Add debugging option to write vmservice address to file after starting (#41583)

packages/flutter_tools/lib/src/commands/run.dart

@@ -43,6 +43,11 @@ abstract class RunCommandBase extends FlutterCommand with DeviceBasedDevelopment
       )
       ..addOption('route',
         help: 'Which route to load when running the app.',
+      )
+      ..addOption('vmservice-out-file',
+        help: 'A file to write the attached vmservice uri to after an'
+          ' application is started.',
+        valueHelp: 'project/example/out.txt'
       );
     usesWebOptions(hide: !verboseHelp);
     usesTargetOption();
@@ -307,6 +312,7 @@ class RunCommand extends RunCommandBase {
         hostname: featureFlags.isWebEnabled ? argResults['web-hostname'] : '',
         port: featureFlags.isWebEnabled ? argResults['web-port'] : '',
         browserLaunch: featureFlags.isWebEnabled ? argResults['web-browser-launch'] : null,
+        vmserviceOutFile: argResults['vmservice-out-file'],
       );
     }
   }

packages/flutter_tools/lib/src/device.dart

@@ -499,6 +499,7 @@ class DebuggingOptions {
     this.hostname,
     this.port,
     this.browserLaunch = true,
+    this.vmserviceOutFile,
    }) : debuggingEnabled = true;
 
   DebuggingOptions.disabled(this.buildInfo, { this.initializePlatform = true, this.port, this.hostname })
@@ -514,7 +515,8 @@ class DebuggingOptions {
       dumpSkpOnShaderCompilation = false,
       verboseSystemLogs = false,
       observatoryPort = null,
-      browserLaunch = true;
+      browserLaunch = true,
+      vmserviceOutFile = null;
 
   final bool debuggingEnabled;
 
@@ -535,6 +537,8 @@ class DebuggingOptions {
   final String port;
   final String hostname;
   final bool browserLaunch;
+  /// A file where the vmservice uri should be written after the application is started.
+  final String vmserviceOutFile;
 
   bool get hasObservatoryPort => observatoryPort != null;
 }

packages/flutter_tools/lib/src/resident_runner.dart

@@ -643,6 +643,20 @@ abstract class ResidentRunner {
     throw '${fullRestart ? 'Restart' : 'Reload'} is not supported in $mode mode';
   }
 
+  @protected
+  void writeVmserviceFile() {
+    if (debuggingOptions.vmserviceOutFile != null) {
+      try {
+        final String address = flutterDevices.first.vmServices.first.wsAddress.toString();
+        final File vmserviceOutFile = fs.file(debuggingOptions.vmserviceOutFile);
+        vmserviceOutFile.createSync(recursive: true);
+        vmserviceOutFile.writeAsStringSync(address);
+      } on FileSystemException {
+        printError('Failed to write vmservice-out-file at ${debuggingOptions.vmserviceOutFile}');
+      }
+    }
+  }
+
   Future<void> exit() async {
     _exited = true;
     await stopEchoingDeviceLog();

packages/flutter_tools/lib/src/run_cold.dart

@@ -114,6 +114,8 @@ class ColdRunner extends ResidentRunner {
 
     appStartedCompleter?.complete();
 
+    writeVmserviceFile();
+
     if (stayResident && !traceStartup) {
       return waitForAppToFinish();
     }

packages/flutter_tools/lib/src/run_hot.dart

@@ -228,6 +228,7 @@ class HotRunner extends ResidentRunner {
       benchmarkOutput.writeAsStringSync(toPrettyJson(benchmarkData));
       return 0;
     }
+    writeVmserviceFile();
 
     int result = 0;
     if (stayResident) {

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

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -11,8 +12,10 @@ import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/devfs.dart';
 import 'package:flutter_tools/src/device.dart';
+import 'package:flutter_tools/src/globals.dart';
 import 'package:flutter_tools/src/reporting/reporting.dart';
 import 'package:flutter_tools/src/resident_runner.dart';
+import 'package:flutter_tools/src/run_cold.dart';
 import 'package:flutter_tools/src/run_hot.dart';
 import 'package:flutter_tools/src/vmservice.dart';
 import 'package:json_rpc_2/json_rpc_2.dart';
@@ -532,6 +535,70 @@ void main() {
     verify(mockFlutterDevice.refreshViews()).called(1);
     verify(mockFlutterDevice.toggleProfileWidgetBuilds()).called(1);
   }));
+
+  test('HotRunner writes vm service file when providing debugging option', () => testbed.run(() async {
+    fs.file(fs.path.join('lib', 'main.dart')).createSync(recursive: true);
+    residentRunner = HotRunner(
+      <FlutterDevice>[
+        mockFlutterDevice,
+      ],
+      stayResident: false,
+      debuggingOptions: DebuggingOptions.enabled(BuildInfo.debug, vmserviceOutFile: 'foo'),
+    );
+    when(mockFlutterDevice.runHot(
+      hotRunner: anyNamed('hotRunner'),
+      route: anyNamed('route'),
+    )).thenAnswer((Invocation invocation) async {
+      return 0;
+    });
+    await residentRunner.run();
+
+    expect(await fs.file('foo').readAsString(), testUri.toString());
+  }));
+
+  test('HotRunner handles failure to write vmservice file', () => testbed.run(() async {
+    final BufferLogger bufferLogger = logger;
+    fs.file(fs.path.join('lib', 'main.dart')).createSync(recursive: true);
+    residentRunner = HotRunner(
+      <FlutterDevice>[
+        mockFlutterDevice,
+      ],
+      stayResident: false,
+      debuggingOptions: DebuggingOptions.enabled(BuildInfo.debug, vmserviceOutFile: 'foo'),
+    );
+    when(mockFlutterDevice.runHot(
+      hotRunner: anyNamed('hotRunner'),
+      route: anyNamed('route'),
+    )).thenAnswer((Invocation invocation) async {
+      return 0;
+    });
+    await residentRunner.run();
+
+    expect(bufferLogger.errorText, contains('Failed to write vmservice-out-file at foo'));
+  }, overrides: <Type, Generator>{
+    FileSystem: () => ThrowingForwardingFileSystem(MemoryFileSystem()),
+  }));
+
+
+  test('ColdRunner writes vm service file when providing debugging option', () => testbed.run(() async {
+    fs.file(fs.path.join('lib', 'main.dart')).createSync(recursive: true);
+    residentRunner = ColdRunner(
+      <FlutterDevice>[
+        mockFlutterDevice,
+      ],
+      stayResident: false,
+      debuggingOptions: DebuggingOptions.enabled(BuildInfo.profile, vmserviceOutFile: 'foo'),
+    );
+    when(mockFlutterDevice.runCold(
+      coldRunner: anyNamed('coldRunner'),
+      route: anyNamed('route'),
+    )).thenAnswer((Invocation invocation) async {
+      return 0;
+    });
+    await residentRunner.run();
+
+    expect(await fs.file('foo').readAsString(), testUri.toString());
+  }));
 }
 
 class MockFlutterDevice extends Mock implements FlutterDevice {}
@@ -550,3 +617,14 @@ class TestFlutterDevice extends FlutterDevice {
   final List<FlutterView> views;
 }
 
+class ThrowingForwardingFileSystem extends ForwardingFileSystem {
+  ThrowingForwardingFileSystem(FileSystem delegate) : super(delegate);
+
+  @override
+  File file(dynamic path) {
+    if (path == 'foo') {
+      throw const FileSystemException();
+    }
+    return delegate.file(path);
+  }
+}