vidforward: simplify manager file save/load

When saving and loading manager state to and from file, we don't
need to worry about the slate exit signals. Now that we have
broadcast status i.e. "play" or "slate", we can derive whether we
need an exit signal based only on that.

Approved-by: Trek Hopton

cmd/vidforward/file.go

@@ -52,7 +52,6 @@ type BroadcastBasic struct {
 // marshal/unmarshal overriding.
 type ManagerBasic struct {
 	Broadcasts map[MAC]*Broadcast
-	SlateExitSignals []MAC
 }
 
 // MarshalJSON calls the default marshalling behaviour for the BroadcastBasic
@@ -94,14 +93,7 @@ func (b *Broadcast) UnmarshalJSON(data []byte) error {
 // MarshalJSON calls the default marshaller for a ManagerBasic value using data
 // from a broadcastManager value.
 func (m *broadcastManager) MarshalJSON() ([]byte, error) {
-	var signals []MAC
-	for k := range m.slateExitSignals {
-		signals = append(signals, k)
-	}
-	return json.Marshal(ManagerBasic{
-		Broadcasts:       m.broadcasts,
-		SlateExitSignals: signals,
-	})
+	return json.Marshal(ManagerBasic{Broadcasts: m.broadcasts})
 }
 
 // UnmarshalJSON populates a ManagerBasic value from the provided data and then
@@ -123,7 +115,8 @@ func (m *broadcastManager) UnmarshalJSON(data []byte) error {
 	}
 	m.dogNotifier = notifier
 
-	for _, mac := range mb.SlateExitSignals {
+	for mac, b := range m.broadcasts {
+		if b.status == statusSlate {
 			sigCh := make(chan struct{})
 			m.slateExitSignals[mac] = sigCh
 			rv := m.getPipeline(mac)
@@ -137,6 +130,8 @@ func (m *broadcastManager) UnmarshalJSON(data []byte) error {
 				}
 			}
 		}
+	}
+
 	return nil
 }