pub trait StreamExt: Stream {
Show 23 methods
// Provided methods
fn next(&mut self) -> Next<'_, Self>
where Self: Unpin { ... }
fn try_next<T, E>(&mut self) -> TryNext<'_, Self>
where Self: Stream<Item = Result<T, E>> + Unpin { ... }
fn map<T, F>(self, f: F) -> Map<Self, F>
where F: FnMut(Self::Item) -> T,
Self: Sized { ... }
fn map_while<T, F>(self, f: F) -> MapWhile<Self, F>
where F: FnMut(Self::Item) -> Option<T>,
Self: Sized { ... }
fn then<F, Fut>(self, f: F) -> Then<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut,
Fut: Future,
Self: Sized { ... }
fn merge<U>(self, other: U) -> Merge<Self, U>
where U: Stream<Item = Self::Item>,
Self: Sized { ... }
fn filter<F>(self, f: F) -> Filter<Self, F>
where F: FnMut(&Self::Item) -> bool,
Self: Sized { ... }
fn filter_map<T, F>(self, f: F) -> FilterMap<Self, F>
where F: FnMut(Self::Item) -> Option<T>,
Self: Sized { ... }
fn fuse(self) -> Fuse<Self>
where Self: Sized { ... }
fn take(self, n: usize) -> Take<Self>
where Self: Sized { ... }
fn take_while<F>(self, f: F) -> TakeWhile<Self, F>
where F: FnMut(&Self::Item) -> bool,
Self: Sized { ... }
fn skip(self, n: usize) -> Skip<Self>
where Self: Sized { ... }
fn skip_while<F>(self, f: F) -> SkipWhile<Self, F>
where F: FnMut(&Self::Item) -> bool,
Self: Sized { ... }
fn all<F>(&mut self, f: F) -> AllFuture<'_, Self, F>
where Self: Unpin,
F: FnMut(Self::Item) -> bool { ... }
fn any<F>(&mut self, f: F) -> AnyFuture<'_, Self, F>
where Self: Unpin,
F: FnMut(Self::Item) -> bool { ... }
fn chain<U>(self, other: U) -> Chain<Self, U>
where U: Stream<Item = Self::Item>,
Self: Sized { ... }
fn fold<B, F>(self, init: B, f: F) -> FoldFuture<Self, B, F>
where Self: Sized,
F: FnMut(B, Self::Item) -> B { ... }
fn collect<T>(self) -> Collect<Self, T>
where T: FromStream<Self::Item>,
Self: Sized { ... }
fn timeout(self, duration: Duration) -> Timeout<Self>
where Self: Sized { ... }
fn timeout_repeating(self, interval: Interval) -> TimeoutRepeating<Self>
where Self: Sized { ... }
fn throttle(self, duration: Duration) -> Throttle<Self>
where Self: Sized { ... }
fn chunks_timeout(
self,
max_size: usize,
duration: Duration,
) -> ChunksTimeout<Self>
where Self: Sized { ... }
fn peekable(self) -> Peekable<Self>
where Self: Sized { ... }
}
Expand description
An extension trait for the Stream
trait that provides a variety of
convenient combinator functions.
Be aware that the Stream
trait in Tokio is a re-export of the trait found
in the futures crate, however both Tokio and futures provide separate
StreamExt
utility traits, and some utilities are only available on one of
these traits. Click here to see the other StreamExt
trait in the futures crate.
If you need utilities from both StreamExt
traits, you should prefer to
import one of them, and use the other through the fully qualified call
syntax. For example:
// import one of the traits:
use futures::stream::StreamExt;
let a = tokio_stream::iter(vec![1, 3, 5]);
let b = tokio_stream::iter(vec![2, 4, 6]);
// use the fully qualified call syntax for the other trait:
let merged = tokio_stream::StreamExt::merge(a, b);
// use normal call notation for futures::stream::StreamExt::collect
let output: Vec<_> = merged.collect().await;
assert_eq!(output, vec![1, 2, 3, 4, 5, 6]);
Provided Methods§
Sourcefn next(&mut self) -> Next<'_, Self>where
Self: Unpin,
fn next(&mut self) -> Next<'_, Self>where
Self: Unpin,
Consumes and returns the next value in the stream or None
if the
stream is finished.
