How to get notified when there are data need send to quic from nghttp3?

[taikulawo]

We have build a nghttp3 rust library with tokio(an async runtime) support. #281
But I want to optimize reduce unnecessary call to nghttp3_conn_writev_stream

Current, nghttp3_conn_writev_stream need be called almost everywhere to check if there are some data to send

1. poll new raw data from quic, write to nghttp3, call nghttp3_conn_writev_stream check whether need to send back to quic.
2. when send request, we call nghttp3_conn_submit_request, then call nghttp3_conn_writev_stream to check.
3. timer fired, call nghttp3_conn_writev_stream

Does there has a callback to notify us:

please, I(nghttp3) has some data to send, here are, please send to quic right now

int http_need_send_data_callback(nghttp3_conn *conn, int64_t stream_id, const uint8_t *data,
                   size_t datalen, void *user_data, void *stream_user_data) 

Or does we have nice method to get notified when need to poll from nghttp3 then send to quic?

[tatsuhiro-t]

There is no such method. You only need to call nghttp3_conn_writev_stream after you input some data to nghttp3 (e.g., after submit something, or read some thing with nghttp3_conn_read_stream).

[taikulawo]

Current, we share nghttp3_conn across threads by using Arc<Mutex<Nghttp3Connection>>. Http3RequestStream maybe in another thread. Since I don't sure what the stream_id will nghttp3_conn_writev_stream returned.

I have to forward all nghttp3_conn_writev_stream return value to separate task-A. find quic stream related to that stream_id from hashmap, then send to quic stream.

There have some way to simplify implementation
If I submit data to nghttp3 with stream_id == 3, Does the next call nghttp3_conn_writev_stream will 100% return stream_id == 3 not other stream_id?

If it does, will make my implementation more easy.

[tatsuhiro-t]

If I submit data to nghttp3 with stream_id == 3, Does the next call nghttp3_conn_writev_stream will 100% return stream_id == 3 not other stream_id?

No. Depending on the priorities and many variables, you cannot predict any particular stream is returned unless you are using single stream.

[taikulawo]

Got it, thankyou