async_sink/ext/
with_flat_map.rs

1use core::fmt;
2use core::marker::PhantomData;
3use core::pin::Pin;
4use core::task::{Context, Poll};
5use tokio_stream::Stream;
6use tokio_stream_util::FusedStream;
7
8use super::Sink;
9
10/// Sink for the [`with_flat_map`](super::SinkExt::with_flat_map) method.
11#[must_use = "sinks do nothing unless polled"]
12pub struct WithFlatMap<Si, Item, U, St, F> {
13    sink: Si,
14    f: F,
15    stream: Option<St>,
16    buffer: Option<Item>,
17    _marker: PhantomData<fn(U)>,
18}
19
20impl<Si: Unpin, Item, U, St: Unpin, F> Unpin for WithFlatMap<Si, Item, U, St, F> {}
21
22impl<Si, Item, U, St, F> fmt::Debug for WithFlatMap<Si, Item, U, St, F>
23where
24    Si: fmt::Debug,
25    St: fmt::Debug,
26    Item: fmt::Debug,
27{
28    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
29        f.debug_struct("WithFlatMap")
30            .field("sink", &self.sink)
31            .field("stream", &self.stream)
32            .field("buffer", &self.buffer)
33            .finish()
34    }
35}
36
37impl<Si, Item, U, St, F> WithFlatMap<Si, Item, U, St, F>
38where
39    Si: Sink<Item>,
40    F: FnMut(U) -> St,
41    St: Stream<Item = Result<Item, Si::Error>>,
42{
43    pub(super) fn new(sink: Si, f: F) -> Self {
44        Self {
45            sink,
46            f,
47            stream: None,
48            buffer: None,
49            _marker: PhantomData,
50        }
51    }
52
53    /// Acquires a reference to the underlying sink.
54    pub fn get_ref(&self) -> &Si {
55        &self.sink
56    }
57
58    /// Acquires a mutable reference to the underlying sink.
59    ///
60    /// Note that care must be taken to avoid tampering with the state of the
61    /// sink which may otherwise confuse this combinator.
62    pub fn get_mut(&mut self) -> &mut Si {
63        &mut self.sink
64    }
65
66    /// Acquires a pinned mutable reference to the underlying sink.
67    ///
68    /// Note that care must be taken to avoid tampering with the state of the
69    /// sink which may otherwise confuse this combinator.
70    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut Si> {
71        unsafe { Pin::new_unchecked(&mut self.get_unchecked_mut().sink) }
72    }
73
74    /// Consumes this combinator, returning the underlying sink.
75    ///
76    /// Note that this may discard intermediate state of this combinator, so
77    /// care should be taken to avoid losing resources when this is called.
78    pub fn into_inner(self) -> Si {
79        self.sink
80    }
81
82    fn try_empty_stream(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
83        let this = unsafe { self.get_unchecked_mut() };
84        let mut sink = unsafe { Pin::new_unchecked(&mut this.sink) };
85
86        if this.buffer.is_some() {
87            match sink.as_mut().poll_ready(cx) {
88                Poll::Ready(Ok(())) => {}
89                Poll::Ready(Err(e)) => return Poll::Ready(Err(e)),
90                Poll::Pending => return Poll::Pending,
91            }
92            let item = this.buffer.take().unwrap();
93            if let Err(e) = sink.as_mut().start_send(item) {
94                return Poll::Ready(Err(e));
95            }
96        }
97        let stream_pin = unsafe { Pin::new_unchecked(&mut this.stream) };
98        if let Some(mut some_stream) = stream_pin.as_pin_mut() {
99            loop {
100                let item = match some_stream.as_mut().poll_next(cx) {
101                    Poll::Ready(Some(Ok(item))) => Some(item),
102                    Poll::Ready(Some(Err(e))) => return Poll::Ready(Err(e)),
103                    Poll::Ready(None) => None,
104                    Poll::Pending => return Poll::Pending,
105                };
106
107                if let Some(item) = item {
108                    match sink.as_mut().poll_ready(cx) {
109                        Poll::Ready(Ok(())) => {
110                            if let Err(e) = sink.as_mut().start_send(item) {
111                                return Poll::Ready(Err(e));
112                            }
113                        }
114                        Poll::Ready(Err(e)) => return Poll::Ready(Err(e)),
115                        Poll::Pending => {
116                            this.buffer = Some(item);
117                            return Poll::Pending;
118                        }
119                    };
120                } else {
121                    break;
122                }
123            }
124        }
125        this.stream = None;
126        Poll::Ready(Ok(()))
127    }
128}
129
130// Forwarding impl of Stream from the underlying sink
131impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
132where
133    S: Stream + Sink<Item>,
134    F: FnMut(U) -> St,
135    St: Stream<Item = Result<Item, S::Error>>,
136{
137    type Item = S::Item;
138
139    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
140        unsafe { Pin::new_unchecked(&mut self.get_unchecked_mut().sink) }.poll_next(cx)
141    }
142
143    fn size_hint(&self) -> (usize, Option<usize>) {
144        self.sink.size_hint()
145    }
146}
147
148impl<S, Item, U, St, F> FusedStream for WithFlatMap<S, Item, U, St, F>
149where
150    S: FusedStream + Sink<Item>,
151    F: FnMut(U) -> St,
152    St: Stream<Item = Result<Item, S::Error>>,
153{
154    fn is_terminated(&self) -> bool {
155        self.sink.is_terminated()
156    }
157}
158
159impl<Si, Item, U, St, F> Sink<U> for WithFlatMap<Si, Item, U, St, F>
160where
161    Si: Sink<Item>,
162    F: FnMut(U) -> St,
163    St: Stream<Item = Result<Item, Si::Error>>,
164{
165    type Error = Si::Error;
166
167    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
168        self.try_empty_stream(cx)
169    }
170
171    fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
172        let this = unsafe { self.get_unchecked_mut() };
173
174        assert!(this.stream.is_none());
175        this.stream = Some((this.f)(item));
176        Ok(())
177    }
178
179    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
180        match self.as_mut().try_empty_stream(cx) {
181            Poll::Ready(Ok(())) => {}
182            Poll::Ready(Err(e)) => return Poll::Ready(Err(e)),
183            Poll::Pending => return Poll::Pending,
184        };
185        unsafe { Pin::new_unchecked(&mut self.get_unchecked_mut().sink) }.poll_flush(cx)
186    }
187
188    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
189        match self.as_mut().try_empty_stream(cx) {
190            Poll::Ready(Ok(())) => {}
191            Poll::Ready(Err(e)) => return Poll::Ready(Err(e)),
192            Poll::Pending => return Poll::Pending,
193        };
194        unsafe { Pin::new_unchecked(&mut self.get_unchecked_mut().sink) }.poll_close(cx)
195    }
196}
async_sink/ext/with_flat_map.rs

async_sink/ext/
with_flat_map.rs
