internal void zeroPage(int flags)
{
var data = this.Data;
var pBt = this.Shared;
var hdr = this.HeaderOffset;
Debug.Assert(Pager.GetPageID(this.DbPage) == this.ID);
Debug.Assert(Pager.sqlite3PagerGetExtra <MemPage>(this.DbPage) == this);
Debug.Assert(Pager.sqlite3PagerGetData(this.DbPage) == data);
Debug.Assert(Pager.IsPageWriteable(this.DbPage));
Debug.Assert(MutexEx.Held(pBt.Mutex));
if (pBt.SecureDelete)
{
Array.Clear(data, hdr, (int)(pBt.UsableSize - hdr));
}
data[hdr] = (byte)flags;
var first = (ushort)(hdr + 8 + 4 * ((flags & Btree.PTF_LEAF) == 0 ? 1 : 0));
Array.Clear(data, hdr + 1, 4);
data[hdr + 7] = 0;
ConvertEx.Put2(data, hdr + 5, pBt.UsableSize);
this.FreeBytes = (ushort)(pBt.UsableSize - first);
decodeFlags(flags);
this.HeaderOffset = hdr;
this.CellOffset = first;
this.NOverflows = 0;
Debug.Assert(pBt.PageSize >= 512 && pBt.PageSize <= 65536);
this.MaskPage = (ushort)(pBt.PageSize - 1);
this.Cells = 0;
this.HasInit = true;
}
internal RC btreeInitPage()
{
Debug.Assert(this.Shared != null);
Debug.Assert(MutexEx.Held(this.Shared.Mutex));
Debug.Assert(this.ID == Pager.GetPageID(this.DbPage));
Debug.Assert(this == Pager.sqlite3PagerGetExtra <MemPage>(this.DbPage));
Debug.Assert(this.Data == Pager.sqlite3PagerGetData(this.DbPage));
if (!this.HasInit)
{
var pBt = this.Shared; // The main btree structure
var hdr = this.HeaderOffset; // Offset to beginning of page header
var data = this.Data;
if (decodeFlags(data[hdr]) != 0)
{
return(SysEx.SQLITE_CORRUPT_BKPT());
}
Debug.Assert(pBt.PageSize >= 512 && pBt.PageSize <= 65536);
this.MaskPage = (ushort)(pBt.PageSize - 1);
this.NOverflows = 0;
var usableSize = (int)pBt.UsableSize; // Amount of usable space on each page
ushort cellOffset; // Offset from start of page to first cell pointer
this.CellOffset = (cellOffset = (ushort)(hdr + 12 - 4 * this.Leaf));
var top = ConvertEx.Get2nz(data, hdr + 5); // First byte of the cell content area
this.Cells = (ushort)(ConvertEx.Get2(data, hdr + 3));
if (this.Cells > Btree.MX_CELL(pBt))
{
// To many cells for a single page. The page must be corrupt
return(SysEx.SQLITE_CORRUPT_BKPT());
}
// A malformed database page might cause us to read past the end of page when parsing a cell.
// The following block of code checks early to see if a cell extends past the end of a page boundary and causes SQLITE_CORRUPT to be
// returned if it does.
var iCellFirst = cellOffset + 2 * this.Cells; // First allowable cell or freeblock offset
var iCellLast = usableSize - 4; // Last possible cell or freeblock offset
#if SQLITE_ENABLE_OVERSIZE_CELL_CHECK
if (pPage.leaf == 0)
{
iCellLast--;
}
for (var i = 0; i < pPage.nCell; i++)
{
pc = (ushort)ConvertEx.get2byte(data, cellOffset + i * 2);
if (pc < iCellFirst || pc > iCellLast)
{
return(SysEx.SQLITE_CORRUPT_BKPT());
}
var sz = cellSizePtr(pPage, data, pc);
if (pc + sz > usableSize)
{
return(SysEx.SQLITE_CORRUPT_BKPT());
}
}
if (pPage.leaf == 0)
{
iCellLast++;
}
#endif
// Compute the total free space on the page
var pc = (ushort)ConvertEx.Get2(data, hdr + 1); // Address of a freeblock within pPage.aData[]
var nFree = (ushort)(data[hdr + 7] + top); // Number of unused bytes on the page
while (pc > 0)
{
if (pc < iCellFirst || pc > iCellLast)
{
// Start of free block is off the page
return(SysEx.SQLITE_CORRUPT_BKPT());
}
var next = (ushort)ConvertEx.Get2(data, pc);
var size = (ushort)ConvertEx.Get2(data, pc + 2);
if ((next > 0 && next <= pc + size + 3) || pc + size > usableSize)
{
// Free blocks must be in ascending order. And the last byte of the free-block must lie on the database page.
return(SysEx.SQLITE_CORRUPT_BKPT());
}
nFree = (ushort)(nFree + size);
pc = next;
}
// At this point, nFree contains the sum of the offset to the start of the cell-content area plus the number of free bytes within
// the cell-content area. If this is greater than the usable-size of the page, then the page must be corrupted. This check also
// serves to verify that the offset to the start of the cell-content area, according to the page header, lies within the page.
if (nFree > usableSize)
{
return(SysEx.SQLITE_CORRUPT_BKPT());
}
this.FreeBytes = (ushort)(nFree - iCellFirst);
this.HasInit = true;
}
return(RC.OK);
}
