1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
use core::fmt;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_project_lite::pin_project;

// FIXME: docs, tests

pin_project! {
    /// Stream for the [`take_until`](super::StreamExt::take_until) method.
    #[must_use = "streams do nothing unless polled"]
    pub struct TakeUntil<St: Stream, Fut: Future> {
        #[pin]
        stream: St,
        // Contains the inner Future on start and None once the inner Future is resolved
        // or taken out by the user.
        #[pin]
        fut: Option<Fut>,
        // Contains fut's return value once fut is resolved
        fut_result: Option<Fut::Output>,
        // Whether the future was taken out by the user.
        free: bool,
    }
}

impl<St, Fut> fmt::Debug for TakeUntil<St, Fut>
where
    St: Stream + fmt::Debug,
    St::Item: fmt::Debug,
    Fut: Future + fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("TakeUntil")
            .field("stream", &self.stream)
            .field("fut", &self.fut)
            .finish()
    }
}

impl<St, Fut> TakeUntil<St, Fut>
where
    St: Stream,
    Fut: Future,
{
    pub(super) fn new(stream: St, fut: Fut) -> Self {
        Self {
            stream,
            fut: Some(fut),
            fut_result: None,
            free: false,
        }
    }

    delegate_access_inner!(stream, St, ());

    /// Extract the stopping future out of the combinator.
    /// The future is returned only if it isn't resolved yet, ie. if the stream isn't stopped yet.
    /// Taking out the future means the combinator will be yielding
    /// elements from the wrapped stream without ever stopping it.
    pub fn take_future(&mut self) -> Option<Fut> {
        if self.fut.is_some() {
            self.free = true;
        }

        self.fut.take()
    }

    /// Once the stopping future is resolved, this method can be used
    /// to extract the value returned by the stopping future.
    ///
    /// This may be used to retrieve arbitrary data from the stopping
    /// future, for example a reason why the stream was stopped.
    ///
    /// This method will return `None` if the future isn't resolved yet,
    /// or if the result was already taken out.
    ///
    /// # Examples
    ///
    /// ```
    /// # futures::executor::block_on(async {
    /// use futures::future;
    /// use futures::stream::{self, StreamExt};
    /// use futures::task::Poll;
    ///
    /// let stream = stream::iter(1..=10);
    ///
    /// let mut i = 0;
    /// let stop_fut = future::poll_fn(|_cx| {
    ///     i += 1;
    ///     if i <= 5 {
    ///         Poll::Pending
    ///     } else {
    ///         Poll::Ready("reason")
    ///     }
    /// });
    ///
    /// let mut stream = stream.take_until(stop_fut);
    /// let _ = stream.by_ref().collect::<Vec<_>>().await;
    ///
    /// let result = stream.take_result().unwrap();
    /// assert_eq!(result, "reason");
    /// # });
    /// ```
    pub fn take_result(&mut self) -> Option<Fut::Output> {
        self.fut_result.take()
    }

    /// Whether the stream was stopped yet by the stopping future
    /// being resolved.
    pub fn is_stopped(&self) -> bool {
        !self.free && self.fut.is_none()
    }
}

impl<St, Fut> Stream for TakeUntil<St, Fut>
where
    St: Stream,
    Fut: Future,
{
    type Item = St::Item;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
        let mut this = self.project();

        if let Some(f) = this.fut.as_mut().as_pin_mut() {
            if let Poll::Ready(result) = f.poll(cx) {
                this.fut.set(None);
                *this.fut_result = Some(result);
            }
        }

        if !*this.free && this.fut.is_none() {
            // Future resolved, inner stream stopped
            Poll::Ready(None)
        } else {
            // Future either not resolved yet or taken out by the user
            let item = ready!(this.stream.poll_next(cx));
            if item.is_none() {
                this.fut.set(None);
            }
            Poll::Ready(item)
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        if self.is_stopped() {
            return (0, Some(0));
        }

        self.stream.size_hint()
    }
}

impl<St, Fut> FusedStream for TakeUntil<St, Fut>
where
    St: Stream,
    Fut: Future,
{
    fn is_terminated(&self) -> bool {
        self.is_stopped()
    }
}

// Forwarding impl of Sink from the underlying stream
#[cfg(feature = "sink")]
impl<S, Fut, Item> Sink<Item> for TakeUntil<S, Fut>
where
    S: Stream + Sink<Item>,
    Fut: Future,
{
    type Error = S::Error;

    delegate_sink!(stream, Item);
}