content: /*
   *
   * 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.bookkeeper.bookie.storage.directentrylogger;
  
  import static org.apache.bookkeeper.common.util.ExceptionMessageHelper.exMsg;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.Unpooled;
  import java.io.IOException;
  
  /**
   * The 1K block at the head of the entry logger file
   * that contains the fingerprint and meta-data.
   *
   * <pre>
   * Header is composed of:
   * Fingerprint: 4 bytes "BKLO"
   * Log file HeaderVersion enum: 4 bytes
   * Ledger map offset: 8 bytes
   * Ledgers Count: 4 bytes
   * </pre>
   */
  class Header {
      static final int LOGFILE_LEGACY_HEADER_SIZE = 1024;
      static final int LOGFILE_DIRECT_HEADER_SIZE = Buffer.ALIGNMENT;
      static final int HEADER_VERSION_OFFSET = 4;
      static final int LEDGERS_MAP_OFFSET = HEADER_VERSION_OFFSET + Integer.BYTES;
      static final int LEDGER_COUNT_OFFSET = LEDGERS_MAP_OFFSET + Long.BYTES;
      static final int HEADER_V0 = 0; // Old log file format (no ledgers map index)
      static final int HEADER_V1 = 1; // Introduced ledger map index
      static final int HEADER_CURRENT_VERSION = HEADER_V1;
  
      static final byte[] EMPTY_HEADER = new byte[LOGFILE_DIRECT_HEADER_SIZE];
      static {
          ByteBuf buf = Unpooled.wrappedBuffer(EMPTY_HEADER);
          buf.setByte(0, 'B');
          buf.setByte(1, 'K');
          buf.setByte(2, 'L');
          buf.setByte(3, 'O');
          buf.setInt(HEADER_VERSION_OFFSET, HEADER_V1);
          // legacy header size is 1024, while direct is 4096 so that it can be written as a single block
          // to avoid legacy failing when it encounters the header in direct, create a dummy entry, which
          // skips to the start of the second block
          buf.setInt(LOGFILE_LEGACY_HEADER_SIZE, (buf.capacity() - LOGFILE_LEGACY_HEADER_SIZE) - Integer.BYTES);
          buf.setLong(LOGFILE_LEGACY_HEADER_SIZE + Integer.BYTES, LogMetadata.INVALID_LID);
      };
      static int extractVersion(ByteBuf header) throws IOException {
          assertFingerPrint(header);
          return header.getInt(HEADER_VERSION_OFFSET);
      }
  
      static long extractLedgerMapOffset(ByteBuf header) throws IOException {
          assertFingerPrint(header);
          return header.getLong(LEDGERS_MAP_OFFSET);
      }
  
      static int extractLedgerCount(ByteBuf header) throws IOException {
          assertFingerPrint(header);
          return header.getInt(LEDGER_COUNT_OFFSET);
      }
  
      static void assertFingerPrint(ByteBuf header) throws IOException {
          if (header.getByte(0) != 'B'
              || header.getByte(1) != 'K'
              || header.getByte(2) != 'L'
              || header.getByte(3) != 'O') {
              throw new IOException(exMsg("Bad fingerprint (should be BKLO)")
                                    .kv("byte0", header.getByte(0))
                                    .kv("byte1", header.getByte(1))
                                    .kv("byte2", header.getByte(2))
                                    .kv("byte3", header.getByte(3))
                                    .toString());
          }
      }
  
      static void writeEmptyHeader(ByteBuf header) throws IOException {
          header.writeBytes(EMPTY_HEADER);
      }
  
      static void writeHeader(ByteBuf header,
                              long ledgerMapOffset, int ledgerCount) throws IOException {
          header.writeBytes(EMPTY_HEADER);
          header.setLong(LEDGERS_MAP_OFFSET, ledgerMapOffset);
          header.setInt(LEDGER_COUNT_OFFSET, ledgerCount);
      }
  
  }
  