minidlna: Implement force upgrading from older version

Fixes: #2026.

Upgrade from 1.2.1+dfsg-1+b1 to 1.3.x.

Tests:

- Install version 1.2.1+dfsg-1+b1. Change the default media directory. Run
unattended upgrades it will fail to upgrade. With the new patch, run apt update.
This will force upgrade. After upgrade the earlier set media directory is
retained.

- Functional tests run.

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

plinth/modules/minidlna/__init__.py

@@ -11,6 +11,7 @@ from plinth.modules.apache.components import Webserver
 from plinth.modules.backups.components import BackupRestore
 from plinth.modules.firewall.components import Firewall
 from plinth.modules.users.components import UsersAndGroups
+from plinth.utils import Version
 
 from . import manifest
 
@@ -103,3 +104,20 @@ def get_media_dir():
 def set_media_dir(media_dir):
     """Set the media directory from which files will be scanned for sharing."""
     actions.superuser_run('minidlna', ['set-media-dir', '--dir', media_dir])
+
+
+def force_upgrade(helper, packages):
+    """Force upgrade minidlna to resolve conffile prompt."""
+    if 'minidlna' not in packages:
+        return False
+
+    # Allow upgrade from 1.2.1+dfsg-1+b1 to 1.3.x
+    package = packages['minidlna']
+    if Version(package['new_version']) > Version('1.4~'):
+        return False
+
+    media_dir = get_media_dir()
+    helper.install(['minidlna'], force_configuration='new')
+    set_media_dir(media_dir)
+
+    return True