Use media storage for maintenance mode state file

Previously, we relied on either explicit configuration to place the
file in a writable location, or the webserver being able to write to
the source tree.

With a (probably even replicated) setup where nothing runs as root,
and al lstorages are thus read-only except for the media storage, we
need to put the maintenance file there.

aleksis/core/settings.py

@@ -484,9 +484,10 @@ MAINTENANCE_MODE_IGNORE_IP_ADDRESSES = _settings.get(
 )
 MAINTENANCE_MODE_GET_CLIENT_IP_ADDRESS = "ipware.ip.get_ip"
 MAINTENANCE_MODE_IGNORE_SUPERUSER = True
-MAINTENANCE_MODE_STATE_FILE_PATH = _settings.get(
+MAINTENANCE_MODE_STATE_FILE_NAME = _settings.get(
     "maintenance.statefile", "maintenance_mode_state.txt"
 )
+MAINTENANCE_MODE_STATE_BACKEND = "aleksis.core.util.maintenance.DefaultStorageBackend"
 
 DBBACKUP_STORAGE = _settings.get("backup.storage", "django.core.files.storage.FileSystemStorage")
 DBBACKUP_STORAGE_OPTIONS = {"location": _settings.get("backup.location", "/var/backups/aleksis")}

aleksis/core/util/maintenance.py

+from django.conf import settings
+from django.core.files.base import ContentFile
+from django.core.files.storage import default_storage
+
+from maintenance_mode.backends import AbstractStateBackend
+
+
+class DefaultStorageBackend(AbstractStateBackend):
+    """django-maintenance-mode backend using default cache."""
+
+    def get_value(self) -> bool:
+        filename = settings.MAINTENANCE_MODE_STATE_FILE_NAME
+
+        try:
+            with default_storage.open(filename) as statefile:
+                return bool(int(statefile.read()))
+        except IOError:
+            return False
+
+    def set_value(self, value: bool) -> None:
+        filename = settings.MAINTENANCE_MODE_STATE_FILE_NAME
+
+        if default_storage.exists(filename):
+            default_storage.delete(filename)
+        default_storage.save(filename, ContentFile(str(int(value))))