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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.nio.ByteOrder;
24  
25  import org.apache.mina.coap.CoapMessage;
26  import org.apache.mina.coap.CoapOption;
27  import org.apache.mina.codec.StatelessProtocolEncoder;
28  import org.slf4j.Logger;
29  import org.slf4j.LoggerFactory;
30  
31  /**
32   * Encode a CoAP message following the RFC.
33   * 
34   * Encode {@link CoapMessage} into {@link ByteBuffer}
35   * 
36   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
37   */
38  public class CoapEncoder implements StatelessProtocolEncoder<CoapMessage, ByteBuffer> {
39  
40      private static final Logger LOG = LoggerFactory.getLogger(CoapEncoder.class);
41  
42      private static final int HEADER_SIZE = 4;
43  
44      /**
45       * {@inheritDoc}
46       */
47      @Override
48      public Void createEncoderState() {
49          return null;
50      }
51  
52      /**
53       * {@inheritDoc}
54       */
55      @Override
56      public ByteBuffer encode(CoapMessage message, Void context) {
57  
58          LOG.debug("encoding {}", message);
59  
60          // compute size of the needed buffer
61          int size = HEADER_SIZE + message.getToken().length;
62  
63          int delta = 0;
64          for (CoapOption opt : message.getOptions()) {
65              // compute delta encoding size
66              int code = opt.getType().getCode();
67              delta = code - delta;
68              if (delta < 13) {
69                  size += 1;
70              } else if (delta < 256 + 13) {
71                  size += 2;
72              } else if (delta < 65536 + 269) {
73                  size += 3;
74              }
75  
76              // compute option length encoding size
77              int optLength = opt.getData().length;
78              if (optLength < 13) {
79                  size += 0;
80              } else if (optLength < 256 + 13) {
81                  size += 1;
82              } else if (optLength < 65536 + 269) {
83                  size += 2;
84              }
85  
86              // compute option data encoding size
87              size += optLength;
88          }
89  
90          // if we have a payload, we place the marker and the payload
91          if (message.getPayload() != null && message.getPayload().length > 0) {
92              // payload marker
93              size += 1;
94              size += message.getPayload().length;
95          }
96  
97          ByteBuffer buffer = ByteBuffer.allocate(size);
98  
99          buffer.order(ByteOrder.BIG_ENDIAN);
100 
101         // encode header
102         buffer.put((byte) (((message.getVersion() & 0x03) << 6) | (message.getType().getCode() & 0x03) << 4 | (message
103                 .getToken().length & 0x0F)));
104         buffer.put((byte) message.getCode());
105         buffer.putShort((short) message.getId());
106         buffer.put(message.getToken());
107 
108         // encode options
109         int lastOptCode = 0;
110 
111         for (CoapOption opt : message.getOptions()) {
112             int optionDelta = opt.getType().getCode() - lastOptCode;
113             int deltaQuartet = getQuartet(optionDelta);
114             int optionLength = opt.getData().length;
115 
116             int optionQuartet = getQuartet(optionLength);
117 
118             buffer.put((byte) ((deltaQuartet << 4) | optionQuartet));
119 
120             // write extended option delta field (0 - 2 bytes)
121             if (deltaQuartet == 13) {
122                 buffer.put((byte) (optionDelta - 13));
123             } else if (deltaQuartet == 14) {
124                 buffer.putShort((short) (optionDelta - 269));
125             }
126 
127             if (optionQuartet == 13) {
128                 buffer.put((byte) (optionLength - 13));
129             } else if (optionQuartet == 14) {
130                 buffer.putShort((short) (optionLength - 269));
131             }
132             buffer.put(opt.getData());
133 
134             lastOptCode = opt.getType().getCode();
135         }
136 
137         if (message.getPayload() != null && message.getPayload().length > 0) {
138             buffer.put((byte) 0xFF);
139             buffer.put(message.getPayload());
140         }
141 
142         buffer.flip();
143         return buffer;
144     }
145 
146     private int getQuartet(int value) {
147         if (value <= 12) {
148             return value;
149         } else if (value <= 255 + 13) {
150             return 13;
151         } else {
152             return 14;
153         }
154     }
155 }