Trait polkadot_node_subsystem::gen::futures::prelude::stream::Stream

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>) { ... }
}

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

type Item

Values yielded by the stream.

Required Methods

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

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.

Implementations on Foreign Types

impl Stream for DelayedApprovalTimer

type Item = (H256, ValidatorIndex)

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

impl Stream for BitswapHandle

type Item = BitswapEvent

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

impl Stream for DnsExchangeSend

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsExchangeSend

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsExchangeSend

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsResponseReceiver

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsResponseReceiver

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsResponseReceiver

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsResponseStream

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsResponseStream

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for DnsResponseStream

type Item = Result<DnsResponse, ProtoError>

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

impl Stream for Interval

type Item = ()

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

impl Stream for IntervalStream

type Item = Instant

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

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

impl Stream for KademliaHandle

type Item = KademliaEvent

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

impl Stream for Listen

type Item = TransportEvent<<ExtTransport as Transport>::ListenerUpgrade, JsErr>

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

impl Stream for MdnsClientStream

type Item = Result<SerialMessage, ProtoError>

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

impl Stream for MdnsStream

type Item = Result<SerialMessage, Error>

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

impl Stream for NotificationHandle

type Item = NotificationEvent

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

type Item = RequestResponseEvent

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

impl Stream for Stream

type Item = Result<Packet, Error>

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

impl Stream for Stream

type Item = Result<Packet, Error>

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

impl Stream for Substream

type Item = Result<BytesMut, SubstreamError>

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

impl Stream for TransportService

type Item = TransportEvent

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

impl<'a, Item, S, D, C, MW> Stream for RatelimitedSink<'a, Item, S, D, C, MW>

where S: Stream + Sink<Item> + Unpin, D: DirectStateStore, C: ReasonablyRealtime, MW: RateLimitingMiddleware<<C as Clock>::Instant, NegativeOutcome = NotUntil<<C as Clock>::Instant>>, <S as Stream>::Item: Unpin, Item: Unpin,

Pass-through implementation for futures::Stream if the Sink also implements it.

type Item = <S as Stream>::Item

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

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

impl<'a, S, D, C, MW> Stream for RatelimitedStream<'a, S, D, C, MW>

where S: Stream + Unpin, D: DirectStateStore, C: Clock + ReasonablyRealtime, <S as Stream>::Item: Unpin, RatelimitedStream<'a, S, D, C, MW>: Unpin, MW: RateLimitingMiddleware<<C as Clock>::Instant, NegativeOutcome = NotUntil<<C as Clock>::Instant>>,

Implements the futures::Stream combinator.

type Item = <S as Stream>::Item

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

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

impl<B> Stream for BodyDataStream<B>

where B: Body,

type Item = Result<<B as Body>::Data, <B as Body>::Error>

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

impl<B> Stream for BodyStream<B>

where B: Body,

type Item = Result<Frame<<B as Body>::Data>, <B as Body>::Error>

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

impl<H> Stream for StorageEventStream<H>

type Item = StorageNotification<H>

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

impl<I> Stream for Iter<I>

where I: Iterator,

type Item = <I as Iterator>::Item

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

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

impl<K, S> Stream for SubstreamSet<K, S>

where K: SubstreamSetKey, S: Stream<Item = Result<BytesMut, SubstreamError>> + Unpin,

type Item = (K, <S as Stream>::Item)

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

impl<K, V> Stream for StreamMap<K, V>

where K: Clone + Unpin, V: Stream + Unpin,

type Item = (K, <V as Stream>::Item)

fn poll_next( self: Pin<&mut StreamMap<K, V>>, cx: &mut Context<'_>, ) -> Poll<Option<<StreamMap<K, V> as Stream>::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<M, R> Stream for Receiver<M, R>

where R: Unsubscribe,

type Item = M

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

impl<Notif> Stream for Subscription<Notif>

where Notif: DeserializeOwned,

type Item = Result<Notif, Error>

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

impl<O> Stream for Boxed<O>

type Item = TransportEvent<Pin<Box<dyn Future<Output = Result<O, Error>> + Send>>, Error>

