libreoffice/package/source/zipapi/ZipFile.cxx

/*************************************************************************
 *
 *  $RCSfile: ZipFile.cxx,v $
 *
 *  $Revision: 1.33 $
 *
 *  last change: $Author: mtg $ $Date: 2001-11-15 20:22:18 $
 *
 *  The Contents of this file are made available subject to the terms of
 *  either of the following licenses
 *
 *         - GNU Lesser General Public License Version 2.1
 *         - Sun Industry Standards Source License Version 1.1
 *
 *  Sun Microsystems Inc., October, 2000
 *
 *  GNU Lesser General Public License Version 2.1
 *  =============================================
 *  Copyright 2000 by Sun Microsystems, Inc.
 *  901 San Antonio Road, Palo Alto, CA 94303, USA
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License version 2.1, as published by the Free Software Foundation.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 *  MA  02111-1307  USA
 *
 *
 *  Sun Industry Standards Source License Version 1.1
 *  =================================================
 *  The contents of this file are subject to the Sun Industry Standards
 *  Source License Version 1.1 (the "License"); You may not use this file
 *  except in compliance with the License. You may obtain a copy of the
 *  License at http://www.openoffice.org/license.html.
 *
 *  Software provided under this License is provided on an "AS IS" basis,
 *  WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING,
 *  WITHOUT LIMITATION, WARRANTIES THAT THE SOFTWARE IS FREE OF DEFECTS,
 *  MERCHANTABLE, FIT FOR A PARTICULAR PURPOSE, OR NON-INFRINGING.
 *  See the License for the specific provisions governing your rights and
 *  obligations concerning the Software.
 *
 *  The Initial Developer of the Original Code is: Sun Microsystems, Inc.
 *
 *  Copyright: 2000 by Sun Microsystems, Inc.
 *
 *  All Rights Reserved.
 *
 *  Contributor(s): Martin Gallwey (gallwey@sun.com)
 *
 *
 ************************************************************************/
#ifndef _ZIP_FILE_HXX
#include <ZipFile.hxx>
#endif
#ifndef _ZIP_ENUMERATION_HXX
#include <ZipEnumeration.hxx>
#endif
#ifndef _COM_SUN_STAR_PACKAGES_ZIP_ZIPCONSTANTS_HPP_
#include <com/sun/star/packages/zip/ZipConstants.hpp>
#endif
#ifndef _RTL_CIPHER_H_
#include <rtl/cipher.h>
#endif
#ifndef _RTL_DIGEST_H_
#include <rtl/digest.h>
#endif
#ifndef _XMEMORY_STREAM_HXX
#include <XMemoryStream.hxx>
#endif
#ifndef _XFILE_STREAM_HXX
#include <XFileStream.hxx>
#endif
#ifndef _PACKAGE_CONSTANTS_HXX_
#include <PackageConstants.hxx>
#endif
#ifndef _ENCRYPTED_DATA_HEADER_HXX_
#include <EncryptedDataHeader.hxx>
#endif
#ifndef _ENCRYPTION_DATA_HXX_
#include <EncryptionData.hxx>
#endif
#ifndef _MEMORY_BYTE_GRABBER_HXX_
#include <MemoryByteGrabber.hxx>
#endif
#ifndef _COM_SUN_STAR_LANG_XMULTISERVICEFACTORY_HPP_
#include <com/sun/star/lang/XMultiServiceFactory.hpp>
#endif
#include <string.h> // for memcpy
#include <vector>

using namespace vos;
using namespace rtl;
using namespace com::sun::star;
using namespace com::sun::star::io;
using namespace com::sun::star::uno;
using namespace com::sun::star::lang;
using namespace com::sun::star::packages;
using namespace com::sun::star::packages::zip;
using namespace com::sun::star::packages::zip::ZipConstants;


