[devicelab] allow the devicelab to take a screenshot if the iOS connection fails with FLUTTER_IOS_SCREENSHOT_ON_CONNECTION_FAILURE (flutter#68156)

More attempts to remote diagnose the issues in the iOS devicelab

Author: jonahwilliams

dev/devicelab/lib/framework/utils.dart

@@ -443,11 +443,11 @@ List<String> flutterCommandArgs(String command, List<String> options) {
 Future<int> flutter(String command, {
   List<String> options = const <String>[],
   bool canFail = false, // as in, whether failures are ok. False means that they are fatal.
-  Map<String, String> environment,
+  Map<String, String> environment = const <String, String>{},
 }) {
   final List<String> args = flutterCommandArgs(command, options);
   return exec(path.join(flutterDirectory.path, 'bin', 'flutter'), args,
-      canFail: canFail, environment: environment);
+      canFail: canFail, environment: <String, String>{...?environment, 'FLUTTER_IOS_SCREENSHOT_ON_CONNECTION_FAILURE': 'true'});
 }
 
 /// Runs a `flutter` command and returns the standard output as a string.

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

@@ -11,6 +11,7 @@ import 'package:vm_service/vm_service.dart' as vm_service;
 
 import '../application_package.dart';
 import '../base/common.dart';
+import '../base/error_handling_io.dart';
 import '../base/file_system.dart';
 import '../base/io.dart';
 import '../base/logger.dart';
@@ -439,6 +440,7 @@ class IOSDevice extends Device {
         installationResult = await iosDeployDebugger.launchAndAttach() ? 0 : 1;
       }
       if (installationResult != 0) {
+        await _screenshotOnFailure();
         _logger.printError('Could not run ${bundle.path} on $id.');
         _logger.printError('Try launching Xcode and selecting "Product > Run" to fix the problem:');
         _logger.printError('  open ios/Runner.xcworkspace');
@@ -468,6 +470,7 @@ class IOSDevice extends Device {
         packageName: FlutterProject.current().manifest.appName,
       );
       if (localUri == null) {
+        await _screenshotOnFailure();
         return LaunchResult.failed();
       }
       return LaunchResult.succeeded(observatoryUri: localUri);
@@ -549,6 +552,23 @@ class IOSDevice extends Device {
     });
     await _portForwarder?.dispose();
   }
+
+  Future<void> _screenshotOnFailure() async {
+    final bool screenshotOnConnectionFailure = _platform
+      .environment['FLUTTER_IOS_SCREENSHOT_ON_CONNECTION_FAILURE'] == 'true';
+    if (!screenshotOnConnectionFailure) {
+      return;
+    }
+    final File file = _fileSystem.file('test_screenshot.png');
+    try {
+      await takeScreenshot(file);
+      _logger.printStatus('BASE64 SCREENSHOT:${base64.encode(file.readAsBytesSync())}');
+    } on Exception {
+      _logger.printError('Failed to take screenshot');
+    } finally {
+      ErrorHandlingFileSystem.deleteIfExists(file);
+    }
+  }
 }
 
 /// Decodes a vis-encoded syslog string to a UTF-8 representation.

packages/flutter_tools/tool/screenshot_decoder.dart

@@ -0,0 +1,23 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:io';
+
+/// decodes a base64 screenshot stored in the devicelab.
+///
+/// Usage dart tool/screenshot_decoder.dart path/to/log_file
+void main(List<String> arguments) {
+  int screenshot = 0;
+  final String logFile = arguments.first;
+  for (final String line in File(logFile).readAsLinesSync()) {
+    if (!line.contains('BASE64 SCREENSHOT:')) {
+      continue;
+    }
+    final String message = line.split('BASE64 SCREENSHOT:')[1];
+    final List<int> bytes = base64.decode(message);
+    File('flutter_screenshot_$screenshot.png').writeAsBytesSync(bytes);
+    screenshot += 1;
+  }
+}