Trait protokit_grpc::Stream

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pub trait Stream {
    type Item;

    // Required method
    fn poll_next(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>
    ) -> Poll<Option<Self::Item>>;

    // Provided method
    fn size_hint(&self) -> (usize, Option<usize>) { ... }
}

Expand description

A stream of values produced asynchronously.

If Future<Output = T> is an asynchronous version of T, then Stream<Item = T> is an asynchronous version of Iterator<Item = T>. A stream represents a sequence of value-producing events that occur asynchronously to the caller.

The trait is modeled after Future, but allows poll_next to be called even after a value has been produced, yielding None once the stream has been fully exhausted.

Required Associated Types§

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type Item

Values yielded by the stream.

Required Methods§

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fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Option<Self::Item>>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted.

§Return value

There are several possible return values, each indicating a distinct stream state:

Poll::Pending means that this stream’s next value is not ready yet. Implementations will ensure that the current task will be notified when the next value may be ready.
Poll::Ready(Some(val)) means that the stream has successfully produced a value, val, and may produce further values on subsequent poll_next calls.
Poll::Ready(None) means that the stream has terminated, and poll_next should not be invoked again.

§Panics

Once a stream has finished (returned Ready(None) from poll_next), calling its poll_next method again may panic, block forever, or cause other kinds of problems; the Stream trait places no requirements on the effects of such a call. However, as the poll_next method is not marked unsafe, Rust’s usual rules apply: calls must never cause undefined behavior (memory corruption, incorrect use of unsafe functions, or the like), regardless of the stream’s state.

If this is difficult to guard against then the fuse adapter can be used to ensure that poll_next always returns Ready(None) in subsequent calls.

Provided Methods§

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fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream.

Specifically, size_hint() returns a tuple where the first element is the lower bound, and the second element is the upper bound.

The second half of the tuple that is returned is an Option<usize>. A None here means that either there is no known upper bound, or the upper bound is larger than usize.

§Implementation notes

It is not enforced that a stream implementation yields the declared number of elements. A buggy stream may yield less than the lower bound or more than the upper bound of elements.

size_hint() is primarily intended to be used for optimizations such as reserving space for the elements of the stream, but must not be trusted to e.g., omit bounds checks in unsafe code. An incorrect implementation of size_hint() should not lead to memory safety violations.

That said, the implementation should provide a correct estimation, because otherwise it would be a violation of the trait’s protocol.

The default implementation returns (0, None) which is correct for any stream.

Trait protokit_grpc::Stream

Required Associated Types§

type Item

Required Methods§

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Option<Self::Item>>

§Return value

§Panics

Provided Methods§

fn size_hint(&self) -> (usize, Option<usize>)

§Implementation notes

Implementations on Foreign Types§

impl Stream for BodyStream

type Item = Result<Bytes, Error>

fn poll_next( self: Pin<&mut BodyStream>, cx: &mut Context<'_> ) -> Poll<Option<<BodyStream as Stream>::Item>>

impl Stream for Body

§Optional

type Item = Result<Bytes, Error>

fn poll_next( self: Pin<&mut Body>, cx: &mut Context<'_> ) -> Poll<Option<<Body as Stream>::Item>>

impl Stream for PollSemaphore

type Item = OwnedSemaphorePermit

fn poll_next( self: Pin<&mut PollSemaphore>, cx: &mut Context<'_> ) -> Poll<Option<OwnedSemaphorePermit>>

impl Stream for TcpIncoming

type Item = Result<AddrStream, Error>

fn poll_next( self: Pin<&mut TcpIncoming>, cx: &mut Context<'_> ) -> Poll<Option<<TcpIncoming as Stream>::Item>>

impl<A, B> Stream for Either<A, B>where A: Stream, B: Stream<Item = <A as Stream>::Item>,

type Item = <A as Stream>::Item

fn poll_next( self: Pin<&mut Either<A, B>>, cx: &mut Context<'_> ) -> Poll<Option<<Either<A, B> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<A, F> Stream for RepeatWith<F>where F: FnMut() -> A,

