source: trunk/src/ole32/stg_stream.c

/*
 * Compound Storage (32 bit version)
 * Stream implementation
 *
 * This file contains the implementation of the stream interface
 * for streams contained in a compound storage.
 *
 * Copyright 1999 Francis Beaudet
 * Copyright 1999 Thuy Nguyen
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * 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
 */
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include "winbase.h"
#include "winerror.h"
#include "winternl.h"
#include "wine/debug.h"

#include "storage32.h"

WINE_DEFAULT_DEBUG_CHANNEL(storage);


/*
 * Virtual function table for the StgStreamImpl class.
 */
static ICOM_VTABLE(IStream) StgStreamImpl_Vtbl =
{
    ICOM_MSVTABLE_COMPAT_DummyRTTIVALUE
    StgStreamImpl_QueryInterface,
    StgStreamImpl_AddRef,
    StgStreamImpl_Release,
    StgStreamImpl_Read,
    StgStreamImpl_Write,
    StgStreamImpl_Seek,
    StgStreamImpl_SetSize,
    StgStreamImpl_CopyTo,
    StgStreamImpl_Commit,
    StgStreamImpl_Revert,
    StgStreamImpl_LockRegion,
    StgStreamImpl_UnlockRegion,
    StgStreamImpl_Stat,
    StgStreamImpl_Clone
};

/******************************************************************************
** StgStreamImpl implementation
*/

/***
 * This is the constructor for the StgStreamImpl class.
 *
 * Params:
 *    parentStorage - Pointer to the storage that contains the stream to open
 *    ownerProperty - Index of the property that points to this stream.
 */
StgStreamImpl* StgStreamImpl_Construct(
                StorageBaseImpl* parentStorage,
    DWORD            grfMode,
    ULONG            ownerProperty)
{
  StgStreamImpl* newStream;

  newStream = HeapAlloc(GetProcessHeap(), 0, sizeof(StgStreamImpl));

  if (newStream!=0)
  {
    /*
     * Set-up the virtual function table and reference count.
     */
    ICOM_VTBL(newStream) = &StgStreamImpl_Vtbl;
    newStream->ref       = 0;

    /*
     * We want to nail-down the reference to the storage in case the
     * stream out-lives the storage in the client application.
     */
    newStream->parentStorage = parentStorage;
    IStorage_AddRef((IStorage*)newStream->parentStorage);

    newStream->grfMode = grfMode;
    newStream->ownerProperty = ownerProperty;

    /*
     * Start the stream at the beginning.
     */
    newStream->currentPosition.DUMMYSTRUCTNAME_DOT HighPart = 0;
    newStream->currentPosition.DUMMYSTRUCTNAME_DOT LowPart = 0;

    /*
     * Initialize the rest of the data.
     */
    newStream->streamSize.DUMMYSTRUCTNAME_DOT HighPart = 0;
    newStream->streamSize.DUMMYSTRUCTNAME_DOT LowPart  = 0;
    newStream->bigBlockChain       = 0;
    newStream->smallBlockChain     = 0;

    /*
     * Read the size from the property and determine if the blocks forming
     * this stream are large or small.
     */
    StgStreamImpl_OpenBlockChain(newStream);
  }

  return newStream;
}

/***
 * This is the destructor of the StgStreamImpl class.
 *
 * This method will clean-up all the resources used-up by the given StgStreamImpl
 * class. The pointer passed-in to this function will be freed and will not
 * be valid anymore.
 */
void StgStreamImpl_Destroy(StgStreamImpl* This)
{
  TRACE("(%p)\n", This);

  /*
   * Release the reference we are holding on the parent storage.
   */
  IStorage_Release((IStorage*)This->parentStorage);
  This->parentStorage = 0;

  /*
   * Make sure we clean-up the block chain stream objects that we were using.
   */
  if (This->bigBlockChain != 0)
  {
    BlockChainStream_Destroy(This->bigBlockChain);
    This->bigBlockChain = 0;
  }

  if (This->smallBlockChain != 0)
  {
    SmallBlockChainStream_Destroy(This->smallBlockChain);
    This->smallBlockChain = 0;
  }

  /*
   * Finally, free the memory used-up by the class.
   */
  HeapFree(GetProcessHeap(), 0, This);
}

