1 use core::fmt;
2 use core::pin::Pin;
3 use futures_core::future::Future;
4 use futures_core::stream::{FusedStream, Stream};
5 use futures_core::task::{Context, Poll};
6 #[cfg(feature = "sink")]
7 use futures_sink::Sink;
8 use pin_utils::{unsafe_pinned, unsafe_unpinned};
9 
10 /// Stream for the [`filter`](super::StreamExt::filter) method.
11 #[must_use = "streams do nothing unless polled"]
12 pub struct Filter<St, Fut, F>
13     where St: Stream,
14 {
15     stream: St,
16     f: F,
17     pending_fut: Option<Fut>,
18     pending_item: Option<St::Item>,
19 }
20 
21 impl<St, Fut, F> Unpin for Filter<St, Fut, F>
22 where
23     St: Stream + Unpin,
24     Fut: Unpin,
25 {}
26 
27 impl<St, Fut, F> fmt::Debug for Filter<St, Fut, F>
28 where
29     St: Stream + fmt::Debug,
30     St::Item: fmt::Debug,
31     Fut: fmt::Debug,
32 {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result33     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
34         f.debug_struct("Filter")
35             .field("stream", &self.stream)
36             .field("pending_fut", &self.pending_fut)
37             .field("pending_item", &self.pending_item)
38             .finish()
39     }
40 }
41 
42 impl<St, Fut, F> Filter<St, Fut, F>
43 where St: Stream,
44       F: FnMut(&St::Item) -> Fut,
45       Fut: Future<Output = bool>,
46 {
47     unsafe_pinned!(stream: St);
48     unsafe_unpinned!(f: F);
49     unsafe_pinned!(pending_fut: Option<Fut>);
50     unsafe_unpinned!(pending_item: Option<St::Item>);
51 
new(stream: St, f: F) -> Filter<St, Fut, F>52     pub(super) fn new(stream: St, f: F) -> Filter<St, Fut, F> {
53         Filter {
54             stream,
55             f,
56             pending_fut: None,
57             pending_item: None,
58         }
59     }
60 
61     /// Acquires a reference to the underlying stream that this combinator is
62     /// pulling from.
get_ref(&self) -> &St63     pub fn get_ref(&self) -> &St {
64         &self.stream
65     }
66 
67     /// Acquires a mutable reference to the underlying stream that this
68     /// combinator is pulling from.
69     ///
70     /// Note that care must be taken to avoid tampering with the state of the
71     /// stream which may otherwise confuse this combinator.
get_mut(&mut self) -> &mut St72     pub fn get_mut(&mut self) -> &mut St {
73         &mut self.stream
74     }
75 
76     /// Acquires a pinned mutable reference to the underlying stream that this
77     /// combinator is pulling from.
78     ///
79     /// Note that care must be taken to avoid tampering with the state of the
80     /// stream which may otherwise confuse this combinator.
get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St>81     pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
82         self.stream()
83     }
84 
85     /// Consumes this combinator, returning the underlying stream.
86     ///
87     /// Note that this may discard intermediate state of this combinator, so
88     /// care should be taken to avoid losing resources when this is called.
into_inner(self) -> St89     pub fn into_inner(self) -> St {
90         self.stream
91     }
92 }
93 
94 impl<St, Fut, F> FusedStream for Filter<St, Fut, F>
95     where St: Stream + FusedStream,
96           F: FnMut(&St::Item) -> Fut,
97           Fut: Future<Output = bool>,
98 {
is_terminated(&self) -> bool99     fn is_terminated(&self) -> bool {
100         self.pending_fut.is_none() && self.stream.is_terminated()
101     }
102 }
103 
104 impl<St, Fut, F> Stream for Filter<St, Fut, F>
105     where St: Stream,
106           F: FnMut(&St::Item) -> Fut,
107           Fut: Future<Output = bool>,
108 {
109     type Item = St::Item;
110 
poll_next( mut self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Option<St::Item>>111     fn poll_next(
112         mut self: Pin<&mut Self>,
113         cx: &mut Context<'_>,
114     ) -> Poll<Option<St::Item>> {
115         loop {
116             if self.pending_fut.is_none() {
117                 let item = match ready!(self.as_mut().stream().poll_next(cx)) {
118                     Some(e) => e,
119                     None => return Poll::Ready(None),
120                 };
121                 let fut = (self.as_mut().f())(&item);
122                 self.as_mut().pending_fut().set(Some(fut));
123                 *self.as_mut().pending_item() = Some(item);
124             }
125 
126             let yield_item = ready!(self.as_mut().pending_fut().as_pin_mut().unwrap().poll(cx));
127             self.as_mut().pending_fut().set(None);
128             let item = self.as_mut().pending_item().take().unwrap();
129 
130             if yield_item {
131                 return Poll::Ready(Some(item));
132             }
133         }
134     }
135 
size_hint(&self) -> (usize, Option<usize>)136     fn size_hint(&self) -> (usize, Option<usize>) {
137         let pending_len = if self.pending_item.is_some() { 1 } else { 0 };
138         let (_, upper) = self.stream.size_hint();
139         let upper = match upper {
140             Some(x) => x.checked_add(pending_len),
141             None => None,
142         };
143         (0, upper) // can't know a lower bound, due to the predicate
144     }
145 }
146 
147 // Forwarding impl of Sink from the underlying stream
148 #[cfg(feature = "sink")]
149 impl<S, Fut, F, Item> Sink<Item> for Filter<S, Fut, F>
150     where S: Stream + Sink<Item>,
151           F: FnMut(&S::Item) -> Fut,
152           Fut: Future<Output = bool>,
153 {
154     type Error = S::Error;
155 
156     delegate_sink!(stream, Item);
157 }
158