[flutter_tools] check if stream is open before sending message in ios device (#99947)

Author: christopherfujino

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

@@ -647,14 +647,25 @@ class IOSDeviceLogReader extends DeviceLogReader {
   // Logging from the dart code has no prefixing metadata.
   final RegExp _debuggerLoggingRegex = RegExp(r'^\S* \S* \S*\[[0-9:]*] (.*)');
 
-  late final StreamController<String> _linesController = StreamController<String>.broadcast(
+  @visibleForTesting
+  late final StreamController<String> linesController = StreamController<String>.broadcast(
     onListen: _listenToSysLog,
     onCancel: dispose,
   );
+
+  // Sometimes (race condition?) we try to send a log after the controller has
+  // been closed. See https://github.com/flutter/flutter/issues/99021 for more
+  // context.
+  void _addToLinesController(String message) {
+    if (!linesController.isClosed) {
+      linesController.add(message);
+    }
+  }
+
   final List<StreamSubscription<void>> _loggingSubscriptions = <StreamSubscription<void>>[];
 
   @override
-  Stream<String> get logLines => _linesController.stream;
+  Stream<String> get logLines => linesController.stream;
 
   @override
   FlutterVmService? get connectedVMService => _connectedVMService;
@@ -694,7 +705,7 @@ class IOSDeviceLogReader extends DeviceLogReader {
       }
       final String message = processVmServiceMessage(event);
       if (message.isNotEmpty) {
-        _linesController.add(message);
+        _addToLinesController(message);
       }
     }
 
@@ -717,9 +728,9 @@ class IOSDeviceLogReader extends DeviceLogReader {
     }
     // Add the debugger logs to the controller created on initialization.
     _loggingSubscriptions.add(debugger.logLines.listen(
-      (String line) => _linesController.add(_debuggerLineHandler(line)),
-      onError: _linesController.addError,
-      onDone: _linesController.close,
+      (String line) => _addToLinesController(_debuggerLineHandler(line)),
+      onError: linesController.addError,
+      onDone: linesController.close,
       cancelOnError: true,
     ));
   }
@@ -737,8 +748,8 @@ class IOSDeviceLogReader extends DeviceLogReader {
       process.stdout.transform<String>(utf8.decoder).transform<String>(const LineSplitter()).listen(_newSyslogLineHandler());
       process.stderr.transform<String>(utf8.decoder).transform<String>(const LineSplitter()).listen(_newSyslogLineHandler());
       process.exitCode.whenComplete(() {
-        if (_linesController.hasListener) {
-          _linesController.close();
+        if (linesController.hasListener) {
+          linesController.close();
         }
       });
       assert(idevicesyslogProcess == null);
@@ -761,7 +772,7 @@ class IOSDeviceLogReader extends DeviceLogReader {
     return (String line) {
       if (printing) {
         if (!_anyLineRegex.hasMatch(line)) {
-          _linesController.add(decodeSyslog(line));
+          _addToLinesController(decodeSyslog(line));
           return;
         }
 
@@ -773,7 +784,7 @@ class IOSDeviceLogReader extends DeviceLogReader {
       if (match != null) {
         final String logLine = line.substring(match.end);
         // Only display the log line after the initial device and executable information.
-        _linesController.add(decodeSyslog(logLine));
+        _addToLinesController(decodeSyslog(logLine));
 
         printing = true;
       }

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

@@ -383,7 +383,7 @@ class IOSDeployDebugger {
           // To avoid all lines being double spaced, if the last line from the
           // debugger was not an empty line, skip this empty line.
           // This will still cause "legit" logged newlines to be doubled...
-        } else {
+        } else if (!_debuggerOutput.isClosed) {
           _debuggerOutput.add(line);
         }
         lastLineFromDebugger = line;
@@ -413,11 +413,15 @@ class IOSDeployDebugger {
     } on ProcessException catch (exception, stackTrace) {
       _logger.printTrace('ios-deploy failed: $exception');
       _debuggerState = _IOSDeployDebuggerState.detached;
-      _debuggerOutput.addError(exception, stackTrace);
+      if (!_debuggerOutput.isClosed) {
+        _debuggerOutput.addError(exception, stackTrace);
+      }
     } on ArgumentError catch (exception, stackTrace) {
       _logger.printTrace('ios-deploy failed: $exception');
       _debuggerState = _IOSDeployDebuggerState.detached;
-      _debuggerOutput.addError(exception, stackTrace);
+      if (!_debuggerOutput.isClosed) {
+        _debuggerOutput.addError(exception, stackTrace);
+      }
     }
     // Wait until the debugger attaches, or the attempt fails.
     return debuggerCompleter.future;

packages/flutter_tools/test/general.shard/ios/ios_device_logger_test.dart

@@ -7,6 +7,7 @@
 import 'dart:async';
 
 import 'package:flutter_tools/src/artifacts.dart';
+import 'package:flutter_tools/src/base/async_guard.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/convert.dart';
@@ -309,6 +310,45 @@ Runner(libsystem_asl.dylib)[297] <Notice>: libMobileGestalt
       logReader.dispose();
       expect(iosDeployDebugger.detached, true);
     });
+
+    testWithoutContext('Does not throw if debuggerStream set after logReader closed', () async {
+      final Stream<String> debuggingLogs = Stream<String>.fromIterable(<String>[
+        '2020-09-15 19:15:10.931434-0700 Runner[541:226276] Did finish launching.',
+        '2020-09-15 19:15:10.931434-0700 Runner[541:226276] [Category] Did finish launching from logging category.',
+        'stderr from dart',
+        '',
+      ]);
+
+      final IOSDeviceLogReader logReader = IOSDeviceLogReader.test(
+        iMobileDevice: IMobileDevice(
+          artifacts: artifacts,
+          processManager: processManager,
+          cache: fakeCache,
+          logger: logger,
+        ),
+        useSyslog: false,
+      );
+      Object exception;
+      StackTrace trace;
+      await asyncGuard(
+          () async {
+            await logReader.linesController.close();
+            final FakeIOSDeployDebugger iosDeployDebugger = FakeIOSDeployDebugger();
+            iosDeployDebugger.logLines = debuggingLogs;
+            logReader.debuggerStream = iosDeployDebugger;
+            await logReader.logLines.drain<void>();
+          },
+          onError: (Object err, StackTrace stackTrace) {
+            exception = err;
+            trace = stackTrace;
+          }
+      );
+      expect(
+        exception,
+        isNull,
+        reason: trace.toString(),
+      );
+    });
   });
 }