org.apache.poi.poifs.storage.BlockAllocationTableReader Maven / Gradle / Ivy
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package org.apache.poi.poifs.storage;
import java.io.IOException;
import java.util.*;
import org.apache.poi.poifs.common.POIFSBigBlockSize;
import org.apache.poi.poifs.common.POIFSConstants;
import org.apache.poi.util.*;
/**
* This class manages and creates the Block Allocation Table, which is
* basically a set of linked lists of block indices.
*
* Each block of the filesystem has an index. The first block, the
* header, is skipped; the first block after the header is index 0,
* the next is index 1, and so on.
*
* A block's index is also its index into the Block Allocation
* Table. The entry that it finds in the Block Allocation Table is the
* index of the next block in the linked list of blocks making up a
* file, or it is set to -2: end of list.
*
* @author Marc Johnson (mjohnson at apache dot org)
*/
public final class BlockAllocationTableReader {
private static final POILogger _logger = POILogFactory.getLogger(BlockAllocationTableReader.class);
/**
* Maximum number size (in blocks) of the allocation table as supported by
* POI.
*
* This constant has been chosen to help POI identify corrupted data in the
* header block (rather than crash immediately with {@link OutOfMemoryError}
* ). It's not clear if the compound document format actually specifies any
* upper limits. For files with 512 byte blocks, having an allocation table
* of 65,335 blocks would correspond to a total file size of 4GB. Needless
* to say, POI probably cannot handle files anywhere near that size.
*/
private static final int MAX_BLOCK_COUNT = 65535;
private final IntList _entries;
private POIFSBigBlockSize bigBlockSize;
/**
* create a BlockAllocationTableReader for an existing filesystem. Side
* effect: when this method finishes, the BAT blocks will have
* been removed from the raw block list, and any blocks labeled as
* 'unused' in the block allocation table will also have been
* removed from the raw block list.
*
* @param block_count the number of BAT blocks making up the block
* allocation table
* @param block_array the array of BAT block indices from the
* filesystem's header
* @param xbat_count the number of XBAT blocks
* @param xbat_index the index of the first XBAT block
* @param raw_block_list the list of RawDataBlocks
*
* @exception IOException if, in trying to create the table, we
* encounter logic errors
*/
public BlockAllocationTableReader(POIFSBigBlockSize bigBlockSize, int block_count, int [] block_array,
int xbat_count, int xbat_index, BlockList raw_block_list) throws IOException {
this(bigBlockSize);
sanityCheckBlockCount(block_count);
// We want to get the whole of the FAT table
// To do this:
// * Work through raw_block_list, which points to the
// first (up to) 109 BAT blocks
// * Jump to the XBAT offset, and read in XBATs which
// point to more BAT blocks
int limit = Math.min(block_count, block_array.length);
int block_index;
// This will hold all of the BAT blocks in order
RawDataBlock blocks[] = new RawDataBlock[ block_count ];
// Process the first (up to) 109 BAT blocks
for (block_index = 0; block_index < limit; block_index++)
{
// Check that the sector number of the BAT block is a valid one
int nextOffset = block_array[ block_index ];
if(nextOffset > raw_block_list.blockCount()) {
throw new IOException("Your file contains " + raw_block_list.blockCount() +
" sectors, but the initial DIFAT array at index " + block_index +
" referenced block # " + nextOffset + ". This isn't allowed and " +
" your file is corrupt");
}
// Record the sector number of this BAT block
blocks[ block_index ] =
( RawDataBlock ) raw_block_list.remove(nextOffset);
}
// Process additional BAT blocks via the XBATs
if (block_index < block_count)
{
// must have extended blocks
if (xbat_index < 0)
{
throw new IOException(
"BAT count exceeds limit, yet XBAT index indicates no valid entries");
}
int chain_index = xbat_index;
int max_entries_per_block = bigBlockSize.getXBATEntriesPerBlock();
int chain_index_offset = bigBlockSize.getNextXBATChainOffset();
// Each XBAT block contains either:
// (maximum number of sector indexes) + index of next XBAT
// some sector indexes + FREE sectors to max # + EndOfChain
for (int j = 0; j < xbat_count; j++)
{
limit = Math.min(block_count - block_index,
max_entries_per_block);
byte[] data = raw_block_list.remove(chain_index).getData();
int offset = 0;
for (int k = 0; k < limit; k++)
{
blocks[ block_index++ ] =
( RawDataBlock ) raw_block_list
.remove(LittleEndian.getInt(data, offset));
offset += LittleEndianConsts.INT_SIZE;
}
chain_index = LittleEndian.getInt(data, chain_index_offset);
if (chain_index == POIFSConstants.END_OF_CHAIN)
{
break;
}
}
}
if (block_index != block_count)
{
throw new IOException("Could not find all blocks");
}
// Now that we have all of the raw data blocks which make
// up the FAT, go through and create the indices
setEntries(blocks, raw_block_list);
}
/**
* create a BlockAllocationTableReader from an array of raw data blocks
*
* @param blocks the raw data
* @param raw_block_list the list holding the managed blocks
*
* @exception IOException
*/
BlockAllocationTableReader(POIFSBigBlockSize bigBlockSize, ListManagedBlock[] blocks, BlockList raw_block_list)
throws IOException {
this(bigBlockSize);
setEntries(blocks, raw_block_list);
}
BlockAllocationTableReader(POIFSBigBlockSize bigBlockSize) {
this.bigBlockSize = bigBlockSize;
_entries = new IntList();
}
public static void sanityCheckBlockCount(int block_count) throws IOException {
if (block_count <= 0) {
throw new IOException(
"Illegal block count; minimum count is 1, got " +
block_count + " instead"
);
}
if (block_count > MAX_BLOCK_COUNT) {
throw new IOException(
"Block count " + block_count +
" is too high. POI maximum is " + MAX_BLOCK_COUNT + "."
