connect: simplify check_ref() using skip_prefix() and starts_with()

Both callers of check_ref() pass in NUL-terminated strings for name.
Remove the len parameter and then use skip_prefix() and starts_with()
instead of memcmp() to check if it starts with certain strings.  This
gets rid of several magic string length constants and a strlen() call.

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

connect.c

@@ -13,28 +13,24 @@
 static char *server_capabilities;
 static const char *parse_feature_value(const char *, const char *, int *);
 
-static int check_ref(const char *name, int len, unsigned int flags)
+static int check_ref(const char *name, unsigned int flags)
 {
 	if (!flags)
 		return 1;
 
-	if (len < 5 || memcmp(name, "refs/", 5))
+	if (!skip_prefix(name, "refs/", &name))
 		return 0;
 
-	/* Skip the "refs/" part */
-	name += 5;
-	len -= 5;
-
 	/* REF_NORMAL means that we don't want the magic fake tag refs */
 	if ((flags & REF_NORMAL) && check_refname_format(name, 0))
 		return 0;
 
 	/* REF_HEADS means that we want regular branch heads */
-	if ((flags & REF_HEADS) && !memcmp(name, "heads/", 6))
+	if ((flags & REF_HEADS) && starts_with(name, "heads/"))
 		return 1;
 
 	/* REF_TAGS means that we want tags */
-	if ((flags & REF_TAGS) && !memcmp(name, "tags/", 5))
+	if ((flags & REF_TAGS) && starts_with(name, "tags/"))
 		return 1;
 
 	/* All type bits clear means that we are ok with anything */
@@ -43,7 +39,7 @@ static int check_ref(const char *name, int len, unsigned int flags)
 
 int check_ref_type(const struct ref *ref, int flags)
 {
-	return check_ref(ref->name, strlen(ref->name), flags);
+	return check_ref(ref->name, flags);
 }
 
 static void die_initial_contact(int got_at_least_one_head)
@@ -167,7 +163,7 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 			continue;
 		}
 
-		if (!check_ref(name, name_len, flags))
+		if (!check_ref(name, flags))
 			continue;
 		ref = alloc_ref(buffer + 41);
 		hashcpy(ref->old_sha1, old_sha1);