Equivalent to:
async fn next(&mut self) -> Option<Self::Item>;
Note that because next
doesn’t take ownership over the stream,
the Stream
type must be Unpin
. If you want to use next
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.
§Cancel safety
This method is cancel safe. The returned future only holds onto a reference to the underlying stream, so dropping it will never lose a value.
§Examples
use tokio_stream::{self as stream, StreamExt};
let mut stream = stream::iter(1..=3);
assert_eq!(stream.next().await, Some(1));
assert_eq!(stream.next().await, Some(2));
assert_eq!(stream.next().await, Some(3));
assert_eq!(stream.next().await, None);
Sourcefn try_next<T, E>(&mut self) -> TryNext<'_, Self>
fn try_next<T, E>(&mut self) -> TryNext<'_, Self>
Consumes and returns the next item in the stream. If an error is encountered before the next item, the error is returned instead.
Equivalent to:
async fn try_next(&mut self) -> Result<Option<T>, E>;
This is similar to the next
combinator,
but returns a Result<Option<T>, E>
rather than
an Option<Result<T, E>>
, making for easy use
with the ?
operator.
§Cancel safety
This method is cancel safe. The returned future only holds onto a reference to the underlying stream, so dropping it will never lose a value.
§Examples
use tokio_stream::{self as stream, StreamExt};
let mut stream = stream::iter(vec![Ok(1), Ok(2), Err("nope")]);
assert_eq!(stream.try_next().await, Ok(Some(1)));
assert_eq!(stream.try_next().await, Ok(Some(2)));
assert_eq!(stream.try_next().await, Err("nope"));
Sourcefn map<T, F>(self, f: F) -> Map<Self, F>
fn map<T, F>(self, f: F) -> Map<Self, F>
Maps this stream’s items to a different type, returning a new stream of the resulting type.
The provided closure is executed over all elements of this stream as
they are made available. It is executed inline with calls to
poll_next
.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to the existing map
methods in the
standard library.
§Examples
use tokio_stream::{self as stream, StreamExt};
let stream = stream::iter(1..=3);
let mut stream = stream.map(|x| x + 3);
assert_eq!(stream.next().await, Some(4));
assert_eq!(stream.next().await, Some(5));
assert_eq!(stream.next().await, Some(6));
Sourcefn map_while<T, F>(self, f: F) -> MapWhile<Self, F>
fn map_while<T, F>(self, f: F) -> MapWhile<Self, F>
Map this stream’s items to a different type for as long as determined by
the provided closure. A stream of the target type will be returned,
which will yield elements until the closure returns None
.
The provided closure is executed over all elements of this stream as
they are made available, until it returns None
. It is executed inline
with calls to poll_next
. Once None
is returned,
the underlying stream will not be polled again.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to the Iterator::map_while
method in the
standard library.
§Examples
use tokio_stream::{self as stream, StreamExt};
let stream = stream::iter(1..=10);
let mut stream = stream.map_while(|x| {
if x < 4 {
Some(x + 3)
} else {
None
}
});
assert_eq!(stream.next().await, Some(4));
assert_eq!(stream.next().await, Some(5));
assert_eq!(stream.next().await, Some(6));
assert_eq!(stream.next().await, None);
Sourcefn then<F, Fut>(self, f: F) -> Then<Self, Fut, F>
fn then<F, Fut>(self, f: F) -> Then<Self, Fut, F>
Maps this stream’s items asynchronously to a different type, returning a new stream of the resulting type.
