receive-pack: use find_commit_header() in check_cert_push_options()

Use the public function find_commit_header() instead of find_header() to
simplify the code.  This is possible and safe because we're operating on
a strbuf, which is always NUL-terminated, so there is no risk of running
over the end of the buffer.  It cannot contain NUL within the buffer, as
it is built using strbuf_addstr(), only.

The string comparison becomes more complicated because we need to check
for NUL explicitly after comparing the length-limited option, but on the
flip side we don't need to clean up allocations or track the remaining
buffer length.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: rscharfe

builtin/receive-pack.c

@@ -718,35 +718,29 @@ static const char *check_nonce(const char *buf, size_t len)
 static int check_cert_push_options(const struct string_list *push_options)
 {
 	const char *buf = push_cert.buf;
-	int len = push_cert.len;
 
-	char *option;
-	const char *next_line;
+	const char *option;
+	size_t optionlen;
 	int options_seen = 0;
 
 	int retval = 1;
 
-	if (!len)
+	if (!*buf)
 		return 1;
 
-	while ((option = find_header(buf, len, "push-option", &next_line))) {
-		len -= (next_line - buf);
-		buf = next_line;
+	while ((option = find_commit_header(buf, "push-option", &optionlen))) {
+		buf = option + optionlen + 1;
 		options_seen++;
 		if (options_seen > push_options->nr
-		    || strcmp(option,
-			      push_options->items[options_seen - 1].string)) {
-			retval = 0;
-			goto leave;
-		}
-		free(option);
+		    || strncmp(push_options->items[options_seen - 1].string,
+			       option, optionlen)
+		    || push_options->items[options_seen - 1].string[optionlen])
+			return 0;
 	}
 
 	if (options_seen != push_options->nr)
 		retval = 0;
 
-leave:
-	free(option);
 	return retval;
 }