CheckSumIndexOutput.cs

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/* 
 * 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.
 */

using System;
using Lucene.Net.Support;
using CRC32 = Lucene.Net.Support.CRC32;

namespace Lucene.Net.Store
{
    
    /// <summary>Writes bytes through to a primary IndexOutput, computing
    /// checksum.  Note that you cannot use seek().
    /// </summary>
    public class ChecksumIndexOutput:IndexOutput
    {
        internal IndexOutput main;
        internal IChecksum digest;

        private bool isDisposed;
        
        public ChecksumIndexOutput(IndexOutput main)
        {
            this.main = main;
            digest = new CRC32();
        }
        
        public override void  WriteByte(byte b)
        {
            digest.Update(b);
            main.WriteByte(b);
        }
        
        public override void  WriteBytes(byte[] b, int offset, int length)
        {
            digest.Update(b, offset, length);
            main.WriteBytes(b, offset, length);
        }

        public virtual long Checksum
        {
            get { return digest.Value; }
        }

        public override void  Flush()
        {
            main.Flush();
        }

        protected override void Dispose(bool disposing)
        {
            if (isDisposed) return;

            if (disposing)
            {
                main.Close();
            }

            isDisposed = true;
        }

        public override long FilePointer
        {
            get { return main.FilePointer; }
        }

        public override void  Seek(long pos)
        {
            throw new System.SystemException("not allowed");
        }
        
        /// <summary> Starts but does not complete the commit of this file (=
        /// writing of the final checksum at the end).  After this
        /// is called must call <see cref="FinishCommit" /> and the
        /// <see cref="Dispose" /> to complete the commit.
        /// </summary>
        public virtual void  PrepareCommit()
        {
            long checksum = Checksum;
            // 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.
            long pos = main.FilePointer;
            main.WriteLong(checksum - 1);
            main.Flush();
            main.Seek(pos);
        }
        
        /// <summary>See <see cref="PrepareCommit" /> </summary>
        public virtual void  FinishCommit()
        {
            main.WriteLong(Checksum);
        }

        public override long Length
        {
            get { return main.Length; }
        }
    }
}