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

impl<Payload> Stream for NotificationReceiver<Payload>

type Item = Payload

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

impl<R> Stream for ReaderStream<R>

where R: AsyncRead,

type Item = Result<Bytes, Error>

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

impl<S> Stream for &mut S

where S: Stream + Unpin + ?Sized,

type Item = <S as Stream>::Item

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

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

impl<S> Stream for Box<S>

where S: Stream + Unpin + ?Sized,

type Item = <S as Stream>::Item

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

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

impl<S> Stream for AssertUnwindSafe<S>

where S: Stream,

type Item = <S as Stream>::Item

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

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

impl<S> Stream for ChunksTimeout<S>

where S: Stream,

type Item = Vec<<S as Stream>::Item>

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

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

impl<S> Stream for CopyToBytes<S>

where S: Stream,

type Item = <S as Stream>::Item

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

impl<S> Stream for SinkWriter<S>

where S: Stream,

type Item = <S as Stream>::Item

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

impl<S> Stream for StreamBody<S>

where S: Stream,

type Item = <S as Stream>::Item

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

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

impl<S> Stream for StreamNotifyClose<S>

where S: Stream,

type Item = Option<<S as Stream>::Item>

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

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

impl<S> Stream for TcpClientStream<S>

where S: DnsTcpStream,

type Item = Result<SerialMessage, ProtoError>

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

impl<S> Stream for TcpClientStream<S>

where S: DnsTcpStream,

type Item = Result<SerialMessage, ProtoError>

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

impl<S> Stream for TcpClientStream<S>

where S: DnsTcpStream,

type Item = Result<SerialMessage, ProtoError>

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

impl<S> Stream for TcpStream<S>

where S: DnsTcpStream,

type Item = Result<SerialMessage, Error>

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

impl<S> Stream for TcpStream<S>

where S: DnsTcpStream,

type Item = Result<SerialMessage, Error>

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

impl<S> Stream for TcpStream<S>

where S: DnsTcpStream,

type Item = Result<SerialMessage, Error>

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

impl<S> Stream for Timeout<S>

where S: Stream,

type Item = Result<<S as Stream>::Item, Elapsed>

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

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

impl<S> Stream for TimeoutRepeating<S>

where S: Stream,

type Item = Result<<S as Stream>::Item, Elapsed>

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

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

impl<S> Stream for TimeoutStream<S>

where S: TryStream, <S as TryStream>::Error: From<Error>,

type Item = Result<<S as TryStream>::Ok, <S as TryStream>::Error>

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

impl<S> Stream for UdpStream<S>

where S: DnsUdpSocket + Send + 'static,

type Item = Result<SerialMessage, Error>

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

impl<S> Stream for UdpStream<S>

where S: DnsUdpSocket + Send + 'static,

type Item = Result<SerialMessage, Error>

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

impl<S> Stream for UdpStream<S>

where S: UdpSocket + Send + 'static,

type Item = Result<SerialMessage, Error>

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

impl<S, MF> Stream for DnsMultiplexer<S, MF>

where S: DnsClientStream + Unpin + 'static, MF: MessageFinalizer + Send + Sync + 'static,

type Item = Result<(), ProtoError>

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

impl<S, MF> Stream for DnsMultiplexer<S, MF>

where S: DnsClientStream + Unpin + 'static, MF: MessageFinalizer + Send + Sync + 'static,

type Item = Result<(), ProtoError>

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

impl<S, MF> Stream for DnsMultiplexer<S, MF>

where S: DnsClientStream + Unpin + 'static, MF: MessageFinalizer + Send + Sync + 'static,

type Item = Result<(), ProtoError>

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

impl<S, MF> Stream for UdpClientStream<S, MF>

where S: Send, MF: MessageFinalizer,

type Item = Result<(), ProtoError>

fn poll_next( self: Pin<&mut UdpClientStream<S, MF>>, _cx: &mut Context<'_>, ) -> Poll<Option<<UdpClientStream<S, MF> as Stream>::Item>>

