+doc #15239: Stream cookbook

akka-docs-dev/rst/scala/code/docs/stream/cookbook/RecipeKeepAlive.scala

@@ -0,0 +1,76 @@
+package docs.stream.cookbook
+
+import akka.stream.scaladsl._
+import akka.stream.testkit.StreamTestKit
+import akka.stream.testkit.StreamTestKit.{ SubscriberProbe, PublisherProbe }
+import akka.util.ByteString
+
+class RecipeKeepAlive extends RecipeSpec {
+
+  "Recipe for injecting keepalive messages" must {
+
+    "work" in {
+
+      type Tick = Unit
+
+      val tickPub = PublisherProbe[Tick]()
+      val dataPub = PublisherProbe[ByteString]()
+      val sub = SubscriberProbe[ByteString]()
+      val ticks = Source(tickPub)
+
+      val dataStream = Source(dataPub)
+      val keepaliveMessage = ByteString(11)
+      val sink = Sink(sub)
+
+      //#inject-keepalive
+      val keepAliveStream: Source[ByteString] = ticks
+        .conflate(seed = (tick) => keepaliveMessage)((msg, newTick) => msg)
+
+      import FlowGraphImplicits._
+      val graph = FlowGraph { implicit builder =>
+        val unfairMerge = MergePreferred[ByteString]("keepAliveInjector")
+
+        dataStream ~> unfairMerge.preferred // If data is available then no keepalive is injected
+        keepAliveStream ~> unfairMerge
+
+        unfairMerge ~> sink
+      }
+      //#inject-keepalive
+
+      graph.run()
+
+      val manualTicks = new StreamTestKit.AutoPublisher(tickPub)
+      val manualData = new StreamTestKit.AutoPublisher(dataPub)
+
+      val subscription = sub.expectSubscription()
+
+      manualTicks.sendNext(())
+
+      // pending data will overcome the keepalive
+      manualData.sendNext(ByteString(1))
+      manualData.sendNext(ByteString(2))
+      manualData.sendNext(ByteString(3))
+
+      subscription.request(1)
+      sub.expectNext(ByteString(1))
+      subscription.request(2)
+      sub.expectNext(ByteString(2))
+      sub.expectNext(ByteString(3))
+
+      subscription.request(1)
+      sub.expectNext(keepaliveMessage)
+
+      subscription.request(1)
+      manualTicks.sendNext(())
+      sub.expectNext(keepaliveMessage)
+
+      manualData.sendComplete()
+      manualTicks.sendComplete()
+
+      sub.expectComplete()
+
+    }
+
+  }
+
+}