The provided closure is executed over all elements of this stream as they are made available, and the returned future is executed. Only one future is executed at the time.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to the existing then
methods in the
standard library.
Be aware that if the future is not Unpin
, then neither is the Stream
returned by this method. To handle this, you can use tokio::pin!
as in
the example below or put the stream in a Box
with Box::pin(stream)
.
§Examples
use tokio_stream::{self as stream, StreamExt};
async fn do_async_work(value: i32) -> i32 {
value + 3
}
let stream = stream::iter(1..=3);
let stream = stream.then(do_async_work);
tokio::pin!(stream);
assert_eq!(stream.next().await, Some(4));
assert_eq!(stream.next().await, Some(5));
assert_eq!(stream.next().await, Some(6));
Sourcefn merge<U>(self, other: U) -> Merge<Self, U>
fn merge<U>(self, other: U) -> Merge<Self, U>
Combine two streams into one by interleaving the output of both as it is produced.
Values are produced from the merged stream in the order they arrive from
the two source streams. If both source streams provide values
simultaneously, the merge stream alternates between them. This provides
some level of fairness. You should not chain calls to merge
, as this
will break the fairness of the merging.
The merged stream completes once both source streams complete. When one source stream completes before the other, the merge stream exclusively polls the remaining stream.
For merging multiple streams, consider using StreamMap
instead.
§Examples
use tokio_stream::{StreamExt, Stream};
use tokio::sync::mpsc;
use tokio::time;
use std::time::Duration;
use std::pin::Pin;
#[tokio::main]
async fn main() {
let (tx1, mut rx1) = mpsc::channel::<usize>(10);
let (tx2, mut rx2) = mpsc::channel::<usize>(10);
// Convert the channels to a `Stream`.
let rx1 = Box::pin(async_stream::stream! {
while let Some(item) = rx1.recv().await {
yield item;
}
}) as Pin<Box<dyn Stream<Item = usize> + Send>>;
let rx2 = Box::pin(async_stream::stream! {
while let Some(item) = rx2.recv().await {
yield item;
}
}) as Pin<Box<dyn Stream<Item = usize> + Send>>;
let mut rx = rx1.merge(rx2);
tokio::spawn(async move {
// Send some values immediately
tx1.send(1).await.unwrap();
tx1.send(2).await.unwrap();
// Let the other task send values
time::sleep(Duration::from_millis(20)).await;
tx1.send(4).await.unwrap();
});
tokio::spawn(async move {
// Wait for the first task to send values
time::sleep(Duration::from_millis(5)).await;
tx2.send(3).await.unwrap();
time::sleep(Duration::from_millis(25)).await;
// Send the final value
tx2.send(5).await.unwrap();
});
assert_eq!(1, rx.next().await.unwrap());
assert_eq!(2, rx.next().await.unwrap());
assert_eq!(3, rx.next().await.unwrap());
assert_eq!(4, rx.next().await.unwrap());
assert_eq!(5, rx.next().await.unwrap());
// The merged stream is consumed
assert!(rx.next().await.is_none());
}
Sourcefn filter<F>(self, f: F) -> Filter<Self, F>
fn filter<F>(self, f: F) -> Filter<Self, F>
Filters the values produced by this stream according to the provided predicate.
As values of this stream are made available, the provided predicate f
will be run against them. If the predicate
resolves to true
, then the stream will yield the value, but if the
predicate resolves to false
, then the value
will be discarded and the next value will be produced.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to Iterator::filter
method in the
standard library.
§Examples
use tokio_stream::{self as stream, StreamExt};
let stream = stream::iter(1..=8);
let mut evens = stream.filter(|x| x % 2 == 0);
assert_eq!(Some(2), evens.next().await);
assert_eq!(Some(4), evens.next().await);
assert_eq!(Some(6), evens.next().await);
assert_eq!(Some(8), evens.next().await);
assert_eq!(None, evens.next().await);
Sourcefn filter_map<T, F>(self, f: F) -> FilterMap<Self, F>
fn filter_map<T, F>(self, f: F) -> FilterMap<Self, F>
Filters the values produced by this stream while simultaneously mapping them to a different type according to the provided closure.
