// return the data header from the start of the data file/
private BlobDataFileHeader GetDataHeader()
{
// if the data file is empty create a new header
if (this.FileSize == 0)
{
var header = new BlobDataFileHeader();
UpdateDataHeader(header);
this.FileSize = 64;
return(header);
}
BlobDataFileHeader dataHeader = null;
using (var _fileStreamReader = new FileStream(_dataFilePath, FileMode.OpenOrCreate,
FileAccess.Read,
FileShare.Write,
(int)DiskBufferSizes.Default,
FileOptions.SequentialScan))
{
using (var _binaryReader = new BinaryReader(_fileStreamReader))
{
_binaryReader.BaseStream.Position = 0;
var headerBytes = _binaryReader.ReadBytes(64);
dataHeader = BlobDataFileHeader.Parse(headerBytes);
}
}
return(dataHeader);
}
/// <summary>
/// Parse the 64 Byte array into Data Header object.
/// </summary>
/// <param name="bytes">The 64 Byte array.</param>
public static BlobDataFileHeader Parse(byte[] bytes)
{
if (bytes == null)
{
throw new ArgumentNullException("byte array is required.");
}
if (bytes.Length != 64)
{
throw new ArgumentException("byte array of length 64 is required.");
}
// If the system architecture is little-endian (that is, little end first),
// reverse the byte array.
if (BitConverter.IsLittleEndian)
{
Array.Reverse(bytes);
}
var dataHeader = new BlobDataFileHeader();
dataHeader.RecordCount = BitConverter.ToInt64(bytes, 0);
dataHeader.LastRecordId = BitConverter.ToInt64(bytes, 8);
dataHeader.LargestRecordId = BitConverter.ToInt64(bytes, 16);
return(dataHeader);
}
// update the data header located at the start of the data file.
private void UpdateDataHeader(BlobDataFileHeader dataHeader)
{
var headerBytes = dataHeader.GetBytes();
using (var _fileStreamWriter = new FileStream(_dataFilePath, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read,
(int)DiskBufferSizes.Default, FileOptions.SequentialScan))
{
using (var _binaryWriter = new BinaryWriter(_fileStreamWriter))
{
_binaryWriter.BaseStream.Position = 0;
_binaryWriter.Write(headerBytes);
_binaryWriter.Flush();
}
}
}