impl<S, MF> Stream for UdpClientStream<S, MF>

where S: Send, MF: MessageFinalizer,

type Item = Result<(), ProtoError>

fn poll_next( self: Pin<&mut UdpClientStream<S, MF>>, _cx: &mut Context<'_>, ) -> Poll<Option<<UdpClientStream<S, MF> as Stream>::Item>>

impl<S, MF> Stream for UdpClientStream<S, MF>

where S: Send, MF: MessageFinalizer,

type Item = Result<(), ProtoError>

fn poll_next( self: Pin<&mut UdpClientStream<S, MF>>, _cx: &mut Context<'_>, ) -> Poll<Option<<UdpClientStream<S, MF> as Stream>::Item>>

impl<St> Stream for Skip<St>

where St: Stream,

type Item = <St as Stream>::Item

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

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

impl<St> Stream for Take<St>

where St: Stream,

type Item = <St as Stream>::Item

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

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

impl<St, F> Stream for Filter<St, F>

where St: Stream, F: FnMut(&<St as Stream>::Item) -> bool,

type Item = <St as Stream>::Item

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

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

impl<St, F> Stream for SkipWhile<St, F>

where St: Stream, F: FnMut(&<St as Stream>::Item) -> bool,

type Item = <St as Stream>::Item

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

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

impl<St, F> Stream for TakeWhile<St, F>

where St: Stream, F: FnMut(&<St as Stream>::Item) -> bool,

type Item = <St as Stream>::Item

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

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

impl<St, F, Fut> Stream for Then<St, Fut, F>

where St: Stream, Fut: Future, F: FnMut(<St as Stream>::Item) -> Fut,

type Item = <Fut as Future>::Output

fn poll_next( self: Pin<&mut Then<St, Fut, F>>, cx: &mut Context<'_>, ) -> Poll<Option<<Fut as Future>::Output>>

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

impl<St, F, T> Stream for FilterMap<St, F>

where St: Stream, F: FnMut(<St as Stream>::Item) -> Option<T>,

type Item = T

fn poll_next( self: Pin<&mut FilterMap<St, F>>, cx: &mut Context<'_>, ) -> Poll<Option<T>>

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

impl<St, F, T> Stream for Map<St, F>

where St: Stream, F: FnMut(<St as Stream>::Item) -> T,

type Item = T

fn poll_next( self: Pin<&mut Map<St, F>>, cx: &mut Context<'_>, ) -> Poll<Option<T>>

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

impl<St, F, T> Stream for MapWhile<St, F>

where St: Stream, F: FnMut(<St as Stream>::Item) -> Option<T>,

type Item = T

fn poll_next( self: Pin<&mut MapWhile<St, F>>, cx: &mut Context<'_>, ) -> Poll<Option<T>>

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

impl<Svc, S> Stream for CallAll<Svc, S>

where Svc: Service<<S as Stream>::Item>, <Svc as Service<<S as Stream>::Item>>::Error: Into<Box<dyn Error + Send + Sync>>, S: Stream,

type Item = Result<<Svc as Service<<S as Stream>::Item>>::Response, Box<dyn Error + Send + Sync>>

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

impl<Svc, S> Stream for CallAllUnordered<Svc, S>

where Svc: Service<<S as Stream>::Item>, <Svc as Service<<S as Stream>::Item>>::Error: Into<Box<dyn Error + Send + Sync>>, S: Stream,

type Item = Result<<Svc as Service<<S as Stream>::Item>>::Response, Box<dyn Error + Send + Sync>>

