futures_util/sink/
with_flat_map.rs

1use core::marker::PhantomData;
2
3use futures_core::{Poll, Async, Stream};
4use futures_core::task;
5use futures_sink::Sink;
6
7/// Sink for the `Sink::with_flat_map` combinator, chaining a computation that returns an iterator
8/// to run prior to pushing a value into the underlying sink
9#[derive(Debug)]
10#[must_use = "sinks do nothing unless polled"]
11pub struct WithFlatMap<S, U, St, F>
12where
13    S: Sink,
14    F: FnMut(U) -> St,
15    St: Stream<Item = S::SinkItem, Error=S::SinkError>,
16{
17    sink: S,
18    f: F,
19    stream: Option<St>,
20    buffer: Option<S::SinkItem>,
21    _phantom: PhantomData<fn(U)>,
22}
23
24pub fn new<S, U, St, F>(sink: S, f: F) -> WithFlatMap<S, U, St, F>
25where
26    S: Sink,
27    F: FnMut(U) -> St,
28    St: Stream<Item = S::SinkItem, Error=S::SinkError>,
29{
30    WithFlatMap {
31        sink: sink,
32        f: f,
33        stream: None,
34        buffer: None,
35        _phantom: PhantomData,
36    }
37}
38
39impl<S, U, St, F> WithFlatMap<S, U, St, F>
40where
41    S: Sink,
42    F: FnMut(U) -> St,
43    St: Stream<Item = S::SinkItem, Error=S::SinkError>,
44{
45    /// Get a shared reference to the inner sink.
46    pub fn get_ref(&self) -> &S {
47        &self.sink
48    }
49
50    /// Get a mutable reference to the inner sink.
51    pub fn get_mut(&mut self) -> &mut S {
52        &mut self.sink
53    }
54
55    /// Consumes this combinator, returning the underlying sink.
56    ///
57    /// Note that this may discard intermediate state of this combinator, so
58    /// care should be taken to avoid losing resources when this is called.
59    pub fn into_inner(self) -> S {
60        self.sink
61    }
62
63    fn try_empty_stream(&mut self, cx: &mut task::Context) -> Poll<(), S::SinkError> {
64        if let Some(x) = self.buffer.take() {
65            match self.sink.poll_ready(cx)? {
66                Async::Ready(()) => self.sink.start_send(x)?,
67                Async::Pending => {
68                    self.buffer = Some(x);
69                    return Ok(Async::Pending);
70                }
71            }
72        }
73        if let Some(mut stream) = self.stream.take() {
74            while let Some(x) = try_ready!(stream.poll_next(cx)) {
75                match self.sink.poll_ready(cx)? {
76                    Async::Ready(()) => self.sink.start_send(x)?,
77                    Async::Pending => {
78                        self.stream = Some(stream);
79                        self.buffer = Some(x);
80                        return Ok(Async::Pending);
81                    }
82                }
83            }
84        }
85        Ok(Async::Ready(()))
86    }
87}
88
89impl<S, U, St, F> Stream for WithFlatMap<S, U, St, F>
90where
91    S: Stream + Sink,
92    F: FnMut(U) -> St,
93    St: Stream<Item = S::SinkItem, Error=S::SinkError>,
94{
95    type Item = S::Item;
96    type Error = S::Error;
97    fn poll_next(&mut self, cx: &mut task::Context) -> Poll<Option<S::Item>, S::Error> {
98        self.sink.poll_next(cx)
99    }
100}
101
102impl<S, U, St, F> Sink for WithFlatMap<S, U, St, F>
103where
104    S: Sink,
105    F: FnMut(U) -> St,
106    St: Stream<Item = S::SinkItem, Error=S::SinkError>,
107{
108    type SinkItem = U;
109    type SinkError = S::SinkError;
110
111    fn poll_ready(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
112        self.try_empty_stream(cx)
113    }
114
115    fn start_send(&mut self, i: Self::SinkItem) -> Result<(), Self::SinkError> {
116        assert!(self.stream.is_none());
117        self.stream = Some((self.f)(i));
118        Ok(())
119    }
120
121    fn poll_flush(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
122        if self.try_empty_stream(cx)?.is_pending() {
123            return Ok(Async::Pending);
124        }
125        self.sink.poll_flush(cx)
126    }
127
128    fn poll_close(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
129        if self.try_empty_stream(cx)?.is_pending() {
130            return Ok(Async::Pending);
131        }
132        self.sink.poll_close(cx)
133    }
134}
futures_util/sink/with_flat_map.rs

futures_util/sink/
with_flat_map.rs
