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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.filter.codec.demux;
21  
22  import org.apache.mina.core.buffer.IoBuffer;
23  import org.apache.mina.core.session.AttributeKey;
24  import org.apache.mina.core.session.IoSession;
25  import org.apache.mina.filter.codec.CumulativeProtocolDecoder;
26  import org.apache.mina.filter.codec.ProtocolDecoder;
27  import org.apache.mina.filter.codec.ProtocolDecoderException;
28  import org.apache.mina.filter.codec.ProtocolDecoderOutput;
29  
30  /**
31   * A composite {@link ProtocolDecoder} that demultiplexes incoming {@link IoBuffer}
32   * decoding requests into an appropriate {@link MessageDecoder}.
33   * 
34   * <h2>Internal mechanism of {@link MessageDecoder} selection</h2>
35   * <p>
36   * <ol>
37   * <li>{@link DemuxingProtocolDecoder} iterates the list of candidate
38   * {@link MessageDecoder}s and calls {@link MessageDecoder#decodable(IoSession, IoBuffer)}.
39   * Initially, all registered {@link MessageDecoder}s are candidates.</li>
40   * <li>If {@link MessageDecoderResult#NOT_OK} is returned, it is removed from the candidate
41   *     list.</li>
42   * <li>If {@link MessageDecoderResult#NEED_DATA} is returned, it is retained in the candidate
43   *     list, and its {@link MessageDecoder#decodable(IoSession, IoBuffer)} will be invoked
44   *     again when more data is received.</li>
45   * <li>If {@link MessageDecoderResult#OK} is returned, {@link DemuxingProtocolDecoder}
46   *     found the right {@link MessageDecoder}.</li>
47   * <li>If there's no candidate left, an exception is raised.  Otherwise, 
48   *     {@link DemuxingProtocolDecoder} will keep iterating the candidate list.
49   * </ol>
50   * 
51   * Please note that any change of position and limit of the specified {@link IoBuffer}
52   * in {@link MessageDecoder#decodable(IoSession, IoBuffer)} will be reverted back to its
53   * original value.
54   * <p>
55   * Once a {@link MessageDecoder} is selected, {@link DemuxingProtocolDecoder} calls
56   * {@link MessageDecoder#decode(IoSession, IoBuffer, ProtocolDecoderOutput)} continuously
57   * reading its return value:
58   * <ul>
59   * <li>{@link MessageDecoderResult#NOT_OK} - protocol violation; {@link ProtocolDecoderException}
60   *                                           is raised automatically.</li>
61   * <li>{@link MessageDecoderResult#NEED_DATA} - needs more data to read the whole message;
62   *                                              {@link MessageDecoder#decode(IoSession, IoBuffer, ProtocolDecoderOutput)}
63   *                                              will be invoked again when more data is received.</li>
64   * <li>{@link MessageDecoderResult#OK} - successfully decoded a message; the candidate list will
65   *                                       be reset and the selection process will start over.</li>
66   * </ul>
67   *
68   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
69   *
70   * @see MessageDecoderFactory
71   * @see MessageDecoder
72   */
73  public class DemuxingProtocolDecoder extends CumulativeProtocolDecoder {
74  
75      private final AttributeKey STATE = new AttributeKey(getClass(), "state");
76      
77      private MessageDecoderFactory[] decoderFactories = new MessageDecoderFactory[0];
78      private static final Class<?>[] EMPTY_PARAMS = new Class[0];
79  
80      public DemuxingProtocolDecoder() {
81          // Do nothing
82      }
83  
84      public void addMessageDecoder(Class<? extends MessageDecoder> decoderClass) {
85          if (decoderClass == null) {
86              throw new NullPointerException("decoderClass");
87          }
88  
89          try {
90              decoderClass.getConstructor(EMPTY_PARAMS);
91          } catch (NoSuchMethodException e) {
92              throw new IllegalArgumentException(
93                      "The specified class doesn't have a public default constructor.");
94          }
95  
96          boolean registered = false;
97          if (MessageDecoder.class.isAssignableFrom(decoderClass)) {
98              addMessageDecoder(new DefaultConstructorMessageDecoderFactory(decoderClass));
99              registered = true;
100         }
101 
102         if (!registered) {
103             throw new IllegalArgumentException(
104                     "Unregisterable type: " + decoderClass);
105         }
106     }
107 
108     public void addMessageDecoder(MessageDecoder decoder) {
109         addMessageDecoder(new SingletonMessageDecoderFactory(decoder));
110     }
111 
112     public void addMessageDecoder(MessageDecoderFactory factory) {
113         if (factory == null) {
114             throw new NullPointerException("factory");
115         }
116         MessageDecoderFactory[] decoderFactories = this.decoderFactories;
117         MessageDecoderFactory[] newDecoderFactories = new MessageDecoderFactory[decoderFactories.length + 1];
118         System.arraycopy(decoderFactories, 0, newDecoderFactories, 0,
119                 decoderFactories.length);
120         newDecoderFactories[decoderFactories.length] = factory;
121         this.decoderFactories = newDecoderFactories;
122     }
123     
124     @Override
125     protected boolean doDecode(IoSession session, IoBuffer in,
126             ProtocolDecoderOutput out) throws Exception {
127         State state = getState(session);
128         
129         if (state.currentDecoder == null) {
130             MessageDecoder[] decoders = state.decoders;
131             int undecodables = 0;
132         
133             for (int i = decoders.length - 1; i >= 0; i--) {
134                 MessageDecoder decoder = decoders[i];
135                 int limit = in.limit();
136                 int pos = in.position();
137 
138                 MessageDecoderResult result;
139                 
140                 try {
141                     result = decoder.decodable(session, in);
142                 } finally {
143                     in.position(pos);
144                     in.limit(limit);
145                 }
146 
147                 if (result == MessageDecoder.OK) {
148                     state.currentDecoder = decoder;
149                     break;
150                 } else if (result == MessageDecoder.NOT_OK) {
151                     undecodables++;
152                 } else if (result != MessageDecoder.NEED_DATA) {
153                     throw new IllegalStateException(
154                             "Unexpected decode result (see your decodable()): "
155                                     + result);
156                 }
157             }
158 
159             if (undecodables == decoders.length) {
160                 // Throw an exception if all decoders cannot decode data.