/***
 * This implements the IUnknown method QueryInterface for this
 * class
 */
HRESULT WINAPI StgStreamImpl_QueryInterface(
                  IStream*     iface,
                  REFIID         riid,        /* [in] */
                  void**         ppvObject)   /* [iid_is][out] */
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  /*
   * Perform a sanity check on the parameters.
   */
  if (ppvObject==0)
    return E_INVALIDARG;

  /*
   * Initialize the return parameter.
   */
  *ppvObject = 0;

  /*
   * Compare the riid with the interface IDs implemented by this object.
   */
  if (memcmp(&IID_IUnknown, riid, sizeof(IID_IUnknown)) == 0)
  {
    *ppvObject = (IStream*)This;
  }
  else if (memcmp(&IID_IStream, riid, sizeof(IID_IStream)) == 0)
  {
    *ppvObject = (IStream*)This;
  }

  /*
   * Check that we obtained an interface.
   */
  if ((*ppvObject)==0)
    return E_NOINTERFACE;

  /*
   * Query Interface always increases the reference count by one when it is
   * successful
   */
  StgStreamImpl_AddRef(iface);

  return S_OK;
}

/***
 * This implements the IUnknown method AddRef for this
 * class
 */
ULONG WINAPI StgStreamImpl_AddRef(
                IStream* iface)
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  This->ref++;

  return This->ref;
}

/***
 * This implements the IUnknown method Release for this
 * class
 */
ULONG WINAPI StgStreamImpl_Release(
                IStream* iface)
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  ULONG newRef;

  This->ref--;

  newRef = This->ref;

  /*
   * If the reference count goes down to 0, perform suicide.
   */
  if (newRef==0)
  {
    StgStreamImpl_Destroy(This);
  }

  return newRef;
}

/***
 * This method will open the block chain pointed by the property
 * that describes the stream.
 * If the stream's size is null, no chain is opened.
 */
void StgStreamImpl_OpenBlockChain(
        StgStreamImpl* This)
{
  StgProperty    curProperty;
  BOOL         readSucessful;

  /*
   * Make sure no old object is left over.
   */
  if (This->smallBlockChain != 0)
  {
    SmallBlockChainStream_Destroy(This->smallBlockChain);
    This->smallBlockChain = 0;
  }

  if (This->bigBlockChain != 0)
  {
    BlockChainStream_Destroy(This->bigBlockChain);
    This->bigBlockChain = 0;
  }

  /*
   * Read the information from the property.
   */
  readSucessful = StorageImpl_ReadProperty(This->parentStorage->ancestorStorage,
                                             This->ownerProperty,
                                             &curProperty);

  if (readSucessful)
  {
    This->streamSize = curProperty.size;

    /*
     * This code supports only streams that are <32 bits in size.
     */
    assert(This->streamSize.DUMMYSTRUCTNAME_DOT HighPart == 0);

    if(curProperty.startingBlock == BLOCK_END_OF_CHAIN)
    {
      assert( (This->streamSize.DUMMYSTRUCTNAME_DOT HighPart == 0) && (This->streamSize.DUMMYSTRUCTNAME_DOT LowPart == 0) );
    }
    else
    {
      if ( (This->streamSize.DUMMYSTRUCTNAME_DOT HighPart == 0) &&
           (This->streamSize.DUMMYSTRUCTNAME_DOT LowPart < LIMIT_TO_USE_SMALL_BLOCK) )
      {
        This->smallBlockChain = SmallBlockChainStream_Construct(
                                                                This->parentStorage->ancestorStorage,
                                                                This->ownerProperty);
      }
      else
      {
        This->bigBlockChain = BlockChainStream_Construct(
                                                         This->parentStorage->ancestorStorage,
                                                         NULL,
                                                         This->ownerProperty);
      }
    }
  }
}

/***
 * This method is part of the ISequentialStream interface.
 *
 * It reads a block of information from the stream at the current
 * position. It then moves the current position at the end of the
 * read block
 *
 * See the documentation of ISequentialStream for more info.
 */
HRESULT WINAPI StgStreamImpl_Read(
                  IStream*     iface,
                  void*          pv,        /* [length_is][size_is][out] */
                  ULONG          cb,        /* [in] */
                  ULONG*         pcbRead)   /* [out] */
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  ULONG bytesReadBuffer;
  ULONG bytesToReadFromBuffer;
  HRESULT res = S_FALSE;

  TRACE("(%p, %p, %ld, %p)\n",
        iface, pv, cb, pcbRead);

