futures_util/stream/stream/
forward.rs

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1use crate::stream::Fuse;
2use core::pin::Pin;
3use futures_core::future::{FusedFuture, Future};
4use futures_core::ready;
5use futures_core::stream::Stream;
6use futures_core::task::{Context, Poll};
7use futures_sink::Sink;
8use pin_project_lite::pin_project;
9
10pin_project! {
11    /// Future for the [`forward`](super::StreamExt::forward) method.
12    #[project = ForwardProj]
13    #[derive(Debug)]
14    #[must_use = "futures do nothing unless you `.await` or poll them"]
15    pub struct Forward<St, Si, Item> {
16        #[pin]
17        sink: Option<Si>,
18        #[pin]
19        stream: Fuse<St>,
20        buffered_item: Option<Item>,
21    }
22}
23
24impl<St, Si, Item> Forward<St, Si, Item> {
25    pub(crate) fn new(stream: St, sink: Si) -> Self {
26        Self { sink: Some(sink), stream: Fuse::new(stream), buffered_item: None }
27    }
28}
29
30impl<St, Si, Item, E> FusedFuture for Forward<St, Si, Item>
31where
32    Si: Sink<Item, Error = E>,
33    St: Stream<Item = Result<Item, E>>,
34{
35    fn is_terminated(&self) -> bool {
36        self.sink.is_none()
37    }
38}
39
40impl<St, Si, Item, E> Future for Forward<St, Si, Item>
41where
42    Si: Sink<Item, Error = E>,
43    St: Stream<Item = Result<Item, E>>,
44{
45    type Output = Result<(), E>;
46
47    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
48        let ForwardProj { mut sink, mut stream, buffered_item } = self.project();
49        let mut si = sink.as_mut().as_pin_mut().expect("polled `Forward` after completion");
50
51        loop {
52            // If we've got an item buffered already, we need to write it to the
53            // sink before we can do anything else
54            if buffered_item.is_some() {
55                ready!(si.as_mut().poll_ready(cx))?;
56                si.as_mut().start_send(buffered_item.take().unwrap())?;
57            }
58
59            match stream.as_mut().poll_next(cx)? {
60                Poll::Ready(Some(item)) => {
61                    *buffered_item = Some(item);
62                }
63                Poll::Ready(None) => {
64                    ready!(si.poll_close(cx))?;
65                    sink.set(None);
66                    return Poll::Ready(Ok(()));
67                }
68                Poll::Pending => {
69                    ready!(si.poll_flush(cx))?;
70                    return Poll::Pending;
71                }
72            }
73        }
74    }
75}
futures_util/stream/stream/forward.rs

futures_util/stream/stream/
forward.rs
