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

use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_utils::unsafe_pinned;

/// Stream for the [`flatten`](super::StreamExt::flatten) method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Flatten<St>
where
    St: Stream,
{
    stream: St,
    next: Option<St::Item>,
}

impl<St> Unpin for Flatten<St>
where
    St: Stream + Unpin,
    St::Item: Unpin,
{
}

impl<St> Flatten<St>
where
    St: Stream,
{
    unsafe_pinned!(stream: St);
    unsafe_pinned!(next: Option<St::Item>);
}

impl<St> Flatten<St>
where
    St: Stream,
    St::Item: Stream,
{
    pub(super) fn new(stream: St) -> Self {
        Self { stream, next: None }
    }

    /// Acquires a reference to the underlying stream that this combinator is
    /// pulling from.
    pub fn get_ref(&self) -> &St {
        &self.stream
    }

    /// Acquires a mutable reference to the underlying stream that this
    /// combinator is pulling from.
    ///
    /// Note that care must be taken to avoid tampering with the state of the
    /// stream which may otherwise confuse this combinator.
    pub fn get_mut(&mut self) -> &mut St {
        &mut self.stream
    }

    /// Acquires a pinned mutable reference to the underlying stream that this
    /// combinator is pulling from.
    ///
    /// Note that care must be taken to avoid tampering with the state of the
    /// stream which may otherwise confuse this combinator.
    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
        self.stream()
    }

    /// Consumes this combinator, returning the underlying stream.
    ///
    /// Note that this may discard intermediate state of this combinator, so
    /// care should be taken to avoid losing resources when this is called.
    pub fn into_inner(self) -> St {
        self.stream
    }
}

impl<St> FusedStream for Flatten<St>
where
    St: FusedStream,
    St::Item: Stream,
{
    fn is_terminated(&self) -> bool {
        self.next.is_none() && self.stream.is_terminated()
    }
}

impl<St> Stream for Flatten<St>
where
    St: Stream,
    St::Item: Stream,
{
    type Item = <St::Item as Stream>::Item;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        loop {
            if self.next.is_none() {
                match ready!(self.as_mut().stream().poll_next(cx)) {
                    Some(e) => self.as_mut().next().set(Some(e)),
                    None => return Poll::Ready(None),
                }
            }

            if let Some(item) = ready!(self.as_mut().next().as_pin_mut().unwrap().poll_next(cx)) {
                return Poll::Ready(Some(item));
            } else {
                self.as_mut().next().set(None);
            }
        }
    }
}

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

    delegate_sink!(stream, Item);
}