  /*
   * If the caller is not interested in the number of bytes read,
   * we use another buffer to avoid "if" statements in the code.
   */
  if (pcbRead==0)
    pcbRead = &bytesReadBuffer;

  /*
   * Using the known size of the stream, calculate the number of bytes
   * to read from the block chain
   */
  bytesToReadFromBuffer = min( This->streamSize.DUMMYSTRUCTNAME_DOT LowPart - This->currentPosition.DUMMYSTRUCTNAME_DOT LowPart, cb);

  /*
   * Depending on the type of chain that was opened when the stream was constructed,
   * we delegate the work to the method that reads the block chains.
   */
  if (This->smallBlockChain!=0)
  {
    SmallBlockChainStream_ReadAt(This->smallBlockChain,
                                 This->currentPosition,
                                 bytesToReadFromBuffer,
                                 pv,
                                 pcbRead);

  }
  else if (This->bigBlockChain!=0)
  {
    BlockChainStream_ReadAt(This->bigBlockChain,
                            This->currentPosition,
                            bytesToReadFromBuffer,
                            pv,
                            pcbRead);
  }
  else
  {
    /*
     * Small and big block chains are both NULL. This case will happen
     * when a stream starts with BLOCK_END_OF_CHAIN and has size zero.
     */

    *pcbRead = 0;
    res = S_OK;
    goto end;
  }

  /*
   * We should always be able to read the proper amount of data from the
   * chain.
   */
  assert(bytesToReadFromBuffer == *pcbRead);

  /*
   * Advance the pointer for the number of positions read.
   */
  This->currentPosition.DUMMYSTRUCTNAME_DOT LowPart += *pcbRead;

  if(*pcbRead != cb)
  {
    WARN("read %ld instead of the required %ld bytes !\n", *pcbRead, cb);
    /*
     * this used to return S_FALSE, however MSDN docu says that an app should
     * be prepared to handle error in case of stream end reached, as *some*
     * implementations *might* return an error (IOW: most do *not*).
     * As some program fails on returning S_FALSE, I better use S_OK here.
     */
    res = S_OK;
  }
  else
    res = S_OK;

end:
  TRACE("<-- %08lx\n", res);
  return res;
}

/***
 * This method is part of the ISequentialStream interface.
 *
 * It writes a block of information to the stream at the current
 * position. It then moves the current position at the end of the
 * written block. If the stream is too small to fit the block,
 * the stream is grown to fit.
 *
 * See the documentation of ISequentialStream for more info.
 */
HRESULT WINAPI StgStreamImpl_Write(
                  IStream*     iface,
                  const void*    pv,          /* [size_is][in] */
                  ULONG          cb,          /* [in] */
                  ULONG*         pcbWritten)  /* [out] */
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  ULARGE_INTEGER newSize;
  ULONG bytesWritten = 0;

  TRACE("(%p, %p, %ld, %p)\n",
        iface, pv, cb, pcbWritten);

  /*
   * Do we have permission to write to this stream?
   */
  if (!(This->grfMode & (STGM_WRITE | STGM_READWRITE))) {
      return STG_E_ACCESSDENIED;
  }

  /*
   * If the caller is not interested in the number of bytes written,
   * we use another buffer to avoid "if" statements in the code.
   */
  if (pcbWritten == 0)
    pcbWritten = &bytesWritten;

  /*
   * Initialize the out parameter
   */
  *pcbWritten = 0;

  if (cb == 0)
  {
    return S_OK;
  }
  else
  {
    newSize.DUMMYSTRUCTNAME_DOT HighPart = 0;
    newSize.DUMMYSTRUCTNAME_DOT LowPart = This->currentPosition.DUMMYSTRUCTNAME_DOT LowPart + cb;
  }

  /*
   * Verify if we need to grow the stream
   */
  if (newSize.DUMMYSTRUCTNAME_DOT LowPart > This->streamSize.DUMMYSTRUCTNAME_DOT LowPart)
  {
    /* grow stream */
    IStream_SetSize(iface, newSize);
  }

  /*
   * Depending on the type of chain that was opened when the stream was constructed,
   * we delegate the work to the method that readwrites to the block chains.
   */
  if (This->smallBlockChain!=0)
  {
    SmallBlockChainStream_WriteAt(This->smallBlockChain,
                                  This->currentPosition,
                                  cb,
                                  pv,
                                  pcbWritten);

