futures_util/stream/
fuse.rs

1use futures_core::{Poll, Async, Stream};
2use futures_core::task;
3use futures_sink::{Sink};
4
5/// A stream which "fuse"s a stream once it's terminated.
6///
7/// Normally streams can behave unpredictably when used after they have already
8/// finished, but `Fuse` continues to return `None` from `poll` forever when
9/// finished.
10#[derive(Debug)]
11#[must_use = "streams do nothing unless polled"]
12pub struct Fuse<S> {
13    stream: S,
14    done: bool,
15}
16
17// Forwarding impl of Sink from the underlying stream
18impl<S> Sink for Fuse<S>
19    where S: Sink
20{
21    type SinkItem = S::SinkItem;
22    type SinkError = S::SinkError;
23
24    delegate_sink!(stream);
25}
26
27pub fn new<S: Stream>(s: S) -> Fuse<S> {
28    Fuse { stream: s, done: false }
29}
30
31impl<S: Stream> Stream for Fuse<S> {
32    type Item = S::Item;
33    type Error = S::Error;
34
35    fn poll_next(&mut self, cx: &mut task::Context) -> Poll<Option<S::Item>, S::Error> {
36        if self.done {
37            Ok(Async::Ready(None))
38        } else {
39            let r = self.stream.poll_next(cx);
40            if let Ok(Async::Ready(None)) = r {
41                self.done = true;
42            }
43            r
44        }
45    }
46}
47
48impl<S> Fuse<S> {
49    /// Returns whether the underlying stream has finished or not.
50    ///
51    /// If this method returns `true`, then all future calls to poll are
52    /// guaranteed to return `None`. If this returns `false`, then the
53    /// underlying stream is still in use.
54    pub fn is_done(&self) -> bool {
55        self.done
56    }
57
58    /// Acquires a reference to the underlying stream that this combinator is
59    /// pulling from.
60    pub fn get_ref(&self) -> &S {
61        &self.stream
62    }
63
64    /// Acquires a mutable reference to the underlying stream that this
65    /// combinator is pulling from.
66    ///
67    /// Note that care must be taken to avoid tampering with the state of the
68    /// stream which may otherwise confuse this combinator.
69    pub fn get_mut(&mut self) -> &mut S {
70        &mut self.stream
71    }
72
73    /// Consumes this combinator, returning the underlying stream.
74    ///
75    /// Note that this may discard intermediate state of this combinator, so
76    /// care should be taken to avoid losing resources when this is called.
77    pub fn into_inner(self) -> S {
78        self.stream
79    }
80}
futures_util/stream/fuse.rs

futures_util/stream/
fuse.rs
