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>byte</code> values.
028 * 
029 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
030 */
031public abstract class SingleByteDecodingState implements DecodingState {
032
033    public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out) throws Exception {
034        if (in.hasRemaining()) {
035            return finishDecode(in.get(), out);
036        }
037
038        return this;
039    }
040
041    /**
042     * {@inheritDoc}
043     */
044    public DecodingState finishDecode(ProtocolDecoderOutput out) throws Exception {
045        throw new ProtocolDecoderException("Unexpected end of session while waiting for a single byte.");
046    }
047
048    /**
049     * Invoked when this state has consumed a complete <code>byte</code>.
050     * 
051     * @param b the byte.
052     * @param out the current {@link ProtocolDecoderOutput} used to write 
053     *        decoded messages.
054     * @return the next state if a state transition was triggered (use 
055     *         <code>this</code> for loop transitions) or <code>null</code> if 
056     *         the state machine has reached its end.
057     * @throws Exception if the read data violated protocol specification.
058     */
059    protected abstract DecodingState finishDecode(byte b, ProtocolDecoderOutput out) throws Exception;
060}