1 use core::fmt;
2 use core::marker::PhantomData;
3 use core::pin::Pin;
4 use futures_core::future::Future;
5 use futures_core::ready;
6 use futures_core::stream::Stream;
7 use futures_core::task::{Context, Poll};
8 use futures_sink::Sink;
9 use pin_project_lite::pin_project;
10 
11 pin_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 
24 impl<Si, Item, U, Fut, F> fmt::Debug for With<Si, Item, U, Fut, F>
25 where
26     Si: fmt::Debug,
27     Fut: fmt::Debug,
28 {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result29     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 
34 impl<Si, Item, U, Fut, F> With<Si, Item, U, Fut, F>
35 where
36     Si: Sink<Item>,
37     F: FnMut(U) -> Fut,
38     Fut: Future,
39 {
new<E>(sink: Si, f: F) -> Self where Fut: Future<Output = Result<Item, E>>, E: From<Si::Error>,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 
49 impl<Si, Item, U, Fut, F> Clone for With<Si, Item, U, Fut, F>
50 where
51     Si: Clone,
52     F: Clone,
53     Fut: Clone,
54 {
clone(&self) -> Self55     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
66 impl<S, Item, U, Fut, F> Stream for With<S, Item, U, Fut, F>
67 where
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 
77 impl<Si, Item, U, Fut, F, E> With<Si, Item, U, Fut, F>
78 where
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.
poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), E>>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 
100 impl<Si, Item, U, Fut, F, E> Sink<U> for With<Si, Item, U, Fut, F>
101 where
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 
poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>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 
start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error>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 
poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>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 
poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>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 }
135