http://poi.apache.org/: Apache POI - Java API To Access Microsoft Format Files (Apache Software Foundation) 
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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
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package org.apache.poi.poifs.storage;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.Arrays;

import org.apache.poi.hssf.OldExcelFormatException;
import org.apache.poi.poifs.common.POIFSBigBlockSize;
import org.apache.poi.poifs.common.POIFSConstants;
import org.apache.poi.poifs.filesystem.FileMagic;
import org.apache.poi.poifs.filesystem.NotOLE2FileException;
import org.apache.poi.poifs.filesystem.OfficeXmlFileException;
import org.apache.poi.util.HexDump;
import org.apache.poi.util.IOUtils;
import org.apache.poi.util.IntegerField;
import org.apache.poi.util.LittleEndian;
import org.apache.poi.util.LittleEndianConsts;
import org.apache.poi.util.LongField;
import org.apache.poi.util.ShortField;


The block containing the archive header

/**
 * The block containing the archive header
 */
public final class HeaderBlock implements HeaderBlockConstants {

	//arbitrarily selected; may need to increase
	private static final int MAX_RECORD_LENGTH = 100_000;

	private static final byte _default_value = ( byte ) 0xFF;

    
What big block size the file uses. Most files
 use 512 bytes, but a few use 4096

/**
	 * What big block size the file uses. Most files
	 *  use 512 bytes, but a few use 4096
	 */
	private final POIFSBigBlockSize bigBlockSize;

	
Number of big block allocation table blocks (int).
(Number of FAT Sectors in Microsoft parlance).

/** 
	 * Number of big block allocation table blocks (int).
	 * (Number of FAT Sectors in Microsoft parlance).
	 */
	private 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 int _property_start;

	
start of the small block allocation table (int index of small
block allocation table's first big block)

/** 
	 * start of the small block allocation table (int index of small
	 * block allocation table's first big block)
	 */
	private int _sbat_start;
	
Number of small block allocation table blocks (int)
(Number of MiniFAT Sectors in Microsoft parlance)

/**
	 * Number of small block allocation table blocks (int)
	 * (Number of MiniFAT Sectors in Microsoft parlance)
	 */
	private 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 int _xbat_start;
	
Number of big block allocation table blocks (int)
(Number of DIFAT Sectors in Microsoft parlance)

/**
	 * Number of big block allocation table blocks (int)
	 * (Number of DIFAT Sectors in Microsoft parlance)
	 */
	private int _xbat_count;
	
	
The data. Only ever 512 bytes, because 4096 byte
 files use zeros for the extra header space.

/**
	 * The data. Only ever 512 bytes, because 4096 byte
	 *  files use zeros for the extra header space.
	 */
	private final byte[] _data;
	
	
create a new HeaderBlockReader from an InputStream

Params:
  • stream – the source InputStream
Throws:
/**
	 * create a new HeaderBlockReader from an InputStream
	 *
	 * @param stream the source InputStream
	 *
	 * @exception IOException on errors or bad data
	 */
	public HeaderBlock(InputStream stream) throws IOException {
		// Grab the first 512 bytes
	    // (For 4096 sized blocks, the remaining 3584 bytes are zero)
		// Then, process the contents
		this(readFirst512(stream));
		
		// Fetch the rest of the block if needed
		if(bigBlockSize.getBigBlockSize() != 512) {
		   int rest = bigBlockSize.getBigBlockSize() - 512;
		   byte[] tmp = IOUtils.safelyAllocate(rest, MAX_RECORD_LENGTH);
		   IOUtils.readFully(stream, tmp);
		}
	}
	
	public HeaderBlock(ByteBuffer buffer) throws IOException {
	   this(IOUtils.toByteArray(buffer, POIFSConstants.SMALLER_BIG_BLOCK_SIZE));
	}
	
	private HeaderBlock(byte[] data) throws IOException {
	   this._data = data.clone();
	   
		// verify signature
	   FileMagic fm = FileMagic.valueOf(data);
	   
	   switch (fm) {
	   case OLE2:
	       break;
	   case OOXML:
           throw new OfficeXmlFileException("The supplied data appears to be in the Office 2007+ XML. "
               + "You are calling the part of POI that deals with OLE2 Office Documents. "
               + "You need to call a different part of POI to process this data (eg XSSF instead of HSSF)");
	   case XML:
           throw new NotOLE2FileException("The supplied data appears to be a raw XML file. "
               + "Formats such as Office 2003 XML are not supported");
	   case MSWRITE:
           throw new NotOLE2FileException("The supplied data appears to be in the old MS Write format. "
               + "Apache POI doesn't currently support this format");
	   case WORD2:
		   throw new NotOLE2FileException("The supplied data appears to be an old Word version 2 file. "
			   + "Apache POI doesn't currently support this format");
       case BIFF2:
       case BIFF3:
       case BIFF4:
           throw new OldExcelFormatException("The supplied data appears to be in "+fm+" format. "
               + "HSSF only supports the BIFF8 format, try OldExcelExtractor");
	   default:
           // Give a generic error if the OLE2 signature isn't found
	       String exp = HexDump.longToHex(_signature);
	       String act = HexDump.longToHex(LittleEndian.getLong(data, 0));
           throw new NotOLE2FileException(
               "Invalid header signature; read " + act + ", expected " + exp +
               " - Your file appears not to be a valid OLE2 document");
	   }
	   
