+doc #15239: Stream cookbook

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

@@ -0,0 +1,62 @@
+package docs.stream.cookbook
+
+import java.security.MessageDigest
+
+import akka.stream.scaladsl.{ Sink, Source }
+import akka.util.ByteString
+
+import scala.concurrent.Await
+import scala.concurrent.duration._
+
+class RecipeDigest extends RecipeSpec {
+
+  "Recipe for calculating digest" must {
+
+    "work" in {
+
+      val data = Source(List(
+        ByteString("abcdbcdecdef"),
+        ByteString("defgefghfghighijhijkijkljklmklmnlmnomnopnopq")))
+
+      //#calculating-digest
+      import akka.stream.stage._
+      def digestCalculator(algorithm: String) = new PushPullStage[ByteString, ByteString] {
+        val digest = MessageDigest.getInstance(algorithm)
+
+        override def onPush(chunk: ByteString, ctx: Context[ByteString]): Directive = {
+          digest.update(chunk.toArray)
+          ctx.pull()
+        }
+
+        override def onPull(ctx: Context[ByteString]): Directive = {
+          if (ctx.isFinishing) ctx.pushAndFinish(ByteString(digest.digest()))
+          else ctx.pull()
+        }
+
+        override def onUpstreamFinish(ctx: Context[ByteString]): TerminationDirective = {
+          // If the stream is finished, we need to emit the last element in the onPull block.
+          // It is not allowed to directly emit elements from a termination block
+          // (onUpstreamFinish or onUpstreamFailure)
+          ctx.absorbTermination()
+        }
+      }
+
+      val digest: Source[ByteString] = data.transform(() => digestCalculator("SHA-256"))
+      //#calculating-digest
+
+      Await.result(digest.runWith(Sink.head), 3.seconds) should be(
+        ByteString(
+          0x24, 0x8d, 0x6a, 0x61,
+          0xd2, 0x06, 0x38, 0xb8,
+          0xe5, 0xc0, 0x26, 0x93,
+          0x0c, 0x3e, 0x60, 0x39,
+          0xa3, 0x3c, 0xe4, 0x59,
+          0x64, 0xff, 0x21, 0x67,
+          0xf6, 0xec, 0xed, 0xd4,
+          0x19, 0xdb, 0x06, 0xc1))
+
+    }
+
+  }
+
+}