Fix race condition in prompt handling

The current approach to handling prompts involves calling for a prompt
and then registering a signal handler for a response that indicates the
prompt had completed. In most cases, if the user were to take action,
this would be quite slow. However, in the case of automatic responses to
the prompt, the signal response may appear before the signal handler is
configured, resulting in blocking forever.

This commit moves the call for a prompt after the signal handling has
been configured, closing the race window.

Signed-off-by: William Martin <williammartin@github.com>

secret_service/secret_service.go

@@ -186,12 +186,7 @@ func (s *SecretService) CreateItem(collection dbus.BusObject, label string, attr
 // the prompt to the user.
 func (s *SecretService) handlePrompt(prompt dbus.ObjectPath) (bool, dbus.Variant, error) {
 	if prompt != dbus.ObjectPath("/") {
-		err := s.Object(serviceName, prompt).Call(promptInterface+".Prompt", 0, "").Err
-		if err != nil {
-			return false, dbus.MakeVariant(""), err
-		}
-
-		err = s.AddMatchSignal(dbus.WithMatchObjectPath(prompt),
+		err := s.AddMatchSignal(dbus.WithMatchObjectPath(prompt),
 			dbus.WithMatchInterface(promptInterface),
 		)
 		if err != nil {
@@ -205,6 +200,11 @@ func (s *SecretService) handlePrompt(prompt dbus.ObjectPath) (bool, dbus.Variant
 		promptSignal := make(chan *dbus.Signal, 1)
 		s.Signal(promptSignal)
 
+		err = s.Object(serviceName, prompt).Call(promptInterface+".Prompt", 0, "").Err
+		if err != nil {
+			return false, dbus.MakeVariant(""), err
+		}
+
 		signal := <-promptSignal
 		switch signal.Name {
 		case promptInterface + ".Completed":