added the notify module

notify/subscriber.go

@@ -0,0 +1,55 @@
+package notify
+
+import "sync"
+
+// Subscriber represents a client subscribed to receive notifications.
+// Each subscriber has a unique ID and receives notifications through
+// a buffered channel. Subscribers are created via Notifier.Subscribe().
+type Subscriber struct {
+	// ID is the unique identifier for this subscriber.
+	// This is automatically generated using cryptographic random bytes.
+	ID Target
+
+	// notifications is the buffered channel for receiving notifications.
+	// The buffer size is determined by the Notifier's configuration.
+	notifications chan Notification
+
+	// notifier is a reference back to the parent Notifier.
+	notifier *Notifier
+
+	// unsubscribelock protects the unsubscribe operation.
+	unsubscribelock *sync.Mutex
+
+	// unsubscribed tracks whether this subscriber has been unsubscribed.
+	unsubscribed bool
+}
+
+// Listen returns a receive-only channel for reading notifications.
+// Use this channel in a for-range loop to process notifications:
+//
+//	for notification := range sub.Listen() {
+//	    // Process notification
+//	    fmt.Println(notification.Message)
+//	}
+//
+// The channel will be closed when the subscriber unsubscribes or
+// when the notifier is closed.
+func (s *Subscriber) Listen() <-chan Notification {
+	return s.notifications
+}
+
+// Unsubscribe removes this subscriber from the notifier and closes the notification channel.
+// It is safe to call Unsubscribe multiple times; subsequent calls are no-ops.
+// After unsubscribe, the channel returned by Listen() will be closed immediately.
+// Any goroutines reading from Listen() will detect the closure and can exit gracefully.
+func (s *Subscriber) Unsubscribe() {
+	s.unsubscribelock.Lock()
+	if s.unsubscribed {
+		s.unsubscribelock.Unlock()
+		return
+	}
+	s.unsubscribed = true
+	s.unsubscribelock.Unlock()
+
+	s.notifier.RemoveSubscriber(s)
+}