Program: CWE-125
Project: CVE-2019-13615
Buggy source:
/****************************************************************************
** libebml : parse EBML files, see http://embl.sourceforge.net/
**
** <file/class description>
**
** Copyright (C) 2002-2010 Steve Lhomme.  All rights reserved.
**
** 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
**
** See http://www.gnu.org/licenses/lgpl-2.1.html for LGPL licensing information.
**
** Contact license@matroska.org if any conditions of this licensing are
** not clear to you.
**
**********************************************************************/

/*!
  \file
  \version \$Id$
  \author Steve Lhomme     <robux4 @ users.sf.net>
*/

#include <cassert>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <stdexcept>
#include <sstream>

#include "ebml/EbmlElement.h"
#include "ebml/EbmlMaster.h"
#include "ebml/EbmlStream.h"
#include "ebml/EbmlVoid.h"
#include "ebml/EbmlDummy.h"
#include "ebml/EbmlContexts.h"

START_LIBEBML_NAMESPACE

/*!
  \todo handle more than CodedSize of 5
*/
int CodedSizeLength(uint64 Length, unsigned int SizeLength, bool bSizeFinite)
{
  unsigned int CodedSize;
  if (bSizeFinite) {
    // prepare the head of the size (000...01xxxxxx)
    // optimal size
    if (Length < 127) // 2^7 - 1
      CodedSize = 1;
    else if (Length < 16383) // 2^14 - 1
      CodedSize = 2;
    else if (Length < 2097151L) // 2^21 - 1
      CodedSize = 3;
    else if (Length < 268435455L) // 2^28 - 1
      CodedSize = 4;
    else CodedSize = 5;
  } else {
    if (Length <= 127) // 2^7 - 1
      CodedSize = 1;
    else if (Length <= 16383) // 2^14 - 1
      CodedSize = 2;
    else if (Length <= 2097151L) // 2^21 - 1
      CodedSize = 3;
    else if (Length <= 268435455L) // 2^28 - 1
      CodedSize = 4;
    else CodedSize = 5;
  }

  if (SizeLength > 0 && CodedSize < SizeLength) {
    // defined size
    CodedSize = SizeLength;
  }

  return CodedSize;
}

/*!
  \todo handle more than CodedSize of 5
*/
int CodedSizeLengthSigned(int64 Length, unsigned int SizeLength)
{
  unsigned int CodedSize;
  // prepare the head of the size (000...01xxxxxx)
  // optimal size
  if (Length > -64 && Length < 64) // 2^6
    CodedSize = 1;
  else if (Length > -8192 && Length < 8192) // 2^13
    CodedSize = 2;
  else if (Length > -1048576L && Length < 1048576L) // 2^20
    CodedSize = 3;
  else if (Length > -134217728L && Length < 134217728L) // 2^27
    CodedSize = 4;
  else CodedSize = 5;

  if (SizeLength > 0 && CodedSize < SizeLength) {
    // defined size
    CodedSize = SizeLength;
  }

  return CodedSize;
}

int CodedValueLength(uint64 Length, int CodedSize, binary * OutBuffer)
{
  int _SizeMask = 0xFF;
  OutBuffer[0] = 1 << (8 - CodedSize);
  for (int i=1; i<CodedSize; i++) {
    OutBuffer[CodedSize-i] = Length & 0xFF;
    Length >>= 8;
    _SizeMask >>= 1;
  }
  // first one use a OR with the "EBML size head"
  OutBuffer[0] |= Length & 0xFF & _SizeMask;
  return CodedSize;
}

int CodedValueLengthSigned(int64 Length, int CodedSize, binary * OutBuffer)
{
  if (Length > -64 && Length < 64) // 2^6
    Length += 63;
  else if (Length > -8192 && Length < 8192) // 2^13
    Length += 8191;
  else if (Length > -1048576L && Length < 1048576L) // 2^20
    Length += 1048575L;
  else if (Length > -134217728L && Length < 134217728L) // 2^27
    Length += 134217727L;

  return CodedValueLength(Length, CodedSize, OutBuffer);
}

uint64 ReadCodedSizeValue(const binary * InBuffer, uint32 & BufferSize, uint64 & SizeUnknown)
{
  binary SizeBitMask = 1 << 7;
  uint64 Result = 0x7F;
  unsigned int SizeIdx, PossibleSizeLength = 0;
  binary PossibleSize[8];
  memset(PossibleSize, 0, 8);

  SizeUnknown = 0x7F; // the last bit is discarded when computing the size
  for (SizeIdx = 0; SizeIdx < BufferSize && SizeIdx < 8; SizeIdx++) {
    if (InBuffer[0] & (SizeBitMask >> SizeIdx)) {
      // ID found
      PossibleSizeLength = SizeIdx + 1;
      SizeBitMask >>= SizeIdx;

