Trait Sink

pub trait Sink<Item> {
    type Error;

    // Required methods
    fn poll_ready(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Self::Error>>;
    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error>;
    fn poll_flush(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Self::Error>>;
    fn poll_close(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Self::Error>>;
}

Available on crate feature sink only.

A Sink is a value into which other values can be sent, asynchronously.

Basic examples of sinks include the sending side of:

• Channels
• Sockets
• Pipes

In addition to such “primitive” sinks, it’s typical to layer additional functionality, such as buffering, on top of an existing sink.

Sending to a sink is “asynchronous” in the sense that the value may not be sent in its entirety immediately. Instead, values are sent in a two-phase way: first by initiating a send, and then by polling for completion. This two-phase setup is analogous to buffered writing in synchronous code, where writes often succeed immediately, but internally are buffered and are actually written only upon flushing.

In addition, the Sink may be full, in which case it is not even possible to start the sending process.

As with Future and Stream, the Sink trait is built from a few core required methods, and a host of default methods for working in a higher-level way. The Sink::send_all combinator is of particular importance: you can use it to send an entire stream to a sink, which is the simplest way to ultimately consume a stream.

Required Associated Types

type Error

The type of value produced by the sink when an error occurs.

Required Methods

fn poll_ready( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Result<(), Self::Error>>

Attempts to prepare the Sink to receive a value.

This method must be called and return Poll::Ready(Ok(())) prior to each call to start_send.

This method returns Poll::Ready once the underlying sink is ready to receive data. If this method returns Poll::Pending, the current task is registered to be notified (via cx.waker().wake_by_ref()) when poll_ready should be called again.

In most cases, if the sink encounters an error, the sink will permanently be unable to receive items.

fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error>

Begin the process of sending a value to the sink. Each call to this function must be preceded by a successful call to poll_ready which returned Poll::Ready(Ok(())).

As the name suggests, this method only begins the process of sending the item. If the sink employs buffering, the item isn’t fully processed until the buffer is fully flushed. Since sinks are designed to work with asynchronous I/O, the process of actually writing out the data to an underlying object takes place asynchronously. You must use poll_flush or poll_close in order to guarantee completion of a send.

Implementations of poll_ready and start_send will usually involve flushing behind the scenes in order to make room for new messages. It is only necessary to call poll_flush if you need to guarantee that all of the items placed into the Sink have been sent.

In most cases, if the sink encounters an error, the sink will permanently be unable to receive items.

fn poll_flush( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Result<(), Self::Error>>

Flush any remaining output from this sink.

Returns Poll::Ready(Ok(())) when no buffered items remain. If this value is returned then it is guaranteed that all previous values sent via start_send have been flushed.

Returns Poll::Pending if there is more work left to do, in which case the current task is scheduled (via cx.waker().wake_by_ref()) to wake up when poll_flush should be called again.

In most cases, if the sink encounters an error, the sink will permanently be unable to receive items.

fn poll_close( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Result<(), Self::Error>>

Flush any remaining output and close this sink, if necessary.

Returns Poll::Ready(Ok(())) when no buffered items remain and the sink has been successfully closed.

Returns Poll::Pending if there is more work left to do, in which case the current task is scheduled (via cx.waker().wake_by_ref()) to wake up when poll_close should be called again.

If this function encounters an error, the sink should be considered to have failed permanently, and no more Sink methods should be called.

Implementations on Foreign Types

impl<P, Item> Sink<Item> for Pin<P>

where P: DerefMut + Unpin, <P as Deref>::Target: Sink<Item>,

type Error = <<P as Deref>::Target as Sink<Item>>::Error

fn poll_ready( self: Pin<&mut Pin<P>>, cx: &mut Context<'_>, ) -> Poll<Result<(), <Pin<P> as Sink<Item>>::Error>>

fn start_send( self: Pin<&mut Pin<P>>, item: Item, ) -> Result<(), <Pin<P> as Sink<Item>>::Error>

fn poll_flush( self: Pin<&mut Pin<P>>, cx: &mut Context<'_>, ) -> Poll<Result<(), <Pin<P> as Sink<Item>>::Error>>

fn poll_close( self: Pin<&mut Pin<P>>, cx: &mut Context<'_>, ) -> Poll<Result<(), <Pin<P> as Sink<Item>>::Error>>

impl<S, Item> Sink<Item> for &mut S

where S: Sink<Item> + Unpin + ?Sized,

type Error = <S as Sink<Item>>::Error

fn poll_ready( self: Pin<&mut &mut S>, cx: &mut Context<'_>, ) -> Poll<Result<(), <&mut S as Sink<Item>>::Error>>

fn start_send( self: Pin<&mut &mut S>, item: Item, ) -> Result<(), <&mut S as Sink<Item>>::Error>

fn poll_flush( self: Pin<&mut &mut S>, cx: &mut Context<'_>, ) -> Poll<Result<(), <&mut S as Sink<Item>>::Error>>

fn poll_close( self: Pin<&mut &mut S>, cx: &mut Context<'_>, ) -> Poll<Result<(), <&mut S as Sink<Item>>::Error>>