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

impl<T> Stream for TracingUnboundedReceiver<T>

type Item = T

fn poll_next( self: Pin<&mut TracingUnboundedReceiver<T>>, cx: &mut Context<'_>, ) -> Poll<Option<T>>

impl<T> Stream for BroadcastStream<T>

where T: 'static + Clone + Send,

type Item = Result<T, BroadcastStreamRecvError>

fn poll_next( self: Pin<&mut BroadcastStream<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<BroadcastStream<T> as Stream>::Item>>

impl<T> Stream for BytesConnection<T>

where T: AsyncRead + AsyncWrite + Send + Unpin + 'static,

type Item = Result<Vec<u8>, Error>

fn poll_next( self: Pin<&mut BytesConnection<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<BytesConnection<T> as Stream>::Item>>

impl<T> Stream for Chan<T>

type Item = Result<T, Error>

fn poll_next( self: Pin<&mut Chan<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<Chan<T> as Stream>::Item>>

impl<T> Stream for Connection<T>

where T: AsyncRead + AsyncWrite + Send + Unpin + 'static,

type Item = Result<Incoming, Error>

fn poll_next( self: Pin<&mut Connection<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<Connection<T> as Stream>::Item>>

impl<T> Stream for ControlledConnection<T>

where T: AsyncRead + AsyncWrite + Unpin + Send + 'static,

type Item = Result<Stream, ConnectionError>

fn poll_next( self: Pin<&mut ControlledConnection<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<ControlledConnection<T> as Stream>::Item>>

impl<T> Stream for DelayQueue<T>

type Item = Expired<T>

fn poll_next( self: Pin<&mut DelayQueue<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<DelayQueue<T> as Stream>::Item>>

impl<T> Stream for Empty<T>

type Item = T

fn poll_next(self: Pin<&mut Empty<T>>, _: &mut Context<'_>) -> Poll<Option<T>>

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

impl<T> Stream for Fuse<T>

where T: Stream,

type Item = <T as Stream>::Item

fn poll_next( self: Pin<&mut Fuse<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<T as Stream>::Item>>

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

impl<T> Stream for Once<T>

type Item = T

fn poll_next(self: Pin<&mut Once<T>>, cx: &mut Context<'_>) -> Poll<Option<T>>

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

impl<T> Stream for Peekable<T>

where T: Stream,

type Item = <T as Stream>::Item

fn poll_next( self: Pin<&mut Peekable<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<Peekable<T> as Stream>::Item>>

impl<T> Stream for Pending<T>

type Item = T

fn poll_next(self: Pin<&mut Pending<T>>, _: &mut Context<'_>) -> Poll<Option<T>>

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

impl<T> Stream for Receiver<T>

type Item = T

fn poll_next( self: Pin<&mut Receiver<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<Receiver<T> as Stream>::Item>>

impl<T> Stream for ReceiverStream<T>

type Item = T

fn poll_next( self: Pin<&mut ReceiverStream<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<ReceiverStream<T> as Stream>::Item>>

impl<T> Stream for UnboundedReceiverStream<T>

type Item = T

fn poll_next( self: Pin<&mut UnboundedReceiverStream<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<UnboundedReceiverStream<T> as Stream>::Item>>

impl<T> Stream for WatchStream<T>

where T: Clone + 'static + Send + Sync,

type Item = T

fn poll_next( self: Pin<&mut WatchStream<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<WatchStream<T> as Stream>::Item>>

impl<T> Stream for WebSocketStream<T>

where T: AsyncRead + AsyncWrite + Unpin,

type Item = Result<Message, Error>

fn poll_next( self: Pin<&mut WebSocketStream<T>>, cx: &mut Context<'_>, ) -> Poll<Option<<WebSocketStream<T> as Stream>::Item>>

impl<T, D> Stream for FramedRead<T, D>

where T: AsyncRead + Unpin, D: Decoder,

type Item = Result<<D as Decoder>::Item, <D as Decoder>::Error>

fn poll_next( self: Pin<&mut FramedRead<T, D>>, cx: &mut Context<'_>, ) -> Poll<Option<<FramedRead<T, D> as Stream>::Item>>

impl<T, D> Stream for FramedRead<T, D>

where T: AsyncRead, D: Decoder,

type Item = Result<<D as Decoder>::Item, <D as Decoder>::Error>

fn poll_next( self: Pin<&mut FramedRead<T, D>>, cx: &mut Context<'_>, ) -> Poll<Option<<FramedRead<T, D> as Stream>::Item>>

