[SPARK-2936] Migrate Netty network module from Java to Scala

The Netty network module was originally written when Scala 2.9.x had a bug that prevents a pure Scala implementation, and a subset of the files were done in Java. We have since upgraded to Scala 2.10, and can migrate all Java files now to Scala.

netty/netty#781

mesos/spark#522

Author: Reynold Xin <[email protected]>

Closes apache#1865 from rxin/netty and squashes the following commits:

332422f [Reynold Xin] Code review feedback
ca9eeee [Reynold Xin] Minor update.
7f1434b [Reynold Xin] [SPARK-2936] Migrate Netty network module from Java to Scala

core/src/main/scala/org/apache/spark/network/netty/FileClient.scala

@@ -0,0 +1,85 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.network.netty
+
+import java.util.concurrent.TimeUnit
+
+import io.netty.bootstrap.Bootstrap
+import io.netty.channel.{Channel, ChannelOption, EventLoopGroup}
+import io.netty.channel.oio.OioEventLoopGroup
+import io.netty.channel.socket.oio.OioSocketChannel
+
+import org.apache.spark.Logging
+
+class FileClient(handler: FileClientHandler, connectTimeout: Int) extends Logging {
+
+  private var channel: Channel = _
+  private var bootstrap: Bootstrap = _
+  private var group: EventLoopGroup = _
+  private val sendTimeout = 60
+
+  def init(): Unit = {
+    group = new OioEventLoopGroup
+    bootstrap = new Bootstrap
+    bootstrap.group(group)
+      .channel(classOf[OioSocketChannel])
+      .option(ChannelOption.SO_KEEPALIVE, java.lang.Boolean.TRUE)
+      .option(ChannelOption.TCP_NODELAY, java.lang.Boolean.TRUE)
+      .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, Integer.valueOf(connectTimeout))
+      .handler(new FileClientChannelInitializer(handler))
+  }
+
+  def connect(host: String, port: Int) {
+    try {
+      channel = bootstrap.connect(host, port).sync().channel()
+    } catch {
+      case e: InterruptedException =>
+        logWarning("FileClient interrupted while trying to connect", e)
+        close()
+    }
+  }
+
+  def waitForClose(): Unit = {
+    try {
+      channel.closeFuture.sync()
+    } catch {
+      case e: InterruptedException =>
+        logWarning("FileClient interrupted", e)
+    }
+  }
+
+  def sendRequest(file: String): Unit = {
+    try {
+      val bSent = channel.writeAndFlush(file + "\r\n").await(sendTimeout, TimeUnit.SECONDS)
+      if (!bSent) {
+        throw new RuntimeException("Failed to send")
+      }
+    } catch {
+      case e: InterruptedException =>
+        logError("Error", e)
+    }
+  }
+
+  def close(): Unit = {
+    if (group != null) {
+      group.shutdownGracefully()
+      group = null
+      bootstrap = null
+    }
+  }
+}