tls_content_cbs
CBS_dup(tls_content_cbs(rl->rcontent), cbs);
if (!CBS_get_u8(tls_content_cbs(rl->rcontent), &alert_level))
if (!CBS_get_u8(tls_content_cbs(rl->rcontent), &alert_desc))
CBS *tls_content_cbs(struct tls_content *content);