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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License.
18   *
19   */
20  package org.apache.mina.coap.codec;
21  
22  import java.nio.ByteBuffer;
23  import java.util.ArrayList;
24  import java.util.List;
25  
26  import org.apache.mina.coap.CoapMessage;
27  import org.apache.mina.coap.CoapOption;
28  import org.apache.mina.coap.CoapOptionType;
29  import org.apache.mina.coap.MessageType;
30  import org.apache.mina.codec.ProtocolDecoderException;
31  import org.apache.mina.codec.StatelessProtocolDecoder;
32  import org.slf4j.Logger;
33  import org.slf4j.LoggerFactory;
34  
35  /**
36   * Decoder CoAP messages from the ByteBuffer of a received UDP Datagram.
37   * 
38   * Decode {@link ByteBuffer} into {@link CoapMessage}.
39   * 
40   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
41   */
42  public class CoapDecoder implements StatelessProtocolDecoder<ByteBuffer, CoapMessage> {
43  
44      private static final Logger LOG = LoggerFactory.getLogger(CoapDecoder.class);
45  
46      private static final CoapOption[] EMPTY_OPTION = new CoapOption[0];
47  
48      private static final byte[] EMPTY_PAYLOAD = new byte[0];
49  
50      /**
51       * {@inheritDoc}
52       */
53      @Override
54      public Void createDecoderState() {
55          return null;
56      }
57  
58      /**
59       * {@inheritDoc}
60       */
61      @Override
62      public CoapMessage decode(ByteBuffer input, Void context) {
63          LOG.debug("decode");
64  
65          if (input.remaining() <= 0) {
66              LOG.debug("nothing to decode");
67              return null;
68          }
69          int byte0 = input.get() & 0xFF;
70          int version = (byte0 >> 6) & 0x3;
71          MessageType type = MessageType.fromCode((byte0 >> 4) & 0x3);
72          byte[] token = new byte[byte0 & 0xF];
73          int code = input.get() & 0xFF;
74          int id = input.getShort() & 0xFFFF;
75          input.get(token);
76  
77          // decode options
78          int optionCode = 0;
79          byte[] payload = EMPTY_PAYLOAD;
80          List<CoapOption> options = new ArrayList<CoapOption>();
81          while (input.hasRemaining()) {
82              int next = input.get() & 0xFF;
83  
84              // start of payload ?
85              if (next == 0xFF) {
86                  payload = new byte[input.remaining()];
87                  input.get(payload);
88                  break;
89              } else {
90                  int optionDeltaQuartet = (next >> 4) & 0xF;
91  
92                  optionCode += optionFromQuartet(optionDeltaQuartet, input);
93  
94                  // decode the option length
95                  int optionLenQuartet = next & 0x0F;
96                  int optionLength = optionFromQuartet(optionLenQuartet, input);
97  
98                  // create the option DTO
99                  CoapOptionType optType = CoapOptionType.fromCode(optionCode);
100                 if (optType == null) {
101                     throw new ProtocolDecoderException("unknown option code : " + optionCode);
102                 }
103 
104                 // get the value
105                 byte[] optionValue = new byte[optionLength];
106                 input.get(optionValue);
107 
108                 options.add(new CoapOption(optType, optionValue));
109             }
110         }
111 
112         if (input.hasRemaining()) {
113             throw new ProtocolDecoderException("trailling " + input.remaining() + " bytes in the UDP datagram");
114         }
115         return new CoapMessage(version, type, code, id, token, options.toArray(EMPTY_OPTION), payload);
116     }
117 
118     /**
119      * {@inheritDoc}
120      */
121     @Override
122     public void finishDecode(Void context) {
123     }
124 
125     private int optionFromQuartet(int value, ByteBuffer input) {
126         if (value < 13) {
127             return value;
128         } else if (value == 13) {
129             return (input.get() & 0xFF) + 13;
130         } else if (value == 14) {
131             return (input.getShort() & 0xFFFF) + 269;
132         } else {
133             throw new ProtocolDecoderException("illegal option quartet value : " + value);
134         }
135     }
136 }