Solution for `08_futures/03_runtime` is inconsistent with `08/02_spawn`.

[kimhanm]

The intended solution for 02_spawn spawns a task for each listener and within that task, spawns another task every time the listener accepts a connection.

// inside the loop of the helper function
let (mut socket, _) = listener.accept().await?;
tokio::spawn(async move {
    let (mut reader, mut writer) = socket.split();
    tokio::io::copy(&mut reader, &mut writer).await.unwrap();
});

For 03_runtime however, the solution does not spawn a new task.

let (mut socket, _) = listener.accept().await.unwrap();
let (_reader, mut writer) = socket.split();
writer
    .write_all(format!("{}", reply).as_bytes())
    .await
    .unwrap();

If I understand the exercise correctly, this would block the listener until the response is finished.

I would think the solution should be something like

let (mut socket, _) = listener.accept().await.unwrap();
let reply = reply.clone(); /* reply: Arc<T>, so cloneable */
tokio::spawn(async move {
    let (_, mut writer) = socket.split();
    writer
        .write_all(format!("{}", reply).as_bytes())
        .await
        .unwrap();
});

On a tangential note, it took me quite a while until I tread Arc because I assumed that the solution would not require us to add use std::sync::Arc ourselves.
Perhaps it would be a good idea to add this difficulty at an earlier time instead.