Trait futures::stream::TryStreamExt [−][src]
Adapters specific to Result
-returning streams
Provided methods
pub fn err_into<E>(self) -> ErrInto<Self, E> where
Self::Error: Into<E>,
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Self::Error: Into<E>,
Wraps the current stream in a new stream which converts the error type into the one provided.
Examples
use futures::stream::{self, TryStreamExt}; let mut stream = stream::iter(vec![Ok(()), Err(5i32)]) .err_into::<i64>(); assert_eq!(stream.try_next().await, Ok(Some(()))); assert_eq!(stream.try_next().await, Err(5i64));
pub fn map_ok<T, F>(self, f: F) -> MapOk<Self, F> where
F: FnMut(Self::Ok) -> T,
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F: FnMut(Self::Ok) -> T,
Wraps the current stream in a new stream which maps the success value using the provided closure.
Examples
use futures::stream::{self, TryStreamExt}; let mut stream = stream::iter(vec![Ok(5), Err(0)]) .map_ok(|x| x + 2); assert_eq!(stream.try_next().await, Ok(Some(7))); assert_eq!(stream.try_next().await, Err(0));
pub fn map_err<E, F>(self, f: F) -> MapErr<Self, F> where
F: FnMut(Self::Error) -> E,
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F: FnMut(Self::Error) -> E,
Wraps the current stream in a new stream which maps the error value using the provided closure.
Examples
use futures::stream::{self, TryStreamExt}; let mut stream = stream::iter(vec![Ok(5), Err(0)]) .map_err(|x| x + 2); assert_eq!(stream.try_next().await, Ok(Some(5))); assert_eq!(stream.try_next().await, Err(2));
pub fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
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F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
Chain on a computation for when a value is ready, passing the successful
results to the provided closure f
.
This function can be used to run a unit of work when the next successful value on a stream is ready. The closure provided will be yielded a value when ready, and the returned future will then be run to completion to produce the next value on this stream.
Any errors produced by this stream will not be passed to the closure, and will be passed through.
The returned value of the closure must implement the TryFuture
trait
and can represent some more work to be done before the composed stream
is finished.
Note that this function consumes the receiving stream and returns a wrapped version of it.
To process the entire stream and return a single future representing
success or error, use try_for_each
instead.
Examples
use futures::channel::mpsc; use futures::future; use futures::stream::TryStreamExt; let (_tx, rx) = mpsc::channel::<Result<i32, ()>>(1); let rx = rx.and_then(|result| { future::ok(if result % 2 == 0 { Some(result) } else { None }) });
pub fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F> where
F: FnMut(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
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F: FnMut(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
Chain on a computation for when an error happens, passing the
erroneous result to the provided closure f
.
This function can be used to run a unit of work and attempt to recover from an error if one happens. The closure provided will be yielded an error when one appears, and the returned future will then be run to completion to produce the next value on this stream.
Any successful values produced by this stream will not be passed to the closure, and will be passed through.
The returned value of the closure must implement the TryFuture
trait
and can represent some more work to be done before the composed stream
is finished.
Note that this function consumes the receiving stream and returns a wrapped version of it.
pub fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F> where
F: FnMut(&Self::Ok),
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F: FnMut(&Self::Ok),
Do something with the success value of this stream, afterwards passing it on.
This is similar to the StreamExt::inspect
method where it allows
easily inspecting the success value as it passes through the stream, for
example to debug what’s going on.
pub fn inspect_err<F>(self, f: F) -> InspectErr<Self, F> where
F: FnMut(&Self::Error),
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F: FnMut(&Self::Error),
Do something with the error value of this stream, afterwards passing it on.
This is similar to the StreamExt::inspect
method where it allows
easily inspecting the error value as it passes through the stream, for
example to debug what’s going on.
pub fn into_stream(self) -> IntoStream<Self>
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Wraps a TryStream
into a type that implements
Stream
TryStream
s currently do not implement the
Stream
trait because of limitations
of the compiler.
