Adding support for publishing messages with an expiration.

- Added WithPublishOptionsExpiration which permits message expiry when the TTL has been reached
- Introduced new message var to permit the confidiontal injection of amp.Publishing options in the future.

publish.go

@@ -40,6 +40,8 @@ type PublishOptions struct {
 	ContentType string
 	// Transient or Persistent
 	DeliveryMode uint8
+	// Expiration time in ms a message will expire from a queue.
+	Expiration		string
 }
 
 // WithPublishOptionsExchange returns a function that sets the exchange to publish to
@@ -76,6 +78,14 @@ func WithPublishOptionsPersistentDelivery(options *PublishOptions) {
 	options.DeliveryMode = Persistent
 }
 
+// WithPublishOptionsExpiration returns a function that sets the expiry/TTL of a message. As per RabbitMq spec, it must be a
+// string value in milliseconds.
+func WithPublishOptionsExpiration (expiration string) func(options *PublishOptions) {
+	return func(options *PublishOptions) {
+		options.Expiration = expiration
+	}
+}
+
 // Publisher allows you to publish messages safely across an open connection
 type Publisher struct {
 	chManager *channelManager
@@ -176,16 +186,22 @@ func (publisher *Publisher) Publish(
 	}
 
 	for _, routingKey := range routingKeys {
+		var message = amqp.Publishing{}
+		message.ContentType = options.ContentType
+		message.DeliveryMode = options.DeliveryMode
+		message.Body = data
+		// If we have a TTL use it.
+		if options.Expiration != "" {
+			message.Expiration = options.Expiration
+		}
+		// Actual publish.
 		err := publisher.chManager.channel.Publish(
 			options.Exchange,
 			routingKey,
 			options.Mandatory,
 			options.Immediate,
-			amqp.Publishing{
-				ContentType:  options.ContentType,
-				Body:         data,
-				DeliveryMode: options.DeliveryMode,
-			})
+			message,
+			)
 		if err != nil {
 			return err
 		}