As values of this stream are made available, the provided function will
be run on them. If the predicate f
resolves to
Some(item)
then the stream will yield the value item
, but if
it resolves to None
, then the value will be skipped.
Note that this function consumes the stream passed into it and returns a
wrapped version of it, similar to Iterator::filter_map
method in the
standard library.
§Examples
use tokio_stream::{self as stream, StreamExt};
let stream = stream::iter(1..=8);
let mut evens = stream.filter_map(|x| {
if x % 2 == 0 { Some(x + 1) } else { None }
});
assert_eq!(Some(3), evens.next().await);
assert_eq!(Some(5), evens.next().await);
assert_eq!(Some(7), evens.next().await);
assert_eq!(Some(9), evens.next().await);
assert_eq!(None, evens.next().await);
Sourcefn fuse(self) -> Fuse<Self>where
Self: Sized,
fn fuse(self) -> Fuse<Self>where
Self: Sized,
Creates a stream which ends after the first None
.
After a stream returns None
, behavior is undefined. Future calls to
poll_next
may or may not return Some(T)
again or they may panic.
fuse()
adapts a stream, ensuring that after None
is given, it will
return None
forever.
§Examples
use tokio_stream::{Stream, StreamExt};
use std::pin::Pin;
use std::task::{Context, Poll};
// a stream which alternates between Some and None
struct Alternate {
state: i32,
}
impl Stream for Alternate {
type Item = i32;
fn poll_next(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<i32>> {
let val = self.state;
self.state = self.state + 1;
// if it's even, Some(i32), else None
if val % 2 == 0 {
Poll::Ready(Some(val))
} else {
Poll::Ready(None)
}
}
}
#[tokio::main]
async fn main() {
let mut stream = Alternate { state: 0 };
// the stream goes back and forth
assert_eq!(stream.next().await, Some(0));
assert_eq!(stream.next().await, None);
assert_eq!(stream.next().await, Some(2));
assert_eq!(stream.next().await, None);
// however, once it is fused
let mut stream = stream.fuse();
assert_eq!(stream.next().await, Some(4));
assert_eq!(stream.next().await, None);
// it will always return `None` after the first time.
assert_eq!(stream.next().await, None);
assert_eq!(stream.next().await, None);
assert_eq!(stream.next().await, None);
}
Sourcefn take(self, n: usize) -> Take<Self>where
Self: Sized,
fn take(self, n: usize) -> Take<Self>where
Self: Sized,
Creates a new stream of at most n
items of the underlying stream.
Once n
items have been yielded from this stream then it will always
return that the stream is done.
§Examples
use tokio_stream::{self as stream, StreamExt};
let mut stream = stream::iter(1..=10).take(3);
assert_eq!(Some(1), stream.next().await);
assert_eq!(Some(2), stream.next().await);
assert_eq!(Some(3), stream.next().await);
assert_eq!(None, stream.next().await);
Sourcefn take_while<F>(self, f: F) -> TakeWhile<Self, F>
fn take_while<F>(self, f: F) -> TakeWhile<Self, F>
Take elements from this stream while the provided predicate
resolves to true
.
This function, like Iterator::take_while
, will take elements from the
stream until the predicate f
resolves to false
. Once one element
returns false it will always return that the stream is done.
§Examples
use tokio_stream::{self as stream, StreamExt};
let mut stream = stream::iter(1..=10).take_while(|x| *x <= 3);
assert_eq!(Some(1), stream.next().await);
assert_eq!(Some(2), stream.next().await);
assert_eq!(Some(3), stream.next().await);
assert_eq!(None, stream.next().await);
Sourcefn skip(self, n: usize) -> Skip<Self>where
Self: Sized,
fn skip(self, n: usize) -> Skip<Self>where
Self: Sized,
Creates a new stream that will skip the n
first items of the
underlying stream.
