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   /*
    * Copyright 2015 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.handler.codec.protobuf;
  
  import com.google.protobuf.Message;
  import com.google.protobuf.MessageLite;
  import com.google.protobuf.MessageLiteOrBuilder;
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPipeline;
  import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
  import io.netty.handler.codec.LengthFieldPrepender;
  import io.netty.handler.codec.MessageToMessageEncoder;
  
  import java.util.List;
  
  import static io.netty.buffer.Unpooled.*;
  
  /**
   * Encodes the requested <a href="https://github.com/google/protobuf">Google
   * Protocol Buffers</a> {@link Message} and {@link MessageLite} into a
   * {@link ByteBuf}. A typical setup for TCP/IP would be:
   * <pre>
   * {@link ChannelPipeline} pipeline = ...;
   *
   * // Decoders
   * pipeline.addLast("frameDecoder",
   *                  new {@link LengthFieldBasedFrameDecoder}(1048576, 0, 4, 0, 4));
   * pipeline.addLast("protobufDecoder",
   *                  new {@link ProtobufDecoder}(MyMessage.getDefaultInstance()));
   *
   * // Encoder
   * pipeline.addLast("frameEncoder", new {@link LengthFieldPrepender}(4));
   * pipeline.addLast("protobufEncoder", new {@link ProtobufEncoder}());
   * </pre>
   * and then you can use a {@code MyMessage} instead of a {@link ByteBuf}
   * as a message:
   * <pre>
   * void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
   *     MyMessage req = (MyMessage) msg;
   *     MyMessage res = MyMessage.newBuilder().setText(
   *                               "Did you say '" + req.getText() + "'?").build();
   *     ch.write(res);
   * }
   * </pre>
   */
  @Sharable
  public class ProtobufEncoder extends MessageToMessageEncoder<MessageLiteOrBuilder> {
      @Override
      protected void encode(ChannelHandlerContext ctx, MessageLiteOrBuilder msg, List<Object> out)
              throws Exception {
          if (msg instanceof MessageLite) {
              out.add(wrappedBuffer(((MessageLite) msg).toByteArray()));
              return;
          }
          if (msg instanceof MessageLite.Builder) {
              out.add(wrappedBuffer(((MessageLite.Builder) msg).build().toByteArray()));
          }
      }
  }