FileLogRecordStream.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / cdf / src / WCF / Log / System / IO / Log / FileLogRecordStream.cs / 1305376 / FileLogRecordStream.cs
                        
                        
                            //------------------------------------------------------------ 
// Copyright (c) Microsoft Corporation.  All rights reserved.
//-----------------------------------------------------------
using System;
using System.Collections.Generic; 
using System.Text;
using System.Diagnostics; 
 
namespace System.IO.Log
{ 

    // This class is not thread safe.
    // FileLogRecordStream lets the user read log records in the form of a stream.
    internal class FileLogRecordStream : System.IO.Stream 
    {
        // The stream initialy reads the first 4K bytes of the log record. 
        // When need arises, it reads the entire record and creates a new Memory stream with the record data. 
        const int INITIAL_READ = 4096;
 
        // The memory stream is created from the record data.  It handles all stream operations.
        MemoryStream stream;
        SequenceNumber recordSequenceNumber;
        SimpleFileLog log; 
        FileLogRecordHeader header;
 
        // Sequence numbers of the previous and next records.  Returned from ReadRecord and ReadRecordPrefix. 
        SequenceNumber prevSeqNum;
        SequenceNumber nextSeqNum; 
        int recordSize;
        bool entireRecordRead;
        object streamLock;
 
        internal FileLogRecordStream(SimpleFileLog log, SequenceNumber recordSequenceNumber)
        { 
            this.log = log; 
            this.recordSequenceNumber = recordSequenceNumber;
            this.stream = null; 
            this.recordSize = 0;
            this.entireRecordRead = false;
            this.streamLock = new object();
 
            CreateMemoryStream();
        } 
 
        // Creates a memory stream with the first 4K bytes of the record.
        private void CreateMemoryStream() 
        {
            byte[] pData;
            int cbData = INITIAL_READ;
            int totalSize; 

            log.ReadRecordPrefix(this.recordSequenceNumber, out pData, ref cbData, out totalSize, out this.prevSeqNum, out this.nextSeqNum); 
 
            if (cbData < FileLogRecordHeader.Size)
                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.LogCorrupt()); 

            this.header = new FileLogRecordHeader(pData);
            this.recordSize = totalSize - FileLogRecordHeader.Size;
 
            int streamSize = Math.Min(this.recordSize,
                                      INITIAL_READ - FileLogRecordHeader.Size); 
 
            this.stream = new MemoryStream(
                pData, 
                FileLogRecordHeader.Size,
                streamSize,
                false);
 
            if (totalSize <= INITIAL_READ)
            { 
                // Record is smaller than 4K.  We have read the entire record. 
                this.entireRecordRead = true;
            } 
        }

        internal FileLogRecordHeader Header
        { 
            get { return this.header; }
        } 
 
        internal SequenceNumber RecordSequenceNumber
        { 
            get { return this.recordSequenceNumber; }
        }

        internal SequenceNumber PrevLsn 
        {
            get { return this.prevSeqNum; } 
        } 

        internal SequenceNumber NextLsn 
        {
            get { return this.nextSeqNum; }
        }
 
        private MemoryStream Stream
        { 
            get { return this.stream; } 
        }
 
        // Multiple threads in Read can result in corrupt data.
        public override int Read(byte[] buffer, int offset, int count)
        {
            int bytesRead = this.Stream.Read(buffer, offset, count); 

            if (bytesRead == count || this.entireRecordRead) 
            { 
                return bytesRead;
            } 
            else
            {
                // We have reached the end of the stream.  Read the entire record and create a new stream.
                ReadEntireRecord(); 

                return this.Stream.Read(buffer, offset+bytesRead, count-bytesRead) + bytesRead; 
            } 
        }
 
        // The method reads the entire record and creates a new memory stream.
        private void ReadEntireRecord()
        {
            lock (this.streamLock) 
            {
                if (this.entireRecordRead) 
                    return; 

                // Check if the stream is open. 
                if (!this.stream.CanRead)
                {
                    throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.ObjectDisposed());
                } 

                byte[] data; 
                int size; 
                SequenceNumber prev;
                SequenceNumber next; 

                log.ReadRecord(this.recordSequenceNumber, out data, out size, out prev, out next);
                if (!(size == (this.recordSize + FileLogRecordHeader.Size)
                   && next == this.nextSeqNum)) 
                {
                    throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.LogCorrupt()); 
                } 

                long position = this.Stream.Position; 

                // Create a new stream
                this.stream = new MemoryStream(
                    data, 
                    FileLogRecordHeader.Size,
                    data.Length - FileLogRecordHeader.Size, 
                    false); 

                this.Stream.Position = position; 
                this.entireRecordRead = true;
            }
        }
 
        public override bool CanRead
        { 
            get { return this.stream.CanRead; } 
        }
 
        public override bool CanSeek
        {
            get { return this.stream.CanSeek; }
        } 

        public override bool CanWrite 
        { 
            get { return this.stream.CanWrite; }
        } 

        public override void Close()
        {
            lock (this.streamLock) 
            {
                this.stream.Close(); 
            } 
        }
 
        public override void Flush()
        {
            this.Stream.Flush();
        } 

        public override long Length 
        { 
            get
            { 
                if (!this.stream.CanRead)
                {
#pragma warning suppress 56503
                    throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.ObjectDisposed()); 
                }
 
                return this.recordSize; 
            }
        } 

        public override long Position
        {
            get 
            {
                return this.Stream.Position; 
            } 

            set 
            {
                this.Stream.Position = value;
            }
        } 

        public override long Seek(long offset, SeekOrigin origin) 
        { 
            if (origin == SeekOrigin.End &&
                !this.entireRecordRead) 
            {
                // The stream we have was created with the first 4K bytes of the record.
                offset += this.recordSize;
                origin = SeekOrigin.Begin; 
            }
 
            return this.Stream.Seek(offset, origin); 
        }
 
        public override void SetLength(long value)
        {
            this.stream.SetLength(value);
        } 

        public override void Write(byte[] buffer, int offset, int count) 
        { 
            if (!this.stream.CanRead)
            { 
                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.ObjectDisposed());
            }
            else
            { 
                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.NotSupported());
            } 
        } 

        public override void WriteByte(byte value) 
        {
            if (!this.stream.CanRead)
            {
                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.ObjectDisposed()); 
            }
            else 
            { 
                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.NotSupported());
            } 
        }

    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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FileLogRecordStream.cs source code in C# .NET

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