Prevent pending_open streams from being released. (#295)

* Prevent `pending_open` streams from being released.

This fixes a panic that would otherwise occur in some cases. A test
demonstrating said panic is included.

* Clear the pending_open queue together with everything else.

tests/h2-tests/tests/client_request.rs

@@ -971,6 +971,96 @@ fn send_stream_poll_reset() {
     client.join(srv).wait().expect("wait");
 }
 
+#[test]
+fn drop_pending_open() {
+    // This test checks that a stream queued for pending open behaves correctly when its
+    // client drops.
+    let _ = ::env_logger::try_init();
+
+    let (io, srv) = mock::new();
+    let (init_tx, init_rx) = futures::sync::oneshot::channel();
+    let (trigger_go_away_tx, trigger_go_away_rx) = futures::sync::oneshot::channel();
+    let (sent_go_away_tx, sent_go_away_rx) = futures::sync::oneshot::channel();
+    let (drop_tx, drop_rx) = futures::sync::oneshot::channel();
+
+    let mut settings = frame::Settings::default();
+    settings.set_max_concurrent_streams(Some(2));
+
+    let srv = srv
+        .assert_client_handshake_with_settings(settings)
+        .unwrap()
+    // This is the ACK
+        .recv_settings()
+        .map(move |h| {
+            init_tx.send(()).unwrap();
+            h
+        })
+        .recv_frame(
+            frames::headers(1)
+                .request("GET", "https://www.example.com/"),
+        )
+        .recv_frame(
+            frames::headers(3)
+                .request("GET", "https://www.example.com/")
+                .eos(),
+        )
+        .wait_for(trigger_go_away_rx)
+        .send_frame(frames::go_away(3))
+        .map(move |h| {
+            sent_go_away_tx.send(()).unwrap();
+            h
+        })
+        .wait_for(drop_rx)
+        .send_frame(frames::headers(3).response(200).eos())
+        .recv_frame(
+            frames::data(1, vec![]).eos(),
+        )
+        .send_frame(frames::headers(1).response(200).eos())
+        .close()
+        ;
+
+    fn request() -> Request<()> {
+        Request::builder()
+            .uri("https://www.example.com/")
+            .body(())
+            .unwrap()
+    }
+
+    let client = client::Builder::new()
+        .max_concurrent_reset_streams(0)
+        .handshake::<_, Bytes>(io)
+        .expect("handshake")
+        .and_then(move |(mut client, conn)| {
+            conn.expect("h2").join(init_rx.expect("init_rx").and_then(move |()| {
+                // Fill up the concurrent stream limit.
+                assert!(client.poll_ready().unwrap().is_ready());
+                let mut response1 = client.send_request(request(), false).unwrap();
+                assert!(client.poll_ready().unwrap().is_ready());
+                let response2 = client.send_request(request(), true).unwrap();
+                assert!(client.poll_ready().unwrap().is_ready());
+                let response3 = client.send_request(request(), true).unwrap();
+
+                // Trigger a GOAWAY frame to invalidate our third request.
+                trigger_go_away_tx.send(()).unwrap();
+                sent_go_away_rx.expect("sent_go_away_rx").and_then(move |_| {
+                    // Now drop all the references to that stream.
+                    drop(response3);
+                    drop(client);
+                    drop_tx.send(()).unwrap();
+
+                    // Complete the second request, freeing up a stream.
+                    response2.0.expect("resp2")
+                }).and_then(move |_| {
+                    response1.1.send_data(Default::default(), true).unwrap();
+                    response1.0.expect("resp1")
+                })
+            }))
+        });
+
+
+    client.join(srv).wait().unwrap();
+}
+
 const SETTINGS: &'static [u8] = &[0, 0, 0, 4, 0, 0, 0, 0, 0];
 const SETTINGS_ACK: &'static [u8] = &[0, 0, 0, 4, 1, 0, 0, 0, 0];