+str #15588,#17229 Java 6 Synchronous File Sink / Source

These are synchronous implementations, because we need to be Java 6
  compatible while developing on 2.3.x. However asynchronous
  implementations using AsynchronousFileChannel will come soon for JDK7
  users.

+ ActorPublisher/Subscriber now manage stopping of the actor
+ added documentation on configuring dispatcher for File IO
+ properly handle if source file does not exist
+ file sink / source come with default io dispatcher
> verified no actors are leaking
> exceptions are caught and onErrored properly
+ moved files to akka.stream.io
+ Added OutputStreamSink and InputStreamSource

akka-stream/src/main/scala/akka/stream/io/impl/OutputStreamSubscriber.scala

@@ -0,0 +1,60 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.stream.io.impl
+
+import java.io.OutputStream
+
+import akka.actor.{ ActorLogging, Props }
+import akka.stream.actor.{ ActorSubscriberMessage, WatermarkRequestStrategy }
+import akka.util.ByteString
+
+import scala.concurrent.Promise
+
+/** INTERNAL API */
+private[akka] object OutputStreamSubscriber {
+  def props(os: OutputStream, completionPromise: Promise[Long], bufSize: Int) = {
+    require(bufSize > 0, "buffer size must be > 0")
+    Props(classOf[OutputStreamSubscriber], os, completionPromise, bufSize)
+  }
+
+}
+
+/** INTERNAL API */
+private[akka] class OutputStreamSubscriber(os: OutputStream, bytesWrittenPromise: Promise[Long], bufSize: Int)
+  extends akka.stream.actor.ActorSubscriber
+  with ActorLogging {
+
+  override protected val requestStrategy = WatermarkRequestStrategy(highWatermark = bufSize)
+
+  private var bytesWritten: Long = 0
+
+  def receive = {
+    case ActorSubscriberMessage.OnNext(bytes: ByteString) ⇒
+      try {
+        // blocking write
+        os.write(bytes.toArray)
+        bytesWritten += bytes.length
+      } catch {
+        case ex: Exception ⇒
+          println("ex = " + ex)
+          bytesWrittenPromise.failure(ex)
+          cancel()
+      }
+
+    case ActorSubscriberMessage.OnError(cause) ⇒
+      log.error(cause, "Tearing down OutputStreamSink due to upstream error, wrote bytes: {}", bytesWritten)
+      context.stop(self)
+
+    case ActorSubscriberMessage.OnComplete ⇒
+      context.stop(self)
+      os.flush()
+  }
+
+  override def postStop(): Unit = {
+    bytesWrittenPromise.trySuccess(bytesWritten)
+
+    if (os ne null) os.close()
+    super.postStop()
+  }
+}