/** This class is used to read entries from a zip file
 */
ZipFile::ZipFile( Reference < XInputStream > &xInput, const Reference < XMultiServiceFactory > &xNewFactory, sal_Bool bInitialise)
    throw(IOException, ZipException, RuntimeException)
: xStream(xInput)
, xSeek(xInput, UNO_QUERY)
, aGrabber(xInput)
, aInflater (sal_True)
, xFactory ( xNewFactory )
{
    if (bInitialise)
    {
        if ( readCEN() == -1 )
            aEntries.clear();
    }
}

ZipFile::~ZipFile()
{
    aEntries.clear();
}

void ZipFile::setInputStream ( Reference < XInputStream > xNewStream )
{
    xStream = xNewStream;
    xSeek = Reference < XSeekable > ( xStream, UNO_QUERY );
    aGrabber.setInputStream ( xStream );
}

void ZipFile::StaticGetCipher ( const ORef < EncryptionData > & xEncryptionData, rtlCipher &rCipher )
{
    if ( ! xEncryptionData.isEmpty() )
    {
        Sequence < sal_uInt8 > aDerivedKey (16);
        rtlCipherError aResult;
        Sequence < sal_Int8 > aDecryptBuffer;

        // Get the key
        rtl_digest_PBKDF2 ( aDerivedKey.getArray(), 16,
                            reinterpret_cast < const sal_uInt8 * > (xEncryptionData->aKey.getConstArray() ),
                            xEncryptionData->aKey.getLength(),
                            reinterpret_cast < const sal_uInt8 * > ( xEncryptionData->aSalt.getConstArray() ),
                            xEncryptionData->aSalt.getLength(),
                            xEncryptionData->nIterationCount );

        rCipher = rtl_cipher_create (rtl_Cipher_AlgorithmBF, rtl_Cipher_ModeStream);
        aResult = rtl_cipher_init( rCipher, rtl_Cipher_DirectionDecode,
                                   aDerivedKey.getConstArray(),
                                   aDerivedKey.getLength(),
                                   reinterpret_cast < const sal_uInt8 * > ( xEncryptionData->aInitVector.getConstArray() ),
                                   xEncryptionData->aInitVector.getLength());
        OSL_ASSERT (aResult == rtl_Cipher_E_None);
    }
}

void ZipFile::StaticFillHeader ( const ORef < EncryptionData > & rData, sal_Int32 nSize, sal_Int8 * & pHeader )
{
    // I think it's safe to restrict vector and salt length to 2 bytes !
    sal_Int16 nIVLength = static_cast < sal_Int16 > ( rData->aInitVector.getLength() );
    sal_Int16 nSaltLength = static_cast < sal_Int16 > ( rData->aSalt.getLength() );
    sal_Int16 nDigestLength = static_cast < sal_Int16 > ( rData->aDigest.getLength() );

    // First the header
    *(pHeader++) = ( n_ConstHeader >> 0 ) & 0xFF;
    *(pHeader++) = ( n_ConstHeader >> 8 ) & 0xFF;
    *(pHeader++) = ( n_ConstHeader >> 16 ) & 0xFF;
    *(pHeader++) = ( n_ConstHeader >> 24 ) & 0xFF;

    // Then the version
    *(pHeader++) = ( n_ConstCurrentVersion >> 0 ) & 0xFF;
    *(pHeader++) = ( n_ConstCurrentVersion >> 8 ) & 0xFF;

    // Then the iteration Count
    sal_Int32 nIterationCount = rData->nIterationCount;
    *(pHeader++) = ( nIterationCount >> 0 ) & 0xFF;
    *(pHeader++) = ( nIterationCount >> 8 ) & 0xFF;
    *(pHeader++) = ( nIterationCount >> 16 ) & 0xFF;
    *(pHeader++) = ( nIterationCount >> 24 ) & 0xFF;

    // Then the size
    *(pHeader++) = ( nSize >> 0 ) & 0xFF;
    *(pHeader++) = ( nSize >> 8 ) & 0xFF;
    *(pHeader++) = ( nSize >> 16 ) & 0xFF;
    *(pHeader++) = ( nSize >> 24 ) & 0xFF;

    // Then the salt length
    *(pHeader++) = ( nSaltLength >> 0 ) & 0xFF;
    *(pHeader++) = ( nSaltLength >> 8 ) & 0xFF;

