Use mDNS to discover the device port (#26944)

* Discover port over mDNS

* opt in, only for iOS for now

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

@@ -4,6 +4,8 @@
 
 import 'dart:async';
 
+import 'package:multicast_dns/multicast_dns.dart';
+
 import '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/io.dart';
@@ -14,16 +16,14 @@ import '../compile.dart';
 import '../device.dart';
 import '../fuchsia/fuchsia_device.dart';
 import '../globals.dart';
+import '../ios/devices.dart';
+import '../ios/simulators.dart';
 import '../protocol_discovery.dart';
 import '../resident_runner.dart';
 import '../run_cold.dart';
 import '../run_hot.dart';
 import '../runner/flutter_command.dart';
 
-final String ipv4Loopback = InternetAddress.loopbackIPv4.address;
-
-final String ipv6Loopback = InternetAddress.loopbackIPv6.address;
-
 /// A Flutter-command that attaches to applications that have been launched
 /// without `flutter run`.
 ///
@@ -56,7 +56,16 @@ class AttachCommand extends FlutterCommand {
       ..addOption(
         'debug-port',
         help: 'Device port where the observatory is listening.',
-      )..addOption('pid-file',
+      )..addOption(
+        'app-id',
+        help: 'The package name (Android) or bundle identifier (iOS) for the application. '
+              'This can be specified to avoid being prompted if multiple observatory ports '
+              'are advertised.\n'
+              'If you have multiple devices or emulators running, you should include the '
+              'device hostname as well, e.g. "com.example.myApp@my-iphone".\n'
+              'This parameter is case-insensitive.',
+      )..addOption(
+        'pid-file',
         help: 'Specify a file to write the process id to. '
               'You can send SIGUSR1 to trigger a hot reload '
               'and SIGUSR2 to trigger a hot restart.',
@@ -92,6 +101,10 @@ class AttachCommand extends FlutterCommand {
     return null;
   }
 
+  String get appId {
+    return argResults['app-id'];
+  }
+
   @override
   Future<void> validateCommand() async {
     await super.validateCommand();
@@ -114,6 +127,9 @@ class AttachCommand extends FlutterCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    final String ipv4Loopback = InternetAddress.loopbackIPv4.address;
+    final String ipv6Loopback = InternetAddress.loopbackIPv6.address;
+
     Cache.releaseLockEarly();
 
     await _validateArguments();
@@ -121,7 +137,19 @@ class AttachCommand extends FlutterCommand {
     writePidFile(argResults['pid-file']);
 
     final Device device = await findTargetDevice();
-    final int devicePort = debugPort;
+    Future<int> getDevicePort() async {
+      if (debugPort != null) {
+        return debugPort;
+      }
+      // This call takes a non-trivial amount of time, and only iOS devices and
+      // simulators support it.
+      // If/when we do this on Android or other platforms, we can update it here.
+      if (device is IOSDevice || device is IOSSimulator) {
+        return MDnsObservatoryPortDiscovery().queryForPort(applicationId: appId);
+      }
+      return null;
+    }
+    final int devicePort = await getDevicePort();
 