Examples
use futures::stream::{Stream, TryStream, TryStreamExt}; fn make_try_stream() -> impl TryStream<Ok = T, Error = E> { // ... } fn take_stream(stream: impl Stream<Item = Result<T, E>>) { /* ... */ } take_stream(make_try_stream().into_stream());
pub fn try_next(&mut self) -> TryNext<'_, Self>ⓘ where
Self: Unpin,
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Self: Unpin,
Creates a future that attempts to resolve the next item in the stream. If an error is encountered before the next item, the error is returned instead.
This is similar to the Stream::next
combinator, but returns a
Result<Option<T>, E>
rather than an Option<Result<T, E>>
, making
for easy use with the ?
operator.
Examples
use futures::stream::{self, TryStreamExt}; let mut stream = stream::iter(vec![Ok(()), Err(())]); assert_eq!(stream.try_next().await, Ok(Some(()))); assert_eq!(stream.try_next().await, Err(()));
pub fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F>ⓘ where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = Self::Error>,
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F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = Self::Error>,
Attempts to run this stream to completion, executing the provided asynchronous closure for each element on the stream.
The provided closure will be called for each item this stream produces, yielding a future. That future will then be executed to completion before moving on to the next item.
The returned value is a Future
where the
Output
type is
Result<(), Self::Error>
. If any of the intermediate
futures or the stream returns an error, this future will return
immediately with an error.
Examples
use futures::future; use futures::stream::{self, TryStreamExt}; let mut x = 0i32; { let fut = stream::repeat(Ok(1)).try_for_each(|item| { x += item; future::ready(if x == 3 { Err(()) } else { Ok(()) }) }); assert_eq!(fut.await, Err(())); } assert_eq!(x, 3);
pub fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
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F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
Skip elements on this stream while the provided asynchronous predicate
resolves to true
.
This function is similar to
StreamExt::skip_while
but exits
early if an error occurs.
Examples
use futures::future; use futures::stream::{self, TryStreamExt}; let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(3), Ok(2)]); let stream = stream.try_skip_while(|x| future::ready(Ok(*x < 3))); let output: Result<Vec<i32>, i32> = stream.try_collect().await; assert_eq!(output, Ok(vec![3, 2]));
pub fn try_take_while<Fut, F>(self, f: F) -> TryTakeWhile<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
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F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
Take elements on this stream while the provided asynchronous predicate
resolves to true
.
This function is similar to
StreamExt::take_while
but exits
early if an error occurs.
Examples
use futures::future; use futures::stream::{self, TryStreamExt}; let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2), Ok(3), Ok(2)]); let stream = stream.try_take_while(|x| future::ready(Ok(*x < 3))); let output: Result<Vec<i32>, i32> = stream.try_collect().await; assert_eq!(output, Ok(vec![1, 2]));
pub fn try_for_each_concurrent<Fut, F>(
self,
limit: impl Into<Option<usize>>,
f: F
) -> TryForEachConcurrent<Self, Fut, F>ⓘ where
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = Result<(), Self::Error>>,
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self,
limit: impl Into<Option<usize>>,
f: F
) -> TryForEachConcurrent<Self, Fut, F>ⓘ where
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = Result<(), Self::Error>>,
Attempts to run this stream to completion, executing the provided asynchronous closure for each element on the stream concurrently as elements become available, exiting as soon as an error occurs.
This is similar to
StreamExt::for_each_concurrent
,
but will resolve to an error immediately if the underlying stream or the provided
closure return an error.
This method is only available when the std
or alloc
feature of this
library is activated, and it is activated by default.
Examples
use futures::channel::oneshot; use futures::stream::{self, StreamExt, TryStreamExt}; let (tx1, rx1) = oneshot::channel(); let (tx2, rx2) = oneshot::channel(); let (_tx3, rx3) = oneshot::channel(); let stream = stream::iter(vec![rx1, rx2, rx3]); let fut = stream.map(Ok).try_for_each_concurrent( /* limit */ 2, |rx| async move { let res: Result<(), oneshot::Canceled> = rx.await; res } ); tx1.send(()).unwrap(); // Drop the second sender so that `rx2` resolves to `Canceled`. drop(tx2); // The final result is an error because the second future // resulted in an error. assert_eq!(Err(oneshot::Canceled), fut.await);
pub fn try_collect<C>(self) -> TryCollect<Self, C>ⓘ where
C: Default + Extend<Self::Ok>,
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C: Default + Extend<Self::Ok>,
Attempt to transform a stream into a collection, returning a future representing the result of that computation.
