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}
76