      // Guard against invalid memory accesses with incomplete IDs.
      if (PossibleSizeLength > BufferSize)
        break;

      for (SizeIdx = 0; SizeIdx < PossibleSizeLength; SizeIdx++) {
        PossibleSize[SizeIdx] = InBuffer[SizeIdx];
      }
      for (SizeIdx = 0; SizeIdx < PossibleSizeLength - 1; SizeIdx++) {
        Result <<= 7;
        Result |= 0xFF;
      }

      Result = 0;
      Result |= PossibleSize[0] & ~SizeBitMask;
      for (unsigned int i = 1; i<PossibleSizeLength; i++) {
        Result <<= 8;
        Result |= PossibleSize[i];
      }

      BufferSize = PossibleSizeLength;

      return Result;
    }
    SizeUnknown <<= 7;
    SizeUnknown |= 0xFF;
  }

  BufferSize = 0;
  return 0;
}

int64 ReadCodedSizeSignedValue(const binary * InBuffer, uint32 & BufferSize, uint64 & SizeUnknown)
{
  int64 Result = ReadCodedSizeValue(InBuffer, BufferSize, SizeUnknown);

  if (BufferSize != 0) {
    switch (BufferSize) {
      case 1:
        Result -= 63;
        break;
      case 2:
        Result -= 8191;
        break;
      case 3:
        Result -= 1048575L;
        break;
      case 4:
        Result -= 134217727L;
        break;
    }
  }

  return Result;
}


EbmlCallbacks::EbmlCallbacks(EbmlElement & (*Creator)(), const EbmlId & aGlobalId, const char * aDebugName, const EbmlSemanticContext & aContext)
  :Create(Creator)
  ,GlobalId(aGlobalId)
  ,DebugName(aDebugName)
  ,Context(aContext)
{
  assert((Create!=NULL) || !strcmp(aDebugName, "DummyElement"));
}

const EbmlSemantic & EbmlSemanticContext::GetSemantic(size_t i) const
{
  assert(i<Size);
  if (i<Size)
    return MyTable[i];

  std::stringstream ss;
  ss << "EbmlSemanticContext::GetSemantic: programming error: index i outside of table size (" << i << " >= " << Size << ")";
  throw std::logic_error(ss.str());
}


EbmlElement::EbmlElement(uint64 aDefaultSize, bool bValueSet)
  :DefaultSize(aDefaultSize)
  ,SizeLength(0) ///< write optimal size by default
  ,bSizeIsFinite(true)
  ,ElementPosition(0)
  ,SizePosition(0)
  ,bValueIsSet(bValueSet)
  ,DefaultIsSet(false)
  ,bLocked(false)
{
  Size = DefaultSize;
}

EbmlElement::EbmlElement(const EbmlElement & ElementToClone)
  :Size(ElementToClone.Size)
  ,DefaultSize(ElementToClone.DefaultSize)
  ,SizeLength(ElementToClone.SizeLength)
  ,bSizeIsFinite(ElementToClone.bSizeIsFinite)
  ,ElementPosition(ElementToClone.ElementPosition)
  ,SizePosition(ElementToClone.SizePosition)
  ,bValueIsSet(ElementToClone.bValueIsSet)
  ,DefaultIsSet(ElementToClone.DefaultIsSet)
  ,bLocked(ElementToClone.bLocked)
{
}

EbmlElement::~EbmlElement()
{
  assert(!bLocked);
}

/*!
  \todo this method is deprecated and should be called FindThisID
  \todo replace the new RawElement with the appropriate class (when known)
*/
EbmlElement * EbmlElement::FindNextID(IOCallback & DataStream, const EbmlCallbacks & ClassInfos, uint64 MaxDataSize)
{
  binary PossibleId[4];
  int PossibleID_Length = 0;
  binary PossibleSize[8]; // we don't support size stored in more than 64 bits
  uint32 PossibleSizeLength = 0;
  uint64 SizeUnknown = 0;
  uint64 SizeFound = 0;
  bool bElementFound = false;

  binary BitMask;
  uint64 aElementPosition = 0, aSizePosition = 0;
  while (!bElementFound) {
    // read ID
    aElementPosition = DataStream.getFilePointer();
    uint32 ReadSize = 0;
    BitMask = 1 << 7;
    while (1) {
      ReadSize += DataStream.read(&PossibleId[PossibleID_Length], 1);
      if (ReadSize == uint32(PossibleID_Length)) {
        return NULL; // no more data ?
      }
      if (++PossibleID_Length > 4) {
        return NULL; // we don't support element IDs over class D
      }
      if (PossibleId[0] & BitMask) {
        // this is the last octet of the ID
        // check wether that's the one we're looking for
/*      if (PossibleID == EBML_INFO_ID(ClassInfos)) {
          break;
        } else {
          /// \todo This element should be skipped (use a context ?)
        }*/
        bElementFound = true; /// \todo not exactly the one we're looking for
        break;
      }
      BitMask >>= 1;
    }

