futures_util::sink

Trait Sink

source
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.
Expand description

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§

source

type Error

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

Required Methods§

source

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.

source

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.

source

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.

source

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§

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

impl<S, Item> Sink<Item> for &mut S
where S: Sink<Item> + Unpin + ?Sized,

source§

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

source§

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

source§

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

source§

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

source§

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

Implementors§

source§

impl<A, B, Item> Sink<Item> for Either<A, B>
where A: Sink<Item>, B: Sink<Item, Error = A::Error>,

source§

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

source§

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

source§

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

source§

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>,

source§

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

source§

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,

source§

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

source§

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

source§

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

source§

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>,

source§

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

source§

impl<S, Fut, F, Item> Sink<Item> for TakeWhile<S, Fut, F>
where S: Stream + Sink<Item>,

source§

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

source§

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

source§

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

source§

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

source§

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

source§

impl<S, Fut, F, Item, E> Sink<Item> for TryFilter<S, Fut, F>
where S: TryStream + Sink<Item, Error = E>,

source§

type Error = E

source§

impl<S, Fut, F, Item, E> Sink<Item> for TrySkipWhile<S, Fut, F>
where S: TryStream + Sink<Item, Error = E>,

source§

type Error = E

source§

impl<S, Fut, F, Item, E> Sink<Item> for TryTakeWhile<S, Fut, F>
where S: TryStream + Sink<Item, Error = E>,

source§

type Error = E

source§

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

source§

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

source§

impl<S, Item> Sink<Item> for BufferUnordered<S>
where S: Stream + Sink<Item>, S::Item: Future,

source§

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

source§

impl<S, Item> Sink<Item> for Buffered<S>
where S: Stream + Sink<Item>, S::Item: Future,

source§

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

source§

impl<S, Item> Sink<Item> for Chunks<S>
where S: Stream + Sink<Item>,

source§

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

source§

impl<S, Item> Sink<Item> for Enumerate<S>
where S: Stream + Sink<Item>,

source§

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

source§

impl<S, Item> Sink<Item> for Peekable<S>
where S: Sink<Item> + Stream,

source§

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

source§

impl<S, Item> Sink<Item> for ReadyChunks<S>
where S: Stream + Sink<Item>,

source§

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

source§

impl<S, Item> Sink<Item> for Skip<S>
where S: Stream + Sink<Item>,

source§

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

source§

impl<S, Item> Sink<Item> for Take<S>
where S: Stream + Sink<Item>,

source§

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

source§

impl<S, Item> Sink<Item> for TryChunks<S>
where S: TryStream + Sink<Item>,

source§

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

source§

impl<S, Item> Sink<Item> for TryFlatten<S>
where S: TryStream + Sink<Item>,

source§

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

source§

impl<S, Item> Sink<Item> for TryReadyChunks<S>
where S: TryStream + Sink<Item>,

source§

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

source§

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

source§

type Error = E

source§

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

source§

type Error = E

source§

impl<S, SinkItem> Sink<SinkItem> for Compat01As03Sink<S, SinkItem>
where S: Sink01<SinkItem = SinkItem>,

Available on crate feature compat only.
source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

type Error = <Si1 as Sink<Item>>::Error

source§

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

source§

type Error = E

source§

impl<Si, Item, E> Sink<Item> for SinkErrInto<Si, Item, E>
where Si: Sink<Item>, Si::Error: Into<E>,

source§

type Error = E

source§

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>,

source§

type Error = E

source§

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>>,

source§

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

source§

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

source§

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

source§

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

source§

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

source§

impl<St, S, Fut, F, Item> Sink<Item> for Scan<St, S, Fut, F>
where St: Stream + Sink<Item>,

source§

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

source§

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

source§

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>>,

source§

type Error = E

source§

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

Available on crate feature io only.
source§

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

source§

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

source§

impl<_Item, Fut> Sink<_Item> for TryFlattenStream<Fut>
where TryFlatten<Fut, Fut::Ok>: Sink<_Item>, Fut: TryFuture,

source§

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

source§

impl<_Item, Fut, Si> Sink<_Item> for FlattenSink<Fut, Si>
where TryFlatten<Fut, Si>: Sink<_Item>,

source§

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

source§

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

source§

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

source§

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>,

source§

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

source§

impl<_Item, St, E> Sink<_Item> for ErrInto<St, E>
where MapErr<St, IntoFn<E>>: Sink<_Item>,

source§

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

source§

impl<_Item, St, F> Sink<_Item> for Inspect<St, F>
where Map<St, InspectFn<F>>: Sink<_Item>,

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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

source§

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,

source§

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