2 files changed, 25 insertions, 0 deletions
diff --git a/lib/lib.c b/lib/lib.c
index b5825fd2..ffb24f65 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -1416,3 +1416,26 @@ void loggit(int priority, char *format, ...)
   va_end(va);
   closelog();
 }
+
+// Calculate tar packet checksum, with cksum field treated as 8 spaces
+unsigned tar_cksum(void *data)
+{
+  unsigned i, cksum = 8*' ';
+
+  for (i = 0; i<500; i += (i==147) ? 9 : 1) cksum += ((char *)data)[i];
+
+  return cksum;
+}
+
+// is this a valid tar header?
+int is_tar_header(void *pkt)
+{
+  char *p = pkt;
+  int i = 0;
+
+  if (p[257] && memcmp("ustar", p+257, 5)) return 0;
+  if (p[148] != '0') return 0;
+  sscanf(p+148, "%8o", &i);
+
+  return i && tar_cksum(pkt) == i;
+}
diff --git a/lib/lib.h b/lib/lib.h
index 5ce29380..080c533f 100644
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -265,6 +265,8 @@ long long millitime(void);
 char *format_iso_time(char *buf, size_t len, struct timespec *ts);
 void reset_env(struct passwd *p, int clear);
 void loggit(int priority, char *format, ...);
+unsigned tar_cksum(void *data);
+int is_tar_header(void *pkt);
 
 #define HR_SPACE 1 // Space between number and units
 #define HR_B     2 // Use "B" for single byte units