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_skip_while`](super::TryStreamExt::try_skip_while)
13     /// method.
14     #[must_use = "streams do nothing unless polled"]
15     pub struct TrySkipWhile<St, Fut, F> where St: TryStream {
16         #[pin]
17         stream: St,
18         f: F,
19         #[pin]
20         pending_fut: Option<Fut>,
21         pending_item: Option<St::Ok>,
22         done_skipping: bool,
23     }
24 }
25 
26 impl<St, Fut, F> fmt::Debug for TrySkipWhile<St, Fut, F>
27 where
28     St: TryStream + fmt::Debug,
29     St::Ok: fmt::Debug,
30     Fut: fmt::Debug,
31 {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result32     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
33         f.debug_struct("TrySkipWhile")
34             .field("stream", &self.stream)
35             .field("pending_fut", &self.pending_fut)
36             .field("pending_item", &self.pending_item)
37             .field("done_skipping", &self.done_skipping)
38             .finish()
39     }
40 }
41 
42 impl<St, Fut, F> TrySkipWhile<St, Fut, F>
43 where
44     St: TryStream,
45     F: FnMut(&St::Ok) -> Fut,
46     Fut: TryFuture<Ok = bool, Error = St::Error>,
47 {
new(stream: St, f: F) -> Self48     pub(super) fn new(stream: St, f: F) -> Self {
49         Self { stream, f, pending_fut: None, pending_item: None, done_skipping: false }
50     }
51 
52     delegate_access_inner!(stream, St, ());
53 }
54 
55 impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F>
56 where
57     St: TryStream,
58     F: FnMut(&St::Ok) -> Fut,
59     Fut: TryFuture<Ok = bool, Error = St::Error>,
60 {
61     type Item = Result<St::Ok, St::Error>;
62 
poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>63     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
64         let mut this = self.project();
65 
66         if *this.done_skipping {
67             return this.stream.try_poll_next(cx);
68         }
69 
70         Poll::Ready(loop {
71             if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
72                 let res = ready!(fut.try_poll(cx));
73                 this.pending_fut.set(None);
74                 let skipped = res?;
75                 let item = this.pending_item.take();
76                 if !skipped {
77                     *this.done_skipping = true;
78                     break item.map(Ok);
79                 }
80             } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
81                 this.pending_fut.set(Some((this.f)(&item)));
82                 *this.pending_item = Some(item);
83             } else {
84                 break None;
85             }
86         })
87     }
88 
size_hint(&self) -> (usize, Option<usize>)89     fn size_hint(&self) -> (usize, Option<usize>) {
90         let pending_len = if self.pending_item.is_some() { 1 } else { 0 };
91         let (_, upper) = self.stream.size_hint();
92         let upper = match upper {
93             Some(x) => x.checked_add(pending_len),
94             None => None,
95         };
96         (0, upper) // can't know a lower bound, due to the predicate
97     }
98 }
99 
100 impl<St, Fut, F> FusedStream for TrySkipWhile<St, Fut, F>
101 where
102     St: TryStream + FusedStream,
103     F: FnMut(&St::Ok) -> Fut,
104     Fut: TryFuture<Ok = bool, Error = St::Error>,
105 {
is_terminated(&self) -> bool106     fn is_terminated(&self) -> bool {
107         self.pending_item.is_none() && self.stream.is_terminated()
108     }
109 }
110 
111 // Forwarding impl of Sink from the underlying stream
112 #[cfg(feature = "sink")]
113 impl<S, Fut, F, Item, E> Sink<Item> for TrySkipWhile<S, Fut, F>
114 where
115     S: TryStream + Sink<Item, Error = E>,
116 {
117     type Error = E;
118 
119     delegate_sink!(stream, Item);
120 }
121