    // read the data size
    aSizePosition = DataStream.getFilePointer();
    uint32 _SizeLength;
    do {
      if (PossibleSizeLength >= 8)
        // Size is larger than 8 bytes
        return NULL;

      ReadSize += DataStream.read(&PossibleSize[PossibleSizeLength++], 1);
      _SizeLength = PossibleSizeLength;
      SizeFound = ReadCodedSizeValue(&PossibleSize[0], _SizeLength, SizeUnknown);
    } while (_SizeLength == 0);
  }

  EbmlElement *Result = NULL;
  EbmlId PossibleID(PossibleId, PossibleID_Length);
  if (PossibleID == EBML_INFO_ID(ClassInfos)) {
    // the element is the one expected
    Result = &EBML_INFO_CREATE(ClassInfos);
  } else {
    /// \todo find the element in the context
    Result = new (std::nothrow) EbmlDummy(PossibleID);
    if(Result == NULL)
      return NULL;
  }

  Result->SetSizeLength(PossibleSizeLength);

  Result->Size = SizeFound;

  if (!Result->ValidateSize() || (SizeFound != SizeUnknown && MaxDataSize < Result->Size)) {
    delete Result;
    return NULL;
  }

  // check if the size is not all 1s
  if (SizeFound == SizeUnknown) {
    // Size of this element is unknown
    // only possible for Master elements
    if (!Result->SetSizeInfinite()) {
      /// \todo the element is not allowed to be infinite
      delete Result;
      return NULL;
    }
  } else Result->SetSizeInfinite(false);
  Result->ElementPosition = aElementPosition;
  Result->SizePosition = aSizePosition;

  return Result;
}


/*!
  \todo replace the new RawElement with the appropriate class (when known)
  \todo skip data for Dummy elements when they are not allowed
  \todo better check of the size checking for upper elements (using a list of size for each level)
  \param LowLevel Will be returned with the level of the element found compared to the context given
*/
EbmlElement * EbmlElement::FindNextElement(IOCallback & DataStream, const EbmlSemanticContext & Context, int & UpperLevel,
                                           uint64 MaxDataSize, bool AllowDummyElt, unsigned int MaxLowerLevel)
{
  int PossibleID_Length = 0;
  binary PossibleIdNSize[16];
  int PossibleSizeLength;
  uint64 SizeUnknown;
  int ReadIndex = 0; // trick for the algo, start index at 0
  uint32 ReadSize = 0;
  uint64 SizeFound;
  int SizeIdx;
  bool bFound;
  int UpperLevel_original = UpperLevel;

  do {
    // read a potential ID
    do {
      assert(ReadIndex < 16);
      // build the ID with the current Read Buffer
      bFound = false;
      binary IdBitMask = 1 << 7;
      for (SizeIdx = 0; SizeIdx < ReadIndex && SizeIdx < 4; SizeIdx++) {
        if (PossibleIdNSize[0] & (IdBitMask >> SizeIdx)) {
          // ID found
          PossibleID_Length = SizeIdx + 1;
          IdBitMask >>= SizeIdx;
          bFound = true;
          break;
        }
      }
      if (bFound) {
        break;
      }

      if (ReadIndex >= 4) {
        // ID not found
        // shift left the read octets
        memmove(&PossibleIdNSize[0],&PossibleIdNSize[1], --ReadIndex);
      }

      if (MaxDataSize <= ReadSize)
        break;
      if (DataStream.read(&PossibleIdNSize[ReadIndex++], 1) == 0) {
        return NULL; // no more data ?
      }
      ReadSize++;

    } while (!bFound);

    if (!bFound)
      // we reached the maximum we could read without a proper ID
      return NULL;

    SizeIdx = ReadIndex;
    ReadIndex -= PossibleID_Length;

    // read the data size
    uint32 _SizeLength;
    PossibleSizeLength = ReadIndex;
    while (1) {
      _SizeLength = PossibleSizeLength;
      SizeFound = ReadCodedSizeValue(&PossibleIdNSize[PossibleID_Length], _SizeLength, SizeUnknown);
      if (_SizeLength != 0) {
        bFound = true;
        break;
      }
      if (PossibleSizeLength >= 8) {
        bFound = false;
        break;
      }
      if (MaxDataSize <= ReadSize) {
        bFound = false;
        break;
      }
      if( DataStream.read( &PossibleIdNSize[SizeIdx++], 1 ) == 0 ) {
        return NULL; // no more data ?
      }
      ReadSize++;
      PossibleSizeLength++;
    }

    if (bFound) {
      // find the element in the context and use the correct creator
      EbmlId PossibleID(PossibleIdNSize, PossibleID_Length);
      EbmlElement * Result = CreateElementUsingContext(PossibleID, Context, UpperLevel, false, AllowDummyElt, MaxLowerLevel);
      ///< \todo continue is misplaced
      if (Result != NULL) {
        if (AllowDummyElt || !Result->IsDummy()) {
          Result->SetSizeLength(_SizeLength);

