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1   /*
2    * Copyright 2015 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 io.netty.handler.codec.protobuf;
17  
18  import com.google.protobuf.CodedInputStream;
19  import com.google.protobuf.nano.CodedInputByteBufferNano;
20  import io.netty.buffer.ByteBuf;
21  import io.netty.channel.ChannelHandlerContext;
22  import io.netty.handler.codec.ByteToMessageDecoder;
23  import io.netty.handler.codec.CorruptedFrameException;
24  
25  import java.util.List;
26  
27  /**
28   * A decoder that splits the received {@link ByteBuf}s dynamically by the
29   * value of the Google Protocol Buffers
30   * <a href="https://developers.google.com/protocol-buffers/docs/encoding#varints">Base
31   * 128 Varints</a> integer length field in the message. For example:
32   * <pre>
33   * BEFORE DECODE (302 bytes)       AFTER DECODE (300 bytes)
34   * +--------+---------------+      +---------------+
35   * | Length | Protobuf Data |----->| Protobuf Data |
36   * | 0xAC02 |  (300 bytes)  |      |  (300 bytes)  |
37   * +--------+---------------+      +---------------+
38   * </pre>
39   *
40   * @see CodedInputStream
41   * @see CodedInputByteBufferNano
42   */
43  public class ProtobufVarint32FrameDecoder extends ByteToMessageDecoder {
44  
45      // TODO maxFrameLength + safe skip + fail-fast option
46      //      (just like LengthFieldBasedFrameDecoder)
47  
48      @Override
49      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out)
50              throws Exception {
51          in.markReaderIndex();
52          int preIndex = in.readerIndex();
53          int length = readRawVarint32(in);
54          if (preIndex == in.readerIndex()) {
55              return;
56          }
57          if (length < 0) {
58              throw new CorruptedFrameException("negative length: " + length);
59          }
60  
61          if (in.readableBytes() < length) {
62              in.resetReaderIndex();
63          } else {
64              out.add(in.readRetainedSlice(length));
65          }
66      }
67  
68      /**
69       * Reads variable length 32bit int from buffer
70       *
71       * @return decoded int if buffers readerIndex has been forwarded else nonsense value
72       */
73      private static int readRawVarint32(ByteBuf buffer) {
74          if (!buffer.isReadable()) {
75              return 0;
76          }
77          buffer.markReaderIndex();
78          byte tmp = buffer.readByte();
79          if (tmp >= 0) {
80              return tmp;
81          } else {
82              int result = tmp & 127;
83              if (!buffer.isReadable()) {
84                  buffer.resetReaderIndex();
85                  return 0;
86              }
87              if ((tmp = buffer.readByte()) >= 0) {
88                  result |= tmp << 7;
89              } else {
90                  result |= (tmp & 127) << 7;
91                  if (!buffer.isReadable()) {
92                      buffer.resetReaderIndex();
93                      return 0;
94                  }
95                  if ((tmp = buffer.readByte()) >= 0) {
96                      result |= tmp << 14;
97                  } else {
98                      result |= (tmp & 127) << 14;
99                      if (!buffer.isReadable()) {
100                         buffer.resetReaderIndex();
101                         return 0;
102                     }
103                     if ((tmp = buffer.readByte()) >= 0) {
104                         result |= tmp << 21;
105                     } else {
106                         result |= (tmp & 127) << 21;
107                         if (!buffer.isReadable()) {
108                             buffer.resetReaderIndex();
109                             return 0;
110                         }
111                         result |= (tmp = buffer.readByte()) << 28;
112                         if (tmp < 0) {
113                             throw new CorruptedFrameException("malformed varint.");
114                         }
115                     }
116                 }
117             }
118             return result;
119         }
120     }
121 }