    // Then the IV length
    *(pHeader++) = ( nIVLength >> 0 ) & 0xFF;
    *(pHeader++) = ( nIVLength >> 8 ) & 0xFF;

    // Then the digest length
    *(pHeader++) = ( nDigestLength >> 0 ) & 0xFF;
    *(pHeader++) = ( nDigestLength >> 8 ) & 0xFF;

    // Then the salt content
    memcpy ( pHeader, rData->aSalt.getConstArray(), nSaltLength );
    pHeader += nSaltLength;

    // Then the IV content
    memcpy ( pHeader, rData->aInitVector.getConstArray(), nIVLength );
    pHeader += nIVLength;

    // Then the digest content
    memcpy ( pHeader, rData->aDigest.getConstArray(), nDigestLength );
    pHeader += nDigestLength;
}
sal_Bool ZipFile::StaticFillData ( ORef < EncryptionData > & rData, sal_Int32 &rSize, Reference < XInputStream > &rStream )
{
    sal_Bool bOk = sal_False;
    const sal_Int32 nHeaderSize = n_ConstHeaderSize - 4;
    Sequence < sal_Int8 > aBuffer ( nHeaderSize );
    if ( nHeaderSize == rStream->readBytes ( aBuffer, nHeaderSize ) )
    {
        sal_Int16 nPos = 0;
        sal_Int8 *pBuffer = aBuffer.getArray();
        sal_Int16 nVersion = pBuffer[nPos++] & 0xFF;
        nVersion |= ( pBuffer[nPos++] & 0xFF ) << 8;
        if ( nVersion == n_ConstCurrentVersion )
        {
            sal_Int32 nCount = pBuffer[nPos++] & 0xFF;
            nCount |= ( pBuffer[nPos++] & 0xFF ) << 8;
            nCount |= ( pBuffer[nPos++] & 0xFF ) << 16;
            nCount |= ( pBuffer[nPos++] & 0xFF ) << 24;
            rData->nIterationCount = nCount;

            rSize  =   pBuffer[nPos++] & 0xFF;
            rSize |= ( pBuffer[nPos++] & 0xFF ) << 8;
            rSize |= ( pBuffer[nPos++] & 0xFF ) << 16;
            rSize |= ( pBuffer[nPos++] & 0xFF ) << 24;

            sal_Int16 nSaltLength =   pBuffer[nPos++] & 0xFF;
            nSaltLength          |= ( pBuffer[nPos++] & 0xFF ) << 8;
            sal_Int16 nIVLength   = ( pBuffer[nPos++] & 0xFF );
            nIVLength            |= ( pBuffer[nPos++] & 0xFF ) << 8;
            sal_Int16 nDigestLength = pBuffer[nPos++] & 0xFF;
            nDigestLength        |= ( pBuffer[nPos++] & 0xFF ) << 8;

            if ( nSaltLength == rStream->readBytes ( aBuffer, nSaltLength ) )
            {
                rData->aSalt.realloc ( nSaltLength );
                memcpy ( rData->aSalt.getArray(), aBuffer.getConstArray(), nSaltLength );
                if ( nIVLength == rStream->readBytes ( aBuffer, nIVLength ) )
                {
                    rData->aInitVector.realloc ( nIVLength );
                    memcpy ( rData->aInitVector.getArray(), aBuffer.getConstArray(), nIVLength );
                    if ( nDigestLength == rStream->readBytes ( aBuffer, nDigestLength ) )
                    {
                        rData->aDigest.realloc ( nDigestLength );
                        memcpy ( rData->aDigest.getArray(), aBuffer.getConstArray(), nDigestLength );
                        bOk = sal_True;
                    }
                }
            }
        }
    }
    return bOk;
}
Reference < XInputStream > ZipFile::createFileStream(
            ZipEntry & rEntry,
            const ORef < EncryptionData > &rData,
            sal_Bool bRawStream,
            sal_Bool bIsEncrypted )
{
    static OUString sServiceName ( RTL_CONSTASCII_USTRINGPARAM ( "com.sun.star.io.TempFile" ) );
    Reference < XInputStream > xTempStream = Reference < XInputStream > ( xFactory->createInstance ( sServiceName ), UNO_QUERY );
    return new XFileStream ( rEntry, xStream, xTempStream, rData, bRawStream, bIsEncrypted );
}

