content: /*
   * 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<Message> {
  
    private static final Logger logger = LoggerFactory.getLogger(MessageEncoder.class);
  
    /***
     * 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<Object> out) throws Exception {
      Object body = null;
      long bodyLength = 0;
      boolean isBodyInFrame = false;
  
      // If the message has a body, take it out to enable zero-copy transfer for the payload.
      if (in.body() != null) {
        try {
          bodyLength = in.body().size();
          body = in.body().convertToNetty();
          isBodyInFrame = in.isBodyInFrame();
        } catch (Exception e) {
          in.body().release();
          if (in instanceof AbstractResponseMessage) {
            AbstractResponseMessage resp = (AbstractResponseMessage) in;
            // Re-encode this message as a failure response.
            String error = e.getMessage() != null ? e.getMessage() : "null";
            logger.error(String.format("Error processing %s for client %s",
              in, ctx.channel().remoteAddress()), e);
            encode(ctx, resp.createFailureResponse(error), out);
          } else {
            throw e;
          }
          return;
        }
      }
  
      Message.Type msgType = in.type();
      // All messages have the frame length, message type, and message itself. The frame length
      // may optionally include the length of the body data, depending on what message is being
      // sent.
      int headerLength = 8 + msgType.encodedLength() + in.encodedLength();
      long frameLength = headerLength + (isBodyInFrame ? bodyLength : 0);
      ByteBuf header = ctx.alloc().heapBuffer(headerLength);
      header.writeLong(frameLength);
      msgType.encode(header);
      in.encode(header);
      assert header.writableBytes() == 0;
  
      if (body != null) {
        // We transfer ownership of the reference on in.body() to MessageWithHeader.
        // This reference will be freed when MessageWithHeader.deallocate() is called.
        out.add(new MessageWithHeader(in.body(), header, body, bodyLength));
      } else {
        out.add(header);
      }
    }
  
  }
  