/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.hadoop.hbase.io.hfile;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.fs.ChecksumException;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.util.ChecksumType;
  import org.apache.hadoop.util.DataChecksum;
  
  /**
   * Utility methods to compute and validate checksums.
   */
  @InterfaceAudience.Private
  public class ChecksumUtil {
    public static final Log LOG = LogFactory.getLog(ChecksumUtil.class);
  
    /** This is used to reserve space in a byte buffer */
    private static byte[] DUMMY_VALUE = new byte[128 * HFileBlock.CHECKSUM_SIZE];
  
    /** 
     * This is used by unit tests to make checksum failures throw an 
     * exception instead of returning null. Returning a null value from 
     * checksum validation will cause the higher layer to retry that 
     * read with hdfs-level checksums. Instead, we would like checksum 
     * failures to cause the entire unit test to fail.
     */
    private static boolean generateExceptions = false;
  
    /**
     * Generates a checksum for all the data in indata. The checksum is
     * written to outdata.
     * @param indata input data stream
     * @param startOffset starting offset in the indata stream from where to
     *                    compute checkums from
     * @param endOffset ending offset in the indata stream upto
     *                   which checksums needs to be computed
     * @param outdata the output buffer where checksum values are written
     * @param outOffset the starting offset in the outdata where the
     *                  checksum values are written
     * @param checksumType type of checksum
     * @param bytesPerChecksum number of bytes per checksum value
     */
    static void generateChecksums(byte[] indata, int startOffset, int endOffset,
      byte[] outdata, int outOffset, ChecksumType checksumType,
      int bytesPerChecksum) throws IOException {
  
      if (checksumType == ChecksumType.NULL) {
        return; // No checksum for this block.
      }
  
      DataChecksum checksum = DataChecksum.newDataChecksum(
          checksumType.getDataChecksumType(), bytesPerChecksum);
  
      checksum.calculateChunkedSums(
         ByteBuffer.wrap(indata, startOffset, endOffset - startOffset),
         ByteBuffer.wrap(outdata, outOffset, outdata.length - outOffset));
    }
  
    /**
     * Validates that the data in the specified HFileBlock matches the
     * checksum.  Generates the checksum for the data and
     * then validate that it matches the value stored in the header.
     * If there is a checksum mismatch, then return false. Otherwise
     * return true.
     * The header is extracted from the specified HFileBlock while the
     * data-to-be-verified is extracted from 'data'.
     */
    static boolean validateBlockChecksum(Path path, HFileBlock block,
      byte[] data, int hdrSize) throws IOException {
  
      // If this is an older version of the block that does not have
      // checksums, then return false indicating that checksum verification
      // did not succeed. Actually, this methiod should never be called
      // when the minorVersion is 0, thus this is a defensive check for a
      // cannot-happen case. Since this is a cannot-happen case, it is
      // better to return false to indicate a checksum validation failure.
      if (!block.getHFileContext().isUseHBaseChecksum()) {
       return false;
     }
 
     // Get a checksum object based on the type of checksum that is
     // set in the HFileBlock header. A ChecksumType.NULL indicates that 
     // the caller is not interested in validating checksums, so we
     // always return true.
     ChecksumType cktype = ChecksumType.codeToType(block.getChecksumType());
     if (cktype == ChecksumType.NULL) {
       return true; // No checksum validations needed for this block.
     }
 
     // read in the stored value of the checksum size from the header.
     int bytesPerChecksum = block.getBytesPerChecksum();
 
     DataChecksum dataChecksum = DataChecksum.newDataChecksum(
         cktype.getDataChecksumType(), bytesPerChecksum);
     assert dataChecksum != null;
     int sizeWithHeader =  block.getOnDiskDataSizeWithHeader();
     if (LOG.isTraceEnabled()) {
       LOG.info("length of data = " + data.length
           + " OnDiskDataSizeWithHeader = " + sizeWithHeader
           + " checksum type = " + cktype.getName()
           + " file =" + path.toString()
           + " header size = " + hdrSize
           + " bytesPerChecksum = " + bytesPerChecksum);
     }
     try {
       dataChecksum.verifyChunkedSums(ByteBuffer.wrap(data, 0, sizeWithHeader),
           ByteBuffer.wrap(data, sizeWithHeader, data.length - sizeWithHeader),
                           path.toString(), 0);
     } catch (ChecksumException e) {
       return false;
     }
     return true;  // checksum is valid
   }
 
   /**
    * Returns the number of bytes needed to store the checksums for
    * a specified data size
    * @param datasize number of bytes of data
    * @param bytesPerChecksum number of bytes in a checksum chunk
    * @return The number of bytes needed to store the checksum values
    */
   static long numBytes(long datasize, int bytesPerChecksum) {
     return numChunks(datasize, bytesPerChecksum) * 
                      HFileBlock.CHECKSUM_SIZE;
   }
 
   /**
    * Returns the number of checksum chunks needed to store the checksums for
    * a specified data size
    * @param datasize number of bytes of data
    * @param bytesPerChecksum number of bytes in a checksum chunk
    * @return The number of checksum chunks
    */
   static long numChunks(long datasize, int bytesPerChecksum) {
     long numChunks = datasize/bytesPerChecksum;
     if (datasize % bytesPerChecksum != 0) {
       numChunks++;
     }
     return numChunks;
   }
 
   /**
    * Write dummy checksums to the end of the specified bytes array
    * to reserve space for writing checksums later
    * @param baos OutputStream to write dummy checkum values
    * @param numBytes Number of bytes of data for which dummy checksums
    *                 need to be generated
    * @param bytesPerChecksum Number of bytes per checksum value
    */
   static void reserveSpaceForChecksums(ByteArrayOutputStream baos,
     int numBytes, int bytesPerChecksum) throws IOException {
     long numChunks = numChunks(numBytes, bytesPerChecksum);
     long bytesLeft = numChunks * HFileBlock.CHECKSUM_SIZE;
     while (bytesLeft > 0) {
       long count = Math.min(bytesLeft, DUMMY_VALUE.length);
       baos.write(DUMMY_VALUE, 0, (int)count);
       bytesLeft -= count;
     }
   }
 
   /**
    * Mechanism to throw an exception in case of hbase checksum
    * failure. This is used by unit tests only.
    * @param value Setting this to true will cause hbase checksum
    *              verification failures to generate exceptions.
    */
   public static void generateExceptionForChecksumFailureForTest(boolean value) {
     generateExceptions = value;
   }
 }