futures_util/sink/
fanout.rs

1use core::fmt::{Debug, Formatter, Result as FmtResult};
2
3use futures_core::{Async, Poll};
4use futures_core::task;
5use futures_sink::{ Sink};
6
7/// Sink that clones incoming items and forwards them to two sinks at the same time.
8///
9/// Backpressure from any downstream sink propagates up, which means that this sink
10/// can only process items as fast as its _slowest_ downstream sink.
11#[derive(Clone)]
12pub struct Fanout<A: Sink, B: Sink> {
13    left: A,
14    right: B
15}
16
17impl<A: Sink, B: Sink> Fanout<A, B> {
18    /// Consumes this combinator, returning the underlying sinks.
19    ///
20    /// Note that this may discard intermediate state of this combinator,
21    /// so care should be taken to avoid losing resources when this is called.
22    pub fn into_inner(self) -> (A, B) {
23        (self.left, self.right)
24    }
25}
26
27impl<A: Sink + Debug, B: Sink + Debug> Debug for Fanout<A, B>
28    where A::SinkItem: Debug,
29          B::SinkItem: Debug
30{
31    fn fmt(&self, f: &mut Formatter) -> FmtResult {
32        f.debug_struct("Fanout")
33            .field("left", &self.left)
34            .field("right", &self.right)
35            .finish()
36    }
37}
38
39pub fn new<A: Sink, B: Sink>(left: A, right: B) -> Fanout<A, B> {
40    Fanout {left, right}
41}
42
43impl<A, B> Sink for Fanout<A, B>
44    where A: Sink,
45          A::SinkItem: Clone,
46          B: Sink<SinkItem=A::SinkItem, SinkError=A::SinkError>
47{
48    type SinkItem = A::SinkItem;
49    type SinkError = A::SinkError;
50
51    fn poll_ready(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
52        let left_ready = self.left.poll_ready(cx)?.is_ready();
53        let right_ready = self.right.poll_ready(cx)?.is_ready();
54        let ready = left_ready && right_ready;
55        Ok(if ready {Async::Ready(())} else {Async::Pending})
56    }
57
58    fn start_send(&mut self, item: Self::SinkItem) -> Result<(), Self::SinkError> {
59        self.left.start_send(item.clone())?;
60        self.right.start_send(item)?;
61        Ok(())
62    }
63
64    fn poll_flush(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
65        let left_ready = self.left.poll_flush(cx)?.is_ready();
66        let right_ready = self.right.poll_flush(cx)?.is_ready();
67        let ready = left_ready && right_ready;
68        Ok(if ready {Async::Ready(())} else {Async::Pending})
69    }
70
71    fn poll_close(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
72        let left_ready = self.left.poll_close(cx)?.is_ready();
73        let right_ready = self.right.poll_close(cx)?.is_ready();
74        let ready = left_ready && right_ready;
75        Ok(if ready {Async::Ready(())} else {Async::Pending})
76    }
77}
78
79#[cfg(test)]
80#[cfg(feature = "std")]
81mod tests {
82    use future::FutureExt;
83    use futures_channel::mpsc;
84    use futures_executor::block_on;
85    use sink::SinkExt;
86    use std::iter::Iterator;
87    use std::vec::Vec;
88    use stream::{self, StreamExt};
89
90    #[test]
91    fn it_works() {
92        let src = stream::iter_ok::<_, ()>(0..10);
93        let (sender0, receiver0) = mpsc::channel(1);
94        let (sender1, receiver1) = mpsc::channel(2);
95        let senders = sender0.fanout(sender1).sink_map_err(|_| ());
96        let fwd = src.forward(senders).map(|_| ());
97        let list0 = receiver0.collect::<Vec<_>>().map_err(|_| ());
98        let list1 = receiver1.collect::<Vec<_>>().map_err(|_| ());
99        let lists = fwd.join(list0.join(list1)).map(|(_, lists)| lists);
100        let lists = block_on(lists);
101        let lists = lists.as_ref()
102            .map(|&(ref list0, ref list1)| (&**list0, &**list1));
103        let expected = (0..10).collect::<Vec<_>>();
104        assert_eq!(lists, Ok((&*expected, &*expected)));
105    }
106}
futures_util/sink/fanout.rs

futures_util/sink/
fanout.rs
