Remove race conditions involving finding available ports (#18488)

dev/devicelab/bin/tasks/commands_test.dart

@@ -35,13 +35,15 @@ void main() {
         .listen((String line) {
           print('run:stdout: $line');
           stdout.add(line);
-          if (lineContainsServicePort(line)) {
+          if (vmServicePort == null) {
             vmServicePort = parseServicePort(line);
+            if (vmServicePort != null) {
               print('service protocol connection available at port $vmServicePort');
               print('run: ready!');
               ready.complete();
               ok ??= true;
             }
+          }
         });
       run.stderr
         .transform(utf8.decoder)

dev/devicelab/bin/tasks/routing_test.dart

@@ -41,13 +41,15 @@ void main() {
         .transform(const LineSplitter())
         .listen((String line) {
           print('run:stdout: $line');
-          if (lineContainsServicePort(line)) {
+          if (vmServicePort == null) {
             vmServicePort = parseServicePort(line);
+            if (vmServicePort != null) {
               print('service protocol connection available at port $vmServicePort');
               print('run: ready!');
               ready.complete();
               ok ??= true;
             }
+          }
         });
       run.stderr
         .transform(utf8.decoder)

dev/devicelab/bin/tasks/service_extensions_test.dart

@@ -33,13 +33,15 @@ void main() {
           .transform(const LineSplitter())
           .listen((String line) {
         print('run:stdout: $line');
-        if (lineContainsServicePort(line)) {
+        if (vmServicePort == null) {
           vmServicePort = parseServicePort(line);
+          if (vmServicePort != null) {
             print('service protocol connection available at port $vmServicePort');
             print('run: ready!');
             ready.complete();
             ok ??= true;
           }
+        }
       });
       run.stderr
           .transform(utf8.decoder)

dev/devicelab/lib/framework/runner.dart

@@ -28,9 +28,8 @@ Future<Map<String, dynamic>> runTask(String taskName, { bool silent = false }) a
   if (!file(taskExecutable).existsSync())
     throw 'Executable Dart file not found: $taskExecutable';
 
-  final int vmServicePort = await findAvailablePort();
   final Process runner = await startProcess(dartBin, <String>[
-    '--enable-vm-service=$vmServicePort',
+    '--enable-vm-service=0',
     '--no-pause-isolates-on-exit',
     taskExecutable,
   ]);
@@ -41,10 +40,17 @@ Future<Map<String, dynamic>> runTask(String taskName, { bool silent = false }) a
     runnerFinished = true;
   });
 
+  final Completer<int> port = new Completer<int>();
+
   final StreamSubscription<String> stdoutSub = runner.stdout
       .transform(const Utf8Decoder())
       .transform(const LineSplitter())
       .listen((String line) {
+    if (!port.isCompleted) {
+      final int portValue = parseServicePort(line, prefix: 'Observatory listening on ');
+      if (portValue != null)
+        port.complete(portValue);
+    }
     if (!silent) {
       stdout.writeln('[$taskName] [STDOUT] $line');
     }
@@ -59,7 +65,7 @@ Future<Map<String, dynamic>> runTask(String taskName, { bool silent = false }) a
 
   String waitingFor = 'connection';
   try {
-    final VMIsolateRef isolate = await _connectToRunnerIsolate(vmServicePort);
+    final VMIsolateRef isolate = await _connectToRunnerIsolate(await port.future);
     waitingFor = 'task completion';
     final Map<String, dynamic> taskResult =
         await isolate.invokeExtension('ext.cocoonRunTask').timeout(taskTimeoutWithGracePeriod);

dev/devicelab/lib/framework/utils.dart

@@ -480,21 +480,6 @@ Future<Null> runAndCaptureAsyncStacks(Future<Null> callback()) {
   return completer.future;
 }
 
