feat(server): add Server::with_graceful_shutdown method

This adds a "combinator" method to `Server`, which accepts a user's
future to "select" on. All connections received by the `Server` will
be tracked, and if the user's future finishes, graceful shutdown will
begin.

- The listener will be closed immediately.
- The currently active connections will all be notified to start a
  graceful shutdown. For HTTP/1, that means finishing the existing
  response and using `connection: clone`. For HTTP/2, the graceful
  `GOAWAY` process is started.
- Once all active connections have terminated, the graceful future
  will return.

Closes #1575

src/common/drain.rs

@@ -0,0 +1,115 @@
+use std::mem;
+
+use futures::{Async, Future, Poll, Stream};
+use futures::future::Shared;
+use futures::sync::{mpsc, oneshot};
+
+use super::Never;
+
+pub fn channel() -> (Signal, Watch) {
+    let (tx, rx) = oneshot::channel();
+    let (drained_tx, drained_rx) = mpsc::channel(0);
+    (
+        Signal {
+            drained_rx,
+            tx,
+        },
+        Watch {
+            drained_tx,
+            rx: rx.shared(),
+        },
+    )
+}
+
+pub struct Signal {
+    drained_rx: mpsc::Receiver<Never>,
+    tx: oneshot::Sender<()>,
+}
+
+pub struct Draining {
+    drained_rx: mpsc::Receiver<Never>,
+}
+
+#[derive(Clone)]
+pub struct Watch {
+    drained_tx: mpsc::Sender<Never>,
+    rx: Shared<oneshot::Receiver<()>>,
+}
+
+pub struct Watching<F, FN> {
+    future: F,
+    state: State<FN>,
+    watch: Watch,
+}
+
+enum State<F> {
+    Watch(F),
+    Draining,
+}
+
+impl Signal {
+    pub fn drain(self) -> Draining {
+        let _ = self.tx.send(());
+        Draining {
+            drained_rx: self.drained_rx,
+        }
+    }
+}
+
+impl Future for Draining {
+    type Item = ();
+    type Error = ();
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        match try_ready!(self.drained_rx.poll()) {
+            Some(never) => match never {},
+            None => Ok(Async::Ready(())),
+        }
+    }
+}
+
+impl Watch {
+    pub fn watch<F, FN>(self, future: F, on_drain: FN) -> Watching<F, FN>
+    where
+        F: Future,
+        FN: FnOnce(&mut F),
+    {
+        Watching {
+            future,
+            state: State::Watch(on_drain),
+            watch: self,
+        }
+    }
+}
+
+impl<F, FN> Future for Watching<F, FN>
+where
+    F: Future,
+    FN: FnOnce(&mut F),
+{
+    type Item = F::Item;
+    type Error = F::Error;
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        loop {
+            match mem::replace(&mut self.state, State::Draining) {
+                State::Watch(on_drain) => {
+                    match self.watch.rx.poll() {
+                        Ok(Async::Ready(_)) | Err(_) => {
+                            // Drain has been triggered!
+                            on_drain(&mut self.future);
+                        },
+                        Ok(Async::NotReady) => {
+                            self.state = State::Watch(on_drain);
+                            return self.future.poll();
+                        },
+                    }
+                },
+                State::Draining => {
+                    return self.future.poll();
+                },
+            }
+        }
+    }
+}
+

src/common/mod.rs

@@ -1,4 +1,5 @@
 mod buf;
+pub(crate) mod drain;
 mod exec;
 pub(crate) mod io;
 mod lazy;

src/server/conn.rs

@@ -85,7 +85,7 @@ pub struct Connecting<I, F> {
 #[must_use = "futures do nothing unless polled"]
 #[derive(Debug)]
 pub(super) struct SpawnAll<I, S> {
-    serve: Serve<I, S>,
+    pub(super) serve: Serve<I, S>,
 }
 
 /// A future binding a connection with a Service.
@@ -618,7 +618,7 @@ impl<I, S> SpawnAll<I, S> {
     }
 }
 
-impl<I, S, B> Future for SpawnAll<I, S>
+impl<I, S, B> SpawnAll<I, S>
 where
     I: Stream,
     I::Error: Into<Box<::std::error::Error + Send + Sync>>,
@@ -630,16 +630,19 @@ where
     <S::Service as Service>::Future: Send + 'static,
     B: Payload,
 {
-    type Item = ();
-    type Error = ::Error;
-
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+    pub(super) fn poll_with<F1, F2, R>(&mut self, per_connection: F1) -> Poll<(), ::Error>
+    where
+        F1: Fn() -> F2,
+        F2: FnOnce(UpgradeableConnection<I::Item, S::Service>) -> R + Send + 'static,
+        R: Future<Item=(), Error=::Error> + Send + 'static,
+    {
         loop {
             if let Some(connecting) = try_ready!(self.serve.poll()) {
+                let and_then = per_connection();
                 let fut = connecting
                     .map_err(::Error::new_user_new_service)
                     // flatten basically
-                    .and_then(|conn| conn.with_upgrades())
+                    .and_then(|conn| and_then(conn.with_upgrades()))
                     .map_err(|err| debug!("conn error: {}", err));
                 self.serve.protocol.exec.execute(fut)?;
             } else {

src/server/mod.rs

@@ -51,6 +51,7 @@
 //! ```
 
 pub mod conn;
+mod shutdown;
 #[cfg(feature = "runtime")] mod tcp;
 
 use std::fmt;
@@ -67,6 +68,7 @@ use service::{NewService, Service};
 // Renamed `Http` as `Http_` for now so that people upgrading don't see an
 // error that `hyper::server::Http` is private...
 use self::conn::{Http as Http_, SpawnAll};
+use self::shutdown::Graceful;
 #[cfg(feature = "runtime")] use self::tcp::AddrIncoming;
 