          Result->Size = SizeFound;
          // UpperLevel values
          // -1 : global element
          //  0 : child
          //  1 : same level
          //  + : further parent
          if (Result->ValidateSize() && (SizeFound == SizeUnknown || UpperLevel > 0 || MaxDataSize == 0 || MaxDataSize >= (PossibleID_Length + PossibleSizeLength + SizeFound))) {
            if (SizeFound != SizeUnknown || Result->SetSizeInfinite()) {
              Result->SizePosition = DataStream.getFilePointer() - SizeIdx + EBML_ID_LENGTH(PossibleID);
              Result->ElementPosition = Result->SizePosition - EBML_ID_LENGTH(PossibleID);
              // place the file at the beggining of the data
              DataStream.setFilePointer(Result->SizePosition + _SizeLength);
              return Result;
            }
          }
        }
        delete Result;
      }
    }

    // recover all the data in the buffer minus one byte
    ReadIndex = SizeIdx - 1;
    memmove(&PossibleIdNSize[0], &PossibleIdNSize[1], ReadIndex);
    UpperLevel = UpperLevel_original;
  } while ( MaxDataSize > DataStream.getFilePointer() - SizeIdx + PossibleID_Length );

  return NULL;
}

/*!
  \todo what happens if we are in a upper element with a known size ?
*/
EbmlElement * EbmlElement::SkipData(EbmlStream & DataStream, const EbmlSemanticContext & Context, EbmlElement * TestReadElt, bool AllowDummyElt)
{
  EbmlElement * Result = NULL;
  if (bSizeIsFinite) {
    assert(TestReadElt == NULL);
    assert(ElementPosition < SizePosition);
    DataStream.I_O().setFilePointer(SizePosition + CodedSizeLength(Size, SizeLength, bSizeIsFinite) + Size, seek_beginning);
    //    DataStream.I_O().setFilePointer(Size, seek_current);
  } else {
    /////////////////////////////////////////////////
    // read elements until an upper element is found
    /////////////////////////////////////////////////
    bool bEndFound = false;
    while (!bEndFound && Result == NULL) {
      // read an element
      /// \todo 0xFF... and true should be configurable
      //      EbmlElement * NewElt;
      if (TestReadElt == NULL) {
        int bUpperElement = 0; // trick to call FindNextID correctly
        Result = DataStream.FindNextElement(Context, bUpperElement, 0xFFFFFFFFL, AllowDummyElt);
      } else {
        Result = TestReadElt;
        TestReadElt = NULL;
      }

      if (Result != NULL) {
        unsigned int EltIndex;
        // data known in this Master's context
        for (EltIndex = 0; EltIndex < EBML_CTX_SIZE(Context); EltIndex++) {
          if (EbmlId(*Result) == EBML_CTX_IDX_ID(Context,EltIndex)) {
            // skip the data with its own context
            Result = Result->SkipData(DataStream, EBML_SEM_CONTEXT(EBML_CTX_IDX(Context,EltIndex)), NULL);
            break; // let's go to the next ID
          }
        }

        if (EltIndex >= EBML_CTX_SIZE(Context)) {
          if (EBML_CTX_PARENT(Context) != NULL) {
            Result = SkipData(DataStream, *EBML_CTX_PARENT(Context), Result);
          } else {
            assert(Context.GetGlobalContext != NULL);
            if (Context != Context.GetGlobalContext()) {
              Result = SkipData(DataStream, Context.GetGlobalContext(), Result);
            } else {
              bEndFound = true;
            }
          }
        }
      } else {
        bEndFound = true;
      }
    }
  }
  return Result;
}

EbmlElement *EbmlElement::CreateElementUsingContext(const EbmlId & aID, const EbmlSemanticContext & Context,
                                                    int & LowLevel, bool IsGlobalContext, bool bAllowDummy, unsigned int MaxLowerLevel)
{
  unsigned int ContextIndex;
  EbmlElement *Result = NULL;

  // elements at the current level
  for (ContextIndex = 0; ContextIndex < EBML_CTX_SIZE(Context); ContextIndex++) {
    if (aID == EBML_CTX_IDX_ID(Context,ContextIndex)) {
      return &EBML_SEM_CREATE(EBML_CTX_IDX(Context,ContextIndex));
    }
  }

