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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*/
package org.apache.mina.filter.codec.demux;
import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.AttributeKey;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.CumulativeProtocolDecoder;
import org.apache.mina.filter.codec.ProtocolDecoder;
import org.apache.mina.filter.codec.ProtocolDecoderException;
import org.apache.mina.filter.codec.ProtocolDecoderOutput;
/**
* A composite {@link ProtocolDecoder} that demultiplexes incoming {@link IoBuffer}
* decoding requests into an appropriate {@link MessageDecoder}.
*
* <h2>Internal mechanism of {@link MessageDecoder} selection</h2>
* <p>
* <ol>
* <li>{@link DemuxingProtocolDecoder} iterates the list of candidate
* {@link MessageDecoder}s and calls {@link MessageDecoder#decodable(IoSession, IoBuffer)}.
* Initially, all registered {@link MessageDecoder}s are candidates.</li>
* <li>If {@link MessageDecoderResult#NOT_OK} is returned, it is removed from the candidate
* list.</li>
* <li>If {@link MessageDecoderResult#NEED_DATA} is returned, it is retained in the candidate
* list, and its {@link MessageDecoder#decodable(IoSession, IoBuffer)} will be invoked
* again when more data is received.</li>
* <li>If {@link MessageDecoderResult#OK} is returned, {@link DemuxingProtocolDecoder}
* found the right {@link MessageDecoder}.</li>
* <li>If there's no candidate left, an exception is raised. Otherwise,
* {@link DemuxingProtocolDecoder} will keep iterating the candidate list.
* </ol>
*
* Please note that any change of position and limit of the specified {@link IoBuffer}
* in {@link MessageDecoder#decodable(IoSession, IoBuffer)} will be reverted back to its
* original value.
* <p>
* Once a {@link MessageDecoder} is selected, {@link DemuxingProtocolDecoder} calls
* {@link MessageDecoder#decode(IoSession, IoBuffer, ProtocolDecoderOutput)} continuously
* reading its return value:
* <ul>
* <li>{@link MessageDecoderResult#NOT_OK} - protocol violation; {@link ProtocolDecoderException}
* is raised automatically.</li>
* <li>{@link MessageDecoderResult#NEED_DATA} - needs more data to read the whole message;
* {@link MessageDecoder#decode(IoSession, IoBuffer, ProtocolDecoderOutput)}
* will be invoked again when more data is received.</li>
* <li>{@link MessageDecoderResult#OK} - successfully decoded a message; the candidate list will
* be reset and the selection process will start over.</li>
* </ul>
*
* @author The Apache MINA Project (dev@mina.apache.org)
* @version $Rev: 751744 $, $Date: 2009-03-09 17:53:13 +0100 (Mon, 09 Mar 2009) $
*
* @see MessageDecoderFactory
* @see MessageDecoder
*/
public class DemuxingProtocolDecoder extends CumulativeProtocolDecoder {
private final AttributeKey STATE = new AttributeKey(getClass(), "state");
private MessageDecoderFactory[] decoderFactories = new MessageDecoderFactory[0];
private static final Class<?>[] EMPTY_PARAMS = new Class[0];
public DemuxingProtocolDecoder() {
}
public void addMessageDecoder(Class<? extends MessageDecoder> decoderClass) {
if (decoderClass == null) {
throw new NullPointerException("decoderClass");
}
try {
decoderClass.getConstructor(EMPTY_PARAMS);
} catch (NoSuchMethodException e) {
throw new IllegalArgumentException(
"The specified class doesn't have a public default constructor.");
}
boolean registered = false;
if (MessageDecoder.class.isAssignableFrom(decoderClass)) {
addMessageDecoder(new DefaultConstructorMessageDecoderFactory(decoderClass));
registered = true;
}
if (!registered) {
throw new IllegalArgumentException(
"Unregisterable type: " + decoderClass);
}
}
public void addMessageDecoder(MessageDecoder decoder) {
addMessageDecoder(new SingletonMessageDecoderFactory(decoder));
}
public void addMessageDecoder(MessageDecoderFactory factory) {
if (factory == null) {
throw new NullPointerException("factory");
}
MessageDecoderFactory[] decoderFactories = this.decoderFactories;
MessageDecoderFactory[] newDecoderFactories = new MessageDecoderFactory[decoderFactories.length + 1];
System.arraycopy(decoderFactories, 0, newDecoderFactories, 0,
decoderFactories.length);
newDecoderFactories[decoderFactories.length] = factory;
this.decoderFactories = newDecoderFactories;
}
@Override
protected boolean doDecode(IoSession session, IoBuffer in,
ProtocolDecoderOutput out) throws Exception {
State state = getState(session);
if (state.currentDecoder == null) {
MessageDecoder[] decoders = state.decoders;
int undecodables = 0;
for (int i = decoders.length - 1; i >= 0; i--) {
MessageDecoder decoder = decoders[i];
int limit = in.limit();
int pos = in.position();
MessageDecoderResult result;
try {
result = decoder.decodable(session, in);
} finally {
in.position(pos);
in.limit(limit);
}
if (result == MessageDecoder.OK) {
state.currentDecoder = decoder;
break;
} else if (result == MessageDecoder.NOT_OK) {
undecodables++;
} else if (result != MessageDecoder.NEED_DATA) {
throw new IllegalStateException(
"Unexpected decode result (see your decodable()): "
+ result);
}
}
if (undecodables == decoders.length) {
// Throw an exception if all decoders cannot decode data.
