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.core.filterchain.IoFilter.NextFilter;
27 import org.apache.mina.core.session.IoSession;
28 import org.apache.mina.filter.codec.ProtocolCodecFilter;
29 import org.apache.mina.filter.codec.ProtocolDecoderOutput;
30 import org.slf4j.Logger;
31 import org.slf4j.LoggerFactory;
32
33 /**
34 * Abstract base class for decoder state machines. Calls {@link #init()} to
35 * get the start {@link DecodingState} of the state machine. Calls
36 * {@link #destroy()} when the state machine has reached its end state or when
37 * the session is closed.
38 * <p>
39 * NOTE: The {@link ProtocolDecoderOutput} used by this class when calling
40 * {@link DecodingState#decode(IoBuffer, ProtocolDecoderOutput)} buffers decoded
41 * messages in a {@link List}. Once the state machine has reached its end state
42 * this class will call {@link #finishDecode(List, ProtocolDecoderOutput)}. The
43 * implementation will have to take care of writing the decoded messages to the
44 * real {@link ProtocolDecoderOutput} used by the configured
45 * {@link ProtocolCodecFilter}.
46 * </p>
47 *
48 * @author The Apache MINA Project (dev@mina.apache.org)
49 */
50 public abstract class DecodingStateMachine implements DecodingState {
51 private final Logger log = LoggerFactory
52 .getLogger(DecodingStateMachine.class);
53
54 private final List<Object> childProducts = new ArrayList<Object>();
55
56 private final ProtocolDecoderOutput childOutput = new ProtocolDecoderOutput() {
57 public void flush(NextFilter nextFilter, IoSession session) {
58 // Do nothing
59 }
60
61 public void write(Object message) {
62 childProducts.add(message);
63 }
64 };
65
66 private DecodingState currentState;
67 private boolean initialized;
68
69 /**
70 * Invoked to initialize this state machine.
71 *
72 * @return the start {@link DecodingState}.
73 */
74 protected abstract DecodingState init() throws Exception;
75
76 /**
77 * Called once the state machine has reached its end.
78 *
79 * @param childProducts contains the messages generated by each of the
80 * {@link DecodingState}s which were exposed to the received data
81 * during the life time of this state machine.
82 * @param out the real {@link ProtocolDecoderOutput} used by the
83 * {@link ProtocolCodecFilter}.
84 * @return the next state if the state machine should resume.
85 */
86 protected abstract DecodingState finishDecode(List<Object> childProducts,
87 ProtocolDecoderOutput out) throws Exception;
88
89 /**
90 * Invoked to destroy this state machine once the end state has been reached
91 * or the session has been closed.
92 */
93 protected abstract void destroy() throws Exception;
94
95 /**
96 * {@inheritDoc}
97 */
98 public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out)
99 throws Exception {
100 DecodingState state = getCurrentState();
101
102 final int limit = in.limit();
103 int pos = in.position();
104
105 try {
106 for (;;) {
107 // Wait for more data if all data is consumed.
108 if (pos == limit) {
109 break;
110 }
111
112 DecodingState oldState = state;
113 state = state.decode(in, childOutput);
114
115 // If finished, call finishDecode
116 if (state == null) {
117 return finishDecode(childProducts, out);
118 }
119
120 int newPos = in.position();
121
122 // Wait for more data if nothing is consumed and state didn't change.
123 if (newPos == pos && oldState == state) {
124 break;
125 }
126 pos = newPos;
127 }
128
129 return this;
130 } catch (Exception e) {
131 state = null;
132 throw e;
133 } finally {
134 this.currentState = state;
135
136 // Destroy if decoding is finished or failed.
137 if (state == null) {
138 cleanup();
139 }
140 }
141 }
142
143 /**
144 * {@inheritDoc}
145 */
146 public DecodingState finishDecode(ProtocolDecoderOutput out)
147 throws Exception {
148 DecodingState nextState;
149 DecodingState state = getCurrentState();
150 try {
151 for (;;) {
152 DecodingState oldState = state;
153 state = state.finishDecode(childOutput);
154 if (state == null) {
155 // Finished
156 break;
157 }
158
159 // Exit if state didn't change.
160 if (oldState == state) {
161 break;
162 }
163 }
164 } catch (Exception e) {
165 state = null;
166 log.debug(
167 "Ignoring the exception caused by a closed session.", e);
168 } finally {
169 this.currentState = state;
170 nextState = finishDecode(childProducts, out);
171 if (state == null) {
172 cleanup();
173 }
174 }
175 return nextState;
176 }
177
178 private void cleanup() {
179 if (!initialized) {
180 throw new IllegalStateException();
181 }
182
183 initialized = false;
184 childProducts.clear();
185 try {
186 destroy();
187 } catch (Exception e2) {
188 log.warn("Failed to destroy a decoding state machine.", e2);
189 }
190 }
191
192 private DecodingState getCurrentState() throws Exception {
193 DecodingState state = this.currentState;
194 if (state == null) {
195 state = init();
196 initialized = true;
197 }
198 return state;
199 }
200 }