content: package org.apache.lucene.store;
  
  /**
   * 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.
   */
  
  import java.io.IOException;
  import java.util.zip.CRC32;
  import java.util.zip.Checksum;
  
  /** Writes bytes through to a primary IndexOutput, computing
   *  checksum.  Note that you cannot use seek().
   *
   * @lucene.internal
   */
  public class ChecksumIndexOutput extends IndexOutput {
    IndexOutput main;
    Checksum digest;
    
    Directory directory;
   String filename;
  
  
   public ChecksumIndexOutput(IndexOutput main,Directory directory,String filename) {
      this.main = main;
      digest = new CRC32();
      this.directory=directory;
      this.filename=filename;
  
    }
  
    @Override
    public void writeByte(byte b) throws IOException {
      digest.update(b);
      main.writeByte(b);
    }
  
    @Override
    public void writeBytes(byte[] b, int offset, int length) throws IOException {
      digest.update(b, offset, length);
      main.writeBytes(b, offset, length);
    }
  
    public long getChecksum() {
      return digest.getValue();
    }
  
    @Override
    public void flush() throws IOException {
      main.flush();
    }
  
    @Override
    public void close() throws IOException {
      main.close();
    }
  
    @Override
    public long getFilePointer() {
      return main.getFilePointer();
    }
  
    @Override
    public void seek(long pos) {
      throw new RuntimeException("not allowed");    
    }
  
    /**
     * Starts but does not complete the commit of this file (=
     * writing of the final checksum at the end).  After this
     * is called must call {@link #finishCommit} and the
     * {@link #close} to complete the commit.
     */
    public void prepareCommit() throws IOException {
      final long checksum = getChecksum();
  //    // Intentionally write a mismatched checksum.  This is
  //    // because we want to 1) test, as best we can, that we
  //    // are able to write a long to the file, but 2) not
  //    // actually "commit" the file yet.  This (prepare
  //    // commit) is phase 1 of a two-phase commit.
  //    final long pos = main.getFilePointer();
  //    main.writeLong(checksum-1);
  //    main.flush();
  //    main.seek(pos);
        
        if(this.directory.fileExists(this.filename))
  	{
  	this.directory.deleteFile(this.filename);
  	}
  	
  	IndexOutput check=directory.createOutput(this.filename);
  	check.writeLong(checksum-1);
  	check.close();
  
    }
  
    /** See {@link #prepareCommit} */
      public void finishCommit() throws IOException {
  	if (this.directory.fileExists(this.filename)) {
  	    this.directory.deleteFile(this.filename);
  	}
  
  	IndexOutput check = directory.createOutput(this.filename);
  	check.writeLong(getChecksum());
  	check.close();
  
      }
  
    @Override
    public long length() throws IOException {
      return main.length();
    }
  }
  