1 use core::pin::Pin;
2 use futures_core::ready;
3 use futures_core::stream::{FusedStream, Stream};
4 use futures_core::task::{Context, Poll};
5 #[cfg(feature = "sink")]
6 use futures_sink::Sink;
7 use pin_project_lite::pin_project;
8 
9 pin_project! {
10     /// Stream for the [`fuse`](super::StreamExt::fuse) method.
11     #[derive(Debug)]
12     #[must_use = "streams do nothing unless polled"]
13     pub struct Fuse<St> {
14         #[pin]
15         stream: St,
16         done: bool,
17     }
18 }
19 
20 impl<St> Fuse<St> {
new(stream: St) -> Self21     pub(super) fn new(stream: St) -> Self {
22         Self { stream, done: false }
23     }
24 
25     /// Returns whether the underlying stream has finished or not.
26     ///
27     /// If this method returns `true`, then all future calls to poll are
28     /// guaranteed to return `None`. If this returns `false`, then the
29     /// underlying stream is still in use.
is_done(&self) -> bool30     pub fn is_done(&self) -> bool {
31         self.done
32     }
33 
34     delegate_access_inner!(stream, St, ());
35 }
36 
37 impl<S: Stream> FusedStream for Fuse<S> {
is_terminated(&self) -> bool38     fn is_terminated(&self) -> bool {
39         self.done
40     }
41 }
42 
43 impl<S: Stream> Stream for Fuse<S> {
44     type Item = S::Item;
45 
poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>>46     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
47         let this = self.project();
48 
49         if *this.done {
50             return Poll::Ready(None);
51         }
52 
53         let item = ready!(this.stream.poll_next(cx));
54         if item.is_none() {
55             *this.done = true;
56         }
57         Poll::Ready(item)
58     }
59 
size_hint(&self) -> (usize, Option<usize>)60     fn size_hint(&self) -> (usize, Option<usize>) {
61         if self.done {
62             (0, Some(0))
63         } else {
64             self.stream.size_hint()
65         }
66     }
67 }
68 
69 // Forwarding impl of Sink from the underlying stream
70 #[cfg(feature = "sink")]
71 impl<S: Stream + Sink<Item>, Item> Sink<Item> for Fuse<S> {
72     type Error = S::Error;
73 
74     delegate_sink!(stream, Item);
75 }
76