tls_buffer_finish
if (!tls_buffer_finish(msg->buf, &msg->data, &msg->data_len))
if (!tls_buffer_finish(rec->buf, &rec->data, &rec->data_len))
int tls_buffer_finish(struct tls_buffer *buf, uint8_t **out, size_t *out_len);
if (!tls_buffer_finish(buf, &data, &data_len)) {