CHACHA20_MAX_ASKED_LEN
MUST_HAVE((stream_len <= CHACHA20_MAX_ASKED_LEN), ret, err);
MUST_HAVE((seedlen == SHA256_DIGEST_SIZE) && (scalar_len <= CHACHA20_MAX_ASKED_LEN), ret, err);
remain = ((q_len - size) < CHACHA20_MAX_ASKED_LEN) ? (q_len - size): CHACHA20_MAX_ASKED_LEN;