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.BufferDataException;
23 import org.apache.mina.core.buffer.IoBuffer;
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.ProtocolDecoderOutput;
28
29 import java.nio.charset.Charset;
30
31 /**
32 * A {@link ProtocolDecoder} which decodes a String using a fixed-length length prefix.
33 *
34 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
35 */
36 public class PrefixedStringDecoder extends CumulativeProtocolDecoder {
37 /** The default length for the prefix */
38 public static final int DEFAULT_PREFIX_LENGTH = 4;
39
40 /** The default maximum data length */
41 public static final int DEFAULT_MAX_DATA_LENGTH = 2048;
42
43 private final Charset charset;
44
45 private int prefixLength = DEFAULT_PREFIX_LENGTH;
46
47 private int maxDataLength = DEFAULT_MAX_DATA_LENGTH;
48
49 /**
50 * Creates a new PrefixedStringDecoder instance
51 *
52 * @param charset the {@link Charset} to use for decoding
53 * @param prefixLength the length of the prefix
54 * @param maxDataLength maximum number of bytes allowed for a single String
55 */
56 public PrefixedStringDecoder(Charset charset, int prefixLength, int maxDataLength) {
57 this.charset = charset;
58 this.prefixLength = prefixLength;
59 this.maxDataLength = maxDataLength;
60 }
61
62 /**
63 * Creates a new PrefixedStringDecoder instance
64 *
65 * @param charset the {@link Charset} to use for decoding
66 * @param prefixLength the length of the prefix
67 */
68 public PrefixedStringDecoder(Charset charset, int prefixLength) {
69 this(charset, prefixLength, DEFAULT_MAX_DATA_LENGTH);
70 }
71
72 /**
73 * Creates a new PrefixedStringDecoder instance
74 *
75 * @param charset the {@link Charset} to use for decoding
76 */
77 public PrefixedStringDecoder(Charset charset) {
78 this(charset, DEFAULT_PREFIX_LENGTH);
79 }
80
81 /**
82 * Sets the number of bytes used by the length prefix
83 *
84 * @param prefixLength the length of the length prefix (1, 2, or 4)
85 */
86 public void setPrefixLength(int prefixLength) {
87 this.prefixLength = prefixLength;
88 }
89
90 /**
91 * Gets the length of the length prefix (1, 2, or 4)
92 *
93 * @return length of the length prefix
94 */
95 public int getPrefixLength() {
96 return prefixLength;
97 }
98
99 /**
100 * Sets the maximum allowed value specified as data length in the incoming data
101 * <p>
102 * Useful for preventing an OutOfMemory attack by the peer.
103 * The decoder will throw a {@link BufferDataException} when data length
104 * specified in the incoming data is greater than maxDataLength
105 * The default value is {@link PrefixedStringDecoder#DEFAULT_MAX_DATA_LENGTH}.
106 * </p>
107 *
108 * @param maxDataLength maximum allowed value specified as data length in the incoming data
109 */
110 public void setMaxDataLength(int maxDataLength) {
111 this.maxDataLength = maxDataLength;
112 }
113
114 /**
115 * Gets the maximum number of bytes allowed for a single String
116 *
117 * @return maximum number of bytes allowed for a single String
118 */
119 public int getMaxDataLength() {
120 return maxDataLength;
121 }
122
123 /**
124 * {@inheritDoc}
125 */
126 @Override
127 protected boolean doDecode(IoSession session, IoBuffer in, ProtocolDecoderOutput out) throws Exception {
128 if (in.prefixedDataAvailable(prefixLength, maxDataLength)) {
129 String msg = in.getPrefixedString(prefixLength, charset.newDecoder());
130 out.write(msg);
131 return true;
132 }
133
134 return false;
135 }
136 }