001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License.
018 *
019 */
020package org.apache.mina.filter.codec.statemachine;
021
022import org.apache.mina.core.buffer.IoBuffer;
023import org.apache.mina.filter.codec.ProtocolDecoderException;
024import org.apache.mina.filter.codec.ProtocolDecoderOutput;
025
026/**
027 * {@link DecodingState} which decodes <code>short</code> values in big-endian 
028 * order (high bytes come first).
029 * 
030 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
031 */
032public abstract class ShortIntegerDecodingState implements DecodingState {
033    private int counter;
034
035    /**
036     * {@inheritDoc}
037     */
038    public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out) throws Exception {
039        int highByte = 0;
040
041
042        while (in.hasRemaining()) {
043            switch (counter) {
044            case 0:
045                highByte = in.getUnsigned();
046                break;
047                
048            case 1:
049                counter = 0;
050                return finishDecode((short) ((highByte << 8) | in.getUnsigned()), out);
051                
052            default:
053                throw new InternalError();
054            }
055
056            counter++;
057        }
058        return this;
059    }
060
061    /**
062     * {@inheritDoc}
063     */
064    public DecodingState finishDecode(ProtocolDecoderOutput out) throws Exception {
065        throw new ProtocolDecoderException("Unexpected end of session while waiting for a short integer.");
066    }
067
068    /**
069     * Invoked when this state has consumed a complete <code>short</code>.
070     * 
071     * @param value the short.
072     * @param out the current {@link ProtocolDecoderOutput} used to write 
073     *        decoded messages.
074     * @return the next state if a state transition was triggered (use 
075     *         <code>this</code> for loop transitions) or <code>null</code> if 
076     *         the state machine has reached its end.
077     * @throws Exception if the read data violated protocol specification.
078     */
079    protected abstract DecodingState finishDecode(short value, ProtocolDecoderOutput out) throws Exception;
080}