1 use core::fmt;
2 use core::pin::Pin;
3 use futures_core::future::TryFuture;
4 use futures_core::ready;
5 use futures_core::stream::{FusedStream, Stream, TryStream};
6 use futures_core::task::{Context, Poll};
7 #[cfg(feature = "sink")]
8 use futures_sink::Sink;
9 use pin_project_lite::pin_project;
10 
11 pin_project! {
12     /// Stream for the [`try_take_while`](super::TryStreamExt::try_take_while)
13     /// method.
14     #[must_use = "streams do nothing unless polled"]
15     pub struct TryTakeWhile<St, Fut, F>
16     where
17         St: TryStream,
18     {
19         #[pin]
20         stream: St,
21         f: F,
22         #[pin]
23         pending_fut: Option<Fut>,
24         pending_item: Option<St::Ok>,
25         done_taking: bool,
26     }
27 }
28 
29 impl<St, Fut, F> fmt::Debug for TryTakeWhile<St, Fut, F>
30 where
31     St: TryStream + fmt::Debug,
32     St::Ok: fmt::Debug,
33     Fut: fmt::Debug,
34 {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result35     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
36         f.debug_struct("TryTakeWhile")
37             .field("stream", &self.stream)
38             .field("pending_fut", &self.pending_fut)
39             .field("pending_item", &self.pending_item)
40             .field("done_taking", &self.done_taking)
41             .finish()
42     }
43 }
44 
45 impl<St, Fut, F> TryTakeWhile<St, Fut, F>
46 where
47     St: TryStream,
48     F: FnMut(&St::Ok) -> Fut,
49     Fut: TryFuture<Ok = bool, Error = St::Error>,
50 {
new(stream: St, f: F) -> Self51     pub(super) fn new(stream: St, f: F) -> Self {
52         Self { stream, f, pending_fut: None, pending_item: None, done_taking: false }
53     }
54 
55     delegate_access_inner!(stream, St, ());
56 }
57 
58 impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F>
59 where
60     St: TryStream,
61     F: FnMut(&St::Ok) -> Fut,
62     Fut: TryFuture<Ok = bool, Error = St::Error>,
63 {
64     type Item = Result<St::Ok, St::Error>;
65 
poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>66     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
67         let mut this = self.project();
68 
69         if *this.done_taking {
70             return Poll::Ready(None);
71         }
72 
73         Poll::Ready(loop {
74             if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
75                 let res = ready!(fut.try_poll(cx));
76                 this.pending_fut.set(None);
77                 let take = res?;
78                 let item = this.pending_item.take();
79                 if take {
80                     break item.map(Ok);
81                 } else {
82                     *this.done_taking = true;
83                     break None;
84                 }
85             } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
86                 this.pending_fut.set(Some((this.f)(&item)));
87                 *this.pending_item = Some(item);
88             } else {
89                 break None;
90             }
91         })
92     }
93 
size_hint(&self) -> (usize, Option<usize>)94     fn size_hint(&self) -> (usize, Option<usize>) {
95         if self.done_taking {
96             return (0, Some(0));
97         }
98 
99         let pending_len = usize::from(self.pending_item.is_some());
100         let (_, upper) = self.stream.size_hint();
101         let upper = match upper {
102             Some(x) => x.checked_add(pending_len),
103             None => None,
104         };
105         (0, upper) // can't know a lower bound, due to the predicate
106     }
107 }
108 
109 impl<St, Fut, F> FusedStream for TryTakeWhile<St, Fut, F>
110 where
111     St: TryStream + FusedStream,
112     F: FnMut(&St::Ok) -> Fut,
113     Fut: TryFuture<Ok = bool, Error = St::Error>,
114 {
is_terminated(&self) -> bool115     fn is_terminated(&self) -> bool {
116         self.done_taking || self.pending_item.is_none() && self.stream.is_terminated()
117     }
118 }
119 
120 // Forwarding impl of Sink from the underlying stream
121 #[cfg(feature = "sink")]
122 impl<S, Fut, F, Item, E> Sink<Item> for TryTakeWhile<S, Fut, F>
123 where
124     S: TryStream + Sink<Item, Error = E>,
125 {
126     type Error = E;
127 
128     delegate_sink!(stream, Item);
129 }
130