futures_util/sink/
with.rs

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1use core::fmt;
2use core::marker::PhantomData;
3use core::pin::Pin;
4use futures_core::future::Future;
5use futures_core::ready;
6use futures_core::stream::Stream;
7use futures_core::task::{Context, Poll};
8use futures_sink::Sink;
9use pin_project_lite::pin_project;
10
11pin_project! {
12    /// Sink for the [`with`](super::SinkExt::with) method.
13    #[must_use = "sinks do nothing unless polled"]
14    pub struct With<Si, Item, U, Fut, F> {
15        #[pin]
16        sink: Si,
17        f: F,
18        #[pin]
19        state: Option<Fut>,
20        _phantom: PhantomData<fn(U) -> Item>,
21    }
22}
23
24impl<Si, Item, U, Fut, F> fmt::Debug for With<Si, Item, U, Fut, F>
25where
26    Si: fmt::Debug,
27    Fut: fmt::Debug,
28{
29    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
30        f.debug_struct("With").field("sink", &self.sink).field("state", &self.state).finish()
31    }
32}
33
34impl<Si, Item, U, Fut, F> With<Si, Item, U, Fut, F>
35where
36    Si: Sink<Item>,
37    F: FnMut(U) -> Fut,
38    Fut: Future,
39{
40    pub(super) fn new<E>(sink: Si, f: F) -> Self
41    where
42        Fut: Future<Output = Result<Item, E>>,
43        E: From<Si::Error>,
44    {
45        Self { state: None, sink, f, _phantom: PhantomData }
46    }
47}
48
49impl<Si, Item, U, Fut, F> Clone for With<Si, Item, U, Fut, F>
50where
51    Si: Clone,
52    F: Clone,
53    Fut: Clone,
54{
55    fn clone(&self) -> Self {
56        Self {
57            state: self.state.clone(),
58            sink: self.sink.clone(),
59            f: self.f.clone(),
60            _phantom: PhantomData,
61        }
62    }
63}
64
65// Forwarding impl of Stream from the underlying sink
66impl<S, Item, U, Fut, F> Stream for With<S, Item, U, Fut, F>
67where
68    S: Stream + Sink<Item>,
69    F: FnMut(U) -> Fut,
70    Fut: Future,
71{
72    type Item = S::Item;
73
74    delegate_stream!(sink);
75}
76
77impl<Si, Item, U, Fut, F, E> With<Si, Item, U, Fut, F>
78where
79    Si: Sink<Item>,
80    F: FnMut(U) -> Fut,
81    Fut: Future<Output = Result<Item, E>>,
82    E: From<Si::Error>,
83{
84    delegate_access_inner!(sink, Si, ());
85
86    /// Completes the processing of previous item if any.
87    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), E>> {
88        let mut this = self.project();
89
90        let item = match this.state.as_mut().as_pin_mut() {
91            None => return Poll::Ready(Ok(())),
92            Some(fut) => ready!(fut.poll(cx))?,
93        };
94        this.state.set(None);
95        this.sink.start_send(item)?;
96        Poll::Ready(Ok(()))
97    }
98}
99
100impl<Si, Item, U, Fut, F, E> Sink<U> for With<Si, Item, U, Fut, F>
101where
102    Si: Sink<Item>,
103    F: FnMut(U) -> Fut,
104    Fut: Future<Output = Result<Item, E>>,
105    E: From<Si::Error>,
106{
107    type Error = E;
108
109    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
110        ready!(self.as_mut().poll(cx))?;
111        ready!(self.project().sink.poll_ready(cx)?);
112        Poll::Ready(Ok(()))
113    }
114
115    fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
116        let mut this = self.project();
117
118        assert!(this.state.is_none());
119        this.state.set(Some((this.f)(item)));
120        Ok(())
121    }
122
123    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
124        ready!(self.as_mut().poll(cx))?;
125        ready!(self.project().sink.poll_flush(cx)?);
126        Poll::Ready(Ok(()))
127    }
128
129    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
130        ready!(self.as_mut().poll(cx))?;
131        ready!(self.project().sink.poll_close(cx)?);
132        Poll::Ready(Ok(()))
133    }
134}
futures_util/sink/with.rs

futures_util/sink/
with.rs
