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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.buffer.ChannelBufferOutputStream;
    22  import org.jboss.netty.channel.Channel;
    23  import org.jboss.netty.channel.ChannelHandler.Sharable;
    24  import org.jboss.netty.channel.ChannelHandlerContext;
    25  import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;
    26
    27  import com.google.protobuf.CodedOutputStream;
    28
    29  /**
    30   * An encoder that prepends the the Google Protocol Buffers
    31   * <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints">Base
    32   * 128 Varints</a> integer length field.  For example:
    33   * <pre>
    34   * BEFORE DECODE (300 bytes)       AFTER DECODE (302 bytes)
    35   * +---------------+               +--------+---------------+
    36   * | Protobuf Data |-------------->| Length | Protobuf Data |
    37   * |  (300 bytes)  |               | 0xAC02 |  (300 bytes)  |
    38   * +---------------+               +--------+---------------+
    39   * </pre> *
    40   *
    41   * @see com.google.protobuf.CodedOutputStream
    42   */
    43  @Sharable
    44  public class ProtobufVarint32LengthFieldPrepender extends OneToOneEncoder {
    45
    46      /**
    47       * Creates a new instance.
    48       */
    49      public ProtobufVarint32LengthFieldPrepender() {
    50          super();
    51      }
    52
    53      @Override
    54      protected Object encode(ChannelHandlerContext ctx, Channel channel,
    55              Object msg) throws Exception {
    56          if (!(msg instanceof ChannelBuffer)) {
    57              return msg;
    58          }
    59
    60          ChannelBuffer body = (ChannelBuffer) msg;
    61          int length = body.readableBytes();
    62          ChannelBuffer header =
    63              channel.getConfig().getBufferFactory().getBuffer(
    64                      body.order(),
    65                      CodedOutputStream.computeRawVarint32Size(length));
    66          CodedOutputStream codedOutputStream = CodedOutputStream
    67                  .newInstance(new ChannelBufferOutputStream(header));
    68          codedOutputStream.writeRawVarint32(length);
    69          codedOutputStream.flush();
    70          return wrappedBuffer(header, body);
    71      }
    72
    73  }