sal_Bool ZipFile::hasValidPassword ( ZipEntry & rEntry, const ORef < EncryptionData > &rData )
{
    sal_Bool bRet = sal_False;
    if ( rData->aKey.getLength() )
    {
        // make a temporary cipher
        rtlCipher aCipher;
        StaticGetCipher ( rData, aCipher );

        xSeek->seek( rEntry.nOffset );
        sal_Int32 nSize = rEntry.nMethod == DEFLATED ? rEntry.nCompressedSize : rEntry.nSize;

        // Only want to read enough to verify the digest
        nSize = nSize > n_ConstDigestLength ? n_ConstDigestLength : nSize;
        Sequence < sal_Int8 > aReadBuffer ( nSize ), aDecryptBuffer ( nSize );

        xStream->readBytes( aReadBuffer, nSize );

        rtlDigest aDigest = rtl_digest_createSHA1();
        rtlDigestError aDigestResult;
        Sequence < sal_uInt8 > aDigestSeq ( RTL_DIGEST_LENGTH_SHA1 );
        rtlCipherError aResult = rtl_cipher_decode ( aCipher,
                                      aReadBuffer.getConstArray(),
                                      nSize,
                                      reinterpret_cast < sal_uInt8 * > (aDecryptBuffer.getArray()),
                                      nSize);
        OSL_ASSERT (aResult == rtl_Cipher_E_None);

        aDigestResult = rtl_digest_updateSHA1 ( aDigest, static_cast < const void * > ( aDecryptBuffer.getConstArray() ), nSize );
        OSL_ASSERT ( aDigestResult == rtl_Digest_E_None );

        aDigestResult = rtl_digest_getSHA1 ( aDigest, aDigestSeq.getArray(), RTL_DIGEST_LENGTH_SHA1 );
        OSL_ASSERT ( aDigestResult == rtl_Digest_E_None );

        // If we don't have a digest, then we have to assume that the password is correct
        if (  rData->aDigest.getLength() != 0  &&
              ( aDigestSeq.getLength() != rData->aDigest.getLength() ||
                0 != rtl_compareMemory ( aDigestSeq.getConstArray(),
                                         rData->aDigest.getConstArray(),
                                        aDigestSeq.getLength() ) ) )
        {
            // We should probably tell the user that the password they entered was wrong,
            // but for now we'll just give the upper levels the raw unencrypted data
        }
        else
            bRet = sal_True;

        rtl_digest_destroySHA1 ( aDigest );
    }
    return bRet;
}
Reference < XInputStream > ZipFile::createMemoryStream(
            ZipEntry & rEntry,
            const ORef < EncryptionData > &rData,
            sal_Bool bRawStream,
            sal_Bool bIsEncrypted )
{
    sal_Int32 nUncompressedSize, nEnd;
    if (bRawStream)
    {
        nUncompressedSize = rEntry.nMethod == DEFLATED ? rEntry.nCompressedSize : rEntry.nSize;
        nEnd = rEntry.nOffset + nUncompressedSize;
    }
    else
    {
        nUncompressedSize = rEntry.nSize;
        nEnd = rEntry.nMethod == DEFLATED ? rEntry.nOffset + rEntry.nCompressedSize : rEntry.nOffset + rEntry.nSize;
    }
    sal_Int32 nSize = rEntry.nMethod == DEFLATED ? rEntry.nCompressedSize : rEntry.nSize;
    Sequence < sal_Int8 > aReadBuffer ( nSize ), aDecryptBuffer, aWriteBuffer;
    rtlCipher aCipher;

    // If the encryption key is zero, we need to return the raw stream. First check if
    // we have the salt. If we have the salt, then check if we have the encryption key
    // if not, return rawStream instead.

