001/*
002 * CDDL HEADER START
003 *
004 * The contents of this file are subject to the terms of the
005 * Common Development and Distribution License, Version 1.0 only
006 * (the "License").  You may not use this file except in compliance
007 * with the License.
008 *
009 * You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
010 * or http://forgerock.org/license/CDDLv1.0.html.
011 * See the License for the specific language governing permissions
012 * and limitations under the License.
013 *
014 * When distributing Covered Code, include this CDDL HEADER in each
015 * file and include the License file at legal-notices/CDDLv1_0.txt.
016 * If applicable, add the following below this CDDL HEADER, with the
017 * fields enclosed by brackets "[]" replaced with your own identifying
018 * information:
019 *      Portions Copyright [yyyy] [name of copyright owner]
020 *
021 * CDDL HEADER END
022 *
023 *
024 *      Copyright 2008-2010 Sun Microsystems, Inc.
025 *      Portions Copyright 2015 ForgeRock AS
026 */
027package org.opends.server.replication.plugin;
028
029import java.util.zip.Checksum;
030
031/**
032 * This class computes the generation id used for a replication domain.
033 * It is a checksum based on some special entries/attributes of the domain.
034 * The written stream to this class is the LDIF representation of the entries
035 * we are interested in for computing the generation id. The current
036 * implementation simply does the sum of each written byte and stores the value
037 * in a long. We do not care about the cycling long as the probability of 2
038 * data sets having the same checksum is very low.
039 */
040public class GenerationIdChecksum implements Checksum
041{
042  /** Checksum to be returned. */
043  private long checksum;
044
045  /** This is the generation id for an empty backend. */
046  public static final long EMPTY_BACKEND_GENERATION_ID = 48L;
047
048  /** Update the checksum with one added byte. */
049  private void updateWithOneByte(byte b)
050  {
051    /*
052     * The "end of line" code is CRLF under windows but LF on UNIX. So to get
053     * the same checksum value on every platforms, we always exclude the CR and
054     * LF characters from the computation.
055     */
056    if (b != 0x0D && b != 0x0A) // CR=0D and LF=0A
057    {
058      checksum += b;
059    }
060  }
061
062  /** {@inheritDoc} */
063  public void update(int b)
064  {
065    updateWithOneByte((byte) b);
066  }
067
068  /** {@inheritDoc} */
069  public void update(byte[] b, int off, int len)
070  {
071    for (int i = off; i < off + len; i++)
072    {
073      updateWithOneByte(b[i]);
074    }
075  }
076
077  /** {@inheritDoc} */
078  public long getValue()
079  {
080    if (checksum != 0L)
081    {
082      return checksum;
083    } else
084    {
085      /*
086       * Computing an empty backend writes the number of entries (0) only,
087       * will not be added to the checksum as no entries will follow. To treat
088       * this special case, and to keep consistency with old versions, in that
089       * case we hardcode and return the generation id value for an empty
090       * backend.
091       */
092      return EMPTY_BACKEND_GENERATION_ID;
093    }
094  }
095
096  /** {@inheritDoc} */
097  public void reset()
098  {
099    checksum = 0L;
100  }
101}