impl<T, D> Stream for FramedWrite<T, D>

where T: Stream,

type Item = <T as Stream>::Item

fn poll_next( self: Pin<&mut FramedWrite<T, D>>, cx: &mut Context<'_>, ) -> Poll<Option<<FramedWrite<T, D> as Stream>::Item>>

impl<T, S, C> Stream for NetlinkFramed<T, S, C>

where T: NetlinkDeserializable + Debug, S: AsyncSocket, C: NetlinkMessageCodec,

type Item = (NetlinkMessage<T>, SocketAddr)

fn poll_next( self: Pin<&mut NetlinkFramed<T, S, C>>, cx: &mut Context<'_>, ) -> Poll<Option<<NetlinkFramed<T, S, C> as Stream>::Item>>

impl<T, U> Stream for Chain<T, U>

where T: Stream, U: Stream<Item = <T as Stream>::Item>,

type Item = <T as Stream>::Item

fn poll_next( self: Pin<&mut Chain<T, U>>, cx: &mut Context<'_>, ) -> Poll<Option<<T as Stream>::Item>>

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

impl<T, U> Stream for Framed<T, U>

where T: AsyncRead + Unpin, U: Decoder,

type Item = Result<<U as Decoder>::Item, <U as Decoder>::Error>

fn poll_next( self: Pin<&mut Framed<T, U>>, cx: &mut Context<'_>, ) -> Poll<Option<<Framed<T, U> as Stream>::Item>>

impl<T, U> Stream for Framed<T, U>

where T: AsyncRead, U: Decoder,

type Item = Result<<U as Decoder>::Item, <U as Decoder>::Error>

fn poll_next( self: Pin<&mut Framed<T, U>>, cx: &mut Context<'_>, ) -> Poll<Option<<Framed<T, U> as Stream>::Item>>

impl<T, U> Stream for Merge<T, U>

where T: Stream, U: Stream<Item = <T as Stream>::Item>,

type Item = <T as Stream>::Item

fn poll_next( self: Pin<&mut Merge<T, U>>, cx: &mut Context<'_>, ) -> Poll<Option<<T as Stream>::Item>>

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

impl<TBehaviour> Stream for Swarm<TBehaviour>

where TBehaviour: NetworkBehaviour,

Stream of events returned by [Swarm].

Includes events from the [NetworkBehaviour] as well as events about connection and listener status. See [SwarmEvent] for details.

Note: This stream is infinite and it is guaranteed that futures::Stream::poll_next will never return Poll::Ready(None).

type Item = SwarmEvent<<TBehaviour as NetworkBehaviour>::ToSwarm, <<TBehaviour as NetworkBehaviour>::ConnectionHandler as ConnectionHandler>::Error>

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

Implementors

impl Stream for Metronome

type Item = ()

impl<A, B> Stream for polkadot_node_subsystem::gen::futures::prelude::future::Either<A, B>

where A: Stream, B: Stream<Item = <A as Stream>::Item>,

type Item = <A as Stream>::Item

impl<A, F> Stream for RepeatWith<F>

where F: FnMut() -> A,

type Item = 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>>,

type Item = B

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

impl<F> Stream for polkadot_node_subsystem::gen::futures::prelude::future::IntoStream<F>

