core: add format with va_list function to stringstream

core/stringstream.c

@@ -150,9 +150,18 @@ b_status b_stringstream_addf(struct b_stringstream *ss, const char *format, ...)
 	char str[1024];
 	va_list arg;
 	va_start(arg, format);
-	size_t len = vsnprintf(str, sizeof str, format, arg);
+	enum b_status status = b_stringstream_addvf(ss, format, arg);
 	va_end(arg);
 
+	return status;
+}
+
+b_status b_stringstream_addvf(
+	struct b_stringstream *ss, const char *format, va_list arg)
+{
+	char str[1024];
+	size_t len = vsnprintf(str, sizeof str, format, arg);
+
 	return ss_builder_push_string(ss, str, len);
 }