This combinator will collect all successful results of this stream and collect them into the specified collection type. If an error happens then all collected elements will be dropped and the error will be returned.
The returned future will be resolved when the stream terminates.
Examples
use futures::channel::mpsc; use futures::stream::TryStreamExt; use std::thread; let (tx, rx) = mpsc::unbounded(); thread::spawn(move || { for i in 1..=5 { tx.unbounded_send(Ok(i)).unwrap(); } tx.unbounded_send(Err(6)).unwrap(); }); let output: Result<Vec<i32>, i32> = rx.try_collect().await; assert_eq!(output, Err(6));
pub fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: Future<Output = bool>,
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F: FnMut(&Self::Ok) -> Fut,
Fut: Future<Output = bool>,
Attempt to filter the values produced by this stream according to the provided asynchronous closure.
As values of this stream are made available, the provided predicate f
will be run on them. If the predicate returns a Future
which resolves
to true
, then the stream will yield the value, but if the predicate
return a Future
which resolves to false
, then the value will be
discarded and the next value will be produced.
All errors are passed through without filtering in this combinator.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to the existing filter
methods in
the standard library.
Examples
use futures::future; use futures::stream::{self, StreamExt, TryStreamExt}; let stream = stream::iter(vec![Ok(1i32), Ok(2i32), Ok(3i32), Err("error")]); let mut evens = stream.try_filter(|x| { future::ready(x % 2 == 0) }); assert_eq!(evens.next().await, Some(Ok(2))); assert_eq!(evens.next().await, Some(Err("error")));
pub fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
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F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
Attempt to filter the values produced by this stream while simultaneously mapping them to a different type according to the provided asynchronous closure.
As values of this stream are made available, the provided function will
be run on them. If the future returned by the predicate f
resolves to
Some(item)
then the stream will yield the value item
, but if
it resolves to None
then the next value will be produced.
All errors are passed through without filtering in this combinator.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to the existing filter_map
methods in
the standard library.
Examples
use futures::stream::{self, StreamExt, TryStreamExt}; use futures::pin_mut; let stream = stream::iter(vec![Ok(1i32), Ok(6i32), Err("error")]); let halves = stream.try_filter_map(|x| async move { let ret = if x % 2 == 0 { Some(x / 2) } else { None }; Ok(ret) }); pin_mut!(halves); assert_eq!(halves.next().await, Some(Ok(3))); assert_eq!(halves.next().await, Some(Err("error")));
pub fn try_flatten(self) -> TryFlatten<Self> where
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
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Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
Flattens a stream of streams into just one continuous stream.
If this stream’s elements are themselves streams then this combinator will flatten out the entire stream to one long chain of elements. Any errors are passed through without looking at them, but otherwise each individual stream will get exhausted before moving on to the next.
Examples
use futures::channel::mpsc; use futures::stream::{StreamExt, TryStreamExt}; use std::thread; let (tx1, rx1) = mpsc::unbounded(); let (tx2, rx2) = mpsc::unbounded(); let (tx3, rx3) = mpsc::unbounded(); thread::spawn(move || { tx1.unbounded_send(Ok(1)).unwrap(); }); thread::spawn(move || { tx2.unbounded_send(Ok(2)).unwrap(); tx2.unbounded_send(Err(3)).unwrap(); }); thread::spawn(move || { tx3.unbounded_send(Ok(rx1)).unwrap(); tx3.unbounded_send(Ok(rx2)).unwrap(); tx3.unbounded_send(Err(4)).unwrap(); }); let mut stream = rx3.try_flatten(); assert_eq!(stream.next().await, Some(Ok(1))); assert_eq!(stream.next().await, Some(Ok(2))); assert_eq!(stream.next().await, Some(Err(3)));
pub fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F>ⓘ where
F: FnMut(T, Self::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = Self::Error>,
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F: FnMut(T, Self::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = Self::Error>,
Attempt to execute an accumulating asynchronous computation over a stream, collecting all the values into one final result.
