stream-cancel 0.5.1

# stream-cancel

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This crate provides multiple mechanisms for interrupting a `Stream`.

## Stream combinator

The extension trait [`StreamExt`] provides a single new `Stream` combinator: `take_until`.
[`StreamExt::take_until`] 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`. When a new `Tripwire` is created, an
associated [`Trigger`] is also returned, which interrupts the `Stream` when it is dropped.


```rust
extern crate tokio;

use stream_cancel::{StreamExt, Tripwire};
use tokio::prelude::*;

let listener = tokio::net::TcpListener::bind(&"0.0.0.0:0".parse().unwrap()).unwrap();
let (trigger, tripwire) = Tripwire::new();

let mut rt = tokio::runtime::Runtime::new().unwrap();
rt.spawn(
    listener
        .incoming()
        .take_until(tripwire)
        .map_err(|e| eprintln!("accept failed = {:?}", e))
        .for_each(|sock| {
            let (reader, writer) = sock.split();
            tokio::spawn(
                tokio::io::copy(reader, writer)
                    .map(|amt| println!("wrote {:?} bytes", amt))
                    .map_err(|err| eprintln!("IO error {:?}", err)),
            )
        }),
);

// tell the listener to stop accepting new connections
drop(trigger);
rt.shutdown_on_idle().wait().unwrap();
```

## 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::close`] is called on the handle for a given
stream's [`Valved`], the stream will yield `None` to indicate that it has terminated.

```rust
extern crate tokio;

use stream_cancel::Valved;
use tokio::prelude::*;
use std::thread;

let listener = tokio::net::TcpListener::bind(&"0.0.0.0:0".parse().unwrap()).unwrap();
let (exit, incoming) = Valved::new(listener.incoming());

let server = thread::spawn(move || {
    // start a tokio echo server
    tokio::run(
        incoming
            .map_err(|e| eprintln!("accept failed = {:?}", e))
            .for_each(|sock| {
                let (reader, writer) = sock.split();
                tokio::spawn(
                    tokio::io::copy(reader, writer)
                        .map(|amt| println!("wrote {:?} bytes", amt))
                        .map_err(|err| eprintln!("IO error {:?}", err)),
                )
            }),
    )
});

// 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);
server.join().unwrap();
```

You can share the same [`Trigger`] between multiple streams by first creating a [`Valve`],
and then wrapping multiple streams using [`Valve::Wrap`]:

```rust
extern crate tokio;

use stream_cancel::Valve;
use tokio::prelude::*;

let (exit, valve) = Valve::new();
let listener1 = tokio::net::TcpListener::bind(&"0.0.0.0:0".parse().unwrap()).unwrap();
let listener2 = tokio::net::TcpListener::bind(&"0.0.0.0:0".parse().unwrap()).unwrap();
let incoming1 = valve.wrap(listener1.incoming());
let incoming2 = valve.wrap(listener2.incoming());

let mut rt = tokio::runtime::Runtime::new().unwrap();
rt.spawn(
    incoming1
        .select(incoming2)
        .map_err(|e| eprintln!("accept failed = {:?}", e))
        .for_each(|sock| {
            let (reader, writer) = sock.split();
            tokio::spawn(
                tokio::io::copy(reader, writer)
                    .map(|amt| println!("wrote {:?} bytes", amt))
                    .map_err(|err| eprintln!("IO error {:?}", err)),
            )
        }),
);

// 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);
rt.shutdown_on_idle().wait().unwrap();
```