Various message bus fixes (#212)v1.14.0

1. Move to pure mixin-based ("stackable traits") pattern.
2. Provide a "CreateOnDemand" mixin that ensures topics and
subscriptions have been created before they are used.

1 files changed, 7 insertions, 6 deletions

diff --git a/src/main/scala/xyz/driver/core/messaging/StreamBus.scala b/src/main/scala/xyz/driver/core/messaging/StreamBus.scala
index aa99960..aabd3dc 100644
--- a/src/main/scala/xyz/driver/core/messaging/StreamBus.scala
+++ b/src/main/scala/xyz/driver/core/messaging/StreamBus.scala
@@ -1,10 +1,10 @@
 package xyz.driver.core
 package messaging
 
+import akka.NotUsed
 import akka.stream.scaladsl.{Flow, Sink, Source}
 
 import scala.collection.mutable.ListBuffer
-import scala.concurrent.ExecutionContext
 
 /** An extension to message buses that offers an Akka-Streams API.
   *
@@ -23,11 +23,10 @@ import scala.concurrent.ExecutionContext
   *     .run()
   * }}} */
 trait StreamBus extends Bus {
-  implicit def executionContext: ExecutionContext
 
   /** Flow that publishes any messages to a given topic.
-    * Emits messages once have been published to the underlying bus. */
-  def publish[A](topic: Topic[A]): Flow[A, A, _] = {
+    * Emits messages once they have been published to the underlying bus. */
+  def publish[A](topic: Topic[A]): Flow[A, A, NotUsed] = {
     Flow[A]
       .batch(defaultMaxMessages.toLong, a => ListBuffer[A](a))(_ += _)
       .mapAsync(1) { a =>
@@ -37,7 +36,7 @@ trait StreamBus extends Bus {
   }
 
   /** Sink that acknowledges the receipt of a message. */
-  def acknowledge: Sink[MessageId, _] = {
+  def acknowledge: Sink[MessageId, NotUsed] = {
     Flow[MessageId]
       .batch(defaultMaxMessages.toLong, a => ListBuffer[MessageId](a))(_ += _)
       .mapAsync(1)(acknowledgeMessages(_))
@@ -45,7 +44,9 @@ trait StreamBus extends Bus {
   }
 
   /** Source that listens to a subscription and receives any messages sent to its topic. */
-  def subscribe[A](topic: Topic[A], config: SubscriptionConfig = defaultSubscriptionConfig): Source[Message[A], _] = {
+  def subscribe[A](
+      topic: Topic[A],
+      config: SubscriptionConfig = defaultSubscriptionConfig): Source[Message[A], NotUsed] = {
     Source
       .unfoldAsync((topic, config))(
         topicAndConfig =>