Lots more documentation on how we read in POIFS files and process the sectors/blocks and FATs. Also add a test that shows that bug #46391 is invalid

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@933663 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/poifs/common/POIFSConstants.java

@@ -32,10 +32,21 @@ public interface POIFSConstants
     /** Some use 4096 bytes */
     public static final int LARGER_BIG_BLOCK_SIZE = 0x1000;
     
-    public static final int END_OF_CHAIN   = -2;
     public static final int PROPERTY_SIZE  = 0x0080;
+    
+    /** The highest sector number you're allowed, 0xFFFFFFFA */
+    public static final int LARGEST_REGULAR_SECTOR_NUMBER = -5;
+    
+    /** Indicates the sector holds a DIFAT block (0xFFFFFFFC) */
+    public static final int DIFAT_SECTOR_BLOCK   = -4;
+    /** Indicates the sector holds a FAT block (0xFFFFFFFD) */
+    public static final int FAT_SECTOR_BLOCK   = -3;
+    /** Indicates the sector is the end of a chain (0xFFFFFFFE) */
+    public static final int END_OF_CHAIN   = -2;
+    /** Indicates the sector is not used (0xFFFFFFFF) */
     public static final int UNUSED_BLOCK   = -1;
     
+    /** The first 4 bytes of an OOXML file, used in detection */
     public static final byte[] OOXML_FILE_HEADER = 
     	new byte[] { 0x50, 0x4b, 0x03, 0x04 };
 }   // end public interface POIFSConstants;

src/java/org/apache/poi/poifs/storage/BlockAllocationTableReader.java

@@ -89,17 +89,35 @@ public final class BlockAllocationTableReader {
                     + " is too high. POI maximum is " + MAX_BLOCK_COUNT + ".");
         }
 
-        // acquire raw data blocks containing the BAT block data
+        // We want to get the whole of the FAT table
-        RawDataBlock blocks[] = new RawDataBlock[ block_count ];
+        // 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++)
         {
-            blocks[ block_index ] =
+            // Check that the sector number of the BAT block is a valid one
-                ( RawDataBlock ) raw_block_list
+            int nextOffset = block_array[ block_index ];
-                    .remove(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)
         {
 
@@ -113,6 +131,9 @@ public final class BlockAllocationTableReader {
             int max_entries_per_block = BATBlock.entriesPerXBATBlock();
             int chain_index_offset    = BATBlock.getXBATChainOffset();
 
+            // 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,
@@ -139,8 +160,8 @@ public final class BlockAllocationTableReader {
             throw new IOException("Could not find all blocks");
         }
 
-        // now that we have all of the raw data blocks, go through and
+        // Now that we have all of the raw data blocks which make
-        // create the indices
+        //  up the FAT, go through and create the indices
         setEntries(blocks, raw_block_list);
     }
 

src/java/org/apache/poi/poifs/storage/BlockList.java

@@ -79,5 +79,7 @@ public interface BlockList
 
     public void setBAT(final BlockAllocationTableReader bat)
         throws IOException;
+    
+    public int blockCount();
 }   // end public interface BlockList
 

src/java/org/apache/poi/poifs/storage/BlockListImpl.java

@@ -138,4 +138,21 @@ abstract class BlockListImpl implements BlockList {
         }
         _bat = bat;
     }
+    
+    /**
+     * Returns the count of the number of blocks
+     */
+    public int blockCount() {
+       return _blocks.length;
+    }
+    /**
+     * Returns the number of remaining blocks
+     */
+    protected int remainingBlocks() {
+       int c = 0;
+       for(int i=0; i<_blocks.length; i++) {
+          if(_blocks[i] != null) c++;
+       }
+       return c;
+    }
 }

src/java/org/apache/poi/poifs/storage/HeaderBlockConstants.java

@@ -33,6 +33,11 @@ public interface HeaderBlockConstants
         (POIFSConstants.BIG_BLOCK_SIZE - _bat_array_offset)
         / LittleEndianConsts.INT_SIZE;
 
+    // Note - in Microsoft terms:
+    //  BAT ~= FAT
+    //  SBAT ~= MiniFAT
+    //  XBAT ~= DIFat
+    
     // useful offsets
     public static final int  _signature_offset        = 0;
     public static final int  _bat_count_offset        = 0x2C;

src/java/org/apache/poi/poifs/storage/HeaderBlockReader.java

@@ -22,6 +22,7 @@ import static org.apache.poi.poifs.storage.HeaderBlockConstants._bat_count_offse
 import static org.apache.poi.poifs.storage.HeaderBlockConstants._max_bats_in_header;
 import static org.apache.poi.poifs.storage.HeaderBlockConstants._property_start_offset;
 import static org.apache.poi.poifs.storage.HeaderBlockConstants._sbat_start_offset;
+import static org.apache.poi.poifs.storage.HeaderBlockConstants._sbat_block_count_offset;
 import static org.apache.poi.poifs.storage.HeaderBlockConstants._signature;
 import static org.apache.poi.poifs.storage.HeaderBlockConstants._signature_offset;
 import static org.apache.poi.poifs.storage.HeaderBlockConstants._xbat_count_offset;
@@ -49,21 +50,37 @@ public final class HeaderBlockReader {
 	 */
 	private final int bigBlockSize;
 