    sal_Bool bHaveEncryptData = ( !rData.isEmpty() && rData->aSalt.getLength() && rData->aInitVector.getLength() && rData->nIterationCount != 0 ) ? sal_True : sal_False;
    sal_Bool bMustDecrypt = ( !bRawStream && bHaveEncryptData && bIsEncrypted ) ? sal_True : sal_False;

    if ( bMustDecrypt )
    {
        StaticGetCipher ( rData, aCipher );
        aDecryptBuffer.realloc ( nSize );
    }

    if ( nSize <0 )
        throw IOException ( );

    xSeek->seek( rEntry.nOffset );
    xStream->readBytes( aReadBuffer, nSize ); // Now it holds the raw stuff from disk

    if ( bMustDecrypt )
    {
        rtlCipherError aResult = rtl_cipher_decode ( aCipher,
                                      aReadBuffer.getConstArray(),
                                      nSize,
                                      reinterpret_cast < sal_uInt8 * > (aDecryptBuffer.getArray()),
                                      nSize);
        OSL_ASSERT (aResult == rtl_Cipher_E_None);
        aReadBuffer = aDecryptBuffer; // Now it holds the decrypted data
    }
    if (bRawStream || rEntry.nMethod == STORED)
        aWriteBuffer = aReadBuffer; // bRawStream means the caller doesn't want it decompressed
    else
    {
        aInflater.setInputSegment( aReadBuffer, 0, nSize );
        aWriteBuffer.realloc( nUncompressedSize );
        aInflater.doInflate( aWriteBuffer );
        aInflater.reset();
    }

    if ( bHaveEncryptData && !bMustDecrypt && bIsEncrypted )
    {
        // if we have the data needed to decrypt it, but didn't want it decrypted (or
        // we couldn't decrypt it due to wrong password), then we prepend this
        // data to the stream

        // Make a buffer big enough to hold both the header and the data itself
        Sequence < sal_Int8 > aEncryptedDataHeader ( n_ConstHeaderSize +
                                                     rData->aInitVector.getLength() +
                                                     rData->aSalt.getLength() +
                                                     rData->aDigest.getLength() +
                                                     aWriteBuffer.getLength() );
        sal_Int8 * pHeader = aEncryptedDataHeader.getArray();
        StaticFillHeader ( rData, rEntry.nSize, pHeader );
        memcpy ( pHeader, aWriteBuffer.getConstArray(), aWriteBuffer.getLength() );

        // dump old buffer and point aWriteBuffer to the new one with the header
        aWriteBuffer = aEncryptedDataHeader;
    }
    return Reference < XInputStream > ( new XMemoryStream ( aWriteBuffer ) );
}

ZipEnumeration * SAL_CALL ZipFile::entries(  )
{
    return new ZipEnumeration ( aEntries );
}

::rtl::OUString SAL_CALL ZipFile::getName(  )
    throw(RuntimeException)
{
    return sName;
}

sal_Int32 SAL_CALL ZipFile::getSize(  )
    throw(RuntimeException)
{
    return aEntries.size();
}

Reference< XInputStream > SAL_CALL ZipFile::getInputStream( ZipEntry& rEntry,
        const vos::ORef < EncryptionData > &rData,
        sal_Bool bIsEncrypted )
    throw(IOException, ZipException, RuntimeException)
{
    if ( rEntry.nOffset <= 0 )
        readLOC( rEntry );

    // We want to return a rawStream if we either don't have a key or if the
    // key is wrong

    sal_Bool bNeedRawStream = rEntry.nMethod == STORED;

    // if we have a digest, then this file is an encrypted one and we should
    // check if we can decrypt it or not
    if ( bIsEncrypted && !rData.isEmpty() && rData->aDigest.getLength() )
        bNeedRawStream = !hasValidPassword ( rEntry, rData );

    return rEntry.nSize > n_ConstMaxMemoryStreamSize ?
               createFileStream ( rEntry, rData, bNeedRawStream, bIsEncrypted ) :
               createMemoryStream ( rEntry, rData, bNeedRawStream, bIsEncrypted);
    //return createMemoryStream( rEntry, rData, sal_False );

