gzip: add a function to parse the header

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/common.h

@@ -609,6 +609,7 @@ ulong	usec2ticks    (unsigned long usec);
 ulong	ticks2usec    (unsigned long ticks);
 
 /* lib/gunzip.c */
+int gzip_parse_header(const unsigned char *src, unsigned long len);
 int gunzip(void *, int, unsigned char *, unsigned long *);
 int zunzip(void *dst, int dstlen, unsigned char *src, unsigned long *lenp,
 						int stoponerr, int offset);

lib/gunzip.c

@@ -42,7 +42,7 @@ void gzfree(void *x, void *addr, unsigned nb)
 	free (addr);
 }
 
-int gunzip(void *dst, int dstlen, unsigned char *src, unsigned long *lenp)
+int gzip_parse_header(const unsigned char *src, unsigned long len)
 {
 	int i, flags;
 
@@ -63,12 +63,21 @@ int gunzip(void *dst, int dstlen, unsigned char *src, unsigned long *lenp)
 			;
 	if ((flags & HEAD_CRC) != 0)
 		i += 2;
-	if (i >= *lenp) {
+	if (i >= len) {
 		puts ("Error: gunzip out of data in header\n");
 		return (-1);
 	}
+	return i;
+}
+
+int gunzip(void *dst, int dstlen, unsigned char *src, unsigned long *lenp)
+{
+	int offset = gzip_parse_header(src, *lenp);
+
+	if (offset < 0)
+		return offset;
 
-	return zunzip(dst, dstlen, src, lenp, 1, i);
+	return zunzip(dst, dstlen, src, lenp, 1, offset);
 }
 
 #ifdef CONFIG_CMD_UNZIP