Disable SecretService backend if org.freedesktop.secrets name is not …

…available

Fixes jaraco#162, jaraco#434.

keyring/backends/SecretService.py

@@ -31,6 +31,11 @@ class Keyring(KeyringBackend):
     @properties.ClassProperty
     @classmethod
     def priority(cls):
+        try:
+            from jeepney.bus_messages import message_bus
+            from jeepney.integrate.blocking import Proxy
+        except ImportError:
+            raise RuntimeError("jeepney required")
         with ExceptionRaisedContext() as exc:
             secretstorage.__name__
         if exc:
@@ -39,6 +44,14 @@ def priority(cls):
             raise RuntimeError("SecretStorage 3.0 or newer required")
         try:
             with closing(secretstorage.dbus_init()) as connection:
+                proxy = Proxy(message_bus, connection)
+                has_owner, = proxy.NameHasOwner("org.freedesktop.secrets")
+                if not has_owner:
+                    activatable_names, = proxy.ListActivatableNames()
+                    if "org.freedesktop.secrets" not in activatable_names:
+                        raise RuntimeError(
+                            "The Secret Service daemon is neither running nor "
+                            "activatable through D-Bus")
                 list(secretstorage.get_all_collections(connection))
         except exceptions.SecretStorageException as e:
             raise RuntimeError("Unable to initialize SecretService: %s" % e)