/**
* Initialize the auxiliary information for a disk block.
*
* <p>Return SQLITE_OK on success. If we see that the page does not contain a well-formed database
* page, then return SQLITE_CORRUPT. Note that a return of SQLITE_OK does not guarantee that the
* page is well-formed. It only shows that we failed to detect any corruption.
*/
public void initPage() throws SqlJetException {
assert (pBt != null);
assert (pBt.mutex.held());
assert (pgno == pDbPage.getPageNumber());
assert (this == pDbPage.getExtra());
assert (aData.getBuffer() == pDbPage.getData().getBuffer());
if (!isInit) {
int pc; /* Address of a freeblock within pPage->aData[] */
byte hdr; /* Offset to beginning of page header */
int usableSize; /* Amount of usable space on each page */
int cellOffset; /* Offset from start of page to first cell pointer */
int nFree; /* Number of unused bytes on the page */
int top; /* First byte of the cell content area */
hdr = hdrOffset;
decodeFlags(SqlJetUtility.getUnsignedByte(aData, hdr));
assert (pBt.pageSize >= 512 && pBt.pageSize <= 32768);
maskPage = pBt.pageSize - 1;
nOverflow = 0;
usableSize = pBt.usableSize;
this.cellOffset = cellOffset = hdr + 12 - 4 * (leaf ? 1 : 0);
top = get2byte(aData, hdr + 5);
nCell = get2byte(aData, hdr + 3);
if (nCell > pBt.MX_CELL()) {
/* To many cells for a single page. The page must be corrupt */
throw new SqlJetException(SqlJetErrorCode.CORRUPT);
}
int iCellFirst = cellOffset + 2 * this.nCell;
/* Compute the total free space on the page */
pc = get2byte(aData, hdr + 1);
nFree = SqlJetUtility.getUnsignedByte(aData, hdr + 7) + top; // - (cellOffset + 2 * nCell);
while (pc > 0) {
int next, size;
if (pc > usableSize - 4) {
/* Free block is off the page */
throw new SqlJetException(SqlJetErrorCode.CORRUPT);
}
next = get2byte(aData, pc);
size = get2byte(aData, pc + 2);
if (next > 0 && next <= pc + size + 3) {
/* Free blocks must be in accending order */
throw new SqlJetException(SqlJetErrorCode.CORRUPT);
}
nFree += size;
pc = next;
}
if (nFree > usableSize) {
/* Free space cannot exceed total page size */
throw new SqlJetException(SqlJetErrorCode.CORRUPT);
}
this.nFree = (nFree - iCellFirst);
isInit = true;
}
}
