async-sink 0.3.1

The asynchronous `Sink` trait for the tokio ecosystem.
Documentation 
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use crate::Sink;
use core::fmt::{Debug, Formatter, Result as FmtResult};
use core::pin::Pin;
use core::task::{Context, Poll};

/// Sink that clones incoming items and forwards them to two sinks at the same time.
///
/// Backpressure from any downstream sink propagates up, which means that this sink
/// can only process items as fast as its _slowest_ downstream sink.
#[must_use = "sinks do nothing unless polled"]
pub struct Fanout<Si1, Si2> {
    sink1: Si1,
    sink2: Si2,
}

impl<Si1, Si2> Unpin for Fanout<Si1, Si2>
where
    Si1: Unpin,
    Si2: Unpin,
{
}

impl<Si1, Si2> Fanout<Si1, Si2> {
    pub(super) fn new(sink1: Si1, sink2: Si2) -> Self {
        Self { sink1, sink2 }
    }

    /// Get a shared reference to the inner sinks.
    pub fn get_ref(&self) -> (&Si1, &Si2) {
        (&self.sink1, &self.sink2)
    }

    /// Get a mutable reference to the inner sinks.
    pub fn get_mut(&mut self) -> (&mut Si1, &mut Si2) {
        (&mut self.sink1, &mut self.sink2)
    }

    /// Get a pinned mutable reference to the inner sinks.
    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut Si1>, Pin<&mut Si2>) {
        unsafe {
            let this = self.get_unchecked_mut();
            (
                Pin::new_unchecked(&mut this.sink1),
                Pin::new_unchecked(&mut this.sink2),
            )
        }
    }

    /// Consumes this combinator, returning the underlying sinks.
    ///
    /// Note that this may discard intermediate state of this combinator,
    /// so care should be taken to avoid losing resources when this is called.
    pub fn into_inner(self) -> (Si1, Si2) {
        (self.sink1, self.sink2)
    }
}

impl<Si1: Debug, Si2: Debug> Debug for Fanout<Si1, Si2> {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        f.debug_struct("Fanout")
            .field("sink1", &self.sink1)
            .field("sink2", &self.sink2)
            .finish()
    }
}

impl<Si1, Si2, Item> Sink<Item> for Fanout<Si1, Si2>
where
    Si1: Sink<Item>,
    Item: Clone,
    Si2: Sink<Item, Error = Si1::Error>,
{
    type Error = Si1::Error;

    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        let (sink1, sink2) = self.get_pin_mut();

        match (sink2.poll_ready(cx), sink1.poll_ready(cx)) {
            (Poll::Ready(Ok(())), Poll::Ready(Ok(()))) => Poll::Ready(Ok(())),
            (Poll::Ready(Err(e)), _) | (_, Poll::Ready(Err(e))) => Poll::Ready(Err(e)),
            (_, Poll::Pending) | (Poll::Pending, _) => Poll::Pending,
        }
    }

    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
        let (sink1, sink2) = self.get_pin_mut();

        match (sink1.start_send(item.clone()), sink2.start_send(item)) {
            (Ok(()), Ok(())) => Ok(()),
            (Err(e), _) | (_, Err(e)) => Err(e),
        }
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        let (sink1, sink2) = self.get_pin_mut();

        match (sink2.poll_flush(cx), sink1.poll_flush(cx)) {
            (Poll::Ready(Ok(())), Poll::Ready(Ok(()))) => Poll::Ready(Ok(())),
            (Poll::Ready(Err(e)), _) | (_, Poll::Ready(Err(e))) => Poll::Ready(Err(e)),
            (_, Poll::Pending) | (Poll::Pending, _) => Poll::Pending,
        }
    }

    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        let (sink1, sink2) = self.get_pin_mut();

        match (sink2.poll_close(cx), sink1.poll_close(cx)) {
            (Poll::Ready(Ok(())), Poll::Ready(Ok(()))) => Poll::Ready(Ok(())),
            (Poll::Ready(Err(e)), _) | (_, Poll::Ready(Err(e))) => Poll::Ready(Err(e)),
            (_, Poll::Pending) | (Poll::Pending, _) => Poll::Pending,
        }
    }
}