where Once<F>: Stream,

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

impl<Fut> Stream for FuturesUnordered<Fut>

where Fut: Future,

type Item = <Fut as Future>::Output

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

impl<Fut> Stream for FuturesOrdered<Fut>

where Fut: Future,

type Item = <Fut as Future>::Output

impl<Fut> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Once<Fut>

where Fut: Future,

type Item = <Fut as Future>::Output

impl<Fut, Si> Stream for FlattenSink<Fut, Si>

where TryFlatten<Fut, Si>: Stream,

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

impl<I> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Iter<I>

where I: Iterator,

type Item = <I as Iterator>::Item

impl<P> Stream for Pin<P>

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

type Item = <<P as Deref>::Target as Stream>::Item

impl<R> Stream for Lines<R>

where R: AsyncBufRead,

type Item = Result<String, Error>

impl<S> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Fuse<S>

where S: Stream,

type Item = <S as Stream>::Item

impl<S> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Peekable<S>

where S: Stream,

type Item = <S as Stream>::Item

impl<S> Stream for SplitStream<S>

where S: Stream,

type Item = <S as Stream>::Item

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

where S: Stream,

type Item = <S as Stream>::Item

impl<S, Item> Stream for Buffer<S, Item>

where S: Sink<Item> + Stream,

type Item = <S as Stream>::Item

impl<S, Item, E> Stream for SinkErrInto<S, Item, E>

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

type Item = <S as Stream>::Item

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,

type Item = <S as Stream>::Item

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>>,

type Item = <S as Stream>::Item

impl<St1, St2> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Chain<St1, St2>

where St1: Stream, St2: Stream<Item = <St1 as Stream>::Item>,

type Item = <St1 as Stream>::Item

impl<St1, St2> Stream for Select<St1, St2>

where St1: Stream, St2: Stream<Item = <St1 as Stream>::Item>,

type Item = <St1 as Stream>::Item

impl<St1, St2> Stream for Zip<St1, St2>

where St1: Stream, St2: Stream,

type Item = (<St1 as Stream>::Item, <St2 as Stream>::Item)

impl<St1, St2, Clos, State> Stream for SelectWithStrategy<St1, St2, Clos, State>

where St1: Stream, St2: Stream<Item = <St1 as Stream>::Item>, Clos: FnMut(&mut State) -> PollNext,

type Item = <St1 as Stream>::Item

impl<St> Stream for Abortable<St>

where St: Stream,

type Item = <St as Stream>::Item

impl<St> Stream for BufferUnordered<St>

where St: Stream, <St as Stream>::Item: Future,

type Item = <<St as Stream>::Item as Future>::Output

impl<St> Stream for Buffered<St>

where St: Stream, <St as Stream>::Item: Future,

type Item = <<St as Stream>::Item as Future>::Output

impl<St> Stream for CatchUnwind<St>

where St: Stream + UnwindSafe,

type Item = Result<<St as Stream>::Item, Box<dyn Any + Send>>

impl<St> Stream for Chunks<St>

where St: Stream,

type Item = Vec<<St as Stream>::Item>

impl<St> Stream for Cycle<St>

where St: Clone + Stream,

type Item = <St as Stream>::Item

impl<St> Stream for Enumerate<St>

where St: Stream,

type Item = (usize, <St as Stream>::Item)

impl<St> Stream for Flatten<St>

where Flatten<St, <St as Stream>::Item>: Stream, St: Stream,

type Item = <Flatten<St, <St as Stream>::Item> as Stream>::Item

impl<St> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::IntoStream<St>

where St: TryStream,

type Item = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

impl<St> Stream for ReadyChunks<St>

where St: Stream,

type Item = Vec<<St as Stream>::Item>

impl<St> Stream for SelectAll<St>

where St: Stream + Unpin,

type Item = <St as Stream>::Item

impl<St> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Skip<St>

where St: Stream,

type Item = <St as Stream>::Item

impl<St> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Take<St>

where St: Stream,

type Item = <St as Stream>::Item

impl<St> Stream for TryBufferUnordered<St>

where St: TryStream, <St as TryStream>::Ok: TryFuture<Error = <St as TryStream>::Error>,

type Item = Result<<<St as TryStream>::Ok as TryFuture>::Ok, <St as TryStream>::Error>

impl<St> Stream for TryBuffered<St>

where St: TryStream, <St as TryStream>::Ok: TryFuture<Error = <St as TryStream>::Error>,

type Item = Result<<<St as TryStream>::Ok as TryFuture>::Ok, <St as TryStream>::Error>

