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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.statemachine;
21  
22  import org.apache.mina.core.buffer.IoBuffer;
23  import org.apache.mina.filter.codec.ProtocolDecoderException;
24  import org.apache.mina.filter.codec.ProtocolDecoderOutput;
25  
26  /**
27   * {@link DecodingState} which decodes <code>short</code> values in big-endian 
28   * order (high bytes come first).
29   * 
30   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
31   */
32  public abstract class ShortIntegerDecodingState implements DecodingState {
33  
34      private int highByte;
35  
36      private int counter;
37  
38      /**
39       * {@inheritDoc}
40       */
41      public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out) throws Exception {
42  
43          while (in.hasRemaining()) {
44              switch (counter) {
45              case 0:
46                  highByte = in.getUnsigned();
47                  break;
48              case 1:
49                  counter = 0;
50                  return finishDecode((short) ((highByte << 8) | in.getUnsigned()), out);
51              default:
52                  throw new InternalError();
53              }
54  
55              counter++;
56          }
57          return this;
58      }
59  
60      /**
61       * {@inheritDoc}
62       */
63      public DecodingState finishDecode(ProtocolDecoderOutput out) throws Exception {
64          throw new ProtocolDecoderException("Unexpected end of session while waiting for a short integer.");
65      }
66  
67      /**
68       * Invoked when this state has consumed a complete <code>short</code>.
69       * 
70       * @param value the short.
71       * @param out the current {@link ProtocolDecoderOutput} used to write 
72       *        decoded messages.
73       * @return the next state if a state transition was triggered (use 
74       *         <code>this</code> for loop transitions) or <code>null</code> if 
75       *         the state machine has reached its end.
76       * @throws Exception if the read data violated protocol specification.
77       */
78      protected abstract DecodingState finishDecode(short value, ProtocolDecoderOutput out) throws Exception;
79  }