-/// Return an unused TCP port number.
-Future<int> findAvailablePort() async {
-  int port = 20000;
-  while (true) {
-    try {
-      final ServerSocket socket =
-          await ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, port); // ignore: deprecated_member_use
-      await socket.close();
-      return port;
-    } catch (_) {
-      port++;
-    }
-  }
-}
-
 bool canRun(String path) => _processManager.canRun(path);
 
 String extractCloudAuthTokenArg(List<String> rawArgs) {
@@ -517,13 +502,20 @@ String extractCloudAuthTokenArg(List<String> rawArgs) {
   return token;
 }
 
-// "An Observatory debugger and profiler on ... is available at: http://127.0.0.1:8100/"
-final RegExp _kObservatoryRegExp = new RegExp(r'An Observatory debugger .* is available at: (\S+:(\d+))');
-
-bool lineContainsServicePort(String line) => line.contains(_kObservatoryRegExp);
-
-int parseServicePort(String line) {
-  final Match match = _kObservatoryRegExp.firstMatch(line);
+/// Tries to extract a port from the string.
+///
+/// The `prefix`, if specified, is a regular expression pattern and must not contain groups.
+///
+/// The `multiLine` flag should be set to true if `line` is actually a buffer of many lines.
+int parseServicePort(String line, {
+  String prefix = 'An Observatory debugger .* is available at: ',
+  bool multiLine = false,
+}) {
+  // e.g. "An Observatory debugger and profiler on ... is available at: http://127.0.0.1:8100/"
+  final RegExp pattern = new RegExp('$prefix(\\S+:(\\d+)/\\S*)\$', multiLine: multiLine);
+  final Match match = pattern.firstMatch(line);
+  print(pattern);
+  print(match);
   return match == null ? null : int.parse(match.group(2));
 }
 

dev/devicelab/lib/tasks/perf_tests.dart

@@ -364,8 +364,6 @@ class MemoryTest {
       if (deviceOperatingSystem == DeviceOperatingSystem.ios)
         await prepareProvisioningCertificates(testDirectory);
 
-      final int observatoryPort = await findAvailablePort();
-
       final List<String> runOptions = <String>[
         '-v',
         '--profile',
@@ -373,11 +371,14 @@ class MemoryTest {
         '-d',
         deviceId,
         '--observatory-port',
-        observatoryPort.toString(),
+        '0',
       ];
       if (testTarget != null)
         runOptions.addAll(<String>['-t', testTarget]);
-      await flutter('run', options: runOptions);
+      final String output = await evalFlutter('run', options: runOptions);
+      final int observatoryPort = parseServicePort(output, prefix: 'Successfully connected to service protocol: ', multiLine: true);
+      if (observatoryPort == null)
+        throw new Exception('Could not find observatory port in "flutter run" output.');
 
       final Map<String, dynamic> startData = await device.getMemoryStats(packageName);
 

packages/flutter_tools/lib/src/android/android_device.dart

@@ -15,7 +15,6 @@ import '../base/common.dart' show throwToolExit;
 import '../base/file_system.dart';
 import '../base/io.dart';
 import '../base/logger.dart';
-import '../base/port_scanner.dart';
 import '../base/process.dart';
 import '../base/process_manager.dart';
 import '../base/utils.dart';
@@ -844,7 +843,7 @@ class _AndroidDevicePortForwarder extends DevicePortForwarder {
         final int devicePort = _extractPort(splitLine[2]);
 
         // Failed, skip.
-        if ((hostPort == null) || (devicePort == null))
+        if (hostPort == null || devicePort == null)
           continue;
 
         ports.add(new ForwardedPort(hostPort, devicePort));
@@ -855,16 +854,30 @@ class _AndroidDevicePortForwarder extends DevicePortForwarder {
   }
 
   @override
-  Future<int> forward(int devicePort, { int hostPort }) async {
-    if ((hostPort == null) || (hostPort == 0)) {
-      // Auto select host port.
-      hostPort = await portScanner.findAvailablePort();
-    }
-
-    await runCheckedAsync(device.adbCommandForDevice(
+  Future<int> forward(int devicePort, {int hostPort}) async {
+    hostPort ??= 0;
+    final RunResult process = await runCheckedAsync(device.adbCommandForDevice(
       <String>['forward', 'tcp:$hostPort', 'tcp:$devicePort']
     ));
 
