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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.

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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.index.schema;

import org.apache.commons.lang3.exception.ExceptionUtils;

import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;

import org.neo4j.index.internal.gbptree.Header;

import static java.lang.String.format;
import static org.neo4j.kernel.impl.index.schema.NativeIndexPopulator.BYTE_FAILED;

class NativeIndexHeaderReader implements Header.Reader
{
    byte state;
    String failureMessage;
    private final byte failureByte;

    NativeIndexHeaderReader()
    {
        this( BYTE_FAILED );
    }

    /**
     * Use this if the index uses a custom failure byte (e.g. TokenIndex).
     */
    NativeIndexHeaderReader( byte failureByte )
    {
        this.failureByte = failureByte;
    }

    @Override
    public void read( ByteBuffer headerData )
    {
        try
        {
            state = headerData.get();
            if ( state == failureByte )
            {
                failureMessage = readFailureMessage( headerData );
            }
        }
        catch ( BufferUnderflowException e )
        {
            state = failureByte;
            failureMessage =
                    format( "Could not read header, most likely caused by index not being fully constructed. Index needs to be recreated. Stacktrace:%n%s",
                            ExceptionUtils.getStackTrace( e ) );
        }
    }

    private static String readFailureMessage( ByteBuffer headerData )
    {
        short messageLength = headerData.getShort();
        byte[] failureMessageBytes = new byte[messageLength];
        headerData.get( failureMessageBytes );
        return new String( failureMessageBytes, StandardCharsets.UTF_8 );
    }
}