Repository: google/mobly

Issue:
Zombie port on host when `AndroidDevice.handle_usb_disconnect` is used
In `AndroidDevice.handle_usb_disconnect`, we never explicitly stop snippet client's port forwarding.
Then during service restoration, a new host port is allocated for the snippet client.

This causes leftover ports in adb port forwarding, which on rare occasions can trigger an adb bug where `adb forward --list` command fails, which crashes Mobly.


Discussion:

Resolving patch:
diff --git a/mobly/controllers/android_device_lib/service_manager.py b/mobly/controllers/android_device_lib/service_manager.py
--- a/mobly/controllers/android_device_lib/service_manager.py
+++ b/mobly/controllers/android_device_lib/service_manager.py
@@ -106,18 +106,16 @@ def stop_all(self):
     def pause_all(self):
         """Pauses all active service instances."""
         for alias, service in self._service_objects.items():
-            if service.is_alive:
-                with expects.expect_no_raises(
-                        'Failed to pause service "%s".' % alias):
-                    service.pause()
+            with expects.expect_no_raises(
+                    'Failed to pause service "%s".' % alias):
+                service.pause()
 
     def resume_all(self):
         """Resumes all paused service instances."""
         for alias, service in self._service_objects.items():
-            if not service.is_alive:
-                with expects.expect_no_raises(
-                        'Failed to pause service "%s".' % alias):
-                    service.resume()
+            with expects.expect_no_raises(
+                    'Failed to pause service "%s".' % alias):
+                service.resume()
 
     def __getattr__(self, name):
         """Syntactic sugar to enable direct access of service objects by alias.
diff --git a/mobly/controllers/android_device_lib/services/snippet_management_service.py b/mobly/controllers/android_device_lib/services/snippet_management_service.py
--- a/mobly/controllers/android_device_lib/services/snippet_management_service.py
+++ b/mobly/controllers/android_device_lib/services/snippet_management_service.py
@@ -104,27 +104,50 @@ def start(self):
         """Starts all the snippet clients under management."""
         for client in self._snippet_clients.values():
             if not client.is_alive:
+                self._device.log.debug('Starting SnippetClient<%s>.',
+                                       client.package)
                 client.start_app_and_connect()
+            else:
+                self._device.log.debug(
+                    'Not startng SnippetClient<%s> because it is already alive.',
+                    client.package)
 
     def stop(self):
         """Stops all the snippet clients under management."""
         for client in self._snippet_clients.values():
             if client.is_alive:
+                self._device.log.debug('Stopping SnippetClient<%s>.',
+                                       client.package)
                 client.stop_app()
+            else:
+                self._device.log.debug(
+                    'Not stopping SnippetClient<%s> because it is not alive.',
+                    client.package)
 
     def pause(self):
-        """Intentionally no-op.
+        """Pauses all the snippet clients under management.
 
-        No action on the client side is needed per current snippet clients
-        design. Because snippet clients do not explicitly handle temporary
-        disconnect (Issue #509).
+        This clears the host port of a client because a new port will be
+        allocated in `resume`.
         """
+        for client in self._snippet_clients.values():
+            self._device.log.debug(
+                'Clearing host port %d of SnippetClient<%s>.',
+                client.host_port, client.package)
+            client.clear_host_port()
 
     def resume(self):
         """Resumes all paused snippet clients."""
         for client in self._snippet_clients.values():
-            if not client.is_alive:
+            # Resume is only applicable if a client is alive and does not have
+            # a host port.
+            if client.is_alive and client.host_port is None:
+                self._device.log.debug('Resuming SnippetClient<%s>.',
+                                       client.package)
                 client.restore_app_connection()
+            else:
+                self._device.log.debug('Not resuming SnippetClient<%s>.',
+                                       client.package)
 
     def __getattr__(self, name):
         client = self.get_snippet_client(name)
diff --git a/mobly/controllers/android_device_lib/snippet_client.py b/mobly/controllers/android_device_lib/snippet_client.py
--- a/mobly/controllers/android_device_lib/snippet_client.py
+++ b/mobly/controllers/android_device_lib/snippet_client.py
@@ -236,8 +236,14 @@ def stop_app(self):
                     'Failed to stop existing apk. Unexpected output: %s' % out)
         finally:
             # Always clean up the adb port
-            if self.host_port:
-                self._adb.forward(['--remove', 'tcp:%d' % self.host_port])
+            self.clear_host_port()
+
+    def clear_host_port(self):
+        """Stops the adb port forwarding of the host port used by this client.
+        """
+        if self.host_port:
+            self._adb.forward(['--remove', 'tcp:%d' % self.host_port])
+            self.host_port = None
 
     def _start_event_client(self):
         """Overrides superclass."""