+    if (process.stderr.isNotEmpty)
+      process.throwException('adb returned error:\n${process.stderr}');
+
+    if (process.exitCode != 0) {
+      if (process.stdout.isNotEmpty)
+        process.throwException('adb returned error:\n${process.stdout}');
+      process.throwException('adb failed without a message');
+    }
+
+    if (hostPort == 0) {
+      if (process.stdout.isEmpty)
+        process.throwException('adb did not report forwarded port');
+      hostPort = int.tryParse(process.stdout) ?? (throw 'adb returned invalid port number:\n${process.stdout}');
+    } else {
+      if (process.stdout.isNotEmpty)
+        process.throwException('adb returned error:\n${process.stdout}');
+    }
+
     return hostPort;
   }
 

packages/flutter_tools/lib/src/base/common.dart

@@ -5,8 +5,6 @@
 import 'file_system.dart';
 import 'platform.dart';
 
-const int kDefaultObservatoryPort = 8100;
-
 /// Return the absolute path of the user's home directory
 String get homeDirPath {
   if (_homeDirPath == null) {

packages/flutter_tools/lib/src/base/port_scanner.dart

-// Copyright 2017 The Chromium 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 'context.dart';
-import 'io.dart';
-
-const int _kMaxSearchIterations = 20;
-
-PortScanner get portScanner => context[PortScanner];
-
-abstract class PortScanner {
-  const PortScanner();
-
-  /// Returns true if the specified [port] is available to bind to.
-  Future<bool> isPortAvailable(int port);
-
-  /// Returns an available ephemeral port.
-  Future<int> findAvailablePort();
-
-  /// Returns an available port as close to [defaultPort] as possible.
-  ///
-  /// If [defaultPort] is available, this will return it. Otherwise, it will
-  /// search for an available port close to [defaultPort]. If it cannot find one,
-  /// it will return any available port.
-  Future<int> findPreferredPort(int defaultPort) async {
-    int iterationCount = 0;
-
-    while (iterationCount < _kMaxSearchIterations) {
-      final int port = defaultPort + iterationCount;
-      if (await isPortAvailable(port))
-        return port;
-      iterationCount++;
-    }
-
-    return findAvailablePort();
-  }
-}
-
-class HostPortScanner extends PortScanner {
-  const HostPortScanner();
-
-  @override
-  Future<bool> isPortAvailable(int port) async {
-    try {
-      // TODO(ianh): This is super racy.
-      final ServerSocket socket = await ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, port); // ignore: deprecated_member_use
-      await socket.close();
-      return true;
-    } catch (error) {
-      return false;
-    }
-  }
-
-  @override
-  Future<int> findAvailablePort() async {
-    ServerSocket socket;
-    try {
-      socket = await ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0); // ignore: deprecated_member_use
-    } on SocketException {
-      socket = await ServerSocket.bind(InternetAddress.LOOPBACK_IP_V6, 0, v6Only: true); // ignore: deprecated_member_use
-    }
-    final int port = socket.port;
-    await socket.close();
-    return port;
-  }
-}

packages/flutter_tools/lib/src/base/process.dart

@@ -229,7 +229,7 @@ Future<RunResult> runAsync(List<String> cmd, {
     workingDirectory: workingDirectory,
     environment: _environment(allowReentrantFlutter, environment),
   );
-  final RunResult runResults = new RunResult(results);
+  final RunResult runResults = new RunResult(results, cmd);
   printTrace(runResults.toString());
   return runResults;
 }
@@ -243,7 +243,7 @@ Future<RunResult> runCheckedAsync(List<String> cmd, {
     cmd,
     workingDirectory: workingDirectory,
     allowReentrantFlutter: allowReentrantFlutter,
-      environment: environment
+    environment: environment,
   );
   if (result.exitCode != 0)
     throw 'Exit code ${result.exitCode} from: ${cmd.join(' ')}:\n$result';
@@ -364,10 +364,12 @@ class ProcessExit implements Exception {
 }
 
 class RunResult {
-  RunResult(this.processResult);
+  RunResult(this.processResult, this._command) : assert(_command != null), assert(_command.isNotEmpty);
 
   final ProcessResult processResult;
 