-	/** number of big block allocation table blocks (int) */
+	/** 
+	 * number of big block allocation table blocks (int).
+	 * (Number of FAT Sectors in Microsoft parlance) 
+	 */
 	private final int _bat_count;
 
-	/** start of the property set block (int index of the property set
+	/** 
-	 * chain's first big block)
+	 * Start of the property set block (int index of the property set
+	 * chain's first big block).
 	 */
 	private final int _property_start;
 
-	/** start of the small block allocation table (int index of small
+	/** 
+	 * start of the small block allocation table (int index of small
 	 * block allocation table's first big block)
 	 */
 	private final int _sbat_start;
+	/**
+	 * Number of small block allocation table blocks (int)
+	 * (Number of MiniFAT Sectors in Microsoft parlance)
+	 */
+	private final int _sbat_count;
 
-	/** big block index for extension to the big block allocation table */
+	/** 
+	 * Big block index for extension to the big block allocation table
+	 */
 	private final int _xbat_start;
+	/**
+	 * Number of big block allocation table blocks (int)
+	 * (Number of DIFAT Sectors in Microsoft parlance)
+	 */
 	private final int _xbat_count;
 	private final byte[] _data;
 
@@ -132,6 +149,7 @@ public final class HeaderBlockReader {
 		_bat_count      = getInt(_bat_count_offset, _data);
 		_property_start = getInt(_property_start_offset, _data);
 		_sbat_start     = getInt(_sbat_start_offset, _data);
+		_sbat_count     = getInt(_sbat_block_count_offset, _data);
 		_xbat_start     = getInt(_xbat_start_offset, _data);
 		_xbat_count     = getInt(_xbat_count_offset, _data);
 	}
@@ -169,11 +187,14 @@ public final class HeaderBlockReader {
 	}
 
 	/**
-	 * @return start of small block allocation table
+	 * @return start of small block (MiniFAT) allocation table
 	 */
 	public int getSBATStart() {
 		return _sbat_start;
 	}
+	public int getSBATCount() {
+	   return _sbat_count;
+	}
 
 	/**
 	 * @return number of BAT blocks
@@ -183,7 +204,10 @@ public final class HeaderBlockReader {
 	}
 
 	/**
-	 * @return BAT array
+	 * Returns the offsets to the first (up to) 109
+	 *  BAT sectors.
+	 * Any additional BAT sectors 
+	 * @return BAT offset array
 	 */
 	public int[] getBATArray() {
 		int[] result = new int[ _max_bats_in_header ];
@@ -197,14 +221,14 @@ public final class HeaderBlockReader {
 	}
 
 	/**
-	 * @return XBAT count
+	 * @return XBAT (DIFAT) count
 	 */
 	public int getXBATCount() {
 		return _xbat_count;
 	}
 
 	/**
-	 * @return XBAT index
+	 * @return XBAT (DIFAT) index
 	 */
 	public int getXBATIndex() {
 		return _xbat_start;

src/java/org/apache/poi/poifs/storage/RawDataBlock.java

@@ -112,6 +112,10 @@ public class RawDataBlock
     	return _hasData;
     }
     
+    public String toString() {
+       return "RawDataBlock of size " + _data.length; 
+    }
+
     /* ********** START implementation of ListManagedBlock ********** */
 
     /**

src/testcases/org/apache/poi/poifs/filesystem/TestPOIFSFileSystem.java

@@ -149,6 +149,26 @@ public final class TestPOIFSFileSystem extends TestCase {
 		}
 	}
 	
+	/**
+	 * Check that we do the right thing when the list of which
+	 *  sectors are BAT blocks points off the list of
+	 *  sectors that exist in the file.
+	 */
+	public void testFATandDIFATsectors() throws Exception {
+      POIDataSamples _samples = POIDataSamples.getPOIFSInstance();
+      
+      // Open the file up
+      try {
+         POIFSFileSystem fs = new POIFSFileSystem(
+             _samples.openResourceAsStream("ReferencesInvalidSectors.mpp")
+         );
+         fail("File is corrupt and shouldn't have been opened");
+      } catch(IOException e) {
+         String msg = e.getMessage();
+         assertTrue(msg.startsWith("Your file contains 695 sectors"));
+      }
+	}
+
 	private static InputStream openSampleStream(String sampleFileName) {
 		return HSSFTestDataSamples.openSampleFileStream(sampleFileName);
 	}

src/testcases/org/apache/poi/poifs/storage/LocalRawDataBlockList.java

@@ -181,4 +181,8 @@ public final class LocalRawDataBlockList extends RawDataBlockList {
             _array = _list.toArray(new RawDataBlock[ 0 ]);
         }
     }
+    
+    public int blockCount() {
+       return _list.size();
+    }
 }