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.ProtocolDecoderOutput;
024
025/**
026 * {@link DecodingState} which skips data until {@link #canSkip(byte)} returns 
027 * <tt>false</tt>.
028 *
029 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
030 */
031public abstract class SkippingState implements DecodingState {
032
033    private int skippedBytes;
034
035    /**
036     * {@inheritDoc}
037     */
038    public DecodingState decode(IoBuffer in, ProtocolDecoderOutput out) throws Exception {
039        int beginPos = in.position();
040        int limit = in.limit();
041        for (int i = beginPos; i < limit; i++) {
042            byte b = in.get(i);
043            if (!canSkip(b)) {
044                in.position(i);
045                int answer = this.skippedBytes;
046                this.skippedBytes = 0;
047                return finishDecode(answer);
048            }
049
050            skippedBytes++;
051        }
052
053        in.position(limit);
054        return this;
055    }
056
057    /**
058     * {@inheritDoc}
059     */
060    public DecodingState finishDecode(ProtocolDecoderOutput out) throws Exception {
061        return finishDecode(skippedBytes);
062    }
063
064    /**
065     * Called to determine whether the specified byte can be skipped.
066     * 
067     * @param b the byte to check.
068     * @return <tt>true</tt> if the byte can be skipped.
069     */
070    protected abstract boolean canSkip(byte b);
071
072    /**
073     * Invoked when this state cannot skip any more bytes.
074     * 
075     * @param skippedBytes the number of bytes skipped.
076     * @return the next state if a state transition was triggered (use 
077     *         <code>this</code> for loop transitions) or <code>null</code> if 
078     *         the state machine has reached its end.
079     * @throws Exception if the read data violated protocol specification.
080     */
081    protected abstract DecodingState finishDecode(int skippedBytes) throws Exception;
082}