type Item = A

fn poll_next( self: Pin<&mut RepeatWith<F>>, _: &mut Context<'_> ) -> Poll<Option<<RepeatWith<F> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<B, St, S, Fut, F> Stream for Scan<St, S, Fut, F>where St: Stream, F: FnMut(&mut S, <St as Stream>::Item) -> Fut, Fut: Future<Output = Option<B>>,

type Item = B

fn poll_next( self: Pin<&mut Scan<St, S, Fut, F>>, cx: &mut Context<'_> ) -> Poll<Option<B>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<D, C> Stream for PeakEwmaDiscover<D, C>where D: Discover, C: Clone,

type Item = Result<Change<<D as Discover>::Key, PeakEwma<<D as Discover>::Service, C>>, <D as Discover>::Error>

fn poll_next( self: Pin<&mut PeakEwmaDiscover<D, C>>, cx: &mut Context<'_> ) -> Poll<Option<<PeakEwmaDiscover<D, C> as Stream>::Item>>

impl<D, C> Stream for PendingRequestsDiscover<D, C>where D: Discover, C: Clone,

fn poll_next( self: Pin<&mut PendingRequestsDiscover<D, C>>, cx: &mut Context<'_> ) -> Poll<Option<<PendingRequestsDiscover<D, C> as Stream>::Item>>

type Item = Result<Change<<D as Discover>::Key, PendingRequests<<D as Discover>::Service, C>>, <D as Discover>::Error>

impl<D, M> Stream for Constant<D, M>where D: Discover + Unpin, M: Copy,

fn poll_next( self: Pin<&mut Constant<D, M>>, cx: &mut Context<'_> ) -> Poll<Option<<Constant<D, M> as Stream>::Item>>

type Item = Result<Change<<D as Discover>::Key, Constant<<D as Discover>::Service, M>>, <D as Discover>::Error>

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

type Item = <Flatten<F, <F as Future>::Output> as Stream>::Item

fn poll_next( self: Pin<&mut FlattenStream<F>>, cx: &mut Context<'_> ) -> Poll<Option<<FlattenStream<F> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<F> Stream for IntoStream<F>where Once<F>: Stream,

type Item = <Once<F> as Stream>::Item

fn poll_next( self: Pin<&mut IntoStream<F>>, cx: &mut Context<'_> ) -> Poll<Option<<IntoStream<F> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<Fut> Stream for TryFlattenStream<Fut>where TryFlatten<Fut, <Fut as TryFuture>::Ok>: Stream, Fut: TryFuture,

type Item = <TryFlatten<Fut, <Fut as TryFuture>::Ok> as Stream>::Item

fn poll_next( self: Pin<&mut TryFlattenStream<Fut>>, cx: &mut Context<'_> ) -> Poll<Option<<TryFlattenStream<Fut> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<Fut> Stream for FuturesOrdered<Fut>where Fut: Future,

type Item = <Fut as Future>::Output

fn poll_next( self: Pin<&mut FuturesOrdered<Fut>>, cx: &mut Context<'_> ) -> Poll<Option<<FuturesOrdered<Fut> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<Fut> Stream for FuturesUnordered<Fut>where Fut: Future,

type Item = <Fut as Future>::Output

fn poll_next( self: Pin<&mut FuturesUnordered<Fut>>, cx: &mut Context<'_> ) -> Poll<Option<<FuturesUnordered<Fut> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<Fut> Stream for Once<Fut>where Fut: Future,

type Item = <Fut as Future>::Output

fn poll_next( self: Pin<&mut Once<Fut>>, cx: &mut Context<'_> ) -> Poll<Option<<Once<Fut> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<Fut, Si> Stream for FlattenSink<Fut, Si>where TryFlatten<Fut, Si>: Stream,

type Item = <TryFlatten<Fut, Si> as Stream>::Item

fn poll_next( self: Pin<&mut FlattenSink<Fut, Si>>, cx: &mut Context<'_> ) -> Poll<Option<<FlattenSink<Fut, Si> as Stream>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<I> Stream for Iter<I>where I: Iterator,