+  final List<String> _command;
+
   int get exitCode => processResult.exitCode;
   String get stdout => processResult.stdout;
   String get stderr => processResult.stderr;
@@ -381,4 +383,14 @@ class RunResult {
       out.writeln(processResult.stderr);
     return out.toString().trimRight();
   }
+
+ /// Throws a [ProcessException] with the given `message`.
+ void throwException(String message) {
+    throw new ProcessException(
+      _command.first,
+      _command.skip(1).toList(),
+      message,
+      exitCode,
+    );
+  }
 }

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

@@ -55,8 +55,7 @@ abstract class RunCommandBase extends FlutterCommand {
   void usesPortOptions() {
     argParser.addOption('observatory-port',
         help: 'Listen to the given port for an observatory debugger connection.\n'
-              'Specifying port 0 will find a random free port.\n'
-              'Defaults to the first available port after $kDefaultObservatoryPort.'
+              'Specifying port 0 (the default) will find a random free port.'
     );
   }
 

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

@@ -16,14 +16,18 @@ import '../tracing.dart';
 class TraceCommand extends FlutterCommand {
   TraceCommand() {
     requiresPubspecYaml();
-    argParser.addFlag('start', negatable: false, help: 'Start tracing.');
-    argParser.addFlag('stop', negatable: false, help: 'Stop tracing.');
-    argParser.addOption('out', help: 'Specify the path of the saved trace file.');
-    argParser.addOption('duration',
-        defaultsTo: '10', abbr: 'd', help: 'Duration in seconds to trace.');
     argParser.addOption('debug-port',
-        defaultsTo: kDefaultObservatoryPort.toString(),
-        help: 'Local port where the observatory is listening.');
+      help: 'Local port where the observatory is listening. Required.',
+    );
+    argParser.addFlag('start', negatable: false, help: 'Start tracing. Implied if --stop is also omitted.');
+    argParser.addFlag('stop', negatable: false, help: 'Stop tracing. Implied if --start is also omitted.');
+    argParser.addOption('duration',
+      abbr: 'd',
+      help: 'Time to wait after starting (if --start is specified or implied) and before\n'
+            'stopping (if --stop is specified or implied).\n'
+            'Defaults to ten seconds if --stop is specified or implied, zero otherwise.',
+    );
+    argParser.addOption('out', help: 'Specify the path of the saved trace file.');
   }
 
   @override
@@ -34,13 +38,39 @@ class TraceCommand extends FlutterCommand {
 
   @override
   final String usageFooter =
-    '\`trace\` called with no arguments will automatically start tracing, delay a set amount of\n'
-    'time (controlled by --duration), and stop tracing. To explicitly control tracing, call trace\n'
-    'with --start and later with --stop.';
+    '\`trace\` called without the --start or --stop flags will automatically start tracing,\n'
+    'delay a set amount of time (controlled by --duration), and stop tracing. To explicitly\n'
+    'control tracing, call trace with --start and later with --stop.\n'
+    'The --debug-port argument is required.';
 
