Trait polkadot_node_subsystem::gen::futures::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 polkadot_node_subsystem::gen::futures::Stream

Required Associated Types§

type Item

Required Methods§

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

Provided Methods§

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

Implementations on Foreign Types§

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

type Item = <S as Stream>::Item

fn poll_next( self: Pin<&mut Box<S, Global>>, cx: &mut Context<'_> ) -> Poll<Option<<Box<S, Global> 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 &mut Swhere 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<O> Stream for Boxed<O>

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

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

impl<A, B, I> Stream for EitherOutput<A, B>where A: TryStream<Ok = I>, B: TryStream<Ok = I>,

type Item = Result<I, EitherError<<A as TryStream>::Error, <B as TryStream>::Error>>

fn poll_next( self: Pin<&mut EitherOutput<A, B>>, cx: &mut Context<'_> ) -> Poll<Option<<EitherOutput<A, B> 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, 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, 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 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 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 DnsExchangeSend

type Item = Result<DnsResponse, ProtoError>

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

type Item = Result<SerialMessage, Error>

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

impl<TBehaviour> Stream for Swarm<TBehaviour>where TBehaviour: NetworkBehaviour,

type Item = SwarmEvent<<TBehaviour as NetworkBehaviour>::OutEvent, <<<TBehaviour as NetworkBehaviour>::ConnectionHandler as IntoConnectionHandler>::Handler as ConnectionHandler>::Error>

fn poll_next( self: Pin<&mut Swarm<TBehaviour>>, cx: &mut Context<'_> ) -> Poll<Option<<Swarm<TBehaviour> 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<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 BytesConnection<T>where T: AsyncRead + AsyncWrite + Send + Unpin + 'static,

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

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

impl<T> Stream for Incoming<T>

type Item = Result<Stream, YamuxError>

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