type Item = <I as Iterator>::Item

fn poll_next( self: Pin<&mut Iter<I>>, _: &mut Context<'_> ) -> Poll<Option<<I as Iterator>::Item>>

fn size_hint(&self) -> (usize, Option<usize>)

impl<L, R> Stream for Either<L, R>where L: Stream, R: Stream<Item = <L as Stream>::Item>,

type Item = <L as Stream>::Item

fn poll_next( self: Pin<&mut Either<L, R>>, cx: &mut Context<'_> ) -> Poll<Option<<Either<L, R> as Stream>::Item>>

impl<A, B> Stream for Either<A, B>
where A: Stream, B: Stream<Item = <A as Stream>::Item>,

impl<A, F> Stream for RepeatWith<F>
where F: FnMut() -> A,

impl<B, St, S, Fut, F> Stream for Scan<St, S, Fut, F>
where St: Stream, F: FnMut(&mut S, <St as Stream>::Item) -> Fut, Fut: Future<Output = Option<B>>,

impl<D, C> Stream for PeakEwmaDiscover<D, C>
where D: Discover, C: Clone,

impl<D, C> Stream for PendingRequestsDiscover<D, C>
where D: Discover, C: Clone,

impl<D, M> Stream for Constant<D, M>
where D: Discover + Unpin, M: Copy,

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

impl<F> Stream for IntoStream<F>
where Once<F>: Stream,

impl<Fut> Stream for TryFlattenStream<Fut>
where TryFlatten<Fut, <Fut as TryFuture>::Ok>: Stream, Fut: TryFuture,

impl<Fut> Stream for FuturesOrdered<Fut>
where Fut: Future,

impl<Fut> Stream for FuturesUnordered<Fut>
where Fut: Future,

impl<Fut> Stream for Once<Fut>
where Fut: Future,

impl<Fut, Si> Stream for FlattenSink<Fut, Si>
where TryFlatten<Fut, Si>: Stream,

impl<I> Stream for Iter<I>
where I: Iterator,

impl<L, R> Stream for Either<L, R>
where L: Stream, R: Stream<Item = <L as Stream>::Item>,

impl<MS, Target, Request> Stream for PoolDiscoverer<MS, Target, Request>
where MS: MakeService<Target, Request>, <MS as MakeService<Target, Request>>::MakeError: Into<Box<dyn Error + Send + Sync>>, <MS as MakeService<Target, Request>>::Error: Into<Box<dyn Error + Send + Sync>>, Target: Clone,

impl<R> Stream for Lines<R>
where R: AsyncBufRead,

impl<R> Stream for ReaderStream<R>
where R: AsyncRead,

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

impl<S> Stream for Box<S>
where S: Stream + Unpin + ?Sized,

impl<S> Stream for AssertUnwindSafe<S>
where S: Stream,

impl<S> Stream for Fuse<S>
where S: Stream,

impl<S> Stream for Peekable<S>
where S: Stream,

impl<S> Stream for SplitStream<S>
where S: Stream,

impl<S> Stream for CopyToBytes<S>
where S: Stream,

impl<S> Stream for SinkWriter<S>
where S: Stream,

impl<S, F> Stream for SinkMapErr<S, F>
where S: Stream,

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

impl<S, Item, E> Stream for SinkErrInto<S, Item, E>
where S: Sink<Item> + Stream, <S as Sink<Item>>::Error: Into<E>,

impl<S, Item, U, Fut, F> Stream for With<S, Item, U, Fut, F>
where S: Stream + Sink<Item>, F: FnMut(U) -> Fut, Fut: Future,

impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
where S: Stream + Sink<Item>, F: FnMut(U) -> St, St: Stream<Item = Result<Item, <S as Sink<Item>>::Error>>,

impl<St1, St2> Stream for Select<St1, St2>
where St1: Stream, St2: Stream<Item = <St1 as Stream>::Item>,

impl<St1, St2> Stream for Chain<St1, St2>
where St1: Stream, St2: Stream<Item = <St1 as Stream>::Item>,