§Examples
use tokio_stream::{self as stream, StreamExt};
let mut stream = stream::iter(1..=10).skip(7);
assert_eq!(Some(8), stream.next().await);
assert_eq!(Some(9), stream.next().await);
assert_eq!(Some(10), stream.next().await);
assert_eq!(None, stream.next().await);
Sourcefn skip_while<F>(self, f: F) -> SkipWhile<Self, F>
fn skip_while<F>(self, f: F) -> SkipWhile<Self, F>
Skip elements from the underlying stream while the provided predicate
resolves to true
.
This function, like Iterator::skip_while
, will ignore elements from the
stream until the predicate f
resolves to false
. Once one element
returns false, the rest of the elements will be yielded.
§Examples
use tokio_stream::{self as stream, StreamExt};
let mut stream = stream::iter(vec![1,2,3,4,1]).skip_while(|x| *x < 3);
assert_eq!(Some(3), stream.next().await);
assert_eq!(Some(4), stream.next().await);
assert_eq!(Some(1), stream.next().await);
assert_eq!(None, stream.next().await);
Sourcefn all<F>(&mut self, f: F) -> AllFuture<'_, Self, F>
fn all<F>(&mut self, f: F) -> AllFuture<'_, Self, F>
Tests if every element of the stream matches a predicate.
Equivalent to:
async fn all<F>(&mut self, f: F) -> bool;
all()
takes a closure that returns true
or false
. It applies
this closure to each element of the stream, and if they all return
true
, then so does all
. If any of them return false
, it
returns false
. An empty stream returns true
.
all()
is short-circuiting; in other words, it will stop processing
as soon as it finds a false
, given that no matter what else happens,
the result will also be false
.
An empty stream returns true
.
§Examples
Basic usage:
use tokio_stream::{self as stream, StreamExt};
let a = [1, 2, 3];
assert!(stream::iter(&a).all(|&x| x > 0).await);
assert!(!stream::iter(&a).all(|&x| x > 2).await);
Stopping at the first false
:
use tokio_stream::{self as stream, StreamExt};
let a = [1, 2, 3];
let mut iter = stream::iter(&a);
assert!(!iter.all(|&x| x != 2).await);
// we can still use `iter`, as there are more elements.
assert_eq!(iter.next().await, Some(&3));
Sourcefn any<F>(&mut self, f: F) -> AnyFuture<'_, Self, F>
fn any<F>(&mut self, f: F) -> AnyFuture<'_, Self, F>
Tests if any element of the stream matches a predicate.
Equivalent to:
async fn any<F>(&mut self, f: F) -> bool;
any()
takes a closure that returns true
or false
. It applies
this closure to each element of the stream, and if any of them return
true
, then so does any()
. If they all return false
, it
returns false
.
any()
is short-circuiting; in other words, it will stop processing
as soon as it finds a true
, given that no matter what else happens,
the result will also be true
.
An empty stream returns false
.
Basic usage:
use tokio_stream::{self as stream, StreamExt};
let a = [1, 2, 3];
assert!(stream::iter(&a).any(|&x| x > 0).await);
assert!(!stream::iter(&a).any(|&x| x > 5).await);
Stopping at the first true
:
use tokio_stream::{self as stream, StreamExt};
let a = [1, 2, 3];
let mut iter = stream::iter(&a);
assert!(iter.any(|&x| x != 2).await);
// we can still use `iter`, as there are more elements.
assert_eq!(iter.next().await, Some(&2));
Sourcefn chain<U>(self, other: U) -> Chain<Self, U>
fn chain<U>(self, other: U) -> Chain<Self, U>
Combine two streams into one by first returning all values from the first stream then all values from the second stream.