     final Daemon daemon = argResults['machine']
       ? Daemon(stdinCommandStream, stdoutCommandResponse,
@@ -273,3 +301,99 @@ class HotRunnerFactory {
     ipv6: ipv6,
   );
 }
+
+/// A wrapper around [MDnsClient] to find a Dart observatory port.
+class MDnsObservatoryPortDiscovery {
+  /// Creates a new [MDnsObservatoryPortDiscovery] object.
+  ///
+  /// The [client] parameter will be defaulted to a new [MDnsClient] if null.
+  /// The [applicationId] parameter may be null, and can be used to
+  /// automatically select which application to use if multiple are advertising
+  /// Dart observatory ports.
+  MDnsObservatoryPortDiscovery({MDnsClient mdnsClient})
+    : client = mdnsClient ?? MDnsClient();
+
+  /// The [MDnsClient] used to do a lookup.
+  final MDnsClient client;
+
+  static const String dartObservatoryName = '_dartobservatory._tcp.local';
+
+  /// Executes an mDNS query for a Dart Observatory port.
+  ///
+  /// The [applicationId] parameter may be used to specify which application
+  /// to find.  For Android, it refers to the package name; on iOS, it refers to
+  /// the bundle ID.
+  ///
+  /// If it is not null, this method will find the port of the
+  /// Dart Observatory for that application. If it cannot find a Dart
+  /// Observatory matching that application identifier, it will call
+  /// [throwToolExit].
+  ///
+  /// If it is null and there are multiple ports available, the user will be
+  /// prompted with a list of available observatory ports and asked to select
+  /// one.
+  ///
+  /// If it is null and there is only one available port, it will return that
+  /// port regardless of what application the port is for.
+  Future<int> queryForPort({String applicationId}) async {
+    printStatus('Checking for advertised Dart observatories...');
+    try {
+      await client.start();
+      final List<PtrResourceRecord> pointerRecords = await client
+          .lookup<PtrResourceRecord>(
+            ResourceRecordQuery.serverPointer(dartObservatoryName),
+          )
+          .toList();
+      if (pointerRecords.isEmpty) {
+        return null;
+      }
+      // We have no guarantee that we won't get multiple hits from the same
+      // service on this.
+      final List<String> uniqueDomainNames = pointerRecords
+          .map<String>((PtrResourceRecord record) => record.domainName)
+          .toSet()
+          .toList();
+
+      String domainName;
+      if (applicationId != null) {
+        for (String name in uniqueDomainNames) {
+          if (name.toLowerCase().startsWith(applicationId.toLowerCase())) {
+            domainName = name;
+            break;
+          }
+        }
+        if (domainName == null) {
+          throwToolExit('Did not find a observatory port advertised for $applicationId.');
+        }
+      } else if (uniqueDomainNames.length > 1) {
+        final StringBuffer buffer = StringBuffer();
+        buffer.writeln('There are multiple observatory ports available.');
+        buffer.writeln('Rerun this command with one of the following passed in as the appId:');
+        buffer.writeln('');
+        for (final String uniqueDomainName in uniqueDomainNames) {
+          buffer.writeln('  flutter attach --app-id ${uniqueDomainName.replaceAll('.$dartObservatoryName', '')}');
+        }
+        throwToolExit(buffer.toString());
+      } else {
+        domainName = pointerRecords[0].domainName;
+      }
+      printStatus('Checking for available port on $domainName');
+      // Here, if we get more than one, it should just be a duplicate.
+      final List<SrvResourceRecord> srv = await client
+          .lookup<SrvResourceRecord>(
+            ResourceRecordQuery.service(domainName),
+          )
+          .toList();
+      if (srv.isEmpty) {
+        return null;
+      }
+      if (srv.length > 1) {
+        printError('Unexpectedly found more than one observatory report for $domainName '
+                   '- using first one (${srv.first.port}).');
+      }
+      return srv.first.port;
+    } finally {
+      client.stop();
+    }
+  }
+}

packages/flutter_tools/pubspec.yaml

@@ -23,6 +23,7 @@ dependencies:
   json_schema: 1.0.10
   linter: 0.1.74
   meta: 1.1.6
+  multicast_dns: 0.1.0+1
   mustache: 1.1.0
   package_config: 1.0.5
   platform: 2.2.0
@@ -95,4 +96,4 @@ dartdoc:
   # Exclude this package from the hosted API docs.
   nodoc: true
 
-# PUBSPEC CHECKSUM: 3fcc
+# PUBSPEC CHECKSUM: 78f0

packages/flutter_tools/test/commands/attach_test.dart

@@ -17,6 +17,7 @@ import 'package:flutter_tools/src/resident_runner.dart';
 import 'package:flutter_tools/src/run_hot.dart';
 import 'package:meta/meta.dart';
 import 'package:mockito/mockito.dart';
+import 'package:multicast_dns/multicast_dns.dart';
 