String dump = in.getHexDump();
in.position(in.limit()); // Skip data
ProtocolDecoderException e = new ProtocolDecoderException(
"No appropriate message decoder: " + dump);
e.setHexdump(dump);
throw e;
}
if (state.currentDecoder == null) {
// Decoder is not determined yet (i.e. we need more data)
return false;
}
}
MessageDecoderResult result = state.currentDecoder.decode(session, in,
out);
if (result == MessageDecoder.OK) {
state.currentDecoder = null;
return true;
} else if (result == MessageDecoder.NEED_DATA) {
return false;
} else if (result == MessageDecoder.NOT_OK) {
state.currentDecoder = null;
throw new ProtocolDecoderException(
"Message decoder returned NOT_OK.");
} else {
state.currentDecoder = null;
throw new IllegalStateException(
"Unexpected decode result (see your decode()): "
+ result);
}
}
@Override
public void finishDecode(IoSession session, ProtocolDecoderOutput out)
throws Exception {
super.finishDecode(session, out);
State state = getState(session);
MessageDecoder currentDecoder = state.currentDecoder;
if (currentDecoder == null) {
return;
}
currentDecoder.finishDecode(session, out);
}
@Override
public void dispose(IoSession session) throws Exception {
super.dispose(session);
session.removeAttribute(STATE);
}
private State getState(IoSession session) throws Exception {
State state = (State) session.getAttribute(STATE);
if (state == null) {
state = new State();
State oldState = (State) session.setAttributeIfAbsent(STATE, state);
if (oldState != null) {
state = oldState;
}
}
return state;
}
private class State {
private final MessageDecoder[] decoders;
private MessageDecoder currentDecoder;
private State() throws Exception {
MessageDecoderFactory[] decoderFactories = DemuxingProtocolDecoder.this.decoderFactories;
decoders = new MessageDecoder[decoderFactories.length];
for (int i = decoderFactories.length - 1; i >= 0; i--) {
decoders[i] = decoderFactories[i].getDecoder();
}
}
}
private static class SingletonMessageDecoderFactory implements
MessageDecoderFactory {
private final MessageDecoder decoder;
private SingletonMessageDecoderFactory(MessageDecoder decoder) {
if (decoder == null) {
throw new NullPointerException("decoder");
}
this.decoder = decoder;
}
public MessageDecoder getDecoder() {
return decoder;
}
}
private static class DefaultConstructorMessageDecoderFactory implements
MessageDecoderFactory {
private final Class<?> decoderClass;
private DefaultConstructorMessageDecoderFactory(Class<?> decoderClass) {
if (decoderClass == null) {
throw new NullPointerException("decoderClass");
}
if (!MessageDecoder.class.isAssignableFrom(decoderClass)) {
throw new IllegalArgumentException(
"decoderClass is not assignable to MessageDecoder");
}
this.decoderClass = decoderClass;
}
public MessageDecoder getDecoder() throws Exception {
return (MessageDecoder) decoderClass.newInstance();
}
}
}