 /// A listening HTTP server that accepts connections in both HTTP1 and HTTP2 by default.
@@ -136,6 +138,65 @@ impl<S> Server<AddrIncoming, S> {
     }
 }
 
+impl<I, S, B> Server<I, S>
+where
+    I: Stream,
+    I::Error: Into<Box<::std::error::Error + Send + Sync>>,
+    I::Item: AsyncRead + AsyncWrite + Send + 'static,
+    S: NewService<ReqBody=Body, ResBody=B> + Send + 'static,
+    S::Error: Into<Box<::std::error::Error + Send + Sync>>,
+    S::Service: Send,
+    S::Future: Send + 'static,
+    <S::Service as Service>::Future: Send + 'static,
+    B: Payload,
+{
+    /// Prepares a server to handle graceful shutdown when the provided future
+    /// completes.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # extern crate hyper;
+    /// # extern crate futures;
+    /// # use futures::Future;
+    /// # fn main() {}
+    /// # #[cfg(feature = "runtime")]
+    /// # fn run() {
+    /// # use hyper::{Body, Response, Server};
+    /// # use hyper::service::service_fn_ok;
+    /// # let new_service = || {
+    /// #     service_fn_ok(|_req| {
+    /// #         Response::new(Body::from("Hello World"))
+    /// #     })
+    /// # };
+    ///
+    /// // Make a server from the previous examples...
+    /// let server = Server::bind(&([127, 0, 0, 1], 3000).into())
+    ///     .serve(new_service);
+    ///
+    /// // Prepare some signal for when the server should start
+    /// // shutting down...
+    /// let (tx, rx) = futures::sync::oneshot::channel::<()>();
+    ///
+    /// let graceful = server
+    ///     .with_graceful_shutdown(rx)
+    ///     .map_err(|err| eprintln!("server error: {}", err));
+    ///
+    /// // Spawn `server` onto an Executor...
+    /// hyper::rt::spawn(graceful);
+    ///
+    /// // And later, trigger the signal by calling `tx.send(())`.
+    /// let _ = tx.send(());
+    /// # }
+    /// ```
+    pub fn with_graceful_shutdown<F>(self, signal: F) -> Graceful<I, S, F>
+    where
+        F: Future<Item=()>
+    {
+        Graceful::new(self.spawn_all, signal)
+    }
+}
+
 impl<I, S, B> Future for Server<I, S>
 where
     I: Stream,
@@ -152,7 +213,7 @@ where
     type Error = ::Error;
 
     fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
-        self.spawn_all.poll()
+        self.spawn_all.poll_with(|| |conn| conn)
     }
 }
 

src/server/shutdown.rs

@@ -0,0 +1,93 @@
+use futures::{Async, Future, Stream, Poll};
+use tokio_io::{AsyncRead, AsyncWrite};
+
+use body::{Body, Payload};
+use common::drain::{self, Draining, Signal, Watch};
+use service::{Service, NewService};
+use super::SpawnAll;
+
+#[allow(missing_debug_implementations)]
+pub struct Graceful<I, S, F> {
+    state: State<I, S, F>,
+}
+
+enum State<I, S, F> {
+    Running {
+        drain: Option<(Signal, Watch)>,
+        spawn_all: SpawnAll<I, S>,
+        signal: F,
+    },
+    Draining(Draining),
+}
+
+impl<I, S, F> Graceful<I, S, F> {
+    pub(super) fn new(spawn_all: SpawnAll<I, S>, signal: F) -> Self {
+        let drain = Some(drain::channel());
+        Graceful {
+            state: State::Running {
+                drain,
+                spawn_all,
+                signal,
+            },
+        }
+    }
+}
+
+
+impl<I, S, B, F> Future for Graceful<I, S, F>
+where
+    I: Stream,
+    I::Error: Into<Box<::std::error::Error + Send + Sync>>,
+    I::Item: AsyncRead + AsyncWrite + Send + 'static,
+    S: NewService<ReqBody=Body, ResBody=B> + Send + 'static,
+    S::Error: Into<Box<::std::error::Error + Send + Sync>>,
+    S::Service: Send,
+    S::Future: Send + 'static,
+    <S::Service as Service>::Future: Send + 'static,
+    B: Payload,
+    F: Future<Item=()>,
+{
+    type Item = ();
+    type Error = ::Error;
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        loop {
+            let next = match self.state {
+                State::Running {
+                    ref mut drain,
+                    ref mut spawn_all,
+                    ref mut signal,
+                } => match signal.poll() {
+                    Ok(Async::Ready(())) | Err(_) => {
+                        debug!("signal received, starting graceful shutdown");
+                        let sig = drain
+                            .take()
+                            .expect("drain channel")
+                            .0;
+                        State::Draining(sig.drain())
+                    },
+                    Ok(Async::NotReady) => {
+                        let watch = &drain
+                            .as_ref()
+                            .expect("drain channel")
+                            .1;
+                        return spawn_all.poll_with(|| {
+                            let watch = watch.clone();
+                            move |conn| {
+                                watch.watch(conn, |conn| {
+                                    // on_drain, start conn graceful shutdown
+                                    conn.graceful_shutdown()
+                                })
+                            }
+                        });
+                    },
+                },
+                State::Draining(ref mut draining) => {
+                    return draining.poll()
+                        .map_err(|()| unreachable!("drain mpsc rx never errors"));
+                }
+            };
+            self.state = next;
+        }
+    }
+}