names: Schedule a task to install systemd-resolved when possible

- Don't schedule if the package is already installed.

Tests:

- With systemd-resolved installed and without internet connectivity start a
fresh instance (without first setup). Setup succeeds but systemd-resolved is not
installed.

- Wait in develop mode for 180 seconds. Setup for names app is re-run. Ensure
that internet connectivity is not available and systemd-package is not
installed. Setup still succeeds.

- On next run, ensure that internet connectivity is available, systemd-resolved
is installed. Setup succeeds.

- On next run, setup is not re-run for names app.

- When service is restarted, the task is not even scheduled.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Veiko Aasa <veiko17@disroot.org>

plinth/modules/names/__init__.py

@@ -12,7 +12,7 @@ from django.utils.translation import gettext_lazy as _
 from django.utils.translation import gettext_noop
 
 from plinth import app as app_module
-from plinth import cfg, menu, network
+from plinth import cfg, glib, menu, network, setup
 from plinth.daemon import Daemon
 from plinth.diagnostic_check import (DiagnosticCheck,
                                      DiagnosticCheckParameters, Result)
@@ -90,6 +90,11 @@ class NamesApp(app_module.App):
                                      domain_type='domain-type-static',
                                      name=domain_name, services='__all__')
 
+        # Schedule installation of systemd-resolved if not already installed.
+        if not is_resolved_installed():
+            # Try to install the package hourly.
+            glib.schedule(3600, install_systemd_resolved)
+
     def diagnose(self) -> list[DiagnosticCheck]:
         """Run diagnostics and return the results."""
         results = super().diagnose()
@@ -171,6 +176,12 @@ class ResolvedDaemon(Daemon):
         return super().diagnose()
 
 
+def install_systemd_resolved(_data):
+    """Re-run setup on app to install systemd-resolved."""
+    if not is_resolved_installed():
+        setup.run_setup_on_app('names', rerun=True)
+
+
 def diagnose_resolution(domain: str) -> DiagnosticCheck:
     """Perform a diagnostic check for whether a domain can be resolved."""
     result = Result.NOT_DONE