Websockets: Add GetSubscription by key

exchanges/stream/websocket.go

@@ -51,6 +51,7 @@ var (
 	errSubscriptionNotFound                 = errors.New("subscription not found in list")
 	errAlreadySubscribed                    = errors.New("already subscribed")
 	errNoChannelsInArgs                     = errors.New("no channels in args")
+	errKeyCannotBeNil                       = errors.New("key cannot be nil")
 )
 
 var globalReporter Reporter
@@ -973,8 +974,22 @@ func (w *ChannelSubscription) Equal(s *ChannelSubscription) bool {
 		w.Currency.Equal(s.Currency)
 }
 
-// GetSubscriptions returns a copied list of subscriptions
-// and is a private member that cannot be manipulated
+// GetSubscription returns a pointer to a copy of the subscription at the key provided
+// returns nil if no subscription is at that key or the key is nil
+func (w *Websocket) GetSubscription(key any) *ChannelSubscription {
+	if key == nil || w.subscriptions == nil {
+		return nil
+	}
+	w.subscriptionMutex.RLock()
+	defer w.subscriptionMutex.RUnlock()
+	if s, ok := w.subscriptions[key]; ok {
+		c := s
+		return &c
+	}
+	return nil
+}
+
+// GetSubscriptions returns a new slice of the subscriptions
 func (w *Websocket) GetSubscriptions() []ChannelSubscription {
 	w.subscriptionMutex.RLock()
 	defer w.subscriptionMutex.RUnlock()