+htt 16841 uploadedFile directive

Two new directives for accepting file uploads through multipart forms:

`uploadedFile` which allows for very simple upload into a temporary file
`fileUpload` which allows to simply work with the stream of bytes of an upload

akka-docs-dev/rst/scala/code/docs/http/scaladsl/server/directives/FileUploadDirectivesExamplesSpec.scala

@@ -0,0 +1,81 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package docs.http.scaladsl.server.directives
+
+import java.io.File
+
+import akka.http.scaladsl.model.{ MediaTypes, HttpEntity, Multipart, StatusCodes }
+import akka.stream.io.Framing
+import akka.util.ByteString
+import docs.http.scaladsl.server.RoutingSpec
+
+import scala.concurrent.Future
+import scala.util.{ Success, Failure }
+
+class FileUploadDirectivesExamplesSpec extends RoutingSpec {
+
+  override def testConfigSource = "akka.actor.default-mailbox.mailbox-type = \"akka.dispatch.UnboundedMailbox\""
+
+  "uploadedFile" in {
+
+    val route =
+      uploadedFile("csv") {
+        case (metadata, file) =>
+          // do something with the file and file metadata ...
+          file.delete()
+          complete(StatusCodes.OK)
+      }
+
+    // tests:
+    val multipartForm =
+      Multipart.FormData(
+        Multipart.FormData.BodyPart.Strict(
+          "csv",
+          HttpEntity(MediaTypes.`text/plain`, "1,5,7\n11,13,17"),
+          Map("filename" -> "data.csv")))
+
+    Post("/", multipartForm) ~> route ~> check {
+      status shouldEqual StatusCodes.OK
+    }
+
+  }
+
+  "fileUpload" in {
+
+    // adding integers as a service ;)
+    val route =
+      extractRequestContext { ctx =>
+        implicit val mat = ctx.materializer
+        implicit val ec = ctx.executionContext
+
+        fileUpload("csv") {
+          case (metadata, byteSource) =>
+
+            val sumF: Future[Int] =
+              // sum the numbers as they arrive so that we can
+              // accept any size of file
+              byteSource.via(Framing.delimiter(ByteString("\n"), 1024))
+                .mapConcat(_.utf8String.split(",").toVector)
+                .map(_.toInt)
+                .runFold(0) { (acc, n) => acc + n }
+
+            onSuccess(sumF) { sum => complete(s"Sum: $sum") }
+        }
+      }
+
+    // tests:
+    val multipartForm =
+      Multipart.FormData(Multipart.FormData.BodyPart.Strict(
+        "csv",
+        HttpEntity(MediaTypes.`text/plain`, "2,3,5\n7,11,13,17,23\n29,31,37\n"),
+        Map("filename" -> "primes.csv")))
+
+    Post("/", multipartForm) ~> route ~> check {
+      status shouldEqual StatusCodes.OK
+      responseAs[String] shouldEqual "Sum: 178"
+    }
+
+  }
+
+}