/**
* Finds a free block, and returns its offset. This method will extend the file if needed, and if
* doing so, allocate new FAT blocks to address the extra space.
*/
@Override
protected int getFreeBlock() throws IOException {
// First up, do we have any spare ones?
int offset = 0;
for (int i = 0; i < _bat_blocks.size(); i++) {
int numSectors = bigBlockSize.getBATEntriesPerBlock();
// Check this one
BATBlock bat = _bat_blocks.get(i);
if (bat.hasFreeSectors()) {
// Claim one of them and return it
for (int j = 0; j < numSectors; j++) {
int batValue = bat.getValueAt(j);
if (batValue == POIFSConstants.UNUSED_BLOCK) {
// Bingo
return offset + j;
}
}
}
// Move onto the next BAT
offset += numSectors;
}
// If we get here, then there aren't any free sectors
// in any of the BATs, so we need another BAT
BATBlock bat = createBAT(offset, true);
bat.setValueAt(0, POIFSConstants.FAT_SECTOR_BLOCK);
_bat_blocks.add(bat);
// Now store a reference to the BAT in the required place
if (_header.getBATCount() >= 109) {
// Needs to come from an XBAT
BATBlock xbat = null;
for (BATBlock x : _xbat_blocks) {
if (x.hasFreeSectors()) {
xbat = x;
break;
}
}
if (xbat == null) {
// Oh joy, we need a new XBAT too...
xbat = createBAT(offset + 1, false);
xbat.setValueAt(0, offset);
bat.setValueAt(1, POIFSConstants.DIFAT_SECTOR_BLOCK);
// Will go one place higher as XBAT added in
offset++;
// Chain it
if (_xbat_blocks.size() == 0) {
_header.setXBATStart(offset);
} else {
_xbat_blocks
.get(_xbat_blocks.size() - 1)
.setValueAt(bigBlockSize.getXBATEntriesPerBlock(), offset);
}
_xbat_blocks.add(xbat);
_header.setXBATCount(_xbat_blocks.size());
}
// Allocate us in the XBAT
for (int i = 0; i < bigBlockSize.getXBATEntriesPerBlock(); i++) {
if (xbat.getValueAt(i) == POIFSConstants.UNUSED_BLOCK) {
xbat.setValueAt(i, offset);
}
}
} else {
// Store us in the header
int[] newBATs = new int[_header.getBATCount() + 1];
System.arraycopy(_header.getBATArray(), 0, newBATs, 0, newBATs.length - 1);
newBATs[newBATs.length - 1] = offset;
_header.setBATArray(newBATs);
}
_header.setBATCount(_bat_blocks.size());
// The current offset stores us, but the next one is free
return offset + 1;
}