		// Figure out our block size
		if (_data[30] == 12) {
			this.bigBlockSize = POIFSConstants.LARGER_BIG_BLOCK_SIZE_DETAILS;
		} else if(_data[30] == 9) {
			this.bigBlockSize = POIFSConstants.SMALLER_BIG_BLOCK_SIZE_DETAILS;
		} else {
		   throw new IOException("Unsupported blocksize  (2^"+ _data[30] + "). Expected 2^9 or 2^12.");
		}

	   // Setup the fields to read and write the counts and starts
      _bat_count  = new IntegerField(_bat_count_offset, data).get();
      _property_start = new IntegerField(_property_start_offset,_data).get();
      _sbat_start = new IntegerField(_sbat_start_offset, _data).get();
      _sbat_count = new IntegerField(_sbat_block_count_offset, _data).get();
      _xbat_start = new IntegerField(_xbat_start_offset, _data).get();
      _xbat_count = new IntegerField(_xbat_count_offset, _data).get();
	}
	
   
Create a single instance initialized with default values

/**
    * Create a single instance initialized with default values
    */
   public HeaderBlock(POIFSBigBlockSize bigBlockSize)
   {
      this.bigBlockSize = bigBlockSize;

      // Our data is always 512 big no matter what
      _data = new byte[ POIFSConstants.SMALLER_BIG_BLOCK_SIZE ];
      Arrays.fill(_data, _default_value);
      
      // Set all the default values
      new LongField(_signature_offset, _signature, _data);
      new IntegerField(0x08, 0, _data);
      new IntegerField(0x0c, 0, _data);
      new IntegerField(0x10, 0, _data);
      new IntegerField(0x14, 0, _data);
      new ShortField(0x18, ( short ) 0x3b, _data);
      new ShortField(0x1a, ( short ) 0x3, _data);
      new ShortField(0x1c, ( short ) -2, _data);
       
      new ShortField(0x1e, bigBlockSize.getHeaderValue(), _data);
      new IntegerField(0x20, 0x6, _data);
      new IntegerField(0x24, 0, _data);
      new IntegerField(0x28, 0, _data);
      new IntegerField(0x34, 0, _data);
      new IntegerField(0x38, 0x1000, _data);
      
      // Initialize the variables
      _bat_count = 0;
      _sbat_count = 0;
      _xbat_count = 0;
      _property_start = POIFSConstants.END_OF_CHAIN;
      _sbat_start = POIFSConstants.END_OF_CHAIN;
      _xbat_start = POIFSConstants.END_OF_CHAIN;
   }
   
	private static byte[] readFirst512(InputStream stream) throws IOException {
      // Grab the first 512 bytes
      // (For 4096 sized blocks, the remaining 3584 bytes are zero)
      byte[] data = new byte[512];
      int bsCount = IOUtils.readFully(stream, data);
      if(bsCount != 512) {
         throw alertShortRead(bsCount);
      }
      return data;
	}

	private static IOException alertShortRead(int pRead) {
		int read;
		if (pRead < 0) {
			//Can't have -1 bytes read in the error message!
			read = 0;
		} else {
			read = pRead;
		}
		String type = " byte" + (read == 1 ? (""): ("s"));

		return new IOException("Unable to read entire header; "
				+ read + type + " read; expected 512 bytes");
	}

	
get start of Property Table

Returns:the index of the first block of the Property Table
/**
	 * get start of Property Table
	 *
	 * @return the index of the first block of the Property Table
	 */
	public int getPropertyStart() {
		return _property_start;
	}
   
Set start of Property Table

Params:
  • startBlock – the index of the first block of the Property Table
/**
    * Set start of Property Table
    *
    * @param startBlock the index of the first block of the Property Table
    */
   public void setPropertyStart(final int startBlock) {
       _property_start = startBlock;
   }

	
Returns:start of small block (MiniFAT) allocation table
/**
	 * @return start of small block (MiniFAT) allocation table
	 */
	public int getSBATStart() {
		return _sbat_start;
	}
	public int getSBATCount() {
	   return _sbat_count;
	}
	