This combinator will accumulate all values returned by this stream according to the closure provided. The initial state is also provided to this method and then is returned again by each execution of the closure. Once the entire stream has been exhausted the returned future will resolve to this value.
This method is similar to fold
, but will
exit early if an error is encountered in either the stream or the
provided closure.
Examples
use futures::stream::{self, TryStreamExt}; let number_stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2)]); let sum = number_stream.try_fold(0, |acc, x| async move { Ok(acc + x) }); assert_eq!(sum.await, Ok(3)); let number_stream_with_err = stream::iter(vec![Ok::<i32, i32>(1), Err(2), Ok(1)]); let sum = number_stream_with_err.try_fold(0, |acc, x| async move { Ok(acc + x) }); assert_eq!(sum.await, Err(2));
pub fn try_concat(self) -> TryConcat<Self>ⓘNotable traits for TryConcat<St>
impl<St> Future for TryConcat<St> where
St: TryStream,
<St as TryStream>::Ok: Extend<<<St as TryStream>::Ok as IntoIterator>::Item>,
<St as TryStream>::Ok: IntoIterator,
<St as TryStream>::Ok: Default, type Output = Result<<St as TryStream>::Ok, <St as TryStream>::Error>;
where
Self::Ok: Extend<<Self::Ok as IntoIterator>::Item>,
Self::Ok: IntoIterator,
Self::Ok: Default,
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Notable traits for TryConcat<St>
impl<St> Future for TryConcat<St> where
St: TryStream,
<St as TryStream>::Ok: Extend<<<St as TryStream>::Ok as IntoIterator>::Item>,
<St as TryStream>::Ok: IntoIterator,
<St as TryStream>::Ok: Default, type Output = Result<<St as TryStream>::Ok, <St as TryStream>::Error>;
Self::Ok: Extend<<Self::Ok as IntoIterator>::Item>,
Self::Ok: IntoIterator,
Self::Ok: Default,
Attempt to concatenate all items of a stream into a single extendable destination, returning a future representing the end result.
This combinator will extend the first item with the contents of all the subsequent successful results of the stream. If the stream is empty, the default value will be returned.
Works with all collections that implement the Extend
trait.
This method is similar to concat
, but will
exit early if an error is encountered in the stream.
Examples
use futures::channel::mpsc; use futures::stream::TryStreamExt; use std::thread; let (tx, rx) = mpsc::unbounded::<Result<Vec<i32>, ()>>(); thread::spawn(move || { for i in (0..3).rev() { let n = i * 3; tx.unbounded_send(Ok(vec![n + 1, n + 2, n + 3])).unwrap(); } }); let result = rx.try_concat().await; assert_eq!(result, Ok(vec![7, 8, 9, 4, 5, 6, 1, 2, 3]));
pub fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self> where
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
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Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
Attempt to execute several futures from a stream concurrently (unordered).
This stream’s Ok
type must be a TryFuture
with an Error
type
that matches the stream’s Error
type.
This adaptor will buffer up to n
futures and then return their
outputs in the order in which they complete. If the underlying stream
returns an error, it will be immediately propagated.
The returned stream will be a stream of results, each containing either an error or a future’s output. An error can be produced either by the underlying stream itself or by one of the futures it yielded.
This method is only available when the std
or alloc
feature of this
library is activated, and it is activated by default.
