public override int Read(long pos, byte[] buffer, int offset, int count)
{
int totalRead = 0;
int limitedCount = (int)Math.Min(count, Math.Max(0, Capacity - pos));
while (totalRead < limitedCount)
{
long extentLogicalStart;
ExtentDescriptor extent = FindExtent(pos, out extentLogicalStart);
long extentStreamStart = extent.StartBlock * (long)_context.MasterDirectoryBlock.BlockSize;
long extentSize = extent.BlockCount * (long)_context.MasterDirectoryBlock.BlockSize;
long extentOffset = pos + totalRead - extentLogicalStart;
int toRead = (int)Math.Min(limitedCount - totalRead, extentSize - extentOffset);
// Remaining in extent can create a situation where amount to read is zero, and that appears
// to be OK, just need to exit thie while loop to avoid infinite loop.
if (toRead == 0)
{
break;
}
Stream volStream = _context.VolumeStream;
volStream.Position = extentStreamStart + extentOffset;
int numRead = volStream.Read(buffer, offset + totalRead, toRead);
totalRead += numRead;
}
return(totalRead);
}
private ExtentDescriptor FindExtent(long pos, out long extentLogicalStart)
{
uint blocksSeen = 0;
uint block = (uint)(pos / _context.MasterDirectoryBlock.BlockSize);
for (int i = 0; i < _baseData.Extents.Length; ++i)
{
if (blocksSeen + _baseData.Extents[i].BlockCount > block)
{
extentLogicalStart = blocksSeen * (long)_context.MasterDirectoryBlock.BlockSize;
return(_baseData.Extents[i]);
}
blocksSeen += _baseData.Extents[i].BlockCount;
}
while (blocksSeen < _baseData.TotalBlocks)
{
byte[] extentData = _context.ExtentsOverflow.Find(new ExtentKey(_cnid, blocksSeen, false));
if (extentData != null)
{
int extentDescriptorCount = extentData.Length / 8;
for (int a = 0; a < extentDescriptorCount; a++)
{
ExtentDescriptor extentDescriptor = new ExtentDescriptor();
int bytesRead = extentDescriptor.ReadFrom(extentData, a * 8);
if (blocksSeen + extentDescriptor.BlockCount > block)
{
extentLogicalStart = blocksSeen * (long)_context.MasterDirectoryBlock.BlockSize;
return(extentDescriptor);
}
blocksSeen += extentDescriptor.BlockCount;
}
}
else
{
throw new IOException("Missing extent from extent overflow file: cnid=" + _cnid + ", blocksSeen=" +
blocksSeen);
}
}
throw new InvalidOperationException("Requested file fragment beyond EOF");
}