   
Set start of small block allocation table

Params:
  • startBlock – the index of the first big block of the small
                  block allocation table
/**
    * Set start of small block allocation table
    *
    * @param startBlock the index of the first big block of the small
    *                   block allocation table
    */
   public void setSBATStart(final int startBlock) {
       _sbat_start = startBlock;
   }
   
Set count of SBAT blocks

Params:
  • count – the number of SBAT blocks
/**
    * Set count of SBAT blocks
    *
    * @param count the number of SBAT blocks
    */
   public void setSBATBlockCount(final int count)
   {
      _sbat_count = count;
   }

	
Returns:number of BAT blocks
/**
	 * @return number of BAT blocks
	 */
	public int getBATCount() {
		return _bat_count;
	}
   
Sets the number of BAT blocks that are used.
This is the number used in both the BAT and XBAT. 

/**
    * Sets the number of BAT blocks that are used.
    * This is the number used in both the BAT and XBAT. 
    */
   public void setBATCount(final int count) {
      _bat_count = count;
   }

	
Returns the offsets to the first (up to) 109
 BAT sectors.
Any additional BAT sectors are held in the XBAT (DIFAT)
 sectors in a chain.

Returns:BAT offset array
/**
	 * Returns the offsets to the first (up to) 109
	 *  BAT sectors.
	 * Any additional BAT sectors are held in the XBAT (DIFAT)
	 *  sectors in a chain.
	 * @return BAT offset array
	 */
	public int[] getBATArray() {
      // Read them in
		int[] result = new int[ Math.min(_bat_count,_max_bats_in_header) ];
		int offset = _bat_array_offset;
		for (int j = 0; j < result.length; j++) {
			result[ j ] = LittleEndian.getInt(_data, offset);
			offset     += LittleEndianConsts.INT_SIZE;
		}
		return result;
	}
	
Sets the offsets of the first (up to) 109
 BAT sectors.

/**
	 * Sets the offsets of the first (up to) 109
	 *  BAT sectors.
	 */
	public void setBATArray(int[] bat_array) {
	   int count = Math.min(bat_array.length, _max_bats_in_header);
	   int blank = _max_bats_in_header - count;
	   
      int offset = _bat_array_offset;
	   for(int i=0; i<count; i++) {
	      LittleEndian.putInt(_data, offset, bat_array[i]);
         offset += LittleEndianConsts.INT_SIZE;
	   }
	   for(int i=0; i<blank; i++) {
         LittleEndian.putInt(_data, offset, POIFSConstants.UNUSED_BLOCK);
         offset += LittleEndianConsts.INT_SIZE;
	   }
	}

	
Returns:XBAT (DIFAT) count
/**
	 * @return XBAT (DIFAT) count
	 */
	public int getXBATCount() {
		return _xbat_count;
	}
	
Sets the number of XBAT (DIFAT) blocks used

/**
	 * Sets the number of XBAT (DIFAT) blocks used
	 */
	public void setXBATCount(final int count) {
	   _xbat_count = count;
	}

	
Returns:XBAT (DIFAT) index
/**
	 * @return XBAT (DIFAT) index
	 */
	public int getXBATIndex() {
		return _xbat_start;
	}
	
Sets the first XBAT (DIFAT) block location

/**
	 * Sets the first XBAT (DIFAT) block location
	 */
   public void setXBATStart(final int startBlock) {
      _xbat_start = startBlock;
  }

	
Returns:The Big Block size, normally 512 bytes, sometimes 4096 bytes
/**
	 * @return The Big Block size, normally 512 bytes, sometimes 4096 bytes
	 */
	public POIFSBigBlockSize getBigBlockSize() {
		return bigBlockSize;
	}
	
   
Write the block's data to an OutputStream

Params:
  • stream – the OutputStream to which the stored data should
              be written
Throws:
  • IOException – on problems writing to the specified
           stream
/**
    * Write the block's data to an OutputStream
    *
    * @param stream the OutputStream to which the stored data should
    *               be written
    *
    * @exception IOException on problems writing to the specified
    *            stream
    */
   public void writeData(final OutputStream stream) throws IOException {
      // Update the counts and start positions 
      new IntegerField(_bat_count_offset,      _bat_count, _data);
      new IntegerField(_property_start_offset, _property_start, _data);
      new IntegerField(_sbat_start_offset,     _sbat_start, _data);
      new IntegerField(_sbat_block_count_offset, _sbat_count, _data);
      new IntegerField(_xbat_start_offset,      _xbat_start, _data);
      new IntegerField(_xbat_count_offset,      _xbat_count, _data);
      
      // Write the main data out
      stream.write(_data, 0, 512);
      
      // Now do the padding if needed
      for(int i=POIFSConstants.SMALLER_BIG_BLOCK_SIZE; i<bigBlockSize.getBigBlockSize(); i++) {
         stream.write(0);
      }
   }
}