   @override
   Future<Null> runCommand() async {
-    final int observatoryPort = int.parse(argResults['debug-port']);
+    int observatoryPort;
+    if (argResults.wasParsed('debug-port')) {
+      observatoryPort = int.tryParse(argResults['debug-port']);
+    }
+    if (observatoryPort == null) {
+      throwToolExit('The --debug-port argument must be specified.');
+    }
+
+    bool start = argResults['start'];
+    bool stop = argResults['stop'];
+    if (!start && !stop) {
+      start = true;
+      stop = true;
+    }
+    assert(start || stop);
+
+    Duration duration;
+    if (argResults.wasParsed('duration')) {
+      try {
+        duration = new Duration(seconds: int.parse(argResults['duration']));
+      } on FormatException {
+        throwToolExit('Invalid duration passed to --duration; it should be a positive number of seconds.');
+      }
+    } else {
+      duration = stop ? const Duration(seconds: 10) : Duration.zero;
+    }
 
     // TODO(danrubel): this will break if we move to the new observatory URL
     // See https://github.com/flutter/flutter/issues/7038
@@ -56,20 +86,11 @@ class TraceCommand extends FlutterCommand {
 
     Cache.releaseLockEarly();
 
-    if ((!argResults['start'] && !argResults['stop']) ||
-        (argResults['start'] && argResults['stop'])) {
-      // Setting neither flags or both flags means do both commands and wait
-      // duration seconds in between.
+    if (start)
       await tracing.startTracing();
-      await new Future<Null>.delayed(
-        new Duration(seconds: int.parse(argResults['duration'])),
-        () => _stopTracing(tracing)
-      );
-    } else if (argResults['stop']) {
+    await new Future<Null>.delayed(duration);
+    if (stop)
       await _stopTracing(tracing);
-    } else {
-      await tracing.startTracing();
-    }
   }
 
   Future<Null> _stopTracing(Tracing tracing) async {

packages/flutter_tools/lib/src/context_runner.dart

@@ -19,7 +19,6 @@ import 'base/io.dart';
 import 'base/logger.dart';
 import 'base/os.dart';
 import 'base/platform.dart';
-import 'base/port_scanner.dart';
 import 'base/utils.dart';
 import 'cache.dart';
 import 'compile.dart';
@@ -70,7 +69,6 @@ Future<T> runInContext<T>(
       KernelCompiler: () => const KernelCompiler(),
       Logger: () => platform.isWindows ? new WindowsStdoutLogger() : new StdoutLogger(),
       OperatingSystemUtils: () => new OperatingSystemUtils(),
-      PortScanner: () => const HostPortScanner(),
       SimControl: () => new SimControl(),
       Stdio: () => const Stdio(),
       Usage: () => new Usage(),

packages/flutter_tools/lib/src/device.dart

@@ -7,10 +7,8 @@ import 'dart:math' as math;
 
 import 'android/android_device.dart';
 import 'application_package.dart';
-import 'base/common.dart';
 import 'base/context.dart';
 import 'base/file_system.dart';
-import 'base/port_scanner.dart';
 import 'base/utils.dart';
 import 'build_info.dart';
 import 'globals.dart';
@@ -367,14 +365,6 @@ class DebuggingOptions {
   final int observatoryPort;
 
   bool get hasObservatoryPort => observatoryPort != null;
-
-  /// Return the user specified observatory port. If that isn't available,
-  /// return [kDefaultObservatoryPort], or a port close to that one.
-  Future<int> findBestObservatoryPort() {
-    if (hasObservatoryPort)
-      return new Future<int>.value(observatoryPort);
-    return portScanner.findPreferredPort(observatoryPort ?? kDefaultObservatoryPort);
-  }
 }
 
 class LaunchResult {
@@ -414,9 +404,9 @@ abstract class DevicePortForwarder {
   List<ForwardedPort> get forwardedPorts;
 
   /// Forward [hostPort] on the host to [devicePort] on the device.
-  /// If [hostPort] is null, will auto select a host port.
+  /// If [hostPort] is null or zero, will auto select a host port.
   /// Returns a Future that completes with the host port.
-  Future<int> forward(int devicePort, { int hostPort });
+  Future<int> forward(int devicePort, {int hostPort});
 
   /// Stops forwarding [forwardedPort].
   Future<Null> unforward(ForwardedPort forwardedPort);