As long as self
still has values to emit, no values from other
are
emitted, even if some are ready.
§Examples
use tokio_stream::{self as stream, StreamExt};
#[tokio::main]
async fn main() {
let one = stream::iter(vec![1, 2, 3]);
let two = stream::iter(vec![4, 5, 6]);
let mut stream = one.chain(two);
assert_eq!(stream.next().await, Some(1));
assert_eq!(stream.next().await, Some(2));
assert_eq!(stream.next().await, Some(3));
assert_eq!(stream.next().await, Some(4));
assert_eq!(stream.next().await, Some(5));
assert_eq!(stream.next().await, Some(6));
assert_eq!(stream.next().await, None);
}
Sourcefn fold<B, F>(self, init: B, f: F) -> FoldFuture<Self, B, F>
fn fold<B, F>(self, init: B, f: F) -> FoldFuture<Self, B, F>
A combinator that applies a function to every element in a stream producing a single, final value.
Equivalent to:
async fn fold<B, F>(self, init: B, f: F) -> B;
§Examples
Basic usage:
use tokio_stream::{self as stream, *};
let s = stream::iter(vec![1u8, 2, 3]);
let sum = s.fold(0, |acc, x| acc + x).await;
assert_eq!(sum, 6);
Sourcefn collect<T>(self) -> Collect<Self, T>
fn collect<T>(self) -> Collect<Self, T>
Drain stream pushing all emitted values into a collection.
Equivalent to:
async fn collect<T>(self) -> T;
collect
streams all values, awaiting as needed. Values are pushed into
a collection. A number of different target collection types are
supported, including Vec
, String
, and Bytes
.
§Result
collect()
can also be used with streams of type Result<T, E>
where
T: FromStream<_>
. In this case, collect()
will stream as long as
values yielded from the stream are Ok(_)
. If Err(_)
is encountered,
streaming is terminated and collect()
returns the Err
.
§Notes
FromStream
is currently a sealed trait. Stabilization is pending
enhancements to the Rust language.
§Examples
Basic usage:
use tokio_stream::{self as stream, StreamExt};
#[tokio::main]
async fn main() {
let doubled: Vec<i32> =
stream::iter(vec![1, 2, 3])
.map(|x| x * 2)
.collect()
.await;
assert_eq!(vec![2, 4, 6], doubled);
}
Collecting a stream of Result
values
use tokio_stream::{self as stream, StreamExt};
#[tokio::main]
async fn main() {
// A stream containing only `Ok` values will be collected
let values: Result<Vec<i32>, &str> =
stream::iter(vec![Ok(1), Ok(2), Ok(3)])
.collect()
.await;
assert_eq!(Ok(vec![1, 2, 3]), values);
// A stream containing `Err` values will return the first error.
let results = vec![Ok(1), Err("no"), Ok(2), Ok(3), Err("nein")];
let values: Result<Vec<i32>, &str> =
stream::iter(results)
.collect()
.await;
assert_eq!(Err("no"), values);
}
Sourcefn timeout(self, duration: Duration) -> Timeout<Self>where
Self: Sized,
fn timeout(self, duration: Duration) -> Timeout<Self>where
Self: Sized,
Applies a per-item timeout to the passed stream.
timeout()
takes a Duration
that represents the maximum amount of
time each element of the stream has to complete before timing out.
If the wrapped stream yields a value before the deadline is reached, the
value is returned. Otherwise, an error is returned. The caller may decide
to continue consuming the stream and will eventually get the next source
stream value once it becomes available. See
timeout_repeating
for an alternative
where the timeouts will repeat.
§Notes
This function consumes the stream passed into it and returns a wrapped version of it.
Polling the returned stream will continue to poll the inner stream even if one or more items time out.
