/// <summary>
/// Reads the header information from an sidecar file
/// and reconstructs a header object.
/// </summary>
/// <param name="reader">A binary reader to the sidecar file.</param>
/// <returns>The reconstructed header object.</returns>
private static SidecarFileHeader ReadHeader(BinaryReader reader)
{
SidecarFileHeader header = new SidecarFileHeader
{
SourceFileLastWriteTime = DateTime.FromBinary(reader.ReadInt64()),
SequenceCount = reader.ReadInt32(),
FileVersion = reader.ReadInt32()
};
return(header);
}
/// <summary>
/// Writes the header to the sidecar file, and also writes information
/// about the sidecar file itself.
/// </summary>
/// <param name="sequenceCount">The number of sequences in the source file.</param>
/// <returns>true if the header was successfully created; otherwise, false</returns>
private void WriteHeaderData(int sequenceCount)
{
_header = new SidecarFileHeader(_sourceFileName, sequenceCount);
_streamWriter.Seek(0, SeekOrigin.Begin);
// Write sidecar file size and last written date to the space left at top
_offsetWriter.Write(_streamWriter.Length);
_offsetWriter.Write(DateTime.Now.Date.ToFileTime());
_offsetWriter.Write(_header.SourceFileLastWriteTime.ToBinary());
_offsetWriter.Write(_header.SequenceCount);
_offsetWriter.Write(_header.FileVersion);
}
/// <summary>
/// Opens an existing sidecar file and checks its validity.
/// </summary>
/// <param name="sidecarFileName">The path to the sidecar file.</param>
private void OpenSidecar(string sidecarFileName)
{
// reset flag before proceeding
if (IsSidecarValid)
{
IsSidecarValid = false;
}
try
{
_streamReader = new FileStream(sidecarFileName, FileMode.Open, FileAccess.Read);
_offsetReader = new BinaryReader(_streamReader);
_sidecarLength = _offsetReader.ReadInt64();
_sidecarLastWriteTime = _offsetReader.ReadInt64();
FileInfo sidecarFileInfo = new FileInfo(sidecarFileName);
// validate the sidecar file properties
if ((_sidecarLastWriteTime == sidecarFileInfo.LastWriteTime.Date.ToFileTime()) && (_sidecarLength == sidecarFileInfo.Length))
{
_header = ReadHeader(_offsetReader);
// validate the source file properties
if (_header.FileVersion == FileVersion && _header.SourceFileLastWriteTime == new FileInfo(_sourceFileName).LastWriteTime)
{
IsSidecarValid = true;
// sequence indexes start just after header
_contentsOffset = _streamReader.Position;
}
else
{
CloseInputStream();
}
}
else // close streams if sidecar is invalid
{
CloseInputStream();
}
}
catch (Exception)
{
CloseInputStream();
}
}