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

@@ -10,7 +10,6 @@ import '../base/file_system.dart';
 import '../base/io.dart';
 import '../base/logger.dart';
 import '../base/platform.dart';
-import '../base/port_scanner.dart';
 import '../base/process.dart';
 import '../base/process_manager.dart';
 import '../build_info.dart';
@@ -509,26 +508,40 @@ class _IOSDevicePortForwarder extends DevicePortForwarder {
 
   @override
   Future<int> forward(int devicePort, {int hostPort}) async {
-    if ((hostPort == null) || (hostPort == 0)) {
-      // Auto select host port.
-      hostPort = await portScanner.findAvailablePort();
-    }
+    final bool autoselect = hostPort == null || hostPort == 0;
+    if (autoselect)
+      hostPort = 1024;
+
+    Process process;
 
+    bool connected = false;
+    while (!connected) {
       // Usage: iproxy LOCAL_TCP_PORT DEVICE_TCP_PORT UDID
-    final Process process = await runCommand(<String>[
+      process = await runCommand(<String>[
         device._iproxyPath,
         hostPort.toString(),
         devicePort.toString(),
         device.id,
       ]);
+      connected = !await process.stdout.isEmpty;
+      if (!connected) {
+        if (autoselect) {
+          hostPort += 1;
+          if (hostPort > 65535)
+            throw 'Could not find open port on host.';
+        } else {
+          throw 'Port $hostPort is not available.';
+        }
+      }
+    }
+    assert(connected);
+    assert(process != null);
 
-    final ForwardedPort forwardedPort = new ForwardedPort.withContext(hostPort,
-        devicePort, process);
-
+    final ForwardedPort forwardedPort = new ForwardedPort.withContext(
+      hostPort, devicePort, process,
+    );
     printTrace('Forwarded port $forwardedPort');
-
     _forwardedPorts.add(forwardedPort);
-
     return hostPort;
   }
 

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

@@ -305,8 +305,7 @@ class IOSSimulator extends Device {
         args.add('--skia-deterministic-rendering');
       if (debuggingOptions.useTestFonts)
         args.add('--use-test-fonts');
-
-      final int observatoryPort = await debuggingOptions.findBestObservatoryPort();
+      final int observatoryPort = debuggingOptions.observatoryPort ?? 0;
       args.add('--observatory-port=$observatoryPort');
     }
 
@@ -693,7 +692,7 @@ class _IOSSimulatorDevicePortForwarder extends DevicePortForwarder {
 
   @override
   Future<int> forward(int devicePort, {int hostPort}) async {
-    if ((hostPort == null) || (hostPort == 0)) {
+    if (hostPort == null || hostPort == 0) {
       hostPort = devicePort;
     }
     assert(devicePort == hostPort);

packages/flutter_tools/lib/src/protocol_discovery.dart

@@ -4,9 +4,7 @@
 
 import 'dart:async';
 
-import 'base/common.dart';
 import 'base/io.dart';
-import 'base/port_scanner.dart';
 import 'device.dart';
 import 'globals.dart';
 
@@ -18,10 +16,8 @@ class ProtocolDiscovery {
     this.serviceName, {
     this.portForwarder,
     this.hostPort,
-    this.defaultHostPort,
     this.ipv6,
   }) : assert(logReader != null),
-       assert(portForwarder == null || defaultHostPort != null),
        _prefix = '$serviceName listening on ' {
     _deviceLogSubscription = logReader.logLines.listen(_handleLine);
   }
@@ -37,7 +33,6 @@ class ProtocolDiscovery {
       logReader, kObservatoryService,
       portForwarder: portForwarder,
       hostPort: hostPort,
-      defaultHostPort: kDefaultObservatoryPort,
       ipv6: ipv6,
     );
   }
@@ -46,7 +41,6 @@ class ProtocolDiscovery {
   final String serviceName;
   final DevicePortForwarder portForwarder;
   final int hostPort;
-  final int defaultHostPort;
   final bool ipv6;
 
