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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.prefixedstring;
21  
22  import org.apache.mina.core.buffer.IoBuffer;
23  import org.apache.mina.core.session.IoSession;
24  import org.apache.mina.filter.codec.ProtocolEncoderAdapter;
25  import org.apache.mina.filter.codec.ProtocolEncoderOutput;
26  import org.apache.mina.filter.codec.ProtocolEncoder;
27  
28  import java.nio.charset.Charset;
29  
30  /**
31   * A {@link ProtocolEncoder} which encodes a string
32   * using a fixed-length length prefix.
33   *
34   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
35   */
36  public class PrefixedStringEncoder extends ProtocolEncoderAdapter {
37  
38      public final static int DEFAULT_PREFIX_LENGTH = 4;
39  
40      public final static int DEFAULT_MAX_DATA_LENGTH = 2048;
41  
42      private final Charset charset;
43  
44      private int prefixLength = DEFAULT_PREFIX_LENGTH;
45  
46      private int maxDataLength = DEFAULT_MAX_DATA_LENGTH;
47  
48      public PrefixedStringEncoder(Charset charset, int prefixLength, int maxDataLength) {
49          this.charset = charset;
50          this.prefixLength = prefixLength;
51          this.maxDataLength = maxDataLength;
52      }
53  
54      public PrefixedStringEncoder(Charset charset, int prefixLength) {
55          this(charset, prefixLength, DEFAULT_MAX_DATA_LENGTH);
56      }
57  
58      public PrefixedStringEncoder(Charset charset) {
59          this(charset, DEFAULT_PREFIX_LENGTH);
60      }
61  
62      public PrefixedStringEncoder() {
63          this(Charset.defaultCharset());
64      }
65  
66      /**
67       * Sets the number of bytes used by the length prefix
68       *
69       * @param prefixLength the length of the length prefix (1, 2, or 4)
70       */
71      public void setPrefixLength(int prefixLength) {
72          if (prefixLength != 1 && prefixLength != 2 && prefixLength != 4) {
73              throw new IllegalArgumentException("prefixLength: " + prefixLength);
74          }
75          this.prefixLength = prefixLength;
76      }
77  
78      /**
79       * Gets the length of the length prefix (1, 2, or 4)
80       *
81       * @return length of the length prefix
82       */
83      public int getPrefixLength() {
84          return prefixLength;
85      }
86  
87      /**
88       * Sets the maximum number of bytes allowed for encoding a single String
89       * (including the prefix)
90       * <p>
91       * The encoder will throw a {@link IllegalArgumentException} when more bytes
92       * are needed to encode a String value.
93       * The default value is {@link PrefixedStringEncoder#DEFAULT_MAX_DATA_LENGTH}.
94       * </p>
95       *
96       * @param maxDataLength maximum number of bytes allowed for encoding a single String
97       */
98      public void setMaxDataLength(int maxDataLength) {
99          this.maxDataLength = maxDataLength;
100     }
101 
102     /**
103      * Gets the maximum number of bytes allowed for encoding a single String     *
104      *
105      * @return maximum number of bytes allowed for encoding a single String (prefix included)
106      */
107     public int getMaxDataLength() {
108         return maxDataLength;
109     }
110 
111     public void encode(IoSession session, Object message, ProtocolEncoderOutput out) throws Exception {
112         String value = (String) message;
113         IoBuffer buffer = IoBuffer.allocate(value.length()).setAutoExpand(true);
114         buffer.putPrefixedString(value, prefixLength, charset.newEncoder());
115         if (buffer.position() > maxDataLength) {
116             throw new IllegalArgumentException("Data length: " + buffer.position());
117         }
118         buffer.flip();
119         out.write(buffer);
120     }
121 }