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 java.util.ArrayList;
23 import java.util.List;
24
25 import org.apache.mina.core.buffer.IoBuffer;
26 import org.apache.mina.filter.codec.ProtocolCodecFilter;
27 import org.apache.mina.filter.codec.ProtocolDecoderOutput;
28 import org.slf4j.Logger;
29 import org.slf4j.LoggerFactory;
30
31 /**
32 * Abstract base class for decoder state machines. Calls {@link #init()} to
33 * get the start {@link DecodingState} of the state machine. Calls
34 * {@link #destroy()} when the state machine has reached its end state or when
35 * the session is closed.
36 * <p>
37 * NOTE: The {@link ProtocolDecoderOutput} used by this class when calling
38 * {@link DecodingState#decode(IoBuffer, ProtocolDecoderOutput)} buffers decoded
39 * messages in a {@link List}. Once the state machine has reached its end state
40 * this class will call {@link #finishDecode(List, ProtocolDecoderOutput)}. The
41 * implementation will have to take care of writing the decoded messages to the
42 * real {@link ProtocolDecoderOutput} used by the configured
43 * {@link ProtocolCodecFilter}.
44 * </p>
45 *
46 * @author The Apache MINA Project (dev@mina.apache.org)
47 * @version $Rev: 671827 $, $Date: 2008-06-26 10:49:48 +0200 (jeu, 26 jun 2008) $
48 */
49 public abstract class DecodingStateMachine implements DecodingState {
50 private final Logger log = LoggerFactory
51 .getLogger(DecodingStateMachine.class);
52
53 private final List<Object> childProducts = new ArrayList<Object>();
54
55 private final ProtocolDecoderOutput childOutput = new ProtocolDecoderOutput() {
56 public void flush() {
57 }
58
59 public void write(Object message) {
60 childProducts.add(message);
61 }
62 };
63
64 private DecodingState currentState;
65 private boolean initialized;
66
67 /**
68 * Invoked to initialize this state machine.
69 *
70 * @return the start {@link DecodingState}.
71 */
72 protected abstract DecodingState init() throws Exception;
73
74 /**
75 * Called once the state machine has reached its end.
76 *
77 * @param childProducts contains the messages generated by each of the
78 * {@link DecodingState}s which were exposed to the received data
79 * during the life time of this state machine.
80 * @param out the real {@link ProtocolDecoderOutput} used by the
81 * {@link ProtocolCodecFilter}.
82 * @return the next state if the state machine should resume.
83 */
84 protected abstract DecodingState finishDecode(List<Object> childProducts,
85 ProtocolDecoderOutput out) throws Exception;
86
87 /**
88 * Invoked to destroy this state machine once the end state has been reached
89 * or the session has been closed.
90 */
91 protected abstract void destroy() throws Exception;
92
93 /**
94 * {@inheritDoc}
95 */
96 public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out)
97 throws Exception {
98 DecodingState state = getCurrentState();
99
100 final int limit = in.limit();
101 int pos = in.position();
102
103 try {
104 for (;;) {
105 // Wait for more data if all data is consumed.
106 if (pos == limit) {
107 break;
108 }
109
110 DecodingState oldState = state;
111 state = state.decode(in, childOutput);
112
113 // If finished, call finishDecode
114 if (state == null) {
115 return finishDecode(childProducts, out);
116 }
117
118 int newPos = in.position();
119
120 // Wait for more data if nothing is consumed and state didn't change.
121 if (newPos == pos && oldState == state) {
122 break;
123 }
124 pos = newPos;
125 }
126
127 return this;
128 } catch (Exception e) {
129 state = null;
130 throw e;
131 } finally {
132 this.currentState = state;
133
134 // Destroy if decoding is finished or failed.
135 if (state == null) {
136 cleanup();
137 }
138 }
139 }
140
141 /**
142 * {@inheritDoc}
143 */
144 public DecodingState finishDecode(ProtocolDecoderOutput out)
145 throws Exception {
146 DecodingState nextState;
147 DecodingState state = getCurrentState();
148 try {
149 for (;;) {
150 DecodingState oldState = state;
151 state = state.finishDecode(childOutput);
152 if (state == null) {
153 // Finished
154 break;
155 }
156
157 // Exit if state didn't change.
158 if (oldState == state) {
159 break;
160 }
161 }
162 } catch (Exception e) {
163 state = null;
164 log.debug(
165 "Ignoring the exception caused by a closed session.", e);
166 } finally {
167 this.currentState = state;
168 nextState = finishDecode(childProducts, out);
169 if (state == null) {
170 cleanup();
171 }
172 }
173 return nextState;
174 }
175
176 private void cleanup() {
177 if (!initialized) {
178 throw new IllegalStateException();
179 }
180
181 initialized = false;
182 childProducts.clear();
183 try {
184 destroy();
185 } catch (Exception e2) {
186 log.warn("Failed to destroy a decoding state machine.", e2);
187 }
188 }
189
190 private DecodingState getCurrentState() throws Exception {
191 DecodingState state = this.currentState;
192 if (state == null) {
193 state = init();
194 initialized = true;
195 }
196 return state;
197 }
198 }