Add support for log commands on iOS.

packages/flutter_tools/lib/src/device.dart

@@ -89,6 +89,9 @@ class IOSDevice extends _Device {
   String _debuggerPath;
   String get debuggerPath => _debuggerPath;
 
+  String _loggerPath;
+  String get loggerPath => _loggerPath;
+
   String _name;
   String get name => _name;
 
@@ -103,6 +106,7 @@ class IOSDevice extends _Device {
     _listerPath = _checkForCommand('idevice_id');
     _informerPath = _checkForCommand('ideviceinfo');
     _debuggerPath = _checkForCommand('idevicedebug');
+    _loggerPath = _checkForCommand('idevicesyslog');
   }
 
   static List<IOSDevice> getAttachedDevices([IOSDevice mockIOS]) {
@@ -203,6 +207,11 @@ class IOSDevice extends _Device {
     // Currently we don't have a way to stop an app running on iOS.
     return false;
   }
+
+  Future<int> logs({bool clear: false}) {
+    return runCommandAndStreamOutput([loggerPath],
+        prefix: 'IOS DEV: ', filter: new RegExp(r'.*SkyShell.*'));
+  }
 }
 
 class AndroidDevice extends _Device {

packages/flutter_tools/lib/src/logs.dart

@@ -15,9 +15,10 @@ final Logger _logging = new Logger('sky_tools.logs');
 class LogsCommand extends Command {
   final name = 'logs';
   final description = 'Show logs for running Sky apps.';
-  AndroidDevice android = null;
+  AndroidDevice android;
+  IOSDevice ios;
 
-  LogsCommand([this.android]) {
+  LogsCommand({this.android, this.ios}) {
     argParser.addFlag('clear',
         negatable: false,
         help: 'Clear log history before reading from logs (Android only).');
@@ -28,16 +29,28 @@ class LogsCommand extends Command {
     if (android == null) {
       android = new AndroidDevice();
     }
+    if (ios == null) {
+      ios = new IOSDevice();
+    }
 
     Future<int> androidLogProcess = null;
     if (android.isConnected()) {
       androidLogProcess = android.logs(clear: argResults['clear']);
     }
 
+    Future<int> iosLogProcess = null;
+    if (ios.isConnected()) {
+      iosLogProcess = ios.logs(clear: argResults['clear']);
+    }
+
     if (androidLogProcess != null) {
       await androidLogProcess;
     }
 
+    if (iosLogProcess != null) {
+      await iosLogProcess;
+    }
+
     return 0;
   }
 }

packages/flutter_tools/lib/src/process.dart

@@ -15,15 +15,27 @@ final Logger _logging = new Logger('sky_tools.process');
 /// This runs the command and streams stdout/stderr from the child process to
 /// this process' stdout/stderr.
 Future<int> runCommandAndStreamOutput(List<String> cmd,
-    {String prefix: ''}) async {
+    {String prefix: '', RegExp filter}) async {
   _logging.info(cmd.join(' '));
   Process proc =
       await Process.start(cmd[0], cmd.getRange(1, cmd.length).toList());
-  proc.stdout.transform(UTF8.decoder).listen((data) {
-    stdout.write('$prefix${data.trimRight().split('\n').join('\n$prefix')}\n');
+  proc.stdout.transform(UTF8.decoder).listen((String data) {
+    List<String> dataLines = data.trimRight().split('\n');
+    if (filter != null) {
+      dataLines = dataLines.where((String s) => filter.hasMatch(s));
+    }
+    if (dataLines.length > 0) {
+      stdout.write('$prefix${dataLines.join('\n$prefix')}\n');
+    }
   });
-  proc.stderr.transform(UTF8.decoder).listen((data) {
-    stderr.write('$prefix${data.trimRight().split('\n').join('\n$prefix')}\n');
+  proc.stderr.transform(UTF8.decoder).listen((String data) {
+    List<String> dataLines = data.trimRight().split('\n');
+    if (filter != null) {
+      dataLines = dataLines.where((String s) => filter.hasMatch(s));
+    }
+    if (dataLines.length > 0) {
+      stderr.write('$prefix${dataLines.join('\n$prefix')}\n');
+    }
   });
   return proc.exitCode;
 }

packages/flutter_tools/test/logs_test.dart

@@ -20,7 +20,10 @@ defineTests() {
 
       MockAndroidDevice android = new MockAndroidDevice();
       when(android.isConnected()).thenReturn(false);
-      LogsCommand command = new LogsCommand(android);
+      MockIOSDevice ios = new MockIOSDevice();
+      when(ios.isConnected()).thenReturn(false);
+
+      LogsCommand command = new LogsCommand(android: android, ios: ios);
 
       CommandRunner runner = new CommandRunner('test_flutter', '')
         ..addCommand(command);