  // global elements
  assert(Context.GetGlobalContext != NULL); // global should always exist, at least the EBML ones
  const EbmlSemanticContext & tstContext = Context.GetGlobalContext();
  if (tstContext != Context) {
    LowLevel--;
    MaxLowerLevel--;
    // recursive is good, but be carefull...
    Result = CreateElementUsingContext(aID, tstContext, LowLevel, true, bAllowDummy, MaxLowerLevel);
    if (Result != NULL) {
      return Result;
    }
    LowLevel++;
    MaxLowerLevel++;
  } else {
    return NULL;
  }

  // parent elements
  if (EBML_CTX_MASTER(Context) != NULL && aID == EBML_INFO_ID(*EBML_CTX_MASTER(Context))) {
    LowLevel++; // already one level up (same as context)
    return &EBML_INFO_CREATE(*EBML_CTX_MASTER(Context));
  }

  // check wether it's not part of an upper context
  if (EBML_CTX_PARENT(Context) != NULL) {
    LowLevel++;
    MaxLowerLevel++;
    return CreateElementUsingContext(aID, *EBML_CTX_PARENT(Context), LowLevel, IsGlobalContext, bAllowDummy, MaxLowerLevel);
  }

  if (!IsGlobalContext && bAllowDummy) {
    LowLevel = 0;
    Result = new (std::nothrow) EbmlDummy(aID);
  }

  return Result;
}

/*!
  \todo verify that the size written is the same as the data written
*/
filepos_t EbmlElement::Render(IOCallback & output, bool bWithDefault, bool bKeepPosition, bool bForceRender)
{
  assert(bValueIsSet || (bWithDefault && DefaultISset())); // an element is been rendered without a value set !!!
  // it may be a mandatory element without a default value
  if (!bWithDefault && IsDefaultValue()) {
    return 0;
  }
#if defined(LIBEBML_DEBUG)
  uint64 SupposedSize = UpdateSize(bWithDefault, bForceRender);
#endif // LIBEBML_DEBUG
  filepos_t result = RenderHead(output, bForceRender, bWithDefault, bKeepPosition);
  uint64 WrittenSize = RenderData(output, bForceRender, bWithDefault);
#if defined(LIBEBML_DEBUG)
  if (static_cast<int64>(SupposedSize) != (0-1))
    assert(WrittenSize == SupposedSize);
#endif // LIBEBML_DEBUG
  result += WrittenSize;
  return result;
}

/*!
  \todo store the position of the Size writing for elements with unknown size
  \todo handle exceptions on errors
  \todo handle CodeSize bigger than 5 bytes
*/
filepos_t EbmlElement::RenderHead(IOCallback & output, bool bForceRender, bool bWithDefault, bool bKeepPosition)
{
  if (EBML_ID_LENGTH((const EbmlId&)*this) <= 0 || EBML_ID_LENGTH((const EbmlId&)*this) > 4)
    return 0;

  UpdateSize(bWithDefault, bForceRender);

  return MakeRenderHead(output, bKeepPosition);
}

filepos_t EbmlElement::MakeRenderHead(IOCallback & output, bool bKeepPosition)
{
  binary FinalHead[4+8]; // Class D + 64 bits coded size
  unsigned int FinalHeadSize;

  FinalHeadSize = EBML_ID_LENGTH((const EbmlId&)*this);
  EbmlId(*this).Fill(FinalHead);

  int CodedSize = CodedSizeLength(Size, SizeLength, bSizeIsFinite);
  CodedValueLength(Size, CodedSize, &FinalHead[FinalHeadSize]);
  FinalHeadSize += CodedSize;

  output.writeFully(FinalHead, FinalHeadSize);
  if (!bKeepPosition) {
    ElementPosition = output.getFilePointer() - FinalHeadSize;
    SizePosition = ElementPosition + EBML_ID_LENGTH((const EbmlId&)*this);
  }

  return FinalHeadSize;
}

uint64 EbmlElement::ElementSize(bool bWithDefault) const
{
  if (!bWithDefault && IsDefaultValue())
    return 0; // won't be saved
  return Size + EBML_ID_LENGTH((const EbmlId&)*this) + CodedSizeLength(Size, SizeLength, bSizeIsFinite);
}

bool EbmlElement::IsSmallerThan(const EbmlElement *Cmp) const
{
  return EbmlId(*this) == EbmlId(*Cmp);
}

bool EbmlElement::CompareElements(const EbmlElement *A, const EbmlElement *B)
{
  if (EbmlId(*A) == EbmlId(*B))
    return A->IsSmallerThan(B);
  else
    return false;
}

void EbmlElement::Read(EbmlStream & inDataStream, const EbmlSemanticContext & /* Context */, int & /* UpperEltFound */, EbmlElement * & /* FoundElt */, bool /* AllowDummyElt */, ScopeMode ReadFully)
{
  ReadData(inDataStream.I_O(), ReadFully);
}

bool EbmlElement::ForceSize(uint64 NewSize)
{
  if (bSizeIsFinite) {
    return false;
  }

  int OldSizeLen = CodedSizeLength(Size, SizeLength, bSizeIsFinite);
  uint64 OldSize = Size;

