SwarmController::dial now returns a Future (#290)

* SwarmController::dial now returns a Future

* Minor comment

core/src/swarm.rs

@@ -19,10 +19,10 @@
 // DEALINGS IN THE SOFTWARE.
 
 use futures::stream::{FuturesUnordered, StreamFuture};
-use futures::sync::mpsc;
+use futures::sync::{mpsc, oneshot};
 use futures::{future, Async, Future, IntoFuture, Poll, Stream};
 use std::fmt;
-use std::io::Error as IoError;
+use std::io::{Error as IoError, ErrorKind as IoErrorKind};
 use {Multiaddr, MuxedTransport, Transport};
 
 /// Creates a swarm.
@@ -76,7 +76,7 @@ where
 {
     transport: T,
     new_listeners: mpsc::UnboundedSender<T::Listener>,
-    new_dialers: mpsc::UnboundedSender<Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError>>), Error = IoError>>>,
+    new_dialers: mpsc::UnboundedSender<Box<Future<Item = (T::Output, oneshot::Sender<Result<(), IoError>>, Box<Future<Item = Multiaddr, Error = IoError>>), Error = ()>>>,
     new_toprocess: mpsc::UnboundedSender<Box<Future<Item = (), Error = IoError>>>,
 }
 
@@ -112,8 +112,12 @@ where
     /// Asks the swarm to dial the node with the given multiaddress. The connection is then
     /// upgraded using the `upgrade`, and the output is sent to the handler that was passed when
     /// calling `swarm`.
-    // TODO: consider returning a future so that errors can be processed?
-    pub fn dial<Du>(&self, multiaddr: Multiaddr, transport: Du) -> Result<(), Multiaddr>
+    ///
+    /// Returns a future that is signalled once the closure in the `swarm` has returned its future.
+    /// Therefore if the closure in the swarm has some side effect (eg. write something in a
+    /// variable), this side effect will be observable when this future succeeds.
+    pub fn dial<Du>(&self, multiaddr: Multiaddr, transport: Du)
+        -> Result<impl Future<Item = (), Error = IoError>, Multiaddr>
     where
         Du: Transport + 'static, // TODO: 'static :-/
         Du::Output: Into<T::Output>,
@@ -122,13 +126,31 @@ where
 
         match transport.dial(multiaddr.clone()) {
             Ok(dial) => {
-                let dial = Box::new(
-                    dial.map(|(d, client_addr)| (d.into(), Box::new(client_addr) as Box<Future<Item = _, Error = _>>)),
-                ) as Box<Future<Item = _, Error = _>>;
+                let (tx, rx) = oneshot::channel();
+                let dial = dial.then(|result| {
+                    match result {
+                        Ok((output, client_addr)) => {
+                            let client_addr = Box::new(client_addr) as Box<Future<Item = _, Error = _>>;
+                            Ok((output.into(), tx, client_addr))
+                        }
+                        Err(err) => {
+                            debug!("Error in dialer upgrade: {:?}", err);
+                            let _ = tx.send(Err(err));
+                            Err(())
+                        }
+                    }
+                });
                 // Ignoring errors if the receiver has been closed, because in that situation
                 // nothing is going to be processed anyway.
-                let _ = self.new_dialers.unbounded_send(dial);
-                Ok(())
+                let _ = self.new_dialers.unbounded_send(Box::new(dial) as Box<_>);
+                Ok(rx.then(|result| {
+                    match result {
+                        Ok(Ok(())) => Ok(()),
+                        Ok(Err(err)) => Err(err),
+                        Err(_) => Err(IoError::new(IoErrorKind::ConnectionAborted,
+                            "dial cancelled the swarm future has been destroyed")),
+                    }
+                }))
             }
             Err((_, multiaddr)) => Err(multiaddr),
         }
@@ -171,9 +193,9 @@ where
     >,
     listeners_upgrade:
         FuturesUnordered<Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError>>), Error = IoError>>>,
-    dialers: FuturesUnordered<Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError>>), Error = IoError>>>,
+    dialers: FuturesUnordered<Box<Future<Item = (T::Output, oneshot::Sender<Result<(), IoError>>, Box<Future<Item = Multiaddr, Error = IoError>>), Error = ()>>>,
     new_dialers:
-        mpsc::UnboundedReceiver<Box<Future<Item = (T::Output, Box<Future<Item = Multiaddr, Error = IoError>>), Error = IoError>>>,
+        mpsc::UnboundedReceiver<Box<Future<Item = (T::Output, oneshot::Sender<Result<(), IoError>>, Box<Future<Item = Multiaddr, Error = IoError>>), Error = ()>>>,
     to_process: FuturesUnordered<future::Either<F, Box<Future<Item = (), Error = IoError>>>>,
     new_toprocess: mpsc::UnboundedReceiver<Box<Future<Item = (), Error = IoError>>>,
 }
@@ -291,16 +313,14 @@ where
 
         loop {
             match self.dialers.poll() {
-                Ok(Async::Ready(Some((output, addr)))) => {
+                Ok(Async::Ready(Some((output, notifier, addr)))) => {
                     trace!("Successfully upgraded dialed connection");
                     self.to_process
                         .push(future::Either::A(handler(output, addr).into_future()));
+                    let _  = notifier.send(Ok(()));
                 }
-                Err(err) => {
-                    debug!("Error in dialer upgrade: {:?}", err);
-                    break;
-                }
-                _ => break
+                Err(()) => break,
+                _ => break,
             }
         }