   final String _prefix;
@@ -88,16 +82,15 @@ class ProtocolDiscovery {
     Uri hostUri = deviceUri;
 
     if (portForwarder != null) {
-      final int devicePort = deviceUri.port;
-      int hostPort = this.hostPort ?? await portScanner.findPreferredPort(defaultHostPort);
-      hostPort = await portForwarder.forward(devicePort, hostPort: hostPort);
-      printTrace('Forwarded host port $hostPort to device port $devicePort for $serviceName');
-      hostUri = deviceUri.replace(port: hostPort);
+      final int actualDevicePort = deviceUri.port;
+      final int actualHostPort = await portForwarder.forward(actualDevicePort, hostPort: hostPort);
+      printTrace('Forwarded host port $actualHostPort to device port $actualDevicePort for $serviceName');
+      hostUri = deviceUri.replace(port: actualHostPort);
     }
 
     assert(new InternetAddress(hostUri.host).isLoopback);
     if (ipv6) {
-      hostUri = hostUri.replace(host: InternetAddress.LOOPBACK_IP_V6.host); // ignore: deprecated_member_use
+      hostUri = hostUri.replace(host: InternetAddress.loopbackIPv6.host);
     }
 
     return hostUri;

packages/flutter_tools/lib/src/tester/flutter_tester.dart

@@ -122,8 +122,7 @@ class FlutterTesterDevice extends Device {
         command.add('--start-paused');
       }
       if (debuggingOptions.hasObservatoryPort)
-        command
-            .add('--observatory-port=${debuggingOptions.hasObservatoryPort}');
+        command.add('--observatory-port=${debuggingOptions.observatoryPort}');
     }
 
     // Build assets and perform initial compilation.
@@ -170,9 +169,10 @@ class FlutterTesterDevice extends Device {
       if (!debuggingOptions.debuggingEnabled)
         return new LaunchResult.succeeded();
 
-      final ProtocolDiscovery observatoryDiscovery =
-          new ProtocolDiscovery.observatory(getLogReader(),
-              hostPort: debuggingOptions.observatoryPort);
+      final ProtocolDiscovery observatoryDiscovery = new ProtocolDiscovery.observatory(
+        getLogReader(),
+        hostPort: debuggingOptions.observatoryPort,
+      );
 
       final Uri observatoryUri = await observatoryDiscovery.uri;
       return new LaunchResult.succeeded(observatoryUri: observatoryUri);

packages/flutter_tools/test/base/build_test.dart

@@ -381,7 +381,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'snapshot_assembly.S')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 
@@ -428,7 +428,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'snapshot_assembly.S')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 
@@ -476,7 +476,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'vm_snapshot_data')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 
@@ -528,7 +528,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'vm_snapshot_data')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 
@@ -575,7 +575,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'snapshot_assembly.S')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 
@@ -622,7 +622,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'snapshot_assembly.S')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 
@@ -689,7 +689,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'vm_snapshot_data')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 
@@ -741,7 +741,7 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '${fs.path.join(outputPath, 'vm_snapshot_data')} : ',
       };
 
-      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''), <String>['command name', 'arguments...']);
       when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
       when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
 

packages/flutter_tools/test/protocol_discovery_test.dart

@@ -117,14 +117,14 @@ void main() {
         final ProtocolDiscovery discoverer = new ProtocolDiscovery.observatory(
           logReader,
           portForwarder: new MockPortForwarder(99),
-            hostPort: 54777);
+        );
 
         // Get next port future.
         final Future<Uri> nextUri = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
         final Uri uri = await nextUri;
-        expect(uri.port, 54777);
-        expect('$uri', 'http://127.0.0.1:54777/PTwjm8Ii8qg=/');
+        expect(uri.port, 99);
+        expect('$uri', 'http://127.0.0.1:99/PTwjm8Ii8qg=/');
 
         discoverer.cancel();
         logReader.dispose();
@@ -135,7 +135,8 @@ void main() {
         final ProtocolDiscovery discoverer = new ProtocolDiscovery.observatory(
           logReader,
           portForwarder: new MockPortForwarder(99),
-            hostPort: 1243);
+          hostPort: 1243,
+        );
 
