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    1   /*
    2    * Copyright 2012 The Netty Project
    3    *
    4    * The Netty Project licenses this file to you under the Apache License,
    5    * version 2.0 (the "License"); you may not use this file except in compliance
    6    * with the License. You may obtain a copy of the License at:
    7    *
    8    *   http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
    13   * License for the specific language governing permissions and limitations
    14   * under the License.
    15   */
    16  package org.jboss.netty.handler.codec.protobuf;
    17
    18  import static org.jboss.netty.buffer.ChannelBuffers.*;
    19
    20  import org.jboss.netty.buffer.ChannelBuffer;
    21  import org.jboss.netty.channel.Channel;
    22  import org.jboss.netty.channel.ChannelHandler.Sharable;
    23  import org.jboss.netty.channel.ChannelHandlerContext;
    24  import org.jboss.netty.channel.ChannelPipeline;
    25  import org.jboss.netty.channel.MessageEvent;
    26  import org.jboss.netty.handler.codec.frame.LengthFieldBasedFrameDecoder;
    27  import org.jboss.netty.handler.codec.frame.LengthFieldPrepender;
    28  import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;
    29
    30  import com.google.protobuf.Message;
    31  import com.google.protobuf.MessageLite;
    32
    33  /**
    34   * Encodes the requested <a href="http://code.google.com/p/protobuf/">Google
    35   * Protocol Buffers</a> {@link Message} and {@link MessageLite} into a
    36   * {@link ChannelBuffer}. A typical setup for TCP/IP would be:
    37   * <pre>
    38   * {@link ChannelPipeline} pipeline = ...;
    39   *
    40   * // Decoders
    41   * pipeline.addLast("frameDecoder",
    42   *                  new {@link LengthFieldBasedFrameDecoder}(1048576, 0, 4, 0, 4));
    43   * pipeline.addLast("protobufDecoder",
    44   *                  new {@link ProtobufDecoder}(MyMessage.getDefaultInstance()));
    45   *
    46   * // Encoder
    47   * pipeline.addLast("frameEncoder", new {@link LengthFieldPrepender}(4));
    48   * pipeline.addLast("protobufEncoder", new {@link ProtobufEncoder}());
    49   * </pre>
    50   * and then you can use a {@code MyMessage} instead of a {@link ChannelBuffer}
    51   * as a message:
    52   * <pre>
    53   * void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
    54   *     MyMessage req = (MyMessage) e.getMessage();
    55   *     MyMessage res = MyMessage.newBuilder().setText(
    56   *                               "Did you say '" + req.getText() + "'?").build();
    57   *     ch.write(res);
    58   * }
    59   * </pre>
    60   *
    61   * @apiviz.landmark
    62   */
    63  @Sharable
    64  public class ProtobufEncoder extends OneToOneEncoder {
    65
    66      /**
    67       * Creates a new instance.
    68       */
    69      public ProtobufEncoder() {
    70          super();
    71      }
    72
    73      @Override
    74      protected Object encode(
    75              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
    76          if (msg instanceof MessageLite) {
    77              return wrappedBuffer(((MessageLite) msg).toByteArray());
    78          }
    79          if (msg instanceof MessageLite.Builder) {
    80              return wrappedBuffer(((MessageLite.Builder) msg).build().toByteArray());
    81          }
    82          return msg;
    83      }
    84  }