tokio/tokio-stream/tests/mpsc_bounded_stream.rs

use futures::{Stream, StreamExt};
use tokio::sync::mpsc;
use tokio_stream::wrappers::ReceiverStream;

#[tokio::test]
async fn size_hint_stream_open() {
    let (tx, rx) = mpsc::channel(4);

    tx.send(1).await.unwrap();
    tx.send(2).await.unwrap();

    let mut stream = ReceiverStream::new(rx);

    assert_eq!(stream.size_hint(), (2, None));
    stream.next().await;
    assert_eq!(stream.size_hint(), (1, None));
    stream.next().await;
    assert_eq!(stream.size_hint(), (0, None));
}

#[tokio::test]
async fn size_hint_stream_closed() {
    let (tx, rx) = mpsc::channel(4);

    tx.send(1).await.unwrap();
    tx.send(2).await.unwrap();

    let mut stream = ReceiverStream::new(rx);
    stream.close();

    assert_eq!(stream.size_hint(), (2, Some(2)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (1, Some(1)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (0, Some(0)));
}

#[tokio::test]
async fn size_hint_sender_dropped() {
    let (tx, rx) = mpsc::channel(4);

    tx.send(1).await.unwrap();
    tx.send(2).await.unwrap();

    let mut stream = ReceiverStream::new(rx);
    drop(tx);

    assert_eq!(stream.size_hint(), (2, Some(2)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (1, Some(1)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (0, Some(0)));
}

#[test]
fn size_hint_stream_instantly_closed() {
    let (_tx, rx) = mpsc::channel::<i32>(4);

    let mut stream = ReceiverStream::new(rx);
    stream.close();

    assert_eq!(stream.size_hint(), (0, Some(0)));
}

#[tokio::test]
async fn size_hint_stream_closed_permits_send() {
    let (tx, rx) = mpsc::channel(4);

    tx.send(1).await.unwrap();
    let permit1 = tx.reserve().await.unwrap();
    let permit2 = tx.reserve().await.unwrap();

    let mut stream = ReceiverStream::new(rx);
    stream.close();

    assert_eq!(stream.size_hint(), (1, Some(3)));
    permit1.send(2);
    assert_eq!(stream.size_hint(), (2, Some(3)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (1, Some(2)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (0, Some(1)));
    permit2.send(3);
    assert_eq!(stream.size_hint(), (1, Some(1)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (0, Some(0)));
    assert_eq!(stream.next().await, None);
}

#[tokio::test]
async fn size_hint_stream_closed_permits_drop() {
    let (tx, rx) = mpsc::channel(4);

    tx.send(1).await.unwrap();
    let permit1 = tx.reserve().await.unwrap();
    let permit2 = tx.reserve().await.unwrap();

    let mut stream = ReceiverStream::new(rx);
    stream.close();

    assert_eq!(stream.size_hint(), (1, Some(3)));
    drop(permit1);
    assert_eq!(stream.size_hint(), (1, Some(2)));
    stream.next().await;
    assert_eq!(stream.size_hint(), (0, Some(1)));
    drop(permit2);
    assert_eq!(stream.size_hint(), (0, Some(0)));
    assert_eq!(stream.next().await, None);
}