/// <summary>
/// Try to link to an existing central name file.
/// If the central name file exist, and the link limit is not exceeded, the destination file is linked to the central name file, and the return value is true.
/// In this case, the backup of the destination file is considered finished.
/// If the central name file does not exist, or linking fails due to an exceeded link limit, the return value is false.
/// </summary>
/// <returns>True if linking of the destination file to the existing central name file succeeded;, otherwise, false.</returns>
/// <exception cref="System.IO.IOException">Error creating hard link from {_centralNameFileName} to {_destinationFileName}, ErrorCode: {hlr}</exception>
public bool TryToLinkToExistingNameFile()
{
var fileInfoCentralNameFileName = new FileInfo(_centralNameFileName);
// Compare the FileInfo of the central name file with the FileInfo of the source file
// only if both match, we can link the destination file name to the centralNameFile
if (fileInfoCentralNameFileName.Exists && FileUtilities.AreMetaDataMatching(fileInfoCentralNameFileName, _sourceFile))
{
var hlr = FileUtilities.CreateHardLink(_centralNameFileName, _destinationFileName);
if (hlr == 0)
{
return(true);
}
else
{
if (hlr != FileUtilities.ERROR_TOO_MANY_LINKS) // ignore TooManyLinks error, instead let the content file be created anew
{
throw new System.IO.IOException($"Error creating hard link from {_centralNameFileName} to {_destinationFileName}, ErrorCode: {hlr}");
}
}
}
return(false);
}
public void Write()
{
try
{
if (File.Exists(_centralStorageFileName)) // central storage file already exists
{
// make a hardlink from the central storage file to the source file
// but first we have to delete the source file
if (_sourceFile.IsReadOnly)
{
_sourceFile.IsReadOnly = false;
}
_sourceFile.Delete();
var hlr = FileUtilities.CreateHardLink(_centralStorageFileName, _sourceFile.FullName);
if (hlr != 0)
{
if (hlr == FileUtilities.ERROR_TOO_MANY_LINKS)
{
// if the hardlink limit is exceeded, we need to make a full copy of the source file
// effectively replacing the central storage file
var tempFileName = FileUtilities.FileRenameToTemporaryFileInSameFolder(_centralStorageFileName);
File.Copy(tempFileName, _centralStorageFileName);
File.Delete(tempFileName);
// now, try to create the hardlink again, now there should be no hardlink limit error any more
var hlr2 = FileUtilities.CreateHardLink(_centralStorageFileName, _sourceFile.FullName);
if (hlr2 != 0)
{
throw new System.IO.IOException($"Error create hard link from {_sourceFile.FullName} to {_centralStorageFileName}, ErrorCode: {hlr2}");
}
}
else
{
throw new System.IO.IOException($"Error create hard link from {_sourceFile.FullName} to {_centralStorageFileName}, ErrorCode: {hlr}");
}
}
}
else // Central storage file does not exist yet
{
if (!Directory.Exists(_centralStorageFolder))
{
Directory.CreateDirectory(_centralStorageFolder);
}
// create a hard link from the existing (old) backup file to the central storage file
int hlr = FileUtilities.CreateHardLink(_sourceFile.FullName, _centralStorageFileName);
if (hlr != 0)
{
if (hlr == FileUtilities.ERROR_TOO_MANY_LINKS)
{
// if the hardlink limit is exceeded, we need to make a full copy instead of a
// hard link
File.Copy(_sourceFile.FullName, _centralStorageFileName);
}
else
{
throw new System.IO.IOException($"Error create hard link from {_sourceFile.FullName} to {_centralStorageFileName}");
}
}
}
}
catch (Exception ex)
{
OnFailed(ex);
}
}
/// <summary>
/// Writes the backup file, the central content file and the central name file.
/// </summary>
/// <remarks>
/// All three files, the backup file, the central content file and the central name file have the same data content and are (ideally) linked by hard links.
/// The name of the backup file is the same as the name of the original file.
/// The name of the central content file is determined by the hash of the file content.
/// The name of the central name file is determined by the hash of the original file's metadata (length, last write time, attributes, and full name).
/// </remarks>
public void Write()
{
try
{
var backupMode = _parent._backupMode;
if (backupMode == BackupMode.Fast && TryToLinkToExistingNameFile())
{
NextStation = NextStation.Finished;
}
else
{
if (!IsContentFileNameKnown)
{
NextStation = NextStation.Reader;
}
else
{
bool isRepeatRequired = false;
do
{
if (!File.Exists(_centralContentFileName))
{
if (!Directory.Exists(_centralContentFolder))
{
Directory.CreateDirectory(_centralContentFolder);
}
if (_bytesInBuffer == (_streamLength + FileUtilities.BufferSpaceForLengthWriteTimeAndFileAttributes) && _buffer is { } buffer)
{
using (var destStream = new FileStream(_centralContentFileName, FileMode.CreateNew, FileAccess.Write, FileShare.Read))
{
destStream.Write(_buffer, FileUtilities.BufferSpaceForLengthWriteTimeAndFileAttributes, _bytesInBuffer - FileUtilities.BufferSpaceForLengthWriteTimeAndFileAttributes);
}
// Set attributes on the destination file, such as last write time, and attributes.
File.SetLastWriteTimeUtc(_centralContentFileName, _sourceFile.LastWriteTimeUtc);
File.SetAttributes(_centralContentFileName, _sourceFile.Attributes & FileUtilities.FileAttributeMask);
}
else
{
// we do not use the destination stream here
File.Copy(_sourceFile.FullName, _centralContentFileName);
// note: when copying, attributes and LastWriteTime is already set.
}
}
{
isRepeatRequired = false;
// Central storage file now exists, so create a hard link to it in the backup directory
var hlr = FileUtilities.CreateHardLink(_centralContentFileName, _destinationFileName);
if (hlr != 0)
{
if (hlr == FileUtilities.ERROR_TOO_MANY_LINKS) // is hard link limit exceeded?
{
// in order to circumvent the hard link limit, we delete the file from the central storage, and create it anew
File.Delete(_centralContentFileName);
isRepeatRequired = true;
continue;
}
else
{
throw new System.IO.IOException($"Error creating hard link {_destinationFileName}, ErrorCode: {hlr}");
}
}
}
// Handle the name file (except when in BackupMode.SecureNoNameFile)
if (backupMode == BackupMode.Fast && !File.Exists(_centralNameFileName))
{
var folder = Path.GetDirectoryName(_centralNameFileName);
if (!Directory.Exists(folder))
{
Directory.CreateDirectory(folder);
}
var hlr = FileUtilities.CreateHardLink(_centralContentFileName, _centralNameFileName);
if (hlr != 0)
{
if (hlr == FileUtilities.ERROR_TOO_MANY_LINKS)
{
File.Delete(_centralNameFileName);
}
else
{
throw new System.IO.IOException($"Error creating hard link {_destinationFileName}, ErrorCode: {hlr}");
}
}
}
} while (isRepeatRequired);
_stream?.Close();
_stream?.Dispose();
NextStation = NextStation.Finished;
}
}
}
