mcs/tools/monkeydoc/Lucene.Net/Lucene.Net/Store/CheckSumIndexOutput.cs

   1 /*
   2  * Licensed to the Apache Software Foundation (ASF) under one or more
   3  * contributor license agreements.  See the NOTICE file distributed with
   4  * this work for additional information regarding copyright ownership.
   5  * The ASF licenses this file to You under the Apache License, Version 2.0
   6  * (the "License"); you may not use this file except in compliance with
   7  * the License.  You may obtain a copy of the License at
   8  *
   9  * http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing, software
  12  * distributed under the License is distributed on an "AS IS" BASIS,
  13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14  * See the License for the specific language governing permissions and
  15  * limitations under the License.
  16  */
  17
  18 using System;
  19
  20 using Checksum = SupportClass.Checksum;
  21 using CRC32 = SupportClass.CRC32;
  22
  23 namespace Mono.Lucene.Net.Store
  24 {
  25
  26         /// <summary>Writes bytes through to a primary IndexOutput, computing
  27         /// checksum.  Note that you cannot use seek().
  28         /// </summary>
  29         public class ChecksumIndexOutput:IndexOutput
  30         {
  31                 internal IndexOutput main;
  32                 internal Checksum digest;
  33
  34                 public ChecksumIndexOutput(IndexOutput main)
  35                 {
  36                         this.main = main;
  37                         digest = new CRC32();
  38                 }
  39
  40                 public override void  WriteByte(byte b)
  41                 {
  42                         digest.Update(b);
  43                         main.WriteByte(b);
  44                 }
  45
  46                 public override void  WriteBytes(byte[] b, int offset, int length)
  47                 {
  48                         digest.Update(b, offset, length);
  49                         main.WriteBytes(b, offset, length);
  50                 }
  51
  52                 public virtual long GetChecksum()
  53                 {
  54                         return digest.GetValue();
  55                 }
  56
  57                 public override void  Flush()
  58                 {
  59                         main.Flush();
  60                 }
  61
  62                 public override void  Close()
  63                 {
  64                         main.Close();
  65                 }
  66
  67                 public override long GetFilePointer()
  68                 {
  69                         return main.GetFilePointer();
  70                 }
  71
  72                 public override void  Seek(long pos)
  73                 {
  74                         throw new System.SystemException("not allowed");
  75                 }
  76
  77                 /// <summary> Starts but does not complete the commit of this file (=
  78                 /// writing of the final checksum at the end).  After this
  79                 /// is called must call {@link #finishCommit} and the
  80                 /// {@link #close} to complete the commit.
  81                 /// </summary>
  82                 public virtual void  PrepareCommit()
  83                 {
  84                         long checksum = GetChecksum();
  85                         // Intentionally write a mismatched checksum.  This is
  86                         // because we want to 1) test, as best we can, that we
  87                         // are able to write a long to the file, but 2) not
  88                         // actually "commit" the file yet.  This (prepare
  89                         // commit) is phase 1 of a two-phase commit.
  90                         long pos = main.GetFilePointer();
  91                         main.WriteLong(checksum - 1);
  92                         main.Flush();
  93                         main.Seek(pos);
  94                 }
  95
  96                 /// <summary>See {@link #prepareCommit} </summary>
  97                 public virtual void  FinishCommit()
  98                 {
  99                         main.WriteLong(GetChecksum());
 100                 }
 101
 102                 public override long Length()
 103                 {
 104                         return main.Length();
 105                 }
 106         }
 107 }