         // Get next port future.
         final Future<Uri> nextUri = discoverer.uri;
@@ -148,13 +149,33 @@ void main() {
         logReader.dispose();
       });
 
+      testUsingContext('specified port zero', () async {
+        final MockDeviceLogReader logReader = new MockDeviceLogReader();
+        final ProtocolDiscovery discoverer = new ProtocolDiscovery.observatory(
+          logReader,
+          portForwarder: new MockPortForwarder(99),
+          hostPort: 0,
+        );
+
+        // Get next port future.
+        final Future<Uri> nextUri = discoverer.uri;
+        logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
+        final Uri uri = await nextUri;
+        expect(uri.port, 99);
+        expect('$uri', 'http://127.0.0.1:99/PTwjm8Ii8qg=/');
+
+        discoverer.cancel();
+        logReader.dispose();
+      });
+
       testUsingContext('ipv6', () async {
         final MockDeviceLogReader logReader = new MockDeviceLogReader();
         final ProtocolDiscovery discoverer = new ProtocolDiscovery.observatory(
           logReader,
           portForwarder: new MockPortForwarder(99),
           hostPort: 54777,
-            ipv6: true);
+          ipv6: true,
+        );
 
         // Get next port future.
         final Future<Uri> nextUri = discoverer.uri;
@@ -175,7 +196,12 @@ class MockPortForwarder extends DevicePortForwarder {
   MockPortForwarder([this.availablePort]);
 
   @override
-  Future<int> forward(int devicePort, {int hostPort}) async => hostPort ?? availablePort;
+  Future<int> forward(int devicePort, {int hostPort}) async {
+    hostPort ??= 0;
+    if (hostPort == 0)
+      return availablePort;
+    return hostPort;
+  }
 
   @override
   List<ForwardedPort> get forwardedPorts => throw 'not implemented';

packages/flutter_tools/test/src/context.dart

@@ -12,7 +12,6 @@ import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/os.dart';
-import 'package:flutter_tools/src/base/port_scanner.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/context_runner.dart';
 import 'package:flutter_tools/src/device.dart';
@@ -77,7 +76,6 @@ void testUsingContext(String description, dynamic testMethod(), {
           },
           Logger: () => new BufferLogger(),
           OperatingSystemUtils: () => new MockOperatingSystemUtils(),
-          PortScanner: () => new MockPortScanner(),
           SimControl: () => new MockSimControl(),
           Usage: () => new MockUsage(),
           XcodeProjectInterpreter: () => new MockXcodeProjectInterpreter(),
@@ -127,16 +125,6 @@ void _printBufferedErrors(AppContext testContext) {
   }
 }
 
-class MockPortScanner extends PortScanner {
-  static int _nextAvailablePort = 12345;
-
-  @override
-  Future<bool> isPortAvailable(int port) async => true;
-
-  @override
-  Future<int> findAvailablePort() async => _nextAvailablePort++;
-}
-
 class MockDeviceManager implements DeviceManager {
   List<Device> devices = <Device>[];
 

packages/flutter_tools/test/vmservice_test.dart

@@ -4,7 +4,6 @@
 
 import 'package:test/test.dart';
 
-import 'package:flutter_tools/src/base/port_scanner.dart';
 import 'package:flutter_tools/src/vmservice.dart';
 
 import 'src/common.dart';
@@ -13,9 +12,8 @@ import 'src/context.dart';
 void main() {
   group('VMService', () {
     testUsingContext('fails connection eagerly in the connect() method', () async {
-      final int port = await const HostPortScanner().findAvailablePort();
       expect(
-        VMService.connect(Uri.parse('http://localhost:$port')),
+        VMService.connect(Uri.parse('http://host.invalid:9999/')),
         throwsToolExit(),
       );
     });