[](https://crates.io/crates/stream-cancel)
[](https://docs.rs/stream-cancel/)
[](https://codecov.io/gh/jonhoo/stream-cancel)
This crate provides multiple mechanisms for interrupting a `Stream`.
## Stream combinator
The extension trait [`StreamExt`] provides a single new `Stream` combinator: `take_until_if`.
[`StreamExt::take_until_if`] continues yielding elements from the underlying `Stream` until a
`Future` resolves, and at that moment immediately yields `None` and stops producing further
elements.
For convenience, the crate also includes the [`Tripwire`] type, which produces a cloneable
`Future` that can then be passed to `take_until_if`. When a new `Tripwire` is created, an
associated [`Trigger`] is also returned, which interrupts the `Stream` when it is dropped.
```rust
use stream_cancel::{StreamExt, Tripwire};
use futures::prelude::*;
use tokio_stream::wrappers::TcpListenerStream;
#[tokio::main]
async fn main() {
let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
let (trigger, tripwire) = Tripwire::new();
tokio::spawn(async move {
let mut incoming = TcpListenerStream::new(listener).take_until_if(tripwire);
while let Some(mut s) = incoming.next().await.transpose().unwrap() {
tokio::spawn(async move {
let (mut r, mut w) = s.split();
println!("copied {} bytes", tokio::io::copy(&mut r, &mut w).await.unwrap());
});
}
});
// tell the listener to stop accepting new connections
drop(trigger);
// the spawned async block will terminate cleanly, allowing main to return
}
```
## Stream wrapper
Any stream can be wrapped in a [`Valved`], which enables it to be remotely terminated through
an associated [`Trigger`]. This can be useful to implement graceful shutdown on "infinite"
streams like a `TcpListener`. Once [`Trigger::cancel`] is called on the handle for a given
stream's [`Valved`], the stream will yield `None` to indicate that it has terminated.
```rust
use stream_cancel::Valved;
use futures::prelude::*;
use tokio_stream::wrappers::TcpListenerStream;
use std::thread;
#[tokio::main]
async fn main() {
let (exit_tx, exit_rx) = tokio::sync::oneshot::channel();
let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
tokio::spawn(async move {
let (exit, mut incoming) = Valved::new(TcpListenerStream::new(listener));
exit_tx.send(exit).unwrap();
while let Some(mut s) = incoming.next().await.transpose().unwrap() {
tokio::spawn(async move {
let (mut r, mut w) = s.split();
println!("copied {} bytes", tokio::io::copy(&mut r, &mut w).await.unwrap());
});
}
});
let exit = exit_rx.await;
// the server thread will normally never exit, since more connections
// can always arrive. however, with a Valved, we can turn off the
// stream of incoming connections to initiate a graceful shutdown
drop(exit);
}
```
You can share the same [`Trigger`] between multiple streams by first creating a [`Valve`],
and then wrapping multiple streams using [`Valve::Wrap`]:
```rust
use stream_cancel::Valve;
use futures::prelude::*;
use tokio_stream::wrappers::TcpListenerStream;
#[tokio::main]
async fn main() {
let (exit, valve) = Valve::new();
let listener1 = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
let listener2 = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
tokio::spawn(async move {
let incoming1 = valve.wrap(TcpListenerStream::new(listener1));
let incoming2 = valve.wrap(TcpListenerStream::new(listener2));
use futures_util::stream::select;
let mut incoming = select(incoming1, incoming2);
while let Some(mut s) = incoming.next().await.transpose().unwrap() {
tokio::spawn(async move {
let (mut r, mut w) = s.split();
println!("copied {} bytes", tokio::io::copy(&mut r, &mut w).await.unwrap());
});
}
});
// the runtime will not become idle until both incoming1 and incoming2 have stopped
// (due to the select). this checks that they are indeed both interrupted when the
// valve is closed.
drop(exit);
}
```