How to receive data in blocking way

[wanyt]

In an MQTT communication scenario based on Quinn, the client needs to wait for data being sent by the server. How can the client wait to receive the data from the server? I am currently using a loop, but I feel that this approach consumes CPU resources excessively. Is there a way for the client to block and receive data?

this is my code:

loop {
        let resp = recv
            .read_to_end(usize::max_value())
            .await
            .map_err(|e| anyhow!("failed to read response: {}", e))?;
        let duration = response_start.elapsed();
        eprintln!(
            "response received in {:?} - {} KiB/s",
            duration,
            resp.len() as f32 / (duration_secs(&duration) * 1024.0)
        );

        io::stdout().write_all(&resp).unwrap();
        io::stdout().flush().unwrap();     
    }

[djc]

Why do you feel this approach consumes excessive CPU? Have you measured this?

Why do you even need a loop here? The recv.read_to_end() call should yield only once, after the entire response is available. In fact, polling this future more than once will probably yield undefined behavior.

[wanyt]

How should I continuously wait to receive data when I'm not sure when the data will come?

[djc]

Your async runtime will wake up your task when data has been received. But this is the basics of async Rust, and I don't think our issue tracker is the right place to explain the whole paradigm.