Wakeup waiting tasks when transitioning a stream from pending_open (#277)

tests/h2-tests/tests/client_request.rs

@@ -842,6 +842,90 @@ fn request_options_with_star() {
     client.join(srv).wait().unwrap();
 }
 
+#[test]
+fn notify_on_send_capacity() {
+    // This test ensures that the client gets notified when there is additional
+    // send capacity. In other words, when the server is ready to accept a new
+    // stream, the client is notified.
+    use std::sync::mpsc;
+
+    let _ = ::env_logger::try_init();
+    let (io, srv) = mock::new();
+    let (done_tx, done_rx) = mpsc::channel();
+    let (tx, rx) = mpsc::channel();
+
+    let mut settings = frame::Settings::default();
+    settings.set_max_concurrent_streams(Some(1));
+
+    let srv = srv
+        .assert_client_handshake_with_settings(settings)
+        .unwrap()
+        // This is the ACK
+        .recv_settings()
+        .map(move |h| {
+            tx.send(()).unwrap();
+            h
+        })
+        .recv_frame(
+            frames::headers(1)
+                .request("GET", "https://www.example.com/")
+                .eos(),
+        )
+        .send_frame(frames::headers(1).response(200).eos())
+        .recv_frame(
+            frames::headers(3)
+                .request("GET", "https://www.example.com/")
+                .eos(),
+        )
+        .send_frame(frames::headers(3).response(200).eos())
+        .recv_frame(
+            frames::headers(5)
+                .request("GET", "https://www.example.com/")
+                .eos(),
+        )
+        .send_frame(frames::headers(5).response(200).eos())
+        .close()
+        ;
+
+    let client = client::handshake(io)
+        .expect("handshake")
+        .and_then(move |(mut client, conn)| {
+            ::std::thread::spawn(move || {
+                rx.recv().unwrap();
+
+                let mut responses = vec![];
+
+                for _ in 0..3 {
+                    // Wait for capacity. If the client is **not** notified,
+                    // this hangs.
+                    poll_fn(|| client.poll_ready()).wait().unwrap();
+
+                    let request = Request::builder()
+                        .uri("https://www.example.com/")
+                        .body(())
+                        .unwrap();
+
+                    let response = client.send_request(request, true)
+                        .unwrap().0;
+
+                    responses.push(response);
+                }
+
+                for response in responses {
+                    let response = response.wait().unwrap();
+                    assert_eq!(response.status(), StatusCode::OK);
+                }
+
+                done_tx.send(()).unwrap();
+            });
+
+            conn.expect("h2")
+        });
+
+    client.join(srv).wait().unwrap();
+    done_rx.recv().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];