}

Reference< XInputStream > SAL_CALL ZipFile::getRawStream( ZipEntry& rEntry,
        const vos::ORef < EncryptionData > &rData,
        sal_Bool bIsEncrypted )
    throw(IOException, ZipException, RuntimeException)
{
    if ( rEntry.nOffset <= 0 )
        readLOC( rEntry );

    return ( rEntry.nMethod == DEFLATED ? rEntry.nCompressedSize : rEntry.nSize > n_ConstMaxMemoryStreamSize ) ?
               createFileStream ( rEntry, rData, sal_True, bIsEncrypted ) :
               createMemoryStream ( rEntry, rData, sal_True, bIsEncrypted );
    //return createMemoryStream( rEntry, rData, sal_True );
}

sal_Bool ZipFile::readLOC( ZipEntry &rEntry )
    throw(IOException, ZipException, RuntimeException)
{
    sal_uInt32 nTestSig, nTime, nCRC, nSize, nCompressedSize;
    sal_uInt16 nVersion, nFlag, nHow, nNameLen, nExtraLen;
    sal_Int32 nPos = -rEntry.nOffset;

    aGrabber.seek(nPos);
    aGrabber >> nTestSig;

    if (nTestSig != LOCSIG)
        throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "Invalid LOC header (bad signature") ), Reference < XInterface > () );
    aGrabber >> nVersion;
    aGrabber >> nFlag;
    aGrabber >> nHow;
    aGrabber >> nTime;
    aGrabber >> nCRC;
    aGrabber >> nCompressedSize;
    aGrabber >> nSize;
    aGrabber >> nNameLen;
    aGrabber >> nExtraLen;
    rEntry.nOffset = static_cast < sal_Int32 > (aGrabber.getPosition()) + nNameLen + nExtraLen;
    return sal_True;
}

sal_Int32 ZipFile::findEND( )
    throw(IOException, ZipException, RuntimeException)
{
    sal_Int32 nLength, nPos, nEnd;
    Sequence < sal_Int8 > aBuffer;
    try
    {
        nLength = static_cast <sal_Int32 > (aGrabber.getLength());
        if (nLength == 0 || nLength < ENDHDR)
            return -1;
        nPos = nLength - ENDHDR - ZIP_MAXNAMELEN;
        nEnd = nPos >= 0 ? nPos : 0 ;

        aGrabber.seek( nEnd );
        aGrabber.readBytes ( aBuffer, nLength - nEnd );

        const sal_Int8 *pBuffer = aBuffer.getConstArray();

        nPos = nLength - nEnd - ENDHDR;
        while ( nPos >= 0 )
        {
            if (pBuffer[nPos] == 'P' && pBuffer[nPos+1] == 'K' && pBuffer[nPos+2] == 5 && pBuffer[nPos+3] == 6 )
                return nPos + nEnd;
            nPos--;
        }
    }
    catch ( IllegalArgumentException& )
    {
        throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "Zip END signature not found!") ), Reference < XInterface > () );
    }
    catch ( NotConnectedException& )
    {
        throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "Zip END signature not found!") ), Reference < XInterface > () );
    }
    catch ( BufferSizeExceededException& )
    {
        throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "Zip END signature not found!") ), Reference < XInterface > () );
    }
    throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "Zip END signature not found!") ), Reference < XInterface > () );
}

sal_Int32 ZipFile::readCEN()
    throw(IOException, ZipException, RuntimeException)
{
    sal_Int32 nCenLen, nCenPos = -1, nCenOff, nEndPos, nLocPos;
    sal_Int16 nCount, nTotal;

    try
    {
        nEndPos = findEND();
        if (nEndPos == -1)
            return -1;
        aGrabber.seek(nEndPos + ENDTOT);
        aGrabber >> nTotal;
        aGrabber >> nCenLen;
        aGrabber >> nCenOff;

