[feature] Use SIGUSR1 to update configuration on device openwisp#478

Use SIGUSR1 signal if the openwisp-config version is higher than 0.6.0a.
The old behavior is maintained for old versions. 

Closes openwisp#478

openwisp_controller/connection/connectors/openwrt/ssh.py

@@ -1,12 +1,36 @@
 import logging
 
+from packaging import version
+
 from ..ssh import Ssh
 
 logger = logging.getLogger(__name__)
 
 
 class OpenWrt(Ssh):
     def update_config(self):
+        try:
+            output, exit_code = self.exec_command('openwisp_config --version')
+        except Exception as error:
+            logger.error('Unable to get version of openwisp_config')
+            raise error
+        else:
+            ow_config_version = output.split(' ')[-1]
+            if version.parse(ow_config_version) >= version.parse('0.6.0a'):
+                self.exec_signal_reload()
+            else:
+                self.exec_legacy_restart()
+
+    def exec_signal_reload(self):
+        self.exec_command(
+            (
+                'OW_CONFIG_PID=$(ps | grep "openwisp_config" | '
+                'grep -v "grep" | awk \'{print $1}\'); '
+                'kill -SIGUSR1 $OW_CONFIG_PID'
+            )
+        )
+
+    def exec_legacy_restart(self):
         _, exit_code = self.exec_command(
             'test -f /tmp/openwisp/applying_conf', exit_codes=[0, 1]
         )

openwisp_controller/connection/tests/test_models.py

@@ -739,27 +739,77 @@ def test_device_config_created(self, mocked_sleep, mocked_connect):
     @mock.patch(_connect_path)
     @mock.patch('time.sleep')
     def test_device_config_update(self, mocked_sleep, mocked_connect):
+        def _assert_version_check_command(mocked_exec):
+            args, _ = mocked_exec.call_args_list[0]
+            self.assertEqual(args[0], 'openwisp_config --version')
+
+        def _assert_applying_conf_test_command(mocked_exec):
+            args, _ = mocked_exec_command.call_args_list[1]
+            self.assertEqual(
+                args[0], 'test -f /tmp/openwisp/applying_conf',
+            )
+
         conf = self._prepare_conf_object()
 
-        with self.subTest('exit_code 0'):
+        with self.subTest('Unable to get openwisp_config version'):
             with mock.patch(_exec_command_path) as mocked_exec_command:
-                mocked_exec_command.return_value = self._exec_command_return_value()
+                mocked_exec_command.return_value = self._exec_command_return_value(
+                    exit_code=1
+                )
                 conf.save()
-                mocked_exec_command.assert_called_once()
+                self.assertEqual(mocked_exec_command.call_count, 1)
+                _assert_version_check_command(mocked_exec_command)
+            conf.refresh_from_db()
+            self.assertEqual(conf.status, 'modified')
 
+        with self.subTest('openwisp_config >= 0.6.0a'):
+            conf.config = '{"dns_servers": []}'
+            conf.full_clean()
+            with mock.patch(_exec_command_path) as mocked_exec_command:
+                mocked_exec_command.return_value = self._exec_command_return_value(
+                    stdout='openwisp_config 0.6.0a'
+                )
+                conf.save()
+                self.assertEqual(mocked_exec_command.call_count, 2)
+                _assert_version_check_command(mocked_exec_command)
+                args, _ = mocked_exec_command.call_args_list[1]
+                self.assertIn('OW_CONFIG_PID', args[0])
             conf.refresh_from_db()
             self.assertEqual(conf.status, 'applied')
 
-        with self.subTest('exit_code 1'):
+        with self.subTest('openwisp_config < 0.6.0a: exit_code 0'):
             conf.config = '{"interfaces": []}'
             conf.full_clean()
             with mock.patch(_exec_command_path) as mocked_exec_command:
                 mocked_exec_command.return_value = self._exec_command_return_value(
-                    exit_code=1
+                    stdout='openwisp_config 0.5.0'
                 )
                 conf.save()
                 self.assertEqual(mocked_exec_command.call_count, 2)
+                _assert_version_check_command(mocked_exec_command)
+                _assert_applying_conf_test_command(mocked_exec_command)
+            conf.refresh_from_db()
+            self.assertEqual(conf.status, 'applied')
 
+        with self.subTest('openwisp_config < 0.6.0a: exit_code 1'):
+            conf.config = '{"radios": []}'
+            conf.full_clean()
+            with mock.patch(_exec_command_path) as mocked_exec_command:
+                stdin, stdout, stderr = self._exec_command_return_value(
+                    stdout='openwisp_config 0.5.0'
+                )
+                # An iterable side effect is required for different exit codes:
+                # 1. Checking openwisp_config returns with 0
+                # 2. Testing presence of /tmp/openwisp/applying_conf returns with 1
+                # 3. Restarting openwisp_config returns with 0 exit code
+                stdout.channel.recv_exit_status.side_effect = [0, 1, 1]
+                mocked_exec_command.return_value = (stdin, stdout, stderr)
+                conf.save()
+                self.assertEqual(mocked_exec_command.call_count, 3)
+                _assert_version_check_command(mocked_exec_command)
+                _assert_applying_conf_test_command(mocked_exec_command)
+                args, _ = mocked_exec_command.call_args_list[2]
+                self.assertEqual(args[0], '/etc/init.d/openwisp_config restart')
             conf.refresh_from_db()
             # exit code 1 considers the update not successful
             self.assertEqual(conf.status, 'modified')