View Javadoc
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 CodedOutputStream
42   */
43  @Sharable
44  public class ProtobufVarint32LengthFieldPrepender extends OneToOneEncoder {
45  
46      @Override
47      protected Object encode(ChannelHandlerContext ctx, Channel channel,
48              Object msg) throws Exception {
49          if (!(msg instanceof ChannelBuffer)) {
50              return msg;
51          }
52  
53          ChannelBuffer body = (ChannelBuffer) msg;
54          int length = body.readableBytes();
55          ChannelBuffer header =
56              channel.getConfig().getBufferFactory().getBuffer(
57                      body.order(),
58                      CodedOutputStream.computeRawVarint32Size(length));
59          CodedOutputStream codedOutputStream = CodedOutputStream
60                  .newInstance(new ChannelBufferOutputStream(header));
61          codedOutputStream.writeRawVarint32(length);
62          codedOutputStream.flush();
63          return wrappedBuffer(header, body);
64      }
65  
66  }