§Examples
Suppose we have a stream int_stream
that yields 3 numbers (1, 2, 3):
use tokio_stream::{self as stream, StreamExt};
use std::time::Duration;
let int_stream = int_stream.timeout(Duration::from_secs(1));
tokio::pin!(int_stream);
// When no items time out, we get the 3 elements in succession:
assert_eq!(int_stream.try_next().await, Ok(Some(1)));
assert_eq!(int_stream.try_next().await, Ok(Some(2)));
assert_eq!(int_stream.try_next().await, Ok(Some(3)));
assert_eq!(int_stream.try_next().await, Ok(None));
// If the second item times out, we get an error and continue polling the stream:
assert_eq!(int_stream.try_next().await, Ok(Some(1)));
assert!(int_stream.try_next().await.is_err());
assert_eq!(int_stream.try_next().await, Ok(Some(2)));
assert_eq!(int_stream.try_next().await, Ok(Some(3)));
assert_eq!(int_stream.try_next().await, Ok(None));
// If we want to stop consuming the source stream the first time an
// element times out, we can use the `take_while` operator:
let mut int_stream = int_stream.take_while(Result::is_ok);
assert_eq!(int_stream.try_next().await, Ok(Some(1)));
assert_eq!(int_stream.try_next().await, Ok(None));
Once a timeout error is received, no further events will be received unless the wrapped stream yields a value (timeouts do not repeat).
use tokio_stream::{StreamExt, wrappers::IntervalStream};
use std::time::Duration;
let interval_stream = IntervalStream::new(tokio::time::interval(Duration::from_millis(100)));
let timeout_stream = interval_stream.timeout(Duration::from_millis(10));
tokio::pin!(timeout_stream);
// Only one timeout will be received between values in the source stream.
assert!(timeout_stream.try_next().await.is_ok());
assert!(timeout_stream.try_next().await.is_err(), "expected one timeout");
assert!(timeout_stream.try_next().await.is_ok(), "expected no more timeouts");
Sourcefn timeout_repeating(self, interval: Interval) -> TimeoutRepeating<Self>where
Self: Sized,
fn timeout_repeating(self, interval: Interval) -> TimeoutRepeating<Self>where
Self: Sized,
Applies a per-item timeout to the passed stream.
timeout_repeating()
takes an Interval
that controls the time each
element of the stream has to complete before timing out.
If the wrapped stream yields a value before the deadline is reached, the
value is returned. Otherwise, an error is returned. The caller may decide
to continue consuming the stream and will eventually get the next source
stream value once it becomes available. Unlike timeout()
, if no value
becomes available before the deadline is reached, additional errors are
returned at the specified interval. See timeout
for an alternative where the timeouts do not repeat.
§Notes
This function consumes the stream passed into it and returns a wrapped version of it.
Polling the returned stream will continue to poll the inner stream even if one or more items time out.
§Examples
Suppose we have a stream int_stream
that yields 3 numbers (1, 2, 3):
use tokio_stream::{self as stream, StreamExt};
use std::time::Duration;
let int_stream = int_stream.timeout_repeating(tokio::time::interval(Duration::from_secs(1)));
tokio::pin!(int_stream);
// When no items time out, we get the 3 elements in succession:
assert_eq!(int_stream.try_next().await, Ok(Some(1)));
assert_eq!(int_stream.try_next().await, Ok(Some(2)));
assert_eq!(int_stream.try_next().await, Ok(Some(3)));
assert_eq!(int_stream.try_next().await, Ok(None));
// If the second item times out, we get an error and continue polling the stream:
assert_eq!(int_stream.try_next().await, Ok(Some(1)));
assert!(int_stream.try_next().await.is_err());
assert_eq!(int_stream.try_next().await, Ok(Some(2)));
assert_eq!(int_stream.try_next().await, Ok(Some(3)));
assert_eq!(int_stream.try_next().await, Ok(None));
// If we want to stop consuming the source stream the first time an
// element times out, we can use the `take_while` operator:
let mut int_stream = int_stream.take_while(Result::is_ok);
assert_eq!(int_stream.try_next().await, Ok(Some(1)));
assert_eq!(int_stream.try_next().await, Ok(None));
Timeout errors will be continuously produced at the specified interval until the wrapped stream yields a value.
