Improve VM connection flow in Observatory

runtime/observatory/lib/src/app/application.dart

Index: runtime/observatory/lib/src/app/application.dart
diff --git a/runtime/observatory/lib/src/app/application.dart b/runtime/observatory/lib/src/app/application.dart
index 5306b13ba3e4672ead5979805feb713fc48e7835..f847c231c98902a40125cfa8d0d8875b19a7b63b 100644
--- a/runtime/observatory/lib/src/app/application.dart
+++ b/runtime/observatory/lib/src/app/application.dart
@@ -16,41 +16,75 @@ class ObservatoryApplication {
   LocationManager _locationManager;
   LocationManager get locationManager => _locationManager;
   Page currentPage;
+  bool _vmConnected = false;
   VM _vm;
   VM get vm => _vm;
 
-  _setVM(VM vm) {
-    if (_vm == vm) {
+  bool isConnectedVMTarget(WebSocketVMTarget target) {
+    if (_vm is CommonWebSocketVM) {
+      if ((_vm as CommonWebSocketVM).target == target) {
+        return _vm.isConnected;
+      }
+    }
+    return false;
+  }
+
+  _switchVM(VM newVM) {
+    final VM oldVM = _vm;
+
+    Logger.root.info('_switchVM from:${oldVM} to:${newVM}');
+
+    if (oldVM == newVM) {
       // Do nothing.
       return;
     }
-    if (_vm != null) {
-      _gcSubscription = null;
+
+    if (oldVM != null) {
+      print('disconnecting from the old VM ${oldVM}--');
       // Disconnect from current VM.
+      stopGCEventListener();
       notifications.deleteAll();
-      _vm.disconnect();
+      oldVM.disconnect();
     }
-    if (vm != null) {
-      Logger.root.info('Registering new VM callbacks');
 
-      vm.onConnect.then((_) {
+    if (newVM != null) {
+      // Mark that we haven't connected yet.
+      _vmConnected = false;
+      // On connect:
+      newVM.onConnect.then((_) {
+        // We connected.
+        _vmConnected = true;
         notifications.deleteDisconnectEvents();
       });
-
-      vm.onDisconnect.then((String reason) {
-        if (this.vm != vm) {
+      // On disconnect:
+      newVM.onDisconnect.then((String reason) {
+        if (this.vm != newVM) {
           // This disconnect event occured *after* a new VM was installed.
           return;
         }
-        events.add(new ConnectionClosedEvent(new DateTime.now(), reason));
+        // Let anyone looking at the targets know that we have disconnected
+        // from one.
+        targets.emitDisconnectEvent();
+        if (!_vmConnected) {
+          // Connection error. Navigate back to the connect page.
+          Logger.root.info('Connection failed, navigating to VM connect page.');
+          // Clear the vm.
+          _vm = null;
+          app.locationManager.go(Uris.vmConnect());
+        } else {
+          // Disconnect. Stay at the current page and push an a connection
+          // closed event.
+          Logger.root.info('Lost an existing connection to a VM');
+          events.add(new ConnectionClosedEvent(new DateTime.now(), reason));
+        }
       });
-
       // TODO(cbernaschina) smart connection of streams in the events object.
-      vm.listenEventStream(VM.kVMStream, _onEvent);
-      vm.listenEventStream(VM.kIsolateStream, _onEvent);
-      vm.listenEventStream(VM.kDebugStream, _onEvent);
+      newVM.listenEventStream(VM.kVMStream, _onEvent);
+      newVM.listenEventStream(VM.kIsolateStream, _onEvent);
+      newVM.listenEventStream(VM.kDebugStream, _onEvent);
     }
-    _vm = vm;
+
+    _vm = newVM;
   }
 
   StreamSubscription _gcSubscription;
@@ -192,13 +226,24 @@ class ObservatoryApplication {
 
   ObservatoryApplication(this.rootElement) {
     _locationManager = new LocationManager(this);
-    targets.onChange.listen((e) {
-      if (targets.current == null) return _setVM(null);
-      if ((_vm as WebSocketVM)?.target != targets.current) {
-        _setVM(new WebSocketVM(targets.current));
+    targets.onChange.listen((TargetChangeEvent e) {
+      if (e.disconnected) {
+        // We don't care about disconnected events.
+        return;
+      }
+      if (targets.current == null) {
+        _switchVM(null);
+      }
+      final bool currentTarget =
+          (_vm as WebSocketVM)?.target == targets.current;
+      final bool currentTargetConnected = (_vm != null) && !_vm.isDisconnected;
+      if (!currentTarget || !currentTargetConnected) {
+        _switchVM(new WebSocketVM(targets.current));
       }
     });
-    _setVM(new WebSocketVM(targets.current));
+
+    Logger.root.info('Setting initial target to ${targets.current.name}');
+    _switchVM(new WebSocketVM(targets.current));
     _initOnce();
 
     // delete pause events.
@@ -217,11 +262,12 @@ class ObservatoryApplication {
     events.onPauseInterrupted.listen(_addNotification);
     events.onPauseException.listen(_addNotification);
     events.onInspect.listen(_addNotification);
+    events.onConnectionClosed.listen(_addNotification);
   }
 
   loadCrashDump(Map crashDump) {
-    _setVM(new FakeVM(crashDump['result']));
-    app.locationManager.go('#/vm');
+    _switchVM(new FakeVM(crashDump['result']));
+    app.locationManager.go(Uris.vm());
   }
 
   void handleException(e, st) {