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

use core::marker::PhantomData;
use core::pin::Pin;
use futures_core::stream::Stream;
use futures_core::task::{Context, Poll};
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};

/// Sink for the [`with_flat_map`](super::SinkExt::with_flat_map) method.
#[derive(Debug)]
#[must_use = "sinks do nothing unless polled"]
pub struct WithFlatMap<Si, Item, U, St, F>
where
    Si: Sink<Item>,
    F: FnMut(U) -> St,
    St: Stream<Item = Result<Item, Si::SinkError>>,
{
    sink: Si,
    f: F,
    stream: Option<St>,
    buffer: Option<Item>,
    _marker: PhantomData<fn(U)>,
}

impl<Si, Item, U, St, F> Unpin for WithFlatMap<Si, Item, U, St, F>
where
    Si: Sink<Item> + Unpin,
    F: FnMut(U) -> St,
    St: Stream<Item = Result<Item, Si::SinkError>> + Unpin,
{}

impl<Si, Item, U, St, F> WithFlatMap<Si, Item, U, St, F>
where
    Si: Sink<Item>,
    F: FnMut(U) -> St,
    St: Stream<Item = Result<Item, Si::SinkError>>,
{
    unsafe_pinned!(sink: Si);
    unsafe_unpinned!(f: F);
    unsafe_pinned!(stream: Option<St>);

    pub(super) fn new(sink: Si, f: F) -> Self {
        WithFlatMap {
            sink,
            f,
            stream: None,
            buffer: None,
            _marker: PhantomData,
        }
    }

    /// Get a shared reference to the inner sink.
    pub fn get_ref(&self) -> &Si {
        &self.sink
    }

    /// Get a mutable reference to the inner sink.
    pub fn get_mut(&mut self) -> &mut Si {
        &mut self.sink
    }

    /// Get a pinned mutable reference to the inner sink.
    pub fn get_pin_mut<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut Si> {
        self.sink()
    }

    /// Consumes this combinator, returning the underlying sink.
    ///
    /// 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) -> Si {
        self.sink
    }

    fn try_empty_stream(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Si::SinkError>> {
        let WithFlatMap { sink, stream, buffer, .. } =
            unsafe { Pin::get_unchecked_mut(self) };
        let mut sink = unsafe { Pin::new_unchecked(sink) };
        let mut stream = unsafe { Pin::new_unchecked(stream) };

        if buffer.is_some() {
            ready!(sink.as_mut().poll_ready(cx))?;
            let item = buffer.take().unwrap();
            ready!(Poll::Ready(sink.as_mut().start_send(item)))?;
        }
        if let Some(mut some_stream) = stream.as_mut().as_pin_mut() {
            while let Some(x) = ready!(some_stream.as_mut().poll_next(cx)) {
                let item = ready!(Poll::Ready(x))?;
                match sink.as_mut().poll_ready(cx)? {
                    Poll::Ready(()) => sink.as_mut().start_send(item)?,
                    Poll::Pending => {
                        *buffer = Some(item);
                        return Poll::Pending;
                    }
                };
            }
        }
        stream.set(None);
        Poll::Ready(Ok(()))
    }
}

impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
where
    S: Stream + Sink<Item>,
    F: FnMut(U) -> St,
    St: Stream<Item = Result<Item, S::SinkError>>,
{
    type Item = S::Item;
    fn poll_next(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<S::Item>> {
        self.sink().poll_next(cx)
    }
}

impl<Si, Item, U, St, F> Sink<U> for WithFlatMap<Si, Item, U, St, F>
where
    Si: Sink<Item>,
    F: FnMut(U) -> St,
    St: Stream<Item = Result<Item, Si::SinkError>>,
{
    type SinkError = Si::SinkError;

    fn poll_ready(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Self::SinkError>> {
        self.try_empty_stream(cx)
    }

    fn start_send(
        mut self: Pin<&mut Self>,
        item: U,
    ) -> Result<(), Self::SinkError> {
        assert!(self.stream.is_none());
        let stream = (self.as_mut().f())(item);
        self.stream().set(Some(stream));
        Ok(())
    }

    fn poll_flush(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Self::SinkError>> {
        match self.as_mut().try_empty_stream(cx) {
            Poll::Pending => Poll::Pending,
            Poll::Ready(Ok(())) => self.as_mut().sink().poll_flush(cx),
            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
        }
    }

    fn poll_close(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Self::SinkError>> {
        match self.as_mut().try_empty_stream(cx) {
            Poll::Pending => Poll::Pending,
            Poll::Ready(Ok(())) => self.as_mut().sink().poll_close(cx),
            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
        }
    }
}