  }
  else if (This->bigBlockChain!=0)
  {
    BlockChainStream_WriteAt(This->bigBlockChain,
                             This->currentPosition,
                             cb,
                             pv,
                             pcbWritten);
  }
  else
    assert(FALSE);

  /*
   * Advance the position pointer for the number of positions written.
   */
  This->currentPosition.DUMMYSTRUCTNAME_DOT LowPart += *pcbWritten;

  return S_OK;
}

/***
 * This method is part of the IStream interface.
 *
 * It will move the current stream pointer according to the parameters
 * given.
 *
 * See the documentation of IStream for more info.
 */
HRESULT WINAPI StgStreamImpl_Seek(
                  IStream*      iface,
                  LARGE_INTEGER   dlibMove,         /* [in] */
                  DWORD           dwOrigin,         /* [in] */
                  ULARGE_INTEGER* plibNewPosition) /* [out] */
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  ULARGE_INTEGER newPosition;

  TRACE("(%p, %ld, %ld, %p)\n",
        iface, dlibMove.DUMMYSTRUCTNAME_DOT LowPart, dwOrigin, plibNewPosition);

  /*
   * The caller is allowed to pass in NULL as the new position return value.
   * If it happens, we assign it to a dynamic variable to avoid special cases
   * in the code below.
   */
  if (plibNewPosition == 0)
  {
    plibNewPosition = &newPosition;
  }

  /*
   * The file pointer is moved depending on the given "function"
   * parameter.
   */
  switch (dwOrigin)
  {
    case STREAM_SEEK_SET:
      plibNewPosition->DUMMYSTRUCTNAME_DOT HighPart = 0;
      plibNewPosition->DUMMYSTRUCTNAME_DOT LowPart  = 0;
      break;
    case STREAM_SEEK_CUR:
      *plibNewPosition = This->currentPosition;
      break;
    case STREAM_SEEK_END:
      *plibNewPosition = This->streamSize;
      break;
    default:
      return STG_E_INVALIDFUNCTION;
  }

#ifdef __WIN32OS2__
  *((LARGE_INTEGER*)plibNewPosition )= RtlpLargeIntegerAdd( (LARGE_INTEGER *)plibNewPosition, &dlibMove );
#else
  plibNewPosition->QuadPart = RtlLargeIntegerAdd( plibNewPosition->QuadPart, dlibMove.QuadPart );
#endif
  /*
   * tell the caller what we calculated
   */
  This->currentPosition = *plibNewPosition;

  return S_OK;
}

/***
 * This method is part of the IStream interface.
 *
 * It will change the size of a stream.
 *
 * TODO: Switch from small blocks to big blocks and vice versa.
 *
 * See the documentation of IStream for more info.
 */
HRESULT WINAPI StgStreamImpl_SetSize(
                                     IStream*      iface,
                                     ULARGE_INTEGER  libNewSize)   /* [in] */
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  StgProperty    curProperty;
  BOOL         Success;

  TRACE("(%p, %ld)\n", iface, libNewSize.DUMMYSTRUCTNAME_DOT LowPart);

  /*
   * As documented.
   */
  if (libNewSize.DUMMYSTRUCTNAME_DOT HighPart != 0)
    return STG_E_INVALIDFUNCTION;

  /*
   * Do we have permission?
   */
  if (!(This->grfMode & (STGM_WRITE | STGM_READWRITE)))
    return STG_E_ACCESSDENIED;

  if (This->streamSize.DUMMYSTRUCTNAME_DOT LowPart == libNewSize.DUMMYSTRUCTNAME_DOT LowPart)
    return S_OK;

  /*
   * This will happen if we're creating a stream
   */
  if ((This->smallBlockChain == 0) && (This->bigBlockChain == 0))
  {
    if (libNewSize.DUMMYSTRUCTNAME_DOT LowPart < LIMIT_TO_USE_SMALL_BLOCK)
    {
      This->smallBlockChain = SmallBlockChainStream_Construct(
                                    This->parentStorage->ancestorStorage,
                                    This->ownerProperty);
    }
    else
    {
      This->bigBlockChain = BlockChainStream_Construct(
                                This->parentStorage->ancestorStorage,
                                NULL,
                                This->ownerProperty);
    }
  }

