fix(client): check for dead connections in Pool

Closes #1429

src/client/pool.rs

@@ -15,6 +15,15 @@ pub struct Pool<T> {
     inner: Rc<RefCell<PoolInner<T>>>,
 }
 
+// Before using a pooled connection, make sure the sender is not dead.
+//
+// This is a trait to allow the `client::pool::tests` to work for `i32`.
+//
+// See https://github.com/hyperium/hyper/issues/1429
+pub trait Ready {
+    fn poll_ready(&mut self) -> Poll<(), ()>;
+}
+
 struct PoolInner<T> {
     enabled: bool,
     // These are internal Conns sitting in the event loop in the KeepAlive
@@ -256,7 +265,7 @@ pub struct Checkout<T> {
     parked: Option<relay::Receiver<Entry<T>>>,
 }
 
-impl<T: Clone> Future for Checkout<T> {
+impl<T: Ready + Clone> Future for Checkout<T> {
     type Item = Pooled<T>;
     type Error = io::Error;
 
@@ -282,21 +291,22 @@ impl<T: Clone> Future for Checkout<T> {
         let mut should_remove = false;
         let entry = self.pool.inner.borrow_mut().idle.get_mut(key).and_then(|list| {
             trace!("Checkout::poll key found {:?}", key);
-            while let Some(entry) = list.pop() {
+            while let Some(mut entry) = list.pop() {
                 match entry.status.get() {
                     TimedKA::Idle(idle_at) if !expiration.expires(idle_at) => {
-                        debug!("found idle connection for {:?}", key);
-                        should_remove = list.is_empty();
-                        return Some(entry);
+                        if let Ok(Async::Ready(())) = entry.value.poll_ready() {
+                            debug!("found idle connection for {:?}", key);
+                            should_remove = list.is_empty();
+                            return Some(entry);
+                        }
                     },
-                    _ => {
-                        trace!("Checkout::poll removing unacceptable pooled {:?}", key);
-                        // every other case the Entry should just be dropped
-                        // 1. Idle but expired
-                        // 2. Busy (something else somehow took it?)
-                        // 3. Disabled don't reuse of course
-                    }
+                    _ => {},
                 }
+                trace!("Checkout::poll removing unacceptable pooled {:?}", key);
+                // every other case the Entry should just be dropped
+                // 1. Idle but expired
+                // 2. Busy (something else somehow took it?)
+                // 3. Disabled don't reuse of course
             }
             should_remove = true;
             None
@@ -347,10 +357,16 @@ impl Expiration {
 mod tests {
     use std::rc::Rc;
     use std::time::Duration;
-    use futures::{Async, Future};
+    use futures::{Async, Future, Poll};
     use futures::future;
     use proto::KeepAlive;
-    use super::Pool;
+    use super::{Ready, Pool};
+
+    impl Ready for i32 {
+        fn poll_ready(&mut self) -> Poll<(), ()> {
+            Ok(Async::Ready(()))
+        }
+    }
 
     #[test]
     fn test_pool_checkout_smoke() {