[frdp][connection] Exception checks in _getDartVm (#22386)

Through some integration testing checks, it looks like it's possible
that connecting to a new instance of the Dart VM may fail even after the
Dart VM instance has been discovered.

This means that _getDartVm should be checked in more than just one
place.  This changes the function to return a null value in the event of
a 'well-known' exception (`HttpException` or `TimeoutException`
specifically).

As a result, code now calling _getDartVm checks for null and handles it
as appropriate, and the DartVm RPC calls are all updated with
consistent timeout params.

packages/fuchsia_remote_debug_protocol/lib/src/dart/dart_vm.dart

@@ -120,9 +120,12 @@ class DartVm {
   ///
   /// This is not limited to Isolates running Flutter, but to any Isolate on the
   /// VM.
-  Future<List<IsolateRef>> getMainIsolatesByPattern(Pattern pattern) async {
+  Future<List<IsolateRef>> getMainIsolatesByPattern(
+    Pattern pattern, {
+    Duration timeout = _kRpcTimeout,
+  }) async {
     final Map<String, dynamic> jsonVmRef =
-        await invokeRpc('getVM', timeout: _kRpcTimeout);
+        await invokeRpc('getVM', timeout: timeout);
     final List<IsolateRef> result = <IsolateRef>[];
     for (Map<String, dynamic> jsonIsolate in jsonVmRef['isolates']) {
       final String name = jsonIsolate['name'];
@@ -160,10 +163,12 @@ class DartVm {
   /// the flutter view's name), then the flutter view's ID will be added
   /// instead. If none of these things can be found (isolate has no name or the
   /// flutter view has no ID), then the result will not be added to the list.
-  Future<List<FlutterView>> getAllFlutterViews() async {
+  Future<List<FlutterView>> getAllFlutterViews({
+    Duration timeout = _kRpcTimeout,
+  }) async {
     final List<FlutterView> views = <FlutterView>[];
     final Map<String, dynamic> rpcResponse =
-        await invokeRpc('_flutter.listViews', timeout: _kRpcTimeout);
+        await invokeRpc('_flutter.listViews', timeout: timeout);
     for (Map<String, dynamic> jsonView in rpcResponse['views']) {
       final FlutterView flutterView = FlutterView._fromJson(jsonView);
       if (flutterView != null) {

packages/fuchsia_remote_debug_protocol/lib/src/fuchsia_remote_connection.dart

@@ -249,17 +249,17 @@ class FuchsiaRemoteConnection {
     Pattern pattern,
     Duration timeout = _kIsolateFindTimeout,
   ]) async {
-    final Completer<List<IsolateRef>> completer =
-        Completer<List<IsolateRef>>();
+    final Completer<List<IsolateRef>> completer = Completer<List<IsolateRef>>();
     _onDartVmEvent.listen(
       (DartVmEvent event) async {
         if (event.eventType == DartVmEventType.started) {
           _log.fine('New VM found on port: ${event.servicePort}. Searching '
               'for Isolate: $pattern');
           final DartVm vmService = await _getDartVm(event.uri.port);
+          // If the VM service is null, set the result to the empty list.
           final List<IsolateRef> result = await vmService
-              .getMainIsolatesByPattern(pattern)
-              .timeout(timeout);
+                  ?.getMainIsolatesByPattern(pattern, timeout: timeout) ??
+              <IsolateRef>[];
           if (result.isNotEmpty) {
             if (!completer.isCompleted) {
               completer.complete(result);
@@ -301,6 +301,9 @@ class FuchsiaRemoteConnection {
         <Future<List<IsolateRef>>>[];
     for (PortForwarder fp in _dartVmPortMap.values) {
       final DartVm vmService = await _getDartVm(fp.port).timeout(timeout);
+      if (vmService == null) {
+        continue;
+      }
       isolates.add(vmService.getMainIsolatesByPattern(pattern));
     }
     final List<IsolateRef> result = await Future.wait(isolates)
@@ -379,16 +382,11 @@ class FuchsiaRemoteConnection {
     }
 
     for (PortForwarder pf in _dartVmPortMap.values) {
-      // When raising an HttpException this means that there is no instance of
-      // the Dart VM to communicate with.  The TimeoutException is raised when
-      // the Dart VM instance is shut down in the middle of communicating.
-      try {
-        final DartVm service = await _getDartVm(pf.port);
-        result.add(await vmFunction(service));
-      } on HttpException {
-        await shutDownPortForwarder(pf);
-      } on TimeoutException {
+      final DartVm service = await _getDartVm(pf.port);
+      if (service == null) {
         await shutDownPortForwarder(pf);
+      } else {
+        result.add(await vmFunction(service));
       }
     }
     _stalePorts.forEach(_dartVmPortMap.remove);
@@ -407,10 +405,25 @@ class FuchsiaRemoteConnection {
     return uri;
   }
 
+  /// Attempts to create a connection to a Dart VM.
+  ///
+  /// Returns null if either there is an [HttpException] or a
+  /// [TimeoutException], else a [DartVm] instance.
   Future<DartVm> _getDartVm(int port) async {
     if (!_dartVmCache.containsKey(port)) {
-      final DartVm dartVm = await DartVm.connect(_getDartVmUri(port));
-      _dartVmCache[port] = dartVm;
+      // When raising an HttpException this means that there is no instance of
+      // the Dart VM to communicate with.  The TimeoutException is raised when
+      // the Dart VM instance is shut down in the middle of communicating.
+      try {
+        final DartVm dartVm = await DartVm.connect(_getDartVmUri(port));
+        _dartVmCache[port] = dartVm;
+      } on HttpException {
+        _log.warning('HTTP Exception encountered connecting to new VM');
+        return null;
+      } on TimeoutException {
+        _log.warning('TimeoutException encountered connecting to new VM');
+        return null;
+      }
     }
     return _dartVmCache[port];
   }
@@ -506,7 +519,6 @@ class FuchsiaRemoteConnection {
       final int lastSpace = trimmed.lastIndexOf(' ');
       final String lastWord = trimmed.substring(lastSpace + 1);
       if ((lastWord != '.') && (lastWord != '..')) {
-
         final int value = int.tryParse(lastWord);
         if (value != null) {
           ports.add(value);