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, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.client;
019
020import java.util.Arrays;
021import org.apache.hadoop.hbase.HConstants;
022import org.apache.hadoop.hbase.util.Bytes;
023import org.apache.yetus.audience.InterfaceAudience;
024
025@InterfaceAudience.Private
026public class ClientUtil {
027
028  public static boolean areScanStartRowAndStopRowEqual(byte[] startRow, byte[] stopRow) {
029    return startRow != null && startRow.length > 0 && Bytes.equals(startRow, stopRow);
030  }
031
032  public static Cursor createCursor(byte[] row) {
033    return new Cursor(row);
034  }
035
036  /**
037   * <p>
038   * When scanning for a prefix the scan should stop immediately after the the last row that has the
039   * specified prefix. This method calculates the closest next rowKey immediately following the
040   * given rowKeyPrefix.
041   * </p>
042   * <p>
043   * <b>IMPORTANT: This converts a rowKey<u>Prefix</u> into a rowKey</b>.
044   * </p>
045   * <p>
046   * If the prefix is an 'ASCII' string put into a byte[] then this is easy because you can simply
047   * increment the last byte of the array. But if your application uses real binary rowids you may
048   * run into the scenario that your prefix is something like:
049   * </p>
050   * &nbsp;&nbsp;&nbsp;<b>{ 0x12, 0x23, 0xFF, 0xFF }</b><br/>
051   * Then this stopRow needs to be fed into the actual scan<br/>
052   * &nbsp;&nbsp;&nbsp;<b>{ 0x12, 0x24 }</b> (Notice that it is shorter now)<br/>
053   * This method calculates the correct stop row value for this usecase.
054   * @param rowKeyPrefix the rowKey<u>Prefix</u>.
055   * @return the closest next rowKey immediately following the given rowKeyPrefix.
056   */
057  public static byte[] calculateTheClosestNextRowKeyForPrefix(byte[] rowKeyPrefix) {
058    // Essentially we are treating it like an 'unsigned very very long' and doing +1 manually.
059    // Search for the place where the trailing 0xFFs start
060    int offset = rowKeyPrefix.length;
061    while (offset > 0) {
062      if (rowKeyPrefix[offset - 1] != (byte) 0xFF) {
063        break;
064      }
065      offset--;
066    }
067
068    if (offset == 0) {
069      // We got an 0xFFFF... (only FFs) stopRow value which is
070      // the last possible prefix before the end of the table.
071      // So set it to stop at the 'end of the table'
072      return HConstants.EMPTY_END_ROW;
073    }
074
075    // Copy the right length of the original
076    byte[] newStopRow = Arrays.copyOfRange(rowKeyPrefix, 0, offset);
077    // And increment the last one
078    newStopRow[newStopRow.length - 1]++;
079    return newStopRow;
080  }
081}