Implementors

impl<A, B, Item> Sink<Item> for Either<A, B>

where A: Sink<Item>, B: Sink<Item, Error = A::Error>,

type Error = <A as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for AndThen<S, Fut, F>

where S: Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for Filter<S, Fut, F>

where S: Stream + Sink<Item>, F: FnMut(&S::Item) -> Fut, Fut: Future<Output = bool>,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for FilterMap<S, Fut, F>

where S: Stream + Sink<Item>, F: FnMut1<S::Item, Output = Fut>, Fut: Future,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for OrElse<S, Fut, F>

where S: Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for SkipWhile<S, Fut, F>

where S: Stream + Sink<Item>, F: FnMut(&S::Item) -> Fut, Fut: Future<Output = bool>,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for TakeWhile<S, Fut, F>

where S: Stream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for Then<S, Fut, F>

where S: Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item> Sink<Item> for TryFilterMap<S, Fut, F>

where S: Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Fut, F, Item, E> Sink<Item> for TryFilter<S, Fut, F>

where S: TryStream + Sink<Item, Error = E>,

type Error = E

impl<S, Fut, F, Item, E> Sink<Item> for TrySkipWhile<S, Fut, F>

where S: TryStream + Sink<Item, Error = E>,

type Error = E

impl<S, Fut, F, Item, E> Sink<Item> for TryTakeWhile<S, Fut, F>

where S: TryStream + Sink<Item, Error = E>,

type Error = E

impl<S, Fut, Item> Sink<Item> for TakeUntil<S, Fut>

where S: Stream + Sink<Item>, Fut: Future,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for BufferUnordered<S>

where S: Stream + Sink<Item>, S::Item: Future,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for Buffered<S>

where S: Stream + Sink<Item>, S::Item: Future,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for Chunks<S>

where S: Stream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for Enumerate<S>

where S: Stream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for Peekable<S>

where S: Sink<Item> + Stream,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for ReadyChunks<S>

where S: Stream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for Skip<S>

where S: Stream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for Take<S>

where S: Stream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for TryChunks<S>

where S: TryStream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for TryFlatten<S>

where S: TryStream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item> Sink<Item> for TryReadyChunks<S>

where S: TryStream + Sink<Item>,

type Error = <S as Sink<Item>>::Error

impl<S, Item, E> Sink<Item> for TryBufferUnordered<S>

where S: TryStream + Sink<Item, Error = E>, S::Ok: TryFuture<Error = E>,

type Error = E

impl<S, Item, E> Sink<Item> for TryBuffered<S>

where S: TryStream + Sink<Item, Error = E>, S::Ok: TryFuture<Error = E>,

type Error = E

impl<S, SinkItem> Sink<SinkItem> for Compat01As03Sink<S, SinkItem>

where S: Sink01<SinkItem = SinkItem>,

Available on crate feature compat only.

type Error = <S as Sink>::SinkError

impl<S: Stream + Sink<Item>, Item> Sink<Item> for Fuse<S>

type Error = <S as Sink<Item>>::Error

impl<S: Sink<Item>, Item> Sink<Item> for IntoStream<S>

type Error = <S as Sink<Item>>::Error

impl<S: Sink<Item>, Item> Sink<Item> for SplitSink<S, Item>

type Error = <S as Sink<Item>>::Error

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 as Sink<Item>>::Error

impl<Si, F, E, Item> Sink<Item> for SinkMapErr<Si, F>

where Si: Sink<Item>, F: FnOnce(Si::Error) -> E,

type Error = E

impl<Si, Item, E> Sink<Item> for SinkErrInto<Si, Item, E>

where Si: Sink<Item>, Si::Error: Into<E>,

type Error = E

impl<Si, Item, U, Fut, F, E> Sink<U> for With<Si, Item, U, Fut, F>

where Si: Sink<Item>, F: FnMut(U) -> Fut, Fut: Future<Output = Result<Item, E>>, E: From<Si::Error>,

type Error = E

impl<Si, Item, U, St, F> Sink<U> for WithFlatMap<Si, Item, U, St, F>

where Si: Sink<Item>, F: FnMut(U) -> St, St: Stream<Item = Result<Item, Si::Error>>,