Test patch:
diff --git a/tests/mobly/controllers/android_device_lib/service_manager_test.py b/tests/mobly/controllers/android_device_lib/service_manager_test.py
--- a/tests/mobly/controllers/android_device_lib/service_manager_test.py
+++ b/tests/mobly/controllers/android_device_lib/service_manager_test.py
@@ -25,6 +25,8 @@ def __init__(self, device, configs=None):
         self._device = device
         self._configs = configs
         self._alive = False
+        self.is_pause_called = False
+        self.is_resume_called = False
 
     @property
     def is_alive(self):
@@ -38,15 +40,19 @@ def stop(self):
         self._alive = False
         self._device.stop()
 
+    def pause(self):
+        self.is_pause_called = True
+
+    def resume(self):
+        self.is_resume_called = True
+
 
 class ServiceManagerTest(unittest.TestCase):
     def test_service_manager_instantiation(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
 
     def test_register(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service', MockService)
         service = manager.mock_service
         self.assertTrue(service)
@@ -54,16 +60,14 @@ def test_register(self):
         self.assertTrue(manager.is_any_alive)
 
     def test_register_dup_alias(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service', MockService)
         msg = '.* A service is already registered with alias "mock_service"'
         with self.assertRaisesRegex(service_manager.Error, msg):
             manager.register('mock_service', MockService)
 
     def test_unregister(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service', MockService)
         service = manager.mock_service
         manager.unregister('mock_service')
@@ -71,8 +75,7 @@ def test_unregister(self):
         self.assertFalse(service.is_alive)
 
     def test_unregister_non_existent(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         with self.assertRaisesRegex(
                 service_manager.Error,
                 '.* No service is registered with alias "mock_service"'):
@@ -80,8 +83,7 @@ def test_unregister_non_existent(self):
 
     @mock.patch('mobly.expects.expect_no_raises')
     def test_unregister_handle_error_from_stop(self, mock_expect_func):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service', MockService)
         service = manager.mock_service
         service._device.stop.side_deffect = Exception(
@@ -91,8 +93,7 @@ def test_unregister_handle_error_from_stop(self, mock_expect_func):
             'Failed to stop service instance "mock_service".')
 
     def test_unregister_all(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service1', MockService)
         manager.register('mock_service2', MockService)
         service1 = manager.mock_service1
@@ -103,8 +104,7 @@ def test_unregister_all(self):
         self.assertFalse(service2.is_alive)
 
     def test_unregister_all(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service1', MockService)
         manager.register('mock_service2', MockService)
         service1 = manager.mock_service1
@@ -115,8 +115,7 @@ def test_unregister_all(self):
         self.assertFalse(service2.is_alive)
 
     def test_unregister_all_with_some_failed(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service1', MockService)
         manager.register('mock_service2', MockService)
         service1 = manager.mock_service1
@@ -129,60 +128,54 @@ def test_unregister_all_with_some_failed(self):
         self.assertFalse(service2.is_alive)
 
     def test_pause_all(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service1', MockService)
         manager.register('mock_service2', MockService)
         service1 = manager.mock_service1
         service2 = manager.mock_service2
         manager.pause_all()
-        self.assertFalse(manager.is_any_alive)
-        self.assertFalse(service1.is_alive)
-        self.assertFalse(service2.is_alive)
+        self.assertTrue(service1.is_pause_called)
+        self.assertTrue(service2.is_pause_called)
+        self.assertFalse(service1.is_resume_called)
+        self.assertFalse(service2.is_resume_called)
 
     def test_pause_all_with_some_failed(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service1', MockService)
         manager.register('mock_service2', MockService)
         service1 = manager.mock_service1
         service1._device.pause.side_deffect = Exception(
-            'Something failed in stop.')
+            'Something failed in pause.')
         service2 = manager.mock_service2
         manager.pause_all()
-        self.assertFalse(manager.is_any_alive)
-        # state of service1 is undefined
-        # verify state of service2
-        self.assertFalse(service2.is_alive)
+        self.assertTrue(service2.is_pause_called)
+        self.assertFalse(service1.is_resume_called)
+        self.assertFalse(service2.is_resume_called)
 
