daemon: Added method to ensure a daemon is running in component

This will help apps like zoph that need to have database server running to
install or upgrade a package.

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

plinth/daemon.py

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 """Component for managing a background daemon or any systemd unit."""
 
+import contextlib
 import socket
 import subprocess
 
@@ -86,6 +87,20 @@ class Daemon(app.LeaderComponent):
         """Return whether the daemon/unit is running."""
         return action_utils.service_is_running(self.unit)
 
+    @contextlib.contextmanager
+    def ensure_running(self):
+        """Ensure a service is running and return to previous state."""
+        from plinth.privileged import service as service_privileged
+        starting_state = self.is_running()
+        if not starting_state:
+            service_privileged.enable(self.unit)
+
+        try:
+            yield starting_state
+        finally:
+            if not starting_state:
+                service_privileged.disable(self.unit)
+
     def diagnose(self) -> list[DiagnosticCheck]:
         """Check if the daemon is running and listening on expected ports.
 

plinth/tests/test_daemon.py

@@ -138,6 +138,44 @@ def test_is_running(service_is_running, daemon):
     assert not daemon.is_running()
 
 
+@patch('plinth.app.apps_init')
+@patch('plinth.action_utils.service_is_running')
+@patch('subprocess.run')
+@patch('subprocess.call')
+def test_ensure_running(subprocess_call, subprocess_run, service_is_running,
+                        apps_init, app_list, mock_privileged, daemon):
+    """Test that checking that the daemon is running works."""
+    service_is_running.return_value = True
+    with daemon.ensure_running() as starting_state:
+        assert starting_state
+        assert not subprocess_call.called
+        assert not subprocess_run.called
+
+    assert not subprocess_call.called
+    assert not subprocess_run.called
+
+    service_is_running.return_value = False
+    with daemon.ensure_running() as starting_state:
+        assert not starting_state
+        assert subprocess_run.mock_calls == [
+            call(['systemctl', 'start', 'test-unit'],
+                 stdout=subprocess.DEVNULL, check=False)
+        ]
+        assert subprocess_call.mock_calls == [
+            call(['systemctl', 'enable', 'test-unit'])
+        ]
+        subprocess_run.reset_mock()
+        subprocess_call.reset_mock()
+
+    assert subprocess_run.mock_calls == [
+        call(['systemctl', 'stop', 'test-unit'], stdout=subprocess.DEVNULL,
+             check=False)
+    ]
+    assert subprocess_call.mock_calls == [
+        call(['systemctl', 'disable', 'test-unit'])
+    ]
+
+
 @patch('plinth.action_utils.service_is_running')
 @patch('plinth.daemon.diagnose_port_listening')
 def test_diagnose(port_listening, service_is_running, daemon):