  /*
   * Read this stream's property to see if it's small blocks or big blocks
   */
  Success = StorageImpl_ReadProperty(This->parentStorage->ancestorStorage,
                                       This->ownerProperty,
                                       &curProperty);
  /*
   * Determine if we have to switch from small to big blocks or vice versa
   */
  if ( (This->smallBlockChain!=0) &&
       (curProperty.size.DUMMYSTRUCTNAME_DOT LowPart < LIMIT_TO_USE_SMALL_BLOCK) )
  {
    if (libNewSize.DUMMYSTRUCTNAME_DOT LowPart >= LIMIT_TO_USE_SMALL_BLOCK)
    {
      /*
       * Transform the small block chain into a big block chain
       */
      This->bigBlockChain = Storage32Impl_SmallBlocksToBigBlocks(
                                This->parentStorage->ancestorStorage,
                                &This->smallBlockChain);
    }
  }

  if (This->smallBlockChain!=0)
  {
    Success = SmallBlockChainStream_SetSize(This->smallBlockChain, libNewSize);
  }
  else
  {
    Success = BlockChainStream_SetSize(This->bigBlockChain, libNewSize);
  }

  /*
   * Write the new information about this stream to the property
   */
  Success = StorageImpl_ReadProperty(This->parentStorage->ancestorStorage,
                                       This->ownerProperty,
                                       &curProperty);

  curProperty.size.DUMMYSTRUCTNAME_DOT HighPart = libNewSize.DUMMYSTRUCTNAME_DOT HighPart;
  curProperty.size.DUMMYSTRUCTNAME_DOT LowPart = libNewSize.DUMMYSTRUCTNAME_DOT LowPart;

  if (Success)
  {
    StorageImpl_WriteProperty(This->parentStorage->ancestorStorage,
                                This->ownerProperty,
                                &curProperty);
  }

  This->streamSize = libNewSize;

  return S_OK;
}

/***
 * This method is part of the IStream interface.
 *
 * It will copy the 'cb' Bytes to 'pstm' IStream.
 *
 * See the documentation of IStream for more info.
 */
HRESULT WINAPI StgStreamImpl_CopyTo(
                                    IStream*      iface,
                                    IStream*      pstm,         /* [unique][in] */
                                    ULARGE_INTEGER  cb,           /* [in] */
                                    ULARGE_INTEGER* pcbRead,      /* [out] */
                                    ULARGE_INTEGER* pcbWritten)   /* [out] */
{
  HRESULT        hr = S_OK;
  BYTE           tmpBuffer[128];
  ULONG          bytesRead, bytesWritten, copySize;
  ULARGE_INTEGER totalBytesRead;
  ULARGE_INTEGER totalBytesWritten;

  TRACE("(%p, %p, %ld, %p, %p)\n",
        iface, pstm, cb.DUMMYSTRUCTNAME_DOT LowPart, pcbRead, pcbWritten);

  /*
   * Sanity check
   */
  if ( pstm == 0 )
    return STG_E_INVALIDPOINTER;

  totalBytesRead.DUMMYSTRUCTNAME_DOT LowPart = totalBytesRead.DUMMYSTRUCTNAME_DOT HighPart = 0;
  totalBytesWritten.DUMMYSTRUCTNAME_DOT LowPart = totalBytesWritten.DUMMYSTRUCTNAME_DOT HighPart = 0;

  /*
   * use stack to store data temporarily
   * there is surely a more performant way of doing it, for now this basic
   * implementation will do the job
   */
  while ( cb.DUMMYSTRUCTNAME_DOT LowPart > 0 )
  {
    if ( cb.DUMMYSTRUCTNAME_DOT LowPart >= 128 )
      copySize = 128;
    else
      copySize = cb.DUMMYSTRUCTNAME_DOT LowPart;

    IStream_Read(iface, tmpBuffer, copySize, &bytesRead);

    totalBytesRead.DUMMYSTRUCTNAME_DOT LowPart += bytesRead;

    IStream_Write(pstm, tmpBuffer, bytesRead, &bytesWritten);

    totalBytesWritten.DUMMYSTRUCTNAME_DOT LowPart += bytesWritten;

    /*
     * Check that read & write operations were successful
     */
    if (bytesRead != bytesWritten)
    {
      hr = STG_E_MEDIUMFULL;
      break;
    }

    if (bytesRead!=copySize)
      cb.DUMMYSTRUCTNAME_DOT LowPart = 0;
    else
      cb.DUMMYSTRUCTNAME_DOT LowPart -= bytesRead;
  }