     def test_resume_all(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service1', MockService)
         manager.register('mock_service2', MockService)
         service1 = manager.mock_service1
         service2 = manager.mock_service2
         manager.pause_all()
         manager.resume_all()
-        self.assertTrue(manager.is_any_alive)
-        self.assertTrue(service1.is_alive)
-        self.assertTrue(service2.is_alive)
+        self.assertTrue(service1.is_resume_called)
+        self.assertTrue(service1.is_pause_called)
+        self.assertTrue(service2.is_resume_called)
+        self.assertTrue(service2.is_pause_called)
 
     def test_resume_all_with_some_failed(self):
-        mock_device = mock.MagicMock()
-        manager = service_manager.ServiceManager(mock_device)
+        manager = service_manager.ServiceManager(mock.MagicMock())
         manager.register('mock_service1', MockService)
         manager.register('mock_service2', MockService)
         service1 = manager.mock_service1
         service1._device.resume.side_deffect = Exception(
-            'Something failed in stop.')
+            'Something failed in resume.')
         service2 = manager.mock_service2
         manager.pause_all()
         manager.resume_all()
-        self.assertTrue(manager.is_any_alive)
-        # state of service1 is undefined
-        # verify state of service2
-        self.assertTrue(service2.is_alive)
+        self.assertTrue(service2.is_resume_called)
 
 
 if __name__ == '__main__':
diff --git a/tests/mobly/controllers/android_device_lib/services/snippet_management_service_test.py b/tests/mobly/controllers/android_device_lib/services/snippet_management_service_test.py
--- a/tests/mobly/controllers/android_device_lib/services/snippet_management_service_test.py
+++ b/tests/mobly/controllers/android_device_lib/services/snippet_management_service_test.py
@@ -122,17 +122,46 @@ def test_start_with_live_service(self, mock_class):
         mock_client.start_app_and_connect.assert_called_once_with()
 
     @mock.patch(SNIPPET_CLIENT_CLASS_PATH)
-    def test_resume(self, mock_class):
+    def test_pause(self, mock_class):
+        mock_client = mock_class.return_value
+        manager = snippet_management_service.SnippetManagementService(
+            mock.MagicMock())
+        manager.add_snippet_client('foo', MOCK_PACKAGE)
+        manager.pause()
+        mock_client.clear_host_port.assert_called_once_with()
+
+    @mock.patch(SNIPPET_CLIENT_CLASS_PATH)
+    def test_resume_positive_case(self, mock_class):
         mock_client = mock_class.return_value
         manager = snippet_management_service.SnippetManagementService(
             mock.MagicMock())
         manager.add_snippet_client('foo', MOCK_PACKAGE)
         mock_client.is_alive = True
+        mock_client.host_port = None
+        manager.resume()
+        mock_client.restore_app_connection.assert_called_once_with()
+
+    @mock.patch(SNIPPET_CLIENT_CLASS_PATH)
+    def test_resume_alive_with_host_port(self, mock_class):
+        mock_client = mock_class.return_value
+        manager = snippet_management_service.SnippetManagementService(
+            mock.MagicMock())
+        manager.add_snippet_client('foo', MOCK_PACKAGE)
+        mock_client.is_alive = True
+        mock_client.host_port = 1
         manager.resume()
         mock_client.restore_app_connection.assert_not_called()
+
+    @mock.patch(SNIPPET_CLIENT_CLASS_PATH)
+    def test_resume_not_alive_no_host_port(self, mock_class):
+        mock_client = mock_class.return_value
+        manager = snippet_management_service.SnippetManagementService(
+            mock.MagicMock())
+        manager.add_snippet_client('foo', MOCK_PACKAGE)
         mock_client.is_alive = False
+        mock_client.host_port = None
         manager.resume()
-        mock_client.restore_app_connection.assert_called_once_with()
+        mock_client.restore_app_connection.assert_not_called()
 
     @mock.patch(SNIPPET_CLIENT_CLASS_PATH)
     def test_attribute_access(self, mock_class):