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.
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.
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]:
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);
}