When to call nghttp3_conn_is_drained to know It's time to close

[taikulawo]

From https://nghttp2.org/nghttp3/programmers-guide.html#closing-http-3-connection-gracefully said, the server should call
nghttp3_conn_is_drained() to check whether we should shutdown completely, But when I should call nghttp3_conn_is_drained, by checking repeatly or in stream_close?

I try call nghttp3_conn_is_drained in stream_close callback, but --num_streams run after stream_close, so nghttp3_conn_is_drained always reture false.

nghttp3/lib/nghttp3_conn.c

Line 1074 in 0fd649a

--conn->remote.bidi.num_streams;

here my logic in stream_close callback, when receiver recv ShutdownReason, it will close connection finally

if me.mode == ConnMode::Server && conn.nghttp3_conn_is_drained() && is_bidi_stream {
    // Server want to shutdown, and all streams has been drained, send shutdown signal
   // https://docs.rs/tokio/latest/tokio/sync/mpsc/struct.Sender.html#method.try_send
    let _ = me.shutdown_conn.try_send(ShutdownReason {
        code: AppErrorCode::NGHTTP3_H3_NO_ERROR,
        reason: SmallVec::new(),
    });
}

[tatsuhiro-t]

In my http3 proxy server, I call nghttp3_conn_is_drained every time after writing packets.

[taikulawo]

What the means of writing packets?

Should I call nghttp3_conn_is_drained after nghttp3_conn_read_stream?

I don't found how to use in examples/server.cc