161                 String dump = in.getHexDump();
162                 in.position(in.limit()); // Skip data
163                 ProtocolDecoderException e = new ProtocolDecoderException(
164                         "No appropriate message decoder: " + dump);
165                 e.setHexdump(dump);
166                 throw e;
167             }
168 
169             if (state.currentDecoder == null) {
170                 // Decoder is not determined yet (i.e. we need more data)
171                 return false;
172             }
173         }
174 
175         MessageDecoderResult result = state.currentDecoder.decode(session, in,
176                 out);
177         if (result == MessageDecoder.OK) {
178             state.currentDecoder = null;
179             return true;
180         } else if (result == MessageDecoder.NEED_DATA) {
181             return false;
182         } else if (result == MessageDecoder.NOT_OK) {
183             state.currentDecoder = null;
184             throw new ProtocolDecoderException(
185                     "Message decoder returned NOT_OK.");
186         } else {
187             state.currentDecoder = null;
188             throw new IllegalStateException(
189                     "Unexpected decode result (see your decode()): "
190                             + result);
191         }
192     }
193 
194     @Override
195     public void finishDecode(IoSession session, ProtocolDecoderOutput out)
196             throws Exception {
197         super.finishDecode(session, out);
198         State state = getState(session);
199         MessageDecoder currentDecoder = state.currentDecoder;
200         if (currentDecoder == null) {
201             return;
202         }
203 
204         currentDecoder.finishDecode(session, out);
205     }
206 
207     @Override
208     public void dispose(IoSession session) throws Exception {
209         super.dispose(session);
210         session.removeAttribute(STATE);
211     }
212     
213     private State getState(IoSession session) throws Exception {
214         State state = (State) session.getAttribute(STATE);
215         
216         if (state == null) {
217             state = new State();
218             State oldState = (State) session.setAttributeIfAbsent(STATE, state);
219             
220             if (oldState != null) {
221                 state = oldState;
222             }
223         }
224         
225         return state;
226     }
227     
228     private class State {
229         private final MessageDecoder[] decoders;
230         private MessageDecoder currentDecoder;
231         
232         private State() throws Exception {
233             MessageDecoderFactory[] decoderFactories = DemuxingProtocolDecoder.this.decoderFactories;
234             decoders = new MessageDecoder[decoderFactories.length];
235             for (int i = decoderFactories.length - 1; i >= 0; i--) {
236                 decoders[i] = decoderFactories[i].getDecoder();
237             }
238         }
239     }
240 
241     private static class SingletonMessageDecoderFactory implements
242             MessageDecoderFactory {
243         private final MessageDecoder decoder;
244 
245         private SingletonMessageDecoderFactory(MessageDecoder decoder) {
246             if (decoder == null) {
247                 throw new NullPointerException("decoder");
248             }
249             this.decoder = decoder;
250         }
251 
252         public MessageDecoder getDecoder() {
253             return decoder;
254         }
255     }
256 
257     private static class DefaultConstructorMessageDecoderFactory implements
258             MessageDecoderFactory {
259         private final Class<?> decoderClass;
260 
261         private DefaultConstructorMessageDecoderFactory(Class<?> decoderClass) {
262             if (decoderClass == null) {
263                 throw new NullPointerException("decoderClass");
264             }
265 
266             if (!MessageDecoder.class.isAssignableFrom(decoderClass)) {
267                 throw new IllegalArgumentException(
268                         "decoderClass is not assignable to MessageDecoder");
269             }
270             this.decoderClass = decoderClass;
271         }
272 
273         public MessageDecoder getDecoder() throws Exception {
274             return (MessageDecoder) decoderClass.newInstance();
275         }
276     }
277 }