file_cmds-60.tar.gz

[apple/file_cmds.git] / file / is_tar.c

diff --git a/file/is_tar.c b/file/is_tar.c
new file mode 100644 (file)
index 0000000..5efe88c
--- /dev/null
+++ b/file/is_tar.c
@@ -0,0 +1,124 @@
+/*
+ * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
+ *
+ * @APPLE_LICENSE_HEADER_START@
+ * 
+ * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
+ * Reserved.  This file contains Original Code and/or Modifications of
+ * Original Code as defined in and that are subject to the Apple Public
+ * Source License Version 1.1 (the "License").  You may not use this file
+ * except in compliance with the License.  Please obtain a copy of the
+ * License at http://www.apple.com/publicsource and read it before using
+ * this file.
+ * 
+ * The Original Code and all software distributed under the License are
+ * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE OR NON- INFRINGEMENT.  Please see the
+ * License for the specific language governing rights and limitations
+ * under the License.
+ * 
+ * @APPLE_LICENSE_HEADER_END@
+ */
+/*     $OpenBSD: is_tar.c,v 1.3 1997/02/09 23:58:27 millert Exp $      */
+
+/*
+ * is_tar() -- figure out whether file is a tar archive.
+ *
+ * Stolen (by the author!) from the public domain tar program:
+ * Pubic Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).
+ *
+ * @(#)list.c 1.18 9/23/86 Public Domain - gnu
+ *
+ * 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"
+
+#define        isodigit(c)     ( ((c) >= '0') && ((c) <= '7') )
+
+#if    defined(__STDC__) || defined(__cplusplus)
+static int from_oct(int, char*);       /* Decode octal number */
+#else
+static int from_oct();
+#endif
+
+/*
+ * 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;
+{
+       register union record *header = (union record *)buf;
+       register int    i;
+       register int    sum, recsum;
+       register 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)
+       register int    digs;
+       register char   *where;
+{
+       register int    value;
+
+       while (isspace(*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(*where))
+               return -1;                      /* Ended on non-space/nul */
+
+       return value;
+}