);
}
}
/**
* walk the entries from a specified point and return the
* associated blocks. The associated blocks are removed from the
* block list
*
* @param startBlock the first block in the chain
* @param blockList the raw data block list
*
* @return array of ListManagedBlocks, in their correct order
*
* @exception IOException if there is a problem acquiring the blocks
*/
ListManagedBlock[] fetchBlocks(int startBlock, int headerPropertiesStartBlock,
BlockList blockList) throws IOException {
List blocks = new ArrayList();
int currentBlock = startBlock;
boolean firstPass = true;
ListManagedBlock dataBlock = null;
// Process the chain from the start to the end
// Normally we have header, data, end
// Sometimes we have data, header, end
// For those cases, stop at the header, not the end
while (currentBlock != POIFSConstants.END_OF_CHAIN) {
try {
// Grab the data at the current block offset
dataBlock = blockList.remove(currentBlock);
blocks.add(dataBlock);
// Now figure out which block we go to next
currentBlock = _entries.get(currentBlock);
firstPass = false;
} catch(IOException e) {
if(currentBlock == headerPropertiesStartBlock) {
// Special case where things are in the wrong order
_logger.log(POILogger.WARN, "Warning, header block comes after data blocks in POIFS block listing");
currentBlock = POIFSConstants.END_OF_CHAIN;
} else if(currentBlock == 0 && firstPass) {
// Special case where the termination isn't done right
// on an empty set
_logger.log(POILogger.WARN, "Warning, incorrectly terminated empty data blocks in POIFS block listing (should end at -2, ended at 0)");
currentBlock = POIFSConstants.END_OF_CHAIN;
} else {
// Ripple up
throw e;
}
}
}
return blocks.toArray(new ListManagedBlock[blocks.size()]);
}
// methods for debugging reader
/**
* determine whether the block specified by index is used or not
*
* @param index index of block in question
*
* @return true if the specific block is used, else false
*/
boolean isUsed(int index) {
try {
return _entries.get(index) != -1;
} catch (IndexOutOfBoundsException e) {
// ignored
return false;
}
}
/**
* return the next block index
*
* @param index of the current block
*
* @return index of the next block (may be
* POIFSConstants.END_OF_CHAIN, indicating end of chain
* (duh))
*
* @exception IOException if the current block is unused
*/
int getNextBlockIndex(int index) throws IOException {
if (isUsed(index)) {
return _entries.get(index);
}
throw new IOException("index " + index + " is unused");
}
/**
* Convert an array of blocks into a set of integer indices
*
* @param blocks the array of blocks containing the indices
* @param raw_blocks the list of blocks being managed. Unused
* blocks will be eliminated from the list
*/
private void setEntries(ListManagedBlock[] blocks, BlockList raw_blocks) throws IOException {
int limit = bigBlockSize.getBATEntriesPerBlock();
for (int block_index = 0; block_index < blocks.length; block_index++)
{
byte[] data = blocks[ block_index ].getData();
int offset = 0;
for (int k = 0; k < limit; k++)
{
int entry = LittleEndian.getInt(data, offset);
if (entry == POIFSConstants.UNUSED_BLOCK)
{
raw_blocks.zap(_entries.size());
}
_entries.add(entry);
offset += LittleEndianConsts.INT_SIZE;
}
// discard block
blocks[ block_index ] = null;
}
raw_blocks.setBAT(this);
}
}