impl<St> Stream for TryChunks<St>

where St: TryStream,

type Item = Result<Vec<<St as TryStream>::Ok>, TryChunksError<<St as TryStream>::Ok, <St as TryStream>::Error>>

impl<St> Stream for TryFlatten<St>

where St: TryStream, <St as TryStream>::Ok: TryStream, <<St as TryStream>::Ok as TryStream>::Error: From<<St as TryStream>::Error>,

type Item = Result<<<St as TryStream>::Ok as TryStream>::Ok, <<St as TryStream>::Ok as TryStream>::Error>

impl<St> Stream for TryFlattenUnordered<St>

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

type Item = <FlattenUnorderedWithFlowController<NestedTryStreamIntoEitherTryStream<St>, PropagateBaseStreamError<St>> as Stream>::Item

impl<St> Stream for TryReadyChunks<St>

where St: TryStream,

type Item = Result<Vec<<St as TryStream>::Ok>, TryReadyChunksError<<St as TryStream>::Ok, <St as TryStream>::Error>>

impl<St, E> Stream for ErrInto<St, E>

where MapErr<St, IntoFn<E>>: Stream,

type Item = <MapErr<St, IntoFn<E>> as Stream>::Item

impl<St, F> Stream for Inspect<St, F>

where Map<St, InspectFn<F>>: Stream,

type Item = <Map<St, InspectFn<F>> as Stream>::Item

impl<St, F> Stream for InspectErr<St, F>

where Inspect<IntoStream<St>, InspectErrFn<F>>: Stream,

type Item = <Inspect<IntoStream<St>, InspectErrFn<F>> as Stream>::Item

impl<St, F> Stream for InspectOk<St, F>

where Inspect<IntoStream<St>, InspectOkFn<F>>: Stream,

type Item = <Inspect<IntoStream<St>, InspectOkFn<F>> as Stream>::Item

impl<St, F> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Map<St, F>

where St: Stream, F: FnMut1<<St as Stream>::Item>,

type Item = <F as FnOnce1<<St as Stream>::Item>>::Output

impl<St, F> Stream for MapErr<St, F>

where Map<IntoStream<St>, MapErrFn<F>>: Stream,

type Item = <Map<IntoStream<St>, MapErrFn<F>> as Stream>::Item

impl<St, F> Stream for MapOk<St, F>

where Map<IntoStream<St>, MapOkFn<F>>: Stream,

type Item = <Map<IntoStream<St>, MapOkFn<F>> as Stream>::Item

impl<St, Fut> Stream for TakeUntil<St, Fut>

where St: Stream, Fut: Future,

type Item = <St as Stream>::Item

impl<St, Fut, F> Stream for AndThen<St, Fut, F>

where St: TryStream, F: FnMut(<St as TryStream>::Ok) -> Fut, Fut: TryFuture<Error = <St as TryStream>::Error>,

type Item = Result<<Fut as TryFuture>::Ok, <St as TryStream>::Error>

impl<St, Fut, F> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Filter<St, Fut, F>

where St: Stream, F: for<'a> FnMut1<&'a <St as Stream>::Item, Output = Fut>, Fut: Future<Output = bool>,

type Item = <St as Stream>::Item

impl<St, Fut, F> Stream for OrElse<St, Fut, F>

where St: TryStream, F: FnMut(<St as TryStream>::Error) -> Fut, Fut: TryFuture<Ok = <St as TryStream>::Ok>,

type Item = Result<<St as TryStream>::Ok, <Fut as TryFuture>::Error>

impl<St, Fut, F> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::SkipWhile<St, Fut, F>

where St: Stream, F: FnMut(&<St as Stream>::Item) -> Fut, Fut: Future<Output = bool>,

type Item = <St as Stream>::Item

impl<St, Fut, F> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::TakeWhile<St, Fut, F>

where St: Stream, F: FnMut(&<St as Stream>::Item) -> Fut, Fut: Future<Output = bool>,

type Item = <St as Stream>::Item

impl<St, Fut, F> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Then<St, Fut, F>