type Error = <Si as Sink<Item>>::Error

impl<Si: Sink<Item>, Item> Sink<Item> for Buffer<Si, Item>

type Error = <Si as Sink<Item>>::Error

impl<St, F, Item> Sink<Item> for Map<St, F>

where St: Stream + Sink<Item>, F: FnMut1<St::Item>,

type Error = <St as Sink<Item>>::Error

impl<St, S, Fut, F, Item> Sink<Item> for Scan<St, S, Fut, F>

where St: Stream + Sink<Item>,

type Error = <St as Sink<Item>>::Error

impl<T> Sink<T> for Drain<T>

type Error = Infallible

impl<T, F, R, Item, E> Sink<Item> for Unfold<T, F, R>

where F: FnMut(T, Item) -> R, R: Future<Output = Result<T, E>>,

type Error = E

impl<W: AsyncWrite, Item: AsRef<[u8]>> Sink<Item> for IntoSink<W, Item>

Available on crate feature io only.

type Error = Error

impl<_Item, F> Sink<_Item> for FlattenStream<F>

where Flatten<F, <F as Future>::Output>: Sink<_Item>, F: Future,

type Error = <Flatten<F, <F as Future>::Output> as Sink<_Item>>::Error

impl<_Item, Fut> Sink<_Item> for TryFlattenStream<Fut>

where TryFlatten<Fut, Fut::Ok>: Sink<_Item>, Fut: TryFuture,

type Error = <TryFlatten<Fut, <Fut as TryFuture>::Ok> as Sink<_Item>>::Error

impl<_Item, Fut, Si> Sink<_Item> for FlattenSink<Fut, Si>

where TryFlatten<Fut, Si>: Sink<_Item>,

type Error = <TryFlatten<Fut, Si> as Sink<_Item>>::Error

impl<_Item, St> Sink<_Item> for Flatten<St>

where Flatten<St, St::Item>: Sink<_Item>, St: Stream,

type Error = <Flatten<St, <St as Stream>::Item> as Sink<_Item>>::Error

impl<_Item, St> Sink<_Item> for TryFlattenUnordered<St>

where FlattenUnorderedWithFlowController<NestedTryStreamIntoEitherTryStream<St>, PropagateBaseStreamError<St>>: Sink<_Item>, St: TryStream, St::Ok: TryStream + Unpin, <St::Ok as TryStream>::Error: From<St::Error>,

type Error = <FlattenUnorderedWithFlowController<NestedTryStreamIntoEitherTryStream<St>, PropagateBaseStreamError<St>> as Sink<_Item>>::Error

impl<_Item, St, E> Sink<_Item> for ErrInto<St, E>

where MapErr<St, IntoFn<E>>: Sink<_Item>,

type Error = <MapErr<St, IntoFn<E>> as Sink<_Item>>::Error

impl<_Item, St, F> Sink<_Item> for Inspect<St, F>

where Map<St, InspectFn<F>>: Sink<_Item>,

type Error = <Map<St, InspectFn<F>> as Sink<_Item>>::Error

impl<_Item, St, F> Sink<_Item> for InspectErr<St, F>

where Inspect<IntoStream<St>, InspectErrFn<F>>: Sink<_Item>,

type Error = <Inspect<IntoStream<St>, InspectErrFn<F>> as Sink<_Item>>::Error

impl<_Item, St, F> Sink<_Item> for InspectOk<St, F>

where Inspect<IntoStream<St>, InspectOkFn<F>>: Sink<_Item>,

type Error = <Inspect<IntoStream<St>, InspectOkFn<F>> as Sink<_Item>>::Error

impl<_Item, St, F> Sink<_Item> for MapErr<St, F>

where Map<IntoStream<St>, MapErrFn<F>>: Sink<_Item>,

type Error = <Map<IntoStream<St>, MapErrFn<F>> as Sink<_Item>>::Error

impl<_Item, St, F> Sink<_Item> for MapOk<St, F>

where Map<IntoStream<St>, MapOkFn<F>>: Sink<_Item>,

type Error = <Map<IntoStream<St>, MapOkFn<F>> as Sink<_Item>>::Error

impl<_Item, St, U, F> Sink<_Item> for FlatMap<St, U, F>

where Flatten<Map<St, F>, U>: Sink<_Item>,

type Error = <Flatten<Map<St, F>, U> as Sink<_Item>>::Error

impl<_Item, St, U, F> Sink<_Item> for FlatMapUnordered<St, U, F>

where FlattenUnordered<Map<St, F>>: Sink<_Item>, St: Stream, U: Stream + Unpin, F: FnMut(St::Item) -> U,

type Error = <FlattenUnorderedWithFlowController<Map<St, F>, ()> as Sink<_Item>>::Error