use tokio_stream::{StreamExt, wrappers::IntervalStream};
use std::time::Duration;
let interval_stream = IntervalStream::new(tokio::time::interval(Duration::from_millis(23)));
let timeout_stream = interval_stream.timeout_repeating(tokio::time::interval(Duration::from_millis(9)));
tokio::pin!(timeout_stream);
// Multiple timeouts will be received between values in the source stream.
assert!(timeout_stream.try_next().await.is_ok());
assert!(timeout_stream.try_next().await.is_err(), "expected one timeout");
assert!(timeout_stream.try_next().await.is_err(), "expected a second timeout");
// Will eventually receive another value from the source stream...
assert!(timeout_stream.try_next().await.is_ok(), "expected non-timeout");
Sourcefn throttle(self, duration: Duration) -> Throttle<Self>where
Self: Sized,
fn throttle(self, duration: Duration) -> Throttle<Self>where
Self: Sized,
Slows down a stream by enforcing a delay between items.
The underlying timer behind this utility has a granularity of one millisecond.
§Example
Create a throttled stream.
use std::time::Duration;
use tokio_stream::StreamExt;
let item_stream = futures::stream::repeat("one").throttle(Duration::from_secs(2));
tokio::pin!(item_stream);
loop {
// The string will be produced at most every 2 seconds
println!("{:?}", item_stream.next().await);
}
Sourcefn chunks_timeout(
self,
max_size: usize,
duration: Duration,
) -> ChunksTimeout<Self>where
Self: Sized,
fn chunks_timeout(
self,
max_size: usize,
duration: Duration,
) -> ChunksTimeout<Self>where
Self: Sized,
Batches the items in the given stream using a maximum duration and size for each batch.
This stream returns the next batch of items in the following situations:
- The inner stream has returned at least
max_size
many items since the last batch. - The time since the first item of a batch is greater than the given duration.
- The end of the stream is reached.
The length of the returned vector is never empty or greater than the maximum size. Empty batches will not be emitted if no items are received upstream.
§Panics
This function panics if max_size
is zero
§Example
use std::time::Duration;
use tokio::time;
use tokio_stream::{self as stream, StreamExt};
use futures::FutureExt;
#[tokio::main]
async fn main() {
let iter = vec![1, 2, 3, 4].into_iter();
let stream0 = stream::iter(iter);
let iter = vec![5].into_iter();
let stream1 = stream::iter(iter)
.then(move |n| time::sleep(Duration::from_secs(5)).map(move |_| n));
let chunk_stream = stream0
.chain(stream1)
.chunks_timeout(3, Duration::from_secs(2));
tokio::pin!(chunk_stream);
// a full batch was received
assert_eq!(chunk_stream.next().await, Some(vec![1,2,3]));
// deadline was reached before max_size was reached
assert_eq!(chunk_stream.next().await, Some(vec![4]));
// last element in the stream
assert_eq!(chunk_stream.next().await, Some(vec![5]));
}
Sourcefn peekable(self) -> Peekable<Self>where
Self: Sized,
fn peekable(self) -> Peekable<Self>where
Self: Sized,
Turns the stream into a peekable stream, whose next element can be peeked at without being consumed.
use tokio_stream::{self as stream, StreamExt};
#[tokio::main]
async fn main() {
let iter = vec![1, 2, 3, 4].into_iter();
let mut stream = stream::iter(iter).peekable();
assert_eq!(*stream.peek().await.unwrap(), 1);
assert_eq!(*stream.peek().await.unwrap(), 1);
assert_eq!(stream.next().await.unwrap(), 1);
assert_eq!(*stream.peek().await.unwrap(), 2);
}
Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.