where St: Stream, F: FnMut(<St as Stream>::Item) -> Fut, Fut: Future,

type Item = <Fut as Future>::Output

impl<St, Fut, F> Stream for TryFilter<St, Fut, F>

where St: TryStream, Fut: Future<Output = bool>, F: FnMut(&<St as TryStream>::Ok) -> Fut,

type Item = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F>

where St: TryStream, F: FnMut(&<St as TryStream>::Ok) -> Fut, Fut: TryFuture<Ok = bool, Error = <St as TryStream>::Error>,

type Item = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F>

where St: TryStream, F: FnMut(&<St as TryStream>::Ok) -> Fut, Fut: TryFuture<Ok = bool, Error = <St as TryStream>::Error>,

type Item = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

impl<St, Fut, F, T> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::FilterMap<St, Fut, F>

where St: Stream, F: FnMut1<<St as Stream>::Item, Output = Fut>, Fut: Future<Output = Option<T>>,

type Item = T

impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F>

where St: TryStream, Fut: TryFuture<Ok = Option<T>, Error = <St as TryStream>::Error>, F: FnMut(<St as TryStream>::Ok) -> Fut,

type Item = Result<T, <St as TryStream>::Error>

impl<St, U, F> Stream for FlatMap<St, U, F>

where Flatten<Map<St, F>, U>: Stream,

type Item = <Flatten<Map<St, F>, U> as Stream>::Item

impl<St, U, F> Stream for FlatMapUnordered<St, U, F>

where FlattenUnorderedWithFlowController<Map<St, F>, ()>: Stream, St: Stream, U: Stream + Unpin, F: FnMut(<St as Stream>::Item) -> U,

type Item = <FlattenUnorderedWithFlowController<Map<St, F>, ()> as Stream>::Item

impl<T> Stream for MeteredReceiver<T>

type Item = T

impl<T> Stream for UnboundedMeteredReceiver<T>

type Item = T

impl<T> Stream for polkadot_node_subsystem::gen::futures::channel::mpsc::Receiver<T>

type Item = T

impl<T> Stream for UnboundedReceiver<T>

type Item = T

impl<T> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Empty<T>

type Item = T

impl<T> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::Pending<T>

type Item = T

impl<T> Stream for Repeat<T>

where T: Clone,

type Item = T

impl<T, F> Stream for polkadot_node_subsystem::gen::futures::prelude::future::PollImmediate<F>

where F: Future<Output = T>,

A Stream implementation that can be polled repeatedly until the future is done. The stream will never return Poll::Pending so polling it in a tight loop is worse than using a blocking synchronous function.

use futures::task::Poll;
use futures::{StreamExt, future, pin_mut};
use future::FusedFuture;

let f = async { 1_u32 };
pin_mut!(f);
let mut r = future::poll_immediate(f);
assert_eq!(r.next().await, Some(Poll::Ready(1)));

let f = async {futures::pending!(); 42_u8};
pin_mut!(f);
let mut p = future::poll_immediate(f);
assert_eq!(p.next().await, Some(Poll::Pending));
assert!(!p.is_terminated());
assert_eq!(p.next().await, Some(Poll::Ready(42)));
assert!(p.is_terminated());
assert_eq!(p.next().await, None);

type Item = Poll<T>

impl<T, F> Stream for PollFn<F>

where F: FnMut(&mut Context<'_>) -> Poll<Option<T>>,

type Item = T

impl<T, F, Fut, Item> Stream for TryUnfold<T, F, Fut>

where F: FnMut(T) -> Fut, Fut: TryFuture<Ok = Option<(Item, T)>>,

type Item = Result<Item, <Fut as TryFuture>::Error>

impl<T, F, Fut, Item> Stream for Unfold<T, F, Fut>

where F: FnMut(T) -> Fut, Fut: Future<Output = Option<(Item, T)>>,

type Item = Item

impl<T, S> Stream for polkadot_node_subsystem::gen::futures::prelude::stream::PollImmediate<S>

where S: Stream<Item = T>,

type Item = Poll<T>