  Size = NewSize;

  if (CodedSizeLength(Size, SizeLength, bSizeIsFinite) == OldSizeLen) {
    bSizeIsFinite = true;
    return true;
  }
  Size = OldSize;

  return false;
}

filepos_t EbmlElement::OverwriteHead(IOCallback & output, bool bKeepPosition)
{
  if (ElementPosition == 0) {
    return 0; // the element has not been written
  }

  uint64 CurrentPosition = output.getFilePointer();
  output.setFilePointer(GetElementPosition());
  filepos_t Result = MakeRenderHead(output, bKeepPosition);
  output.setFilePointer(CurrentPosition);
  return Result;
}

uint64 EbmlElement::VoidMe(IOCallback & output, bool bWithDefault)
{
  if (ElementPosition == 0) {
    return 0; // the element has not been written
  }

  EbmlVoid Dummy;
  return Dummy.Overwrite(*this, output, bWithDefault);
}

END_LIBEBML_NAMESPACE


Fixed version (ground truth):
/****************************************************************************
** libebml : parse EBML files, see http://embl.sourceforge.net/
**
** <file/class description>
**
** Copyright (C) 2002-2010 Steve Lhomme.  All rights reserved.
**
** 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
**
** See http://www.gnu.org/licenses/lgpl-2.1.html for LGPL licensing information.
**
** Contact license@matroska.org if any conditions of this licensing are
** not clear to you.
**
**********************************************************************/

/*!
  \file
  \version \$Id$
  \author Steve Lhomme     <robux4 @ users.sf.net>
*/

#include <cassert>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <stdexcept>
#include <sstream>

#include "ebml/EbmlElement.h"
#include "ebml/EbmlMaster.h"
#include "ebml/EbmlStream.h"
#include "ebml/EbmlVoid.h"
#include "ebml/EbmlDummy.h"
#include "ebml/EbmlContexts.h"

START_LIBEBML_NAMESPACE

/*!
  \todo handle more than CodedSize of 5
*/
int CodedSizeLength(uint64 Length, unsigned int SizeLength, bool bSizeFinite)
{
  unsigned int CodedSize;
  if (bSizeFinite) {
    // prepare the head of the size (000...01xxxxxx)
    // optimal size
    if (Length < 127) // 2^7 - 1
      CodedSize = 1;
    else if (Length < 16383) // 2^14 - 1
      CodedSize = 2;
    else if (Length < 2097151L) // 2^21 - 1
      CodedSize = 3;
    else if (Length < 268435455L) // 2^28 - 1
      CodedSize = 4;
    else CodedSize = 5;
  } else {
    if (Length <= 127) // 2^7 - 1
      CodedSize = 1;
    else if (Length <= 16383) // 2^14 - 1
      CodedSize = 2;
    else if (Length <= 2097151L) // 2^21 - 1
      CodedSize = 3;
    else if (Length <= 268435455L) // 2^28 - 1
      CodedSize = 4;
    else CodedSize = 5;
  }

  if (SizeLength > 0 && CodedSize < SizeLength) {
    // defined size
    CodedSize = SizeLength;
  }

  return CodedSize;
}

/*!
  \todo handle more than CodedSize of 5
*/
int CodedSizeLengthSigned(int64 Length, unsigned int SizeLength)
{
  unsigned int CodedSize;
  // prepare the head of the size (000...01xxxxxx)
  // optimal size
  if (Length > -64 && Length < 64) // 2^6
    CodedSize = 1;
  else if (Length > -8192 && Length < 8192) // 2^13
    CodedSize = 2;
  else if (Length > -1048576L && Length < 1048576L) // 2^20
    CodedSize = 3;
  else if (Length > -134217728L && Length < 134217728L) // 2^27
    CodedSize = 4;
  else CodedSize = 5;

  if (SizeLength > 0 && CodedSize < SizeLength) {
    // defined size
    CodedSize = SizeLength;
  }

  return CodedSize;
}

int CodedValueLength(uint64 Length, int CodedSize, binary * OutBuffer)
{
  int _SizeMask = 0xFF;
  OutBuffer[0] = 1 << (8 - CodedSize);
  for (int i=1; i<CodedSize; i++) {
    OutBuffer[CodedSize-i] = Length & 0xFF;
    Length >>= 8;
    _SizeMask >>= 1;
  }
  // first one use a OR with the "EBML size head"
  OutBuffer[0] |= Length & 0xFF & _SizeMask;
  return CodedSize;
}

int CodedValueLengthSigned(int64 Length, int CodedSize, binary * OutBuffer)
{
  if (Length > -64 && Length < 64) // 2^6
    Length += 63;
  else if (Length > -8192 && Length < 8192) // 2^13
    Length += 8191;
  else if (Length > -1048576L && Length < 1048576L) // 2^20
    Length += 1048575L;
  else if (Length > -134217728L && Length < 134217728L) // 2^27
    Length += 134217727L;

  return CodedValueLength(Length, CodedSize, OutBuffer);
}

uint64 ReadCodedSizeValue(const binary * InBuffer, uint32 & BufferSize, uint64 & SizeUnknown)
{
  binary SizeBitMask = 1 << 7;
  uint64 Result = 0x7F;
  unsigned int SizeIdx, PossibleSizeLength = 0;
  binary PossibleSize[8];
  memset(PossibleSize, 0, 8);

