + */ + +#include <string.h> +#include <ctype.h> +#include <sys/types.h> +#include "tar.h" +#include "file.h" + +#ifndef lint +FILE_RCSID("@(#)$Id: is_tar.c,v 1.13 2000/08/05 17:36:48 christos Exp $") +#endif + +#define isodigit(c) ( ((c) >= '0') && ((c) <= '7') ) + +static int from_oct __P((int, char *)); /* Decode octal number */ + +/* + * Return + * 0 if the checksum is bad (i.e., probably not a tar archive), + * 1 for old UNIX tar file, + * 2 for Unix Std (POSIX) tar file. + */ +int +is_tar(buf, nbytes) + unsigned char *buf; + int nbytes; +{ + union record *header = (union record *)buf; + int i; + int sum, recsum; + char *p; + + if (nbytes < sizeof(union record)) + return 0; + + recsum = from_oct(8, header->header.chksum); + + sum = 0; + p = header->charptr; + for (i = sizeof(union record); --i >= 0;) { + /* + * We can't use unsigned char here because of old compilers, + * e.g. V7. + */ + sum += 0xFF & *p++; + } + + /* Adjust checksum to count the "chksum" field as blanks. */ + for (i = sizeof(header->header.chksum); --i >= 0;) + sum -= 0xFF & header->header.chksum[i]; + sum += ' '* sizeof header->header.chksum; + + if (sum != recsum) + return 0; /* Not a tar archive */ + + if (0==strcmp(header->header.magic, TMAGIC)) + return 2; /* Unix Standard tar archive */ + + return 1; /* Old fashioned tar archive */ +} + + +/* + * Quick and dirty octal conversion. + * + * Result is -1 if the field is invalid (all blank, or nonoctal). + */ +static int +from_oct(digs, where) + int digs; + char *where; +{ + int value; + + while (isspace((unsigned char)*where)) { /* Skip spaces */ + where++; + if (--digs <= 0) + return -1; /* All blank field */ + } + value = 0; + while (digs > 0 && isodigit(*where)) { /* Scan til nonoctal */ + value = (value << 3) | (*where++ - '0'); + --digs; + } + + if (digs > 0 && *where && !isspace((unsigned char)*where)) + return -1; /* Ended on non-space/nul */ + + return value; +} |