daemon: Implement diagnostic test for daemon component

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

doc/dev/tutorial/components.rst

@@ -26,14 +26,17 @@ our app's class.
       def __init__(self):
         ...
 
-        daemon = Daemon('daemon-transmission', managed_services[0])
+        daemon = Daemon('daemon-transmission', managed_services[0],
+                        listen_ports=[(9091, 'tcp4')])
         self.add(daemon)
 
 
 The first argument to instantiate the :class:`~plinth.daemon.Daemon` class is a
 unique ID. The second is the name of the `systemd
 <https://www.freedesktop.org/wiki/Software/systemd/>`_ unit file which manages
-the daemon.
+the daemon. The final argument is the list of ports that this daemon listens on.
+This information is used to check if the daemon is listening on the expected
+ports when the user requests diagnostic tests on the app.
 
 Managing web server configuration
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

plinth/daemon.py

@@ -23,7 +23,8 @@ from plinth import action_utils, actions, app
 
 class Daemon(app.LeaderComponent):
     """Component to manage a background daemon or any systemd unit."""
-    def __init__(self, component_id, unit, strict_check=False):
+    def __init__(self, component_id, unit, strict_check=False,
+                 listen_ports=None):
         """Initialize a new daemon component.
 
         'component_id' must be a unique string across all apps and components
@@ -31,11 +32,17 @@ class Daemon(app.LeaderComponent):
 
         'unit' must the name of systemd unit that this component should manage.
 
+        'listen_ports' is a list of tuples. Each tuple contains the port number
+        as integer followed by a string with one of the values 'tcp4', 'tcp6',
+        'tcp', 'udp4', 'udp6', 'udp' indicating the protocol that the daemon
+        listens on. This information is used to run diagnostic tests.
+
         """
         super().__init__(component_id)
 
         self.unit = unit
         self.strict_check = strict_check
+        self.listen_ports = listen_ports or []
 
     def is_enabled(self):
         """Return if the daemon/unit is enabled."""
@@ -54,6 +61,15 @@ class Daemon(app.LeaderComponent):
         """Return whether the daemon/unit is running."""
         return action_utils.service_is_running(self.unit)
 
+    def diagnose(self):
+        """Check if the daemon is listening on expected ports."""
+        results = []
+        for port in self.listen_ports:
+            results.append(
+                action_utils.diagnose_port_listening(port[0], port[1]))
+
+        return results
+
 
 def app_is_running(app_):
     """Return whether all the daemons in the app are running."""

plinth/tests/test_daemon.py

@@ -41,9 +41,13 @@ def test_initialization():
     assert daemon.component_id == 'test-daemon'
     assert daemon.unit == 'test-unit'
     assert not daemon.strict_check
+    assert daemon.listen_ports == []
 
-    daemon = Daemon('test-daemon', 'test-unit', strict_check=True)
+    listen_ports = [(345, 'tcp4'), (123, 'udp')]
+    daemon = Daemon('test-daemon', 'test-unit', strict_check=True,
+                    listen_ports=listen_ports)
     assert daemon.strict_check
+    assert daemon.listen_ports == listen_ports
 
 
 @patch('plinth.action_utils.service_is_enabled')
@@ -88,6 +92,22 @@ def test_is_running(service_is_running, daemon):
     assert not daemon.is_running()
 
 
+@patch('plinth.action_utils.diagnose_port_listening')
+def test_diagnose(diagnose_port_listening, daemon):
+    """Test running diagnostics."""
+    def side_effect(port, kind):
+        return [f'test-result-{port}-{kind}', 'passed']
+
+    daemon = Daemon('test-daemon', 'test-unit', listen_ports=[(8273, 'tcp4'),
+                                                              (345, 'udp')])
+    diagnose_port_listening.side_effect = side_effect
+    results = daemon.diagnose()
+    assert results == [['test-result-8273-tcp4', 'passed'],
+                       ['test-result-345-udp', 'passed']]
+    diagnose_port_listening.assert_has_calls(
+        [call(8273, 'tcp4'), call(345, 'udp')])
+
+
 @patch('plinth.action_utils.service_is_running')
 def test_app_is_running(service_is_running):
     """Test that checking whether app is running works."""