Fix a stream lifecycle bug in CustomDeviceLogReader (#94310)

packages/flutter_tools/lib/src/custom_devices/custom_device.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
 import '../application_package.dart';
@@ -53,7 +54,11 @@ class CustomDeviceLogReader extends DeviceLogReader {
   @override
   final String name;
 
-  final StreamController<String> _logLinesController = StreamController<String>.broadcast();
+  @visibleForTesting
+  final StreamController<String> logLinesController = StreamController<String>.broadcast();
+
+  @visibleForTesting
+  final List<StreamSubscription<String>> subscriptions = <StreamSubscription<String>>[];
 
   /// Listen to [process]' stdout and stderr, decode them using [SystemEncoding]
   /// and add each decoded line to [logLines].
@@ -66,13 +71,17 @@ class CustomDeviceLogReader extends DeviceLogReader {
   void listenToProcessOutput(Process process, {Encoding encoding = systemEncoding}) {
     final Converter<List<int>, String> decoder = encoding.decoder;
 
+    subscriptions.add(
       process.stdout.transform<String>(decoder)
         .transform<String>(const LineSplitter())
-      .listen(_logLinesController.add);
+        .listen(logLinesController.add),
+    );
 
+    subscriptions.add(
       process.stderr.transform<String>(decoder)
         .transform<String>(const LineSplitter())
-      .listen(_logLinesController.add);
+        .listen(logLinesController.add)
+    );
   }
 
   /// Add all lines emitted by [lines] to this [CustomDeviceLogReader]s [logLines]
@@ -83,18 +92,28 @@ class CustomDeviceLogReader extends DeviceLogReader {
   ///
   /// Useful when you want to combine the contents of multiple log readers.
   void listenToLinesStream(Stream<String> lines) {
-    _logLinesController.addStream(lines);
+    subscriptions.add(
+      lines.listen(logLinesController.add)
+    );
   }
 
   /// Dispose this log reader, freeing all associated resources and marking
   /// [logLines] as done.
   @override
-  void dispose() {
-    _logLinesController.close();
+  Future<void> dispose() async {
+    final List<Future<void>> futures = <Future<void>>[];
+
+    for (final StreamSubscription<String> subscription in subscriptions) {
+      futures.add(subscription.cancel());
+    }
+
+    futures.add(logLinesController.close());
+
+    await Future.wait(futures);
   }
 
   @override
-  Stream<String> get logLines => _logLinesController.stream;
+  Stream<String> get logLines => logLinesController.stream;
 }
 
 /// A [DevicePortForwarder] that uses commands to forward / unforward a port.
@@ -170,8 +189,8 @@ class CustomDevicePortForwarder extends DevicePortForwarder {
     }));
 
     unawaited(completer.future.whenComplete(() {
-      logLinesSubscription.cancel();
-      reader.dispose();
+      unawaited(logLinesSubscription.cancel());
+      unawaited(reader.dispose());
     }));
 
     return completer.future;
@@ -440,7 +459,7 @@ class CustomDeviceAppSession {
       _process = null;
     }
 
-    logReader.dispose();
+    unawaited(logReader.dispose());
   }
 }
 

packages/flutter_tools/test/general.shard/custom_devices/custom_device_test.dart

@@ -587,6 +587,54 @@ void main() {
 
     expect(await device.targetPlatform, TargetPlatform.linux_x64);
   });
+
+  testWithoutContext('CustomDeviceLogReader cancels subscriptions before closing logLines stream', () async {
+    final CustomDeviceLogReader logReader = CustomDeviceLogReader('testname');
+
+    final Iterable<List<int>> lines = Iterable<List<int>>.generate(5, (int _) => utf8.encode('test'));
+
+    logReader.listenToProcessOutput(
+      FakeProcess(
+        exitCode: Future<int>.value(0),
+        stdout: Stream<List<int>>.fromIterable(lines),
+        stderr: Stream<List<int>>.fromIterable(lines),
+      ),
+    );
+
+    final List<MyFakeStreamSubscription<String>> subscriptions = <MyFakeStreamSubscription<String>>[];
+    bool logLinesStreamDone = false;
+    logReader.logLines.listen((_) {}, onDone: () {
+      expect(subscriptions, everyElement((MyFakeStreamSubscription<String> s) => s.canceled));
+      logLinesStreamDone = true;
+    });
+
+    logReader.subscriptions.replaceRange(
+      0,
+      logReader.subscriptions.length,
+      logReader.subscriptions.map(
+        (StreamSubscription<String> e) => MyFakeStreamSubscription<String>(e)
+      ),
+    );
+
+    subscriptions.addAll(logReader.subscriptions.cast());
+
+    await logReader.dispose();
+
+    expect(logLinesStreamDone, true);
+  });
+}
+
+class MyFakeStreamSubscription<T> extends Fake implements StreamSubscription<T> {
+  MyFakeStreamSubscription(this.parent);
+
+  StreamSubscription<T> parent;
+  bool canceled = false;
+
+  @override
+  Future<void> cancel() {
+    canceled = true;
+    return parent.cancel();
+  }
 }
 
 class FakeBundleBuilder extends Fake implements BundleBuilder {