[flutter_tools] Handle StateError in ProtocolDiscovery.uri (#52337)

packages/flutter_tools/lib/src/android/android_device.dart

@@ -629,11 +629,16 @@ class AndroidDevice extends Device {
     // TODO(danrubel): Waiting for observatory services can be made common across all devices.
     try {
       Uri observatoryUri;
-
       if (debuggingOptions.buildInfo.isDebug || debuggingOptions.buildInfo.isProfile) {
         observatoryUri = await observatoryDiscovery.uri;
+        if (observatoryUri == null) {
+          globals.printError(
+            'Error waiting for a debug connection: '
+            'The log reader stopped unexpectedly',
+          );
+          return LaunchResult.failed();
+        }
       }
-
       return LaunchResult.succeeded(observatoryUri: observatoryUri);
     } on Exception catch (error) {
       globals.printError('Error waiting for a debug connection: $error');

packages/flutter_tools/lib/src/desktop_device.dart

@@ -114,14 +114,20 @@ abstract class DesktopDevice extends Device {
     );
     try {
       final Uri observatoryUri = await observatoryDiscovery.uri;
-      onAttached(package, buildMode, process);
-      return LaunchResult.succeeded(observatoryUri: observatoryUri);
+      if (observatoryUri != null) {
+        onAttached(package, buildMode, process);
+        return LaunchResult.succeeded(observatoryUri: observatoryUri);
+      }
+      globals.printError(
+        'Error waiting for a debug connection: '
+        'The log reader stopped unexpectedly.',
+      );
     } on Exception catch (error) {
       globals.printError('Error waiting for a debug connection: $error');
-      return LaunchResult.failed();
     } finally {
       await observatoryDiscovery.cancel();
     }
+    return LaunchResult.failed();
   }
 
   @override

packages/flutter_tools/lib/src/ios/fallback_discovery.dart

@@ -42,7 +42,8 @@ class FallbackDiscovery {
     @required MDnsObservatoryDiscovery mDnsObservatoryDiscovery,
     @required Logger logger,
     @required ProtocolDiscovery protocolDiscovery,
-    Future<VmService> Function(String wsUri, {Log log}) vmServiceConnectUri = vm_service_io.vmServiceConnectUri,
+    Future<VmService> Function(String wsUri, {Log log}) vmServiceConnectUri =
+      vm_service_io.vmServiceConnectUri,
   }) : _logger = logger,
        _mDnsObservatoryDiscovery = mDnsObservatoryDiscovery,
        _portForwarder = portForwarder,
@@ -83,19 +84,33 @@ class FallbackDiscovery {
         hostVmservicePort: hostVmservicePort,
       );
       if (result != null) {
-        UsageEvent(_kEventName, 'mdns-success', flutterUsage: globals.flutterUsage).send();
+        UsageEvent(
+          _kEventName,
+          'mdns-success',
+          flutterUsage: globals.flutterUsage,
+        ).send();
         return result;
       }
     } on Exception catch (err) {
       _logger.printTrace(err.toString());
     }
     _logger.printTrace('Failed to connect with mDNS, falling back to log scanning');
-    UsageEvent(_kEventName, 'mdns-failure', flutterUsage: globals.flutterUsage).send();
+    UsageEvent(
+      _kEventName,
+      'mdns-failure',
+      flutterUsage: globals.flutterUsage,
+    ).send();
 
     try {
       final Uri result = await _protocolDiscovery.uri;
-      UsageEvent(_kEventName, 'fallback-success', flutterUsage: globals.flutterUsage).send();
-      return result;
+      if (result != null) {
+        UsageEvent(
+          _kEventName,
+          'fallback-success',
+          flutterUsage: globals.flutterUsage,
+        ).send();
+        return result;
+      }
     } on ArgumentError {
     // In the event of an invalid InternetAddress, this code attempts to catch
     // an ArgumentError from protocol_discovery.dart
@@ -103,7 +118,11 @@ class FallbackDiscovery {
       _logger.printTrace(err.toString());
     }
     _logger.printTrace('Failed to connect with log scanning');
-    UsageEvent(_kEventName, 'fallback-failure', flutterUsage: globals.flutterUsage).send();
+    UsageEvent(
+      _kEventName,
+      'fallback-failure',
+      flutterUsage: globals.flutterUsage,
+    ).send();
     return null;
   }
 
