futures_util/sink/
with.rs

1use core::fmt;
2use core::marker::PhantomData;
3use core::pin::Pin;
4use futures_core::future::Future;
5use futures_core::ready;
6use futures_core::stream::{FusedStream, 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<S, Item, U, Fut, F> FusedStream for With<S, Item, U, Fut, F>
78where
79    S: FusedStream + Sink<Item>,
80    F: FnMut(U) -> Fut,
81    Fut: Future,
82{
83    fn is_terminated(&self) -> bool {
84        self.sink.is_terminated()
85    }
86}
87
88impl<Si, Item, U, Fut, F, E> With<Si, Item, U, Fut, F>
89where
90    Si: Sink<Item>,
91    F: FnMut(U) -> Fut,
92    Fut: Future<Output = Result<Item, E>>,
93    E: From<Si::Error>,
94{
95    delegate_access_inner!(sink, Si, ());
96
97    /// Completes the processing of previous item if any.
98    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), E>> {
99        let mut this = self.project();
100
101        let item = match this.state.as_mut().as_pin_mut() {
102            None => return Poll::Ready(Ok(())),
103            Some(fut) => ready!(fut.poll(cx))?,
104        };
105        this.state.set(None);
106        this.sink.start_send(item)?;
107        Poll::Ready(Ok(()))
108    }
109}
110
111impl<Si, Item, U, Fut, F, E> Sink<U> for With<Si, Item, U, Fut, F>
112where
113    Si: Sink<Item>,
114    F: FnMut(U) -> Fut,
115    Fut: Future<Output = Result<Item, E>>,
116    E: From<Si::Error>,
117{
118    type Error = E;
119
120    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
121        ready!(self.as_mut().poll(cx))?;
122        ready!(self.project().sink.poll_ready(cx)?);
123        Poll::Ready(Ok(()))
124    }
125
126    fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
127        let mut this = self.project();
128
129        assert!(this.state.is_none());
130        this.state.set(Some((this.f)(item)));
131        Ok(())
132    }
133
134    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
135        ready!(self.as_mut().poll(cx))?;
136        ready!(self.project().sink.poll_flush(cx)?);
137        Poll::Ready(Ok(()))
138    }
139
140    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
141        ready!(self.as_mut().poll(cx))?;
142        ready!(self.project().sink.poll_close(cx)?);
143        Poll::Ready(Ok(()))
144    }
145}
futures_util/sink/with.rs

futures_util/sink/
with.rs