  SizeUnknown = 0x7F; // the last bit is discarded when computing the size
  for (SizeIdx = 0; SizeIdx < BufferSize && SizeIdx < 8; SizeIdx++) {
    if (InBuffer[0] & (SizeBitMask >> SizeIdx)) {
      // ID found
      PossibleSizeLength = SizeIdx + 1;
      SizeBitMask >>= SizeIdx;

      // Guard against invalid memory accesses with incomplete IDs.
      if (PossibleSizeLength > BufferSize)
        break;

      for (SizeIdx = 0; SizeIdx < PossibleSizeLength; SizeIdx++) {
        PossibleSize[SizeIdx] = InBuffer[SizeIdx];
      }
      for (SizeIdx = 0; SizeIdx < PossibleSizeLength - 1; SizeIdx++) {
        Result <<= 7;
        Result |= 0xFF;
      }

      Result = 0;
      Result |= PossibleSize[0] & ~SizeBitMask;
      for (unsigned int i = 1; i<PossibleSizeLength; i++) {
        Result <<= 8;
        Result |= PossibleSize[i];
      }

      BufferSize = PossibleSizeLength;

      return Result;
    }
    SizeUnknown <<= 7;
    SizeUnknown |= 0xFF;
  }

  BufferSize = 0;
  return 0;
}

int64 ReadCodedSizeSignedValue(const binary * InBuffer, uint32 & BufferSize, uint64 & SizeUnknown)
{
  int64 Result = ReadCodedSizeValue(InBuffer, BufferSize, SizeUnknown);

  if (BufferSize != 0) {
    switch (BufferSize) {
      case 1:
        Result -= 63;
        break;
      case 2:
        Result -= 8191;
        break;
      case 3:
        Result -= 1048575L;
        break;
      case 4:
        Result -= 134217727L;
        break;
    }
  }

  return Result;
}


EbmlCallbacks::EbmlCallbacks(EbmlElement & (*Creator)(), const EbmlId & aGlobalId, const char * aDebugName, const EbmlSemanticContext & aContext)
  :Create(Creator)
  ,GlobalId(aGlobalId)
  ,DebugName(aDebugName)
  ,Context(aContext)
{
  assert((Create!=NULL) || !strcmp(aDebugName, "DummyElement"));
}

const EbmlSemantic & EbmlSemanticContext::GetSemantic(size_t i) const
{
  assert(i<Size);
  if (i<Size)
    return MyTable[i];

  std::stringstream ss;
  ss << "EbmlSemanticContext::GetSemantic: programming error: index i outside of table size (" << i << " >= " << Size << ")";
  throw std::logic_error(ss.str());
}


EbmlElement::EbmlElement(uint64 aDefaultSize, bool bValueSet)
  :DefaultSize(aDefaultSize)
  ,SizeLength(0) ///< write optimal size by default
  ,bSizeIsFinite(true)
  ,ElementPosition(0)
  ,SizePosition(0)
  ,bValueIsSet(bValueSet)
  ,DefaultIsSet(false)
  ,bLocked(false)
{
  Size = DefaultSize;
}

EbmlElement::EbmlElement(const EbmlElement & ElementToClone)
  :Size(ElementToClone.Size)
  ,DefaultSize(ElementToClone.DefaultSize)
  ,SizeLength(ElementToClone.SizeLength)
  ,bSizeIsFinite(ElementToClone.bSizeIsFinite)
  ,ElementPosition(ElementToClone.ElementPosition)
  ,SizePosition(ElementToClone.SizePosition)
  ,bValueIsSet(ElementToClone.bValueIsSet)
  ,DefaultIsSet(ElementToClone.DefaultIsSet)
  ,bLocked(ElementToClone.bLocked)
{
}