@@ -117,7 +136,10 @@ class FallbackDiscovery {
     int hostPort;
     Uri assumedWsUri;
     try {
-      hostPort = await _portForwarder.forward(assumedDevicePort, hostPort: hostVmservicePort);
+      hostPort = await _portForwarder.forward(
+        assumedDevicePort,
+        hostPort: hostVmservicePort,
+      );
       assumedWsUri = Uri.parse('ws://localhost:$hostPort/ws');
     } on Exception catch (err) {
       _logger.printTrace(err.toString());
@@ -132,17 +154,25 @@ class FallbackDiscovery {
     Exception firstException;
     while (attempts < 5) {
       try {
-        final VmService vmService = await _vmServiceConnectUri(assumedWsUri.toString());
+        final VmService vmService = await _vmServiceConnectUri(
+          assumedWsUri.toString(),
+        );
         final VM vm = await vmService.getVM();
         for (final IsolateRef isolateRefs in vm.isolates) {
-          final dynamic isolateResponse = await vmService.getIsolate(isolateRefs.id);
+          final dynamic isolateResponse = await vmService.getIsolate(
+            isolateRefs.id,
+          );
           if (isolateResponse is Sentinel) {
             // Might have been a Sentinel. Try again later.
             throw Exception('Expected Isolate but found Sentinel: $isolateResponse');
           }
           final LibraryRef library = (isolateResponse as Isolate).rootLib;
           if (library.uri.startsWith('package:$packageName')) {
-            UsageEvent(_kEventName, 'success', flutterUsage: globals.flutterUsage).send();
+            UsageEvent(
+              _kEventName,
+              'success',
+              flutterUsage: globals.flutterUsage,
+            ).send();
             return Uri.parse('http://localhost:$hostPort');
           }
         }

packages/flutter_tools/lib/src/ios/simulators.dart

@@ -445,13 +445,19 @@ class IOSSimulator extends Device {
 
     try {
       final Uri deviceUri = await observatoryDiscovery.uri;
-      return LaunchResult.succeeded(observatoryUri: deviceUri);
+      if (deviceUri != null) {
+        return LaunchResult.succeeded(observatoryUri: deviceUri);
+      }
+      globals.printError(
+        'Error waiting for a debug connection: '
+        'The log reader failed unexpectedly',
+      );
     } on Exception catch (error) {
       globals.printError('Error waiting for a debug connection: $error');
-      return LaunchResult.failed();
     } finally {
-      await observatoryDiscovery.cancel();
+      await observatoryDiscovery?.cancel();
     }
+    return LaunchResult.failed();
   }
 
   Future<void> _setupUpdatedApplicationBundle(covariant BuildableIOSApp app, BuildInfo buildInfo, String mainPath) async {

packages/flutter_tools/lib/src/protocol_discovery.dart

@@ -64,10 +64,17 @@ class ProtocolDiscovery {
   _BufferedStreamController<Uri> _uriStreamController;
 
   /// The discovered service URL.
+  ///
+  /// Returns null if the log reader shuts down before any uri is found.
+  ///
   /// Use [uris] instead.
   // TODO(egarciad): replace `uri` for `uris`.
-  Future<Uri> get uri {
-    return uris.first;
+  Future<Uri> get uri async {
+    try {
+      return await uris.first;
+    } on StateError {
+      return null;
+    }
   }
 
   /// The discovered service URLs.

packages/flutter_tools/lib/src/tester/flutter_tester.dart

@@ -157,6 +157,7 @@ class FlutterTesterDevice extends Device {
 
     command.add(applicationKernelFilePath);
 
+    ProtocolDiscovery observatoryDiscovery;
     try {
       globals.printTrace(command.join(' '));
 
@@ -185,7 +186,7 @@ class FlutterTesterDevice extends Device {
         return LaunchResult.succeeded();
       }
 
-      final ProtocolDiscovery observatoryDiscovery = ProtocolDiscovery.observatory(
+      observatoryDiscovery = ProtocolDiscovery.observatory(
         getLogReader(),
         hostPort: debuggingOptions.hostVmServicePort,
         devicePort: debuggingOptions.deviceVmServicePort,
@@ -193,11 +194,19 @@ class FlutterTesterDevice extends Device {
       );
 
       final Uri observatoryUri = await observatoryDiscovery.uri;
-      return LaunchResult.succeeded(observatoryUri: observatoryUri);
+      if (observatoryUri != null) {
+        return LaunchResult.succeeded(observatoryUri: observatoryUri);
+      }
+      globals.printError(
+        'Failed to launch $package: '
+        'The log reader failed unexpectedly.',
+      );
     } on Exception catch (error) {
       globals.printError('Failed to launch $package: $error');
-      return LaunchResult.failed();
+    } finally {
+      await observatoryDiscovery?.cancel();
     }
+    return LaunchResult.failed();
   }
 
   @override

packages/flutter_tools/test/general.shard/protocol_discovery_test.dart

@@ -112,6 +112,14 @@ void main() {
         expect(discoverer.uri, throwsA(isFormatException));
       });
 
+      testUsingContext('uri is null when the log reader closes early', () async {
+        initialize();
+        final Future<Uri> uriFuture = discoverer.uri;
+        await logReader.dispose();
+
+        expect(await uriFuture, isNull);
+      });
+
       testUsingContext('uri waits for correct log line', () async {
         initialize();
         final Future<Uri> uriFuture = discoverer.uri;