names: Try to install systemd-resolved during app setup

- If installing systemd-resolved for the first time, set fallback DNS setting to
True irrespective of the app version.

Tests:

- Ensure that systemd-resolved is not installed. On a fresh systemd without
first setup done, run service.

- Names app setup is run and systemd-resolved is installed if internet
connection is available. Setup succeeds. Fallback DNS setting is true in privacy
app. systemd-resolved has been restarted and current DNS known to Network
Manager has been populated in it. Name resolution works.

- If Internet connection is not available, setup still succeeds but
systemd-resolved package is not installed.

- Rerun setup without internet connectivity. Setup succeeds without installing
systemd-resolved.

- Rerun setup with internet connectivity. Setup succeeds and installs
systemd-resolved. Fallback DNS setting is true in privacy app. systemd-resolved
has been restarted and current DNS known to Network Manager has been populated
in it. Name resolution works.

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

plinth/modules/names/__init__.py

@@ -102,22 +102,31 @@ class NamesApp(app_module.App):
         """Install and configure the app."""
         super().setup(old_version)
 
-        # Fresh install or upgrading to version 2
-        if old_version < 2:
-            privileged.set_resolved_configuration(dns_fallback=True)
+        if not is_resolved_installed():
+            try:
+                # Requires internet connectivity and could fail
+                privileged.install_resolved()
+                privileged.set_resolved_configuration(dns_fallback=True)
+            except Exception:
+                pass
 
-        # Load the configuration files for systemd-resolved provided by
-        # FreedomBox.
-        service_privileged.restart('systemd-resolved')
+        if is_resolved_installed():
+            # Fresh install or upgrading to version 2
+            if old_version < 2:
+                privileged.set_resolved_configuration(dns_fallback=True)
 
-        # After systemd-resolved is freshly installed, /etc/resolve.conf
-        # becomes a symlink to configuration pointing to systemd-resovled stub
-        # resolver. However, the old contents are not fed from network-manager
-        # (if it was present earlier and wrote to /etc/resolve.conf). Ask
-        # network-manager to feed the DNS servers from the connections it has
-        # established to systemd-resolved so that using fallback DNS servers is
-        # not necessary.
-        network.refeed_dns()
+            # Load the configuration files for systemd-resolved provided by
+            # FreedomBox.
+            service_privileged.restart('systemd-resolved')
+
+            # After systemd-resolved is freshly installed, /etc/resolve.conf
+            # becomes a symlink to configuration pointing to systemd-resovled
+            # stub resolver. However, the old contents are not fed from
+            # network-manager (if it was present earlier and wrote to
+            # /etc/resolve.conf). Ask network-manager to feed the DNS servers
+            # from the connections it has established to systemd-resolved so
+            # that using fallback DNS servers is not necessary.
+            network.refeed_dns()
 
         self.enable()
 

plinth/modules/names/privileged.py

@@ -52,6 +52,20 @@ def set_domain_name(domain_name: str | None = None):
     hosts_path.write_text(''.join(new_lines), encoding='utf-8')
 
 
+@privileged
+def install_resolved():
+    """Install systemd-resolved related packages."""
+    packages = ['systemd-resolved', 'libnss-resolve']
+    subprocess.run(['dpkg', '--configure', '-a'], check=False)
+    with action_utils.apt_hold_freedombox():
+        action_utils.run_apt_command(['--fix-broken', 'install'])
+        returncode = action_utils.run_apt_command(['install'] + packages)
+
+    if returncode:
+        raise RuntimeError(
+            f'Apt command failed with return code: {returncode}')
+
+
 @privileged
 def set_resolved_configuration(dns_fallback: bool | None = None,
                                dns_over_tls: str | None = None,