public static ushort GetFreeSpace(IPage page)
{
PageType pageType = PageHeaderBase.GetPageType(page);
if (pageType != PageType.RadixTree)
{
throw new PageFormatException("Page is not dedicated to variable size items.");
}
return(RadixTreeNodesPageHeader.ReadFreeSpace(page));
}
public static PageHeaderBase GetPageHeader(IPage page)
{
PageHeaderBase ph;
PageType pt = PageHeaderBase.GetPageType(page);
switch (pt)
{
case PageType.FreeSpaceMap:
ph = new FreeSpaceMapPageHeader();
ph.Read(page);
return(ph);
case PageType.Heading:
ph = new HeadingPageHeader();
ph.Read(page);
return(ph);
case PageType.MultipageItem:
ph = new MultipageItemPageHeader();
ph.Read(page);
return(ph);
case PageType.FixedSizeItem:
ph = new FixedSizeItemsPageHeader();
ph.Read(page);
return(ph);
case PageType.BPlusTree:
ph = new BPlusTreeNodePageHeader();
ph.Read(page);
return(ph);
case PageType.RadixTree:
ph = new RadixTreeNodesPageHeader();
ph.Read(page);
return(ph);
}
return(null);
}
public static short AddVariableSizeItem(IPage page, byte[] itemContent)
{
ushort freeSpace = GetFreeSpace(page);
var itemLength = itemContent.Length;
if (freeSpace < itemLength)
{
return(-1);
}
short headerLength = BitConverter.ToInt16(page.Content, OnPageOffsets.HeaderLength);
var lengthMarkers = ReadMarkers(page, headerLength);
int offset = 0;
for (short i = 0; i < lengthMarkers.Length; i++)
{
offset += Math.Abs(lengthMarkers[i]);
if (lengthMarkers[i] <= 0)
{
// we have an empty slot
if (itemLength == -lengthMarkers[i])
{
// simple case: a new item has exactly the same size as deleted one, rewrite it
RewriteVariableSizeItem(page, itemContent, headerLength, i, offset, freeSpace);
}
else
{
PlaceItemToSlot(page, headerLength, itemContent, lengthMarkers, i);
}
return(i);
}
}
// here we need two extra bytes
if (freeSpace < itemLength + OnPagePointerSize)
{
return(-1);
}
// write length of the marker array
var markersLengthBytes = BitConverter.GetBytes((short)(lengthMarkers.Length + 1));
markersLengthBytes.CopyTo(page.Content, headerLength);
// write new length marker
var newMarkerBytes = BitConverter.GetBytes((short)itemContent.Length);
newMarkerBytes.CopyTo(page.Content, headerLength + OnPagePointerSize * (lengthMarkers.Length + 1));
// write item itself
Buffer.BlockCopy(itemContent, 0, page.Content, page.Content.Length - offset - itemLength, itemLength);
// write free space
RadixTreeNodesPageHeader.WriteFreeSpace(page, (ushort)(freeSpace - itemLength - OnPagePointerSize));
return((short)lengthMarkers.Length);
}
private static void WriteFreeSpace(IPage page, ushort freeSpace)
{
RadixTreeNodesPageHeader.WriteFreeSpace(page, freeSpace);
}