View Javadoc

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.ProtocolDecoderOutput;
24  
25  /**
26   * {@link DecodingState} which consumes all received bytes until a configured
27   * number of read bytes has been reached. Please note that this state can
28   * produce a buffer with less data than the configured length if the associated 
29   * session has been closed unexpectedly.
30   *
31   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
32   */
33  public abstract class FixedLengthDecodingState implements DecodingState {
34  
35      private final int length;
36  
37      private IoBuffer buffer;
38  
39      /**
40       * Constructs a new instance using the specified decode length.
41       *
42       * @param length the number of bytes to read.
43       */
44      public FixedLengthDecodingState(int length) {
45          this.length = length;
46      }
47  
48      /**
49       * {@inheritDoc}
50       */
51      public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out)
52              throws Exception {
53          if (buffer == null) {
54              if (in.remaining() >= length) {
55                  int limit = in.limit();
56                  in.limit(in.position() + length);
57                  IoBuffer product = in.slice();
58                  in.position(in.position() + length);
59                  in.limit(limit);
60                  return finishDecode(product, out);
61              }
62  
63              buffer = IoBuffer.allocate(length);
64              buffer.put(in);
65              return this;
66          }
67  
68          if (in.remaining() >= length - buffer.position()) {
69              int limit = in.limit();
70              in.limit(in.position() + length - buffer.position());
71              buffer.put(in);
72              in.limit(limit);
73              IoBuffer product = this.buffer;
74              this.buffer = null;
75              return finishDecode(product.flip(), out);
76          }
77          
78          buffer.put(in);
79          return this;
80      }
81  
82      /**
83       * {@inheritDoc}
84       */
85      public DecodingState finishDecode(ProtocolDecoderOutput out)
86              throws Exception {
87          IoBuffer readData;
88          if (buffer == null) {
89              readData = IoBuffer.allocate(0);
90          } else {
91              readData = buffer.flip();
92              buffer = null;
93          }
94          return finishDecode(readData ,out);
95      }
96  
97      /**
98       * Invoked when this state has consumed the configured number of bytes.
99       * 
100      * @param product the data.
101      * @param out the current {@link ProtocolDecoderOutput} used to write 
102      *        decoded messages.
103      * @return the next state if a state transition was triggered (use 
104      *         <code>this</code> for loop transitions) or <code>null</code> if 
105      *         the state machine has reached its end.
106      * @throws Exception if the read data violated protocol specification.
107      */
108     protected abstract DecodingState finishDecode(IoBuffer product,
109             ProtocolDecoderOutput out) throws Exception;
110 }