 import '../src/common.dart';
 import '../src/context.dart';
@@ -422,8 +423,121 @@ void main() {
       FileSystem: () => testFileSystem,
     });
   });
+
+  group('mDNS Discovery', () {
+    final int year3000 = DateTime(3000).millisecondsSinceEpoch;
+
+    MDnsClient getMockClient(
+      List<PtrResourceRecord> ptrRecords,
+      Map<String, List<SrvResourceRecord>> srvResponse,
+    ) {
+      final MDnsClient client = MockMDnsClient();
+
+      when(client.lookup<PtrResourceRecord>(
+        ResourceRecordQuery.serverPointer(MDnsObservatoryPortDiscovery.dartObservatoryName),
+      )).thenAnswer((_) => Stream<PtrResourceRecord>.fromIterable(ptrRecords));
+
+      for (final MapEntry<String, List<SrvResourceRecord>> entry in srvResponse.entries) {
+        when(client.lookup<SrvResourceRecord>(
+          ResourceRecordQuery.service(entry.key),
+        )).thenAnswer((_) => Stream<SrvResourceRecord>.fromIterable(entry.value));
+      }
+      return client;
+    }
+
+    testUsingContext('No ports available', () async {
+      final MDnsClient client = getMockClient(<PtrResourceRecord>[], <String, List<SrvResourceRecord>>{});
+
+      final MDnsObservatoryPortDiscovery portDiscovery = MDnsObservatoryPortDiscovery(mdnsClient: client);
+      final int port = await portDiscovery.queryForPort();
+      expect(port, isNull);
+    });
+
+    testUsingContext('One port available, no appId', () async {
+      final MDnsClient client = getMockClient(
+        <PtrResourceRecord>[
+          PtrResourceRecord('foo', year3000, domainName: 'bar'),
+        ],
+        <String, List<SrvResourceRecord>>{
+          'bar': <SrvResourceRecord>[
+            SrvResourceRecord('bar', year3000, port: 123, weight: 1, priority: 1, target: 'appId'),
+          ],
+        },
+      );
+
+      final MDnsObservatoryPortDiscovery portDiscovery = MDnsObservatoryPortDiscovery(mdnsClient: client);
+      final int port = await portDiscovery.queryForPort();
+      expect(port, 123);
+    });
+
+    testUsingContext('Multiple ports available, without appId', () async {
+      final MDnsClient client = getMockClient(
+        <PtrResourceRecord>[
+          PtrResourceRecord('foo', year3000, domainName: 'bar'),
+          PtrResourceRecord('baz', year3000, domainName: 'fiz'),
+        ],
+        <String, List<SrvResourceRecord>>{
+          'bar': <SrvResourceRecord>[
+            SrvResourceRecord('bar', year3000, port: 123, weight: 1, priority: 1, target: 'appId'),
+          ],
+          'fiz': <SrvResourceRecord>[
+            SrvResourceRecord('fiz', year3000, port: 321, weight: 1, priority: 1, target: 'local'),
+          ],
+        },
+      );
+
+      final MDnsObservatoryPortDiscovery portDiscovery = MDnsObservatoryPortDiscovery(mdnsClient: client);
+      expect(() => portDiscovery.queryForPort(), throwsToolExit());
+    });
+
+    testUsingContext('Multiple ports available, with appId', () async {
+      final MDnsClient client = getMockClient(
+        <PtrResourceRecord>[
+          PtrResourceRecord('foo', year3000, domainName: 'bar'),
+          PtrResourceRecord('baz', year3000, domainName: 'fiz'),
+        ],
+        <String, List<SrvResourceRecord>>{
+          'bar': <SrvResourceRecord>[
+            SrvResourceRecord('bar', year3000, port: 123, weight: 1, priority: 1, target: 'appId'),
+          ],
+          'fiz': <SrvResourceRecord>[
+            SrvResourceRecord('fiz', year3000, port: 321, weight: 1, priority: 1, target: 'local'),
+          ],
+        },
+      );
+
+      final MDnsObservatoryPortDiscovery portDiscovery = MDnsObservatoryPortDiscovery(mdnsClient: client);
+      final int port = await portDiscovery.queryForPort(applicationId: 'fiz');
+      expect(port, 321);
+    });
+
+    testUsingContext('Multiple ports available per process, with appId', () async {
+      final MDnsClient client = getMockClient(
+        <PtrResourceRecord>[
+          PtrResourceRecord('foo', year3000, domainName: 'bar'),
+          PtrResourceRecord('baz', year3000, domainName: 'fiz'),
+        ],
+        <String, List<SrvResourceRecord>>{
+          'bar': <SrvResourceRecord>[
+            SrvResourceRecord('bar', year3000, port: 1234, weight: 1, priority: 1, target: 'appId'),
+            SrvResourceRecord('bar', year3000, port: 123, weight: 1, priority: 1, target: 'appId'),
+          ],
+          'fiz': <SrvResourceRecord>[
+            SrvResourceRecord('fiz', year3000, port: 4321, weight: 1, priority: 1, target: 'local'),
+            SrvResourceRecord('fiz', year3000, port: 321, weight: 1, priority: 1, target: 'local'),
+          ],
+        },
+      );
+
+      final MDnsObservatoryPortDiscovery portDiscovery = MDnsObservatoryPortDiscovery(mdnsClient: client);
+      final int port = await portDiscovery.queryForPort(applicationId: 'bar');
+      expect(port, 1234);
+    });
+  });
 }
 
+class MockMDnsClient extends Mock implements MDnsClient {}
+
 class MockPortForwarder extends Mock implements DevicePortForwarder {}
 
 class MockHotRunner extends Mock implements HotRunner {}