        if ( nTotal < 0 || nTotal * CENHDR > nCenLen )
            throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "invalid END header (bad entry count)") ), Reference < XInterface > () );

        if ( nTotal > ZIP_MAXENTRIES )
            throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "too many entries in ZIP File") ), Reference < XInterface > () );

        if ( nCenLen < 0 || nCenLen > nEndPos )
            throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "Invalid END header (bad central directory size)") ), Reference < XInterface > () );

        nCenPos = nEndPos - nCenLen;

        if ( nCenOff < 0 || nCenOff > nCenPos )
            throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "Invalid END header (bad central directory size)") ), Reference < XInterface > () );

        nLocPos = nCenPos - nCenOff;
        aGrabber.seek( nCenPos );
        Sequence < sal_Int8 > aCENBuffer ( nCenLen );
        sal_Int64 nRead = aGrabber.readBytes ( aCENBuffer, nCenLen );
        if ( static_cast < sal_Int64 > ( nCenLen ) != nRead )
            throw ZipException ( OUString ( RTL_CONSTASCII_USTRINGPARAM ( "Error reading CEN into memory buffer!") ), Reference < XInterface > () );

        MemoryByteGrabber aMemGrabber ( aCENBuffer );

        ZipEntry aEntry;
        sal_Int32 nTestSig;
        sal_Int16 nNameLen, nExtraLen, nCommentLen;

        for (nCount = 0 ; nCount < nTotal; nCount++)
        {
            aMemGrabber >> nTestSig;
            if ( nTestSig != CENSIG )
                throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "Invalid CEN header (bad signature)") ), Reference < XInterface > () );

            aMemGrabber.skipBytes ( 2 );
            aMemGrabber >> aEntry.nVersion;

            if ( ( aEntry.nVersion & 1 ) == 1 )
                throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "Invalid CEN header (encrypted entry)") ), Reference < XInterface > () );

            aMemGrabber >> aEntry.nFlag;
            aMemGrabber >> aEntry.nMethod;

            if ( aEntry.nMethod != STORED && aEntry.nMethod != DEFLATED)
                throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "Invalid CEN header (bad compression method)") ), Reference < XInterface > () );

            aMemGrabber >> aEntry.nTime;
            aMemGrabber >> aEntry.nCrc;
            aMemGrabber >> aEntry.nCompressedSize;
            aMemGrabber >> aEntry.nSize;
            aMemGrabber >> nNameLen;
            aMemGrabber >> nExtraLen;
            aMemGrabber >> nCommentLen;
            aMemGrabber.skipBytes ( 8 );
            aMemGrabber >> aEntry.nOffset;

            aEntry.nOffset += nLocPos;
            aEntry.nOffset *= -1;

            if ( nNameLen > ZIP_MAXNAMELEN )
                throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "name length exceeds ZIP_MAXNAMELEN bytes" ) ), Reference < XInterface > () );

            if ( nCommentLen > ZIP_MAXNAMELEN )
                throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "comment length exceeds ZIP_MAXNAMELEN bytes" ) ), Reference < XInterface > () );

            if ( nExtraLen > ZIP_MAXEXTRA )
                throw ZipException( OUString( RTL_CONSTASCII_USTRINGPARAM ( "extra header info exceeds ZIP_MAXEXTRA bytes") ), Reference < XInterface > () );

            aEntry.sName = OUString ( (sal_Char *) aMemGrabber.getCurrentPos(),
                                      nNameLen,
                                      RTL_TEXTENCODING_ASCII_US);

            aMemGrabber.skipBytes( nNameLen + nExtraLen + nCommentLen );
            aEntries[aEntry.sName] = aEntry;
        }

        if (nCount != nTotal)
            throw ZipException(OUString( RTL_CONSTASCII_USTRINGPARAM ( "Count != Total") ), Reference < XInterface > () );
    }
    catch ( IllegalArgumentException & )
    {
        // seek can throw this...
        nCenPos = -1; // make sure we return -1 to indicate an error
    }
    return nCenPos;
}