001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.activemq.transport.reliable;
018
019import java.io.IOException;
020
021/**
022 * Throws an exception if packets are dropped causing the transport to be
023 * closed.
024 * 
025 * 
026 */
027public class DefaultReplayStrategy implements ReplayStrategy {
028
029    private int maximumDifference = 5;
030
031    public DefaultReplayStrategy() {
032    }
033
034    public DefaultReplayStrategy(int maximumDifference) {
035        this.maximumDifference = maximumDifference;
036    }
037
038    public boolean onDroppedPackets(ReliableTransport transport, int expectedCounter, int actualCounter, int nextAvailableCounter) throws IOException {
039        int difference = actualCounter - expectedCounter;
040        long count = Math.abs(difference);
041        if (count > maximumDifference) {
042            int upperLimit = actualCounter - 1;
043            if (upperLimit < expectedCounter) {
044                upperLimit = expectedCounter;
045            }
046            transport.requestReplay(expectedCounter, upperLimit);
047        }
048
049        // lets discard old commands
050        return difference > 0;
051    }
052
053    public void onReceivedPacket(ReliableTransport transport, long expectedCounter) {
054        // TODO we could pro-actively evict stuff from the buffer if we knew there was only one client
055    }
056
057    public int getMaximumDifference() {
058        return maximumDifference;
059    }
060
061    /**
062     * Sets the maximum allowed difference between an expected packet and an
063     * actual packet before an error occurs
064     */
065    public void setMaximumDifference(int maximumDifference) {
066        this.maximumDifference = maximumDifference;
067    }
068
069}