Examples
Results are returned in the order of completion:
use futures::channel::oneshot; use futures::stream::{self, StreamExt, TryStreamExt}; let (send_one, recv_one) = oneshot::channel(); let (send_two, recv_two) = oneshot::channel(); let stream_of_futures = stream::iter(vec![Ok(recv_one), Ok(recv_two)]); let mut buffered = stream_of_futures.try_buffer_unordered(10); send_two.send(2i32)?; assert_eq!(buffered.next().await, Some(Ok(2i32))); send_one.send(1i32)?; assert_eq!(buffered.next().await, Some(Ok(1i32))); assert_eq!(buffered.next().await, None);
Errors from the underlying stream itself are propagated:
use futures::channel::mpsc; use futures::stream::{StreamExt, TryStreamExt}; let (sink, stream_of_futures) = mpsc::unbounded(); let mut buffered = stream_of_futures.try_buffer_unordered(10); sink.unbounded_send(Ok(async { Ok(7i32) }))?; assert_eq!(buffered.next().await, Some(Ok(7i32))); sink.unbounded_send(Err("error in the stream"))?; assert_eq!(buffered.next().await, Some(Err("error in the stream")));
pub fn try_buffered(self, n: usize) -> TryBuffered<Self> where
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
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Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
Attempt to execute several futures from a stream concurrently.
This stream’s Ok
type must be a TryFuture
with an Error
type
that matches the stream’s Error
type.
This adaptor will buffer up to n
futures and then return their
outputs in the order. If the underlying stream returns an error, it will
be immediately propagated.
The returned stream will be a stream of results, each containing either an error or a future’s output. An error can be produced either by the underlying stream itself or by one of the futures it yielded.
This method is only available when the std
or alloc
feature of this
library is activated, and it is activated by default.
Examples
Results are returned in the order of addition:
use futures::channel::oneshot; use futures::future::lazy; use futures::stream::{self, StreamExt, TryStreamExt}; let (send_one, recv_one) = oneshot::channel(); let (send_two, recv_two) = oneshot::channel(); let mut buffered = lazy(move |cx| { let stream_of_futures = stream::iter(vec![Ok(recv_one), Ok(recv_two)]); let mut buffered = stream_of_futures.try_buffered(10); assert!(buffered.try_poll_next_unpin(cx).is_pending()); send_two.send(2i32)?; assert!(buffered.try_poll_next_unpin(cx).is_pending()); Ok::<_, i32>(buffered) }).await?; send_one.send(1i32)?; assert_eq!(buffered.next().await, Some(Ok(1i32))); assert_eq!(buffered.next().await, Some(Ok(2i32))); assert_eq!(buffered.next().await, None);
Errors from the underlying stream itself are propagated:
use futures::channel::mpsc; use futures::stream::{StreamExt, TryStreamExt}; let (sink, stream_of_futures) = mpsc::unbounded(); let mut buffered = stream_of_futures.try_buffered(10); sink.unbounded_send(Ok(async { Ok(7i32) }))?; assert_eq!(buffered.next().await, Some(Ok(7i32))); sink.unbounded_send(Err("error in the stream"))?; assert_eq!(buffered.next().await, Some(Err("error in the stream")));
pub fn try_poll_next_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Self::Ok, Self::Error>>> where
Self: Unpin,
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&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Self::Ok, Self::Error>>> where
Self: Unpin,
A convenience method for calling TryStream::try_poll_next
on Unpin
stream types.
pub fn into_async_read(self) -> IntoAsyncRead<Self> where
Self: TryStreamExt<Error = Error> + Unpin,
Self::Ok: AsRef<[u8]>,
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Self: TryStreamExt<Error = Error> + Unpin,
Self::Ok: AsRef<[u8]>,
Adapter that converts this stream into an AsyncRead
.
Note that because into_async_read
moves the stream, the Stream
type must be
Unpin
. If you want to use into_async_read
with a !Unpin
stream, you’ll
first have to pin the stream. This can be done by boxing the stream using Box::pin
or pinning it to the stack using the pin_mut!
macro from the pin_utils
crate.
This method is only available when the std
feature of this
library is activated, and it is activated by default.
Examples
use futures::stream::{self, TryStreamExt}; use futures::io::AsyncReadExt; let stream = stream::iter(vec![Ok(vec![1, 2, 3, 4, 5])]); let mut reader = stream.into_async_read(); let mut buf = Vec::new(); assert!(reader.read_to_end(&mut buf).await.is_ok()); assert_eq!(buf, &[1, 2, 3, 4, 5]);
Implementors
impl<S> TryStreamExt for S where
S: TryStream + ?Sized,
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S: TryStream + ?Sized,