Support legacy behavior for --host-vmservice-port and --observatory-port with DDS (#70336)

Implements the following:
  - If both --host-vmservice-port and --dds-port are specified, use the current behavior
  - If only --host-vmservice-port is specified and dds is enabled, use that for the dds port
  - If only --dds-port is specified, use that for the dds port

Fixes https://github.com/flutter/flutter/issues/70332

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -341,10 +341,27 @@ abstract class FlutterCommand extends Command<void> {
 
   bool get disableDds => boolArg('disable-dds');
 
+  bool get _hostVmServicePortProvided => argResults.wasParsed('observatory-port') ||
+                                         argResults.wasParsed('host-vmservice-port');
+
+  int _tryParseHostVmservicePort() {
+    try {
+      return int.parse(stringArg('observatory-port') ?? stringArg('host-vmservice-port'));
+    } on FormatException catch (error) {
+      throwToolExit('Invalid port for `--observatory-port/--host-vmservice-port`: $error');
+    }
+    return null;
+  }
+
   int get ddsPort {
-    if (argResults.wasParsed('dds-port')) {
+    if (!argResults.wasParsed('dds-port') && _hostVmServicePortProvided) {
+      // If an explicit DDS port is _not_ provided, use the host-vmservice-port for DDS.
+      return _tryParseHostVmservicePort();
+    } else if (argResults.wasParsed('dds-port')) {
+      // If an explicit DDS port is provided, use dds-port for DDS.
       return int.tryParse(stringArg('dds-port')) ?? 0;
     }
+    // Otherwise, DDS can bind to a random port.
     return 0;
   }
 
@@ -356,9 +373,7 @@ abstract class FlutterCommand extends Command<void> {
   ///
   /// If no port is set, returns null.
   int get hostVmservicePort {
-    if (!_usesPortOption ||
-        (argResults['observatory-port'] == null &&
-      argResults['host-vmservice-port'] == null)) {
+    if (!_usesPortOption || !_hostVmServicePortProvided) {
       return null;
     }
     if (argResults.wasParsed('observatory-port') &&
@@ -366,12 +381,13 @@ abstract class FlutterCommand extends Command<void> {
       throwToolExit('Only one of "--observatory-port" and '
         '"--host-vmservice-port" may be specified.');
     }
-    try {
-      return int.parse(stringArg('observatory-port') ?? stringArg('host-vmservice-port'));
-    } on FormatException catch (error) {
-      throwToolExit('Invalid port for `--observatory-port/--host-vmservice-port`: $error');
+    // If DDS is enabled and no explicit DDS port is provided, use the
+    // host-vmservice-port for DDS instead and bind the VM service to a random
+    // port.
+    if (!disableDds && !argResults.wasParsed('dds-port')) {
+      return null;
     }
-    return null;
+    return _tryParseHostVmservicePort();
   }
 
   /// Gets the vmservice port provided to in the 'device-vmservice-port' option.

packages/flutter_tools/test/commands.shard/hermetic/attach_test.dart

@@ -526,6 +526,9 @@ void main() {
             '$devicePort',
             '--observatory-port',
             '$hostPort',
+            // Ensure DDS doesn't use hostPort by binding to a random port.
+            '--dds-port',
+            '0',
           ],
         );
         await completer.future;
@@ -558,6 +561,9 @@ void main() {
             '--observatory-port',
             '$hostPort',
             '--ipv6',
+            // Ensure DDS doesn't use hostPort by binding to a random port.
+            '--dds-port',
+            '0',
           ],
         );
         await completer.future;

packages/flutter_tools/test/integration.shard/observatory_port_test.dart

+// 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:async';
+
+import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/io.dart';
+import 'package:flutter_tools/src/convert.dart';
+
+import '../src/common.dart';
+import '../src/context.dart';
+import 'test_data/basic_project.dart';
+import 'test_utils.dart';
+
+Future<int> getFreePort() async {
+  int port = 0;
+  final ServerSocket serverSocket = await ServerSocket.bind(InternetAddress.loopbackIPv4, 0);
+  port = serverSocket.port;
+  await serverSocket.close();
+  return port;
+}
+
+Future<void> waitForObservatoryMessage(Process process, int port) async {
+  final Completer<void> completer = Completer<void>();
+  process.stdout
+    .transform(utf8.decoder)
+    .listen((String line) {
+      print(line);
+      if (line.contains('An Observatory debugger and profiler on Flutter test device is available at')) {
+        if (line.contains('http://127.0.0.1:$port')) {
+          completer.complete();
+        } else {
+          completer.completeError(Exception('Did not forward to provided port $port, instead found $line'));
+        }
+      }
+    });
+  process.stderr
+    .transform(utf8.decoder)
+    .listen(print);
+  return completer.future;
+}
+
+void main() {
+  Directory tempDir;
+  final BasicProject _project = BasicProject();
+
+  setUp(() async {
+    tempDir = createResolvedTempDirectorySync('run_test.');
+    await _project.setUpIn(tempDir);
+  });
+
+  tearDown(() async {
+    tryToDelete(tempDir);
+  });
+
+  testUsingContext('flutter run --observatory-port', () async {
+    final String flutterBin = fileSystem.path.join(getFlutterRoot(), 'bin', 'flutter');
+    final int port = await getFreePort();
+    // If only --observatory-port is provided, --observatory-port will be used by DDS
+    // and the VM service will bind to a random port.
+    final Process process = await processManager.start(<String>[
+      flutterBin,
+      'run',
+      '--show-test-device',
+      '--observatory-port=$port',
+      '-d',
+      'flutter-tester',
+    ], workingDirectory: tempDir.path);
+    await waitForObservatoryMessage(process, port);
+    process.kill();
+    await process.exitCode;
+  });
+
+  testUsingContext('flutter run --dds-port --observatory-port', () async {
+    final String flutterBin = fileSystem.path.join(getFlutterRoot(), 'bin', 'flutter');
+    final int observatoryPort = await getFreePort();
+    int ddsPort = await getFreePort();
+    while(ddsPort == observatoryPort) {
+      ddsPort = await getFreePort();
+    }
+    // If both --dds-port and --observatory-port are provided, --dds-port will be used by
+    // DDS and --observatory-port will be used by the VM service.
+    final Process process = await processManager.start(<String>[
+      flutterBin,
+      'run',
+      '--show-test-device',
+      '--observatory-port=$observatoryPort',
+      '--dds-port=$ddsPort',
+      '-d',
+      'flutter-tester',
+    ], workingDirectory: tempDir.path);
+    await waitForObservatoryMessage(process, ddsPort);
+    process.kill();
+    await process.exitCode;
+  });
+
+  testUsingContext('flutter run --dds-port', () async {
+    final String flutterBin = fileSystem.path.join(getFlutterRoot(), 'bin', 'flutter');
+    final int ddsPort = await getFreePort();
+    // If only --dds-port is provided, --dds-port will be used by DDS and the VM service
+    // will bind to a random port.
+    final Process process = await processManager.start(<String>[
+      flutterBin,
+      'run',
+      '--show-test-device',
+      '--dds-port=$ddsPort',
+      '-d',
+      'flutter-tester',
+    ], workingDirectory: tempDir.path);
+    await waitForObservatoryMessage(process, ddsPort);
+    process.kill();
+    await process.exitCode;
+  });
+
+}