public override void Write(long pos, byte[] buffer, int offset, int count)
{
var record = _attribute.Record;
if (!CanWrite)
{
throw new IOException("Attempt to write to file not opened for write");
}
if (record.Flags != AttributeFlags.None)
{
throw new NotImplementedException("Writing to compressed / sparse attributes");
}
if (count == 0)
{
return;
}
if (!record.IsNonResident)
{
record.GetDataBuffer(_file).Write(pos, buffer, offset, count);
_file.MarkMftRecordDirty();
}
else
{
NonResidentAttributeRecord lastExtent = (NonResidentAttributeRecord)_attribute.LastExtent;
IBuffer lastExtentBuffer = lastExtent.GetDataBuffer(_file);
long bytesPerCluster = _file.Context.BiosParameterBlock.BytesPerCluster;
if (pos + count > record.AllocatedLength)
{
_file.MarkMftRecordDirty();
long clusterLength = Utilities.RoundUp(pos + count, bytesPerCluster);
lastExtentBuffer.SetCapacity(clusterLength - (lastExtent.StartVcn * bytesPerCluster));
record.AllocatedLength = clusterLength;
}
// Write zeros from end of current initialized data to the start of the new write
if (pos > record.InitializedDataLength + 1)
{
_file.MarkMftRecordDirty();
byte[] wipeBuffer = new byte[bytesPerCluster * 4];
long wipePos = record.InitializedDataLength;
while (wipePos < pos)
{
long extentStartPos;
IBuffer extentBuffer = GetExtentBuffer(wipePos, out extentStartPos);
long writePos = wipePos - extentStartPos;
int numToWrite = (int)Math.Min(Math.Min(extentBuffer.Capacity - writePos, pos - wipePos), wipeBuffer.Length);
extentBuffer.Write(writePos, wipeBuffer, 0, numToWrite);
wipePos += numToWrite;
}
}
long focusPos = pos;
int bytesWritten = 0;
while (bytesWritten < count)
{
long extentStartPos;
IBuffer extentBuffer = GetExtentBuffer(focusPos, out extentStartPos);
long writePos = focusPos - extentStartPos;
int numToWrite = (int)Math.Min(extentBuffer.Capacity - writePos, count - bytesWritten);
extentBuffer.Write(writePos, buffer, offset + bytesWritten, numToWrite);
focusPos += numToWrite;
bytesWritten += numToWrite;
}
if (pos + count > record.InitializedDataLength)
{
_file.MarkMftRecordDirty();
record.InitializedDataLength = pos + count;
}
if (pos + count > record.DataLength)
{
_file.MarkMftRecordDirty();
record.DataLength = pos + count;
}
}
}
