Make notifyReturnChan a property from publisher

It's the channel that never changes so we might
as well keep a copy of it (even to consider closing
it when the publisher is closed as well).

Also add another little buffer.

publish.go

@@ -99,6 +99,8 @@ func WithPublishOptionsHeaders(headers Table) func(*PublishOptions) {
 type Publisher struct {
 	chManager *channelManager
 
+	notifyReturnChan chan Return
+
 	disablePublishDueToFlow    bool
 	disablePublishDueToFlowMux *sync.RWMutex
 
@@ -148,21 +150,21 @@ func NewPublisher(url string, config amqp.Config, optionFuncs ...func(*Publisher
 
 	publisher := Publisher{
 		chManager:                  chManager,
+		notifyReturnChan:           make(chan Return, 1),
 		disablePublishDueToFlow:    false,
 		disablePublishDueToFlowMux: &sync.RWMutex{},
 		logger:                     options.Logger,
 	}
 
-	returnChan := make(chan Return)
 	go func() {
-		publisher.startNotifyHandlers(returnChan)
+		publisher.startNotifyHandlers()
 		for err := range publisher.chManager.notifyCancelOrClose {
 			publisher.logger.Printf("publish cancel/close handler triggered. err: %v", err)
-			publisher.startNotifyHandlers(returnChan)
+			publisher.startNotifyHandlers()
 		}
 	}()
 
-	return publisher, returnChan, nil
+	return publisher, publisher.notifyReturnChan, nil
 }
 
 // Publish publishes the provided data to the given routing keys over the connection
@@ -215,11 +217,11 @@ func (publisher Publisher) StopPublishing() {
 	publisher.chManager.connection.Close()
 }
 
-func (publisher *Publisher) startNotifyHandlers(returnChan chan Return) {
+func (publisher *Publisher) startNotifyHandlers() {
 	returnAMQPChan := publisher.chManager.channel.NotifyReturn(make(chan amqp.Return, 1))
 	go func() {
 		for ret := range returnAMQPChan {
-			returnChan <- Return{ret}
+			publisher.notifyReturnChan <- Return{ret}
 		}
 	}()