org.apache.spark.network.protocol.MessageEncoder Maven / Gradle / Ivy

/*
 * 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.protocol;

import java.util.List;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToMessageEncoder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Encoder used by the server side to encode server-to-client responses.
 * This encoder is stateless so it is safe to be shared by multiple threads.
 */
@ChannelHandler.Sharable
public final class MessageEncoder extends MessageToMessageEncoder {

  private static final Logger logger = LoggerFactory.getLogger(MessageEncoder.class);

  public static final MessageEncoder INSTANCE = new MessageEncoder();

  private MessageEncoder() {}

  /***
   * Encodes a Message by invoking its encode() method. For non-data messages, we will add one
   * ByteBuf to 'out' containing the total frame length, the message type, and the message itself.
   * In the case of a ChunkFetchSuccess, we will also add the ManagedBuffer corresponding to the
   * data to 'out', in order to enable zero-copy transfer.
   */
  @Override
  public void encode(ChannelHandlerContext ctx, Message in, List