EbmlElement::~EbmlElement()
{
  assert(!bLocked);
}

/*!
  \todo this method is deprecated and should be called FindThisID
  \todo replace the new RawElement with the appropriate class (when known)
*/
EbmlElement * EbmlElement::FindNextID(IOCallback & DataStream, const EbmlCallbacks & ClassInfos, uint64 MaxDataSize)
{
  binary PossibleId[4];
  int PossibleID_Length = 0;
  binary PossibleSize[8]; // we don't support size stored in more than 64 bits
  uint32 PossibleSizeLength = 0;
  uint64 SizeUnknown = 0;
  uint64 SizeFound = 0;
  bool bElementFound = false;

  binary BitMask;
  uint64 aElementPosition = 0, aSizePosition = 0;
  while (!bElementFound) {
    // read ID
    aElementPosition = DataStream.getFilePointer();
    uint32 ReadSize = 0;
    BitMask = 1 << 7;
    while (1) {
      ReadSize += DataStream.read(&PossibleId[PossibleID_Length], 1);
      if (ReadSize == uint32(PossibleID_Length)) {
        return NULL; // no more data ?
      }
      if (++PossibleID_Length > 4) {
        return NULL; // we don't support element IDs over class D
      }
      if (PossibleId[0] & BitMask) {
        // this is the last octet of the ID
        // check wether that's the one we're looking for
/*      if (PossibleID == EBML_INFO_ID(ClassInfos)) {
          break;
        } else {
          /// \todo This element should be skipped (use a context ?)
        }*/
        bElementFound = true; /// \todo not exactly the one we're looking for
        break;
      }
      BitMask >>= 1;
    }

    // read the data size
    aSizePosition = DataStream.getFilePointer();
    uint32 _SizeLength;
    do {
      if (PossibleSizeLength >= 8)
        // Size is larger than 8 bytes
        return NULL;

      ReadSize += DataStream.read(&PossibleSize[PossibleSizeLength++], 1);
      _SizeLength = PossibleSizeLength;
      SizeFound = ReadCodedSizeValue(&PossibleSize[0], _SizeLength, SizeUnknown);
    } while (_SizeLength == 0);
  }

  EbmlElement *Result = NULL;
  EbmlId PossibleID(PossibleId, PossibleID_Length);
  if (PossibleID == EBML_INFO_ID(ClassInfos)) {
    // the element is the one expected
    Result = &EBML_INFO_CREATE(ClassInfos);
  } else {
    /// \todo find the element in the context
    Result = new (std::nothrow) EbmlDummy(PossibleID);
    if(Result == NULL)
      return NULL;
  }

  Result->SetSizeLength(PossibleSizeLength);

  Result->Size = SizeFound;

  if (!Result->ValidateSize() || (SizeFound != SizeUnknown && MaxDataSize < Result->Size)) {
    delete Result;
    return NULL;
  }

  // check if the size is not all 1s
  if (SizeFound == SizeUnknown) {
    // Size of this element is unknown
    // only possible for Master elements
    if (!Result->SetSizeInfinite()) {
      /// \todo the element is not allowed to be infinite
      delete Result;
      return NULL;
    }
  } else Result->SetSizeInfinite(false);
  Result->ElementPosition = aElementPosition;
  Result->SizePosition = aSizePosition;

  return Result;
}


/*!
  \todo replace the new RawElement with the appropriate class (when known)
  \todo skip data for Dummy elements when they are not allowed
  \todo better check of the size checking for upper elements (using a list of size for each level)
  \param LowLevel Will be returned with the level of the element found compared to the context given
*/
EbmlElement * EbmlElement::FindNextElement(IOCallback & DataStream, const EbmlSemanticContext & Context, int & UpperLevel,
                                           uint64 MaxDataSize, bool AllowDummyElt, unsigned int MaxLowerLevel)
{
  int PossibleID_Length = 0;
  binary PossibleIdNSize[16];
  int PossibleSizeLength;
  uint64 SizeUnknown;
  int ReadIndex = 0; // trick for the algo, start index at 0
  uint32 ReadSize = 0;
  uint64 SizeFound;
  int SizeIdx;
  bool bFound;
  int UpperLevel_original = UpperLevel;

  do {
    // read a potential ID
    do {
      assert(ReadIndex < 16);
      // build the ID with the current Read Buffer
      bFound = false;
      binary IdBitMask = 1 << 7;
      for (SizeIdx = 0; SizeIdx < ReadIndex && SizeIdx < 4; SizeIdx++) {
        if (PossibleIdNSize[0] & (IdBitMask >> SizeIdx)) {
          // ID found
          PossibleID_Length = SizeIdx + 1;
          IdBitMask >>= SizeIdx;
          bFound = true;
          break;
        }
      }
      if (bFound) {
        break;
      }

      if (ReadIndex >= 4) {
        // ID not found
        // shift left the read octets
        memmove(&PossibleIdNSize[0],&PossibleIdNSize[1], --ReadIndex);
      }

      if (MaxDataSize <= ReadSize)
        break;
      if (DataStream.read(&PossibleIdNSize[ReadIndex++], 1) == 0) {
        return NULL; // no more data ?
      }
      