  /*
   * Update number of bytes read and written
   */
  if (pcbRead)
  {
    pcbRead->DUMMYSTRUCTNAME_DOT LowPart = totalBytesRead.DUMMYSTRUCTNAME_DOT LowPart;
    pcbRead->DUMMYSTRUCTNAME_DOT HighPart = totalBytesRead.DUMMYSTRUCTNAME_DOT HighPart;
  }

  if (pcbWritten)
  {
    pcbWritten->DUMMYSTRUCTNAME_DOT LowPart = totalBytesWritten.DUMMYSTRUCTNAME_DOT LowPart;
    pcbWritten->DUMMYSTRUCTNAME_DOT HighPart = totalBytesWritten.DUMMYSTRUCTNAME_DOT HighPart;
  }
  return hr;
}

/***
 * This method is part of the IStream interface.
 *
 * For streams contained in structured storages, this method
 * does nothing. This is what the documentation tells us.
 *
 * See the documentation of IStream for more info.
 */
HRESULT WINAPI StgStreamImpl_Commit(
                  IStream*      iface,
                  DWORD           grfCommitFlags)  /* [in] */
{
  return S_OK;
}

/***
 * This method is part of the IStream interface.
 *
 * For streams contained in structured storages, this method
 * does nothing. This is what the documentation tells us.
 *
 * See the documentation of IStream for more info.
 */
HRESULT WINAPI StgStreamImpl_Revert(
                  IStream* iface)
{
  return S_OK;
}

HRESULT WINAPI StgStreamImpl_LockRegion(
                                        IStream*     iface,
                                        ULARGE_INTEGER libOffset,   /* [in] */
                                        ULARGE_INTEGER cb,          /* [in] */
                                        DWORD          dwLockType)  /* [in] */
{
  FIXME("not implemented!\n");
  return E_NOTIMPL;
}

HRESULT WINAPI StgStreamImpl_UnlockRegion(
                                          IStream*     iface,
                                          ULARGE_INTEGER libOffset,   /* [in] */
                                          ULARGE_INTEGER cb,          /* [in] */
                                          DWORD          dwLockType)  /* [in] */
{
  FIXME("not implemented!\n");
  return E_NOTIMPL;
}

/***
 * This method is part of the IStream interface.
 *
 * This method returns information about the current
 * stream.
 *
 * See the documentation of IStream for more info.
 */
HRESULT WINAPI StgStreamImpl_Stat(
                  IStream*     iface,
                  STATSTG*       pstatstg,     /* [out] */
                  DWORD          grfStatFlag)  /* [in] */
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;

  StgProperty    curProperty;
  BOOL         readSucessful;

  /*
   * Read the information from the property.
   */
  readSucessful = StorageImpl_ReadProperty(This->parentStorage->ancestorStorage,
                                             This->ownerProperty,
                                             &curProperty);

  if (readSucessful)
  {
    StorageUtl_CopyPropertyToSTATSTG(pstatstg,
                                     &curProperty,
                                     grfStatFlag);

    pstatstg->grfMode = This->grfMode;

    return S_OK;
  }

  return E_FAIL;
}

/***
 * This method is part of the IStream interface.
 *
 * This method returns a clone of the interface that allows for
 * another seek pointer
 *
 * See the documentation of IStream for more info.
 *
 * I am not totally sure what I am doing here but I presume that this
 * should be basically as simple as creating a new stream with the same
 * parent etc and positioning its seek cursor.
 */
HRESULT WINAPI StgStreamImpl_Clone(
                                   IStream*     iface,
                                   IStream**    ppstm) /* [out] */
{
  StgStreamImpl* const This=(StgStreamImpl*)iface;
  HRESULT hres;
  StgStreamImpl* new_stream;
  LARGE_INTEGER seek_pos;

  /*
   * Sanity check
   */
  if ( ppstm == 0 )
    return STG_E_INVALIDPOINTER;

  new_stream = StgStreamImpl_Construct (This->parentStorage, This->grfMode, This->ownerProperty);

  if (!new_stream)
    return STG_E_INSUFFICIENTMEMORY; /* Currently the only reason for new_stream=0 */

  *ppstm = (IStream*) new_stream;
  seek_pos.QuadPart = This->currentPosition.QuadPart;

  hres=StgStreamImpl_Seek (*ppstm, seek_pos, STREAM_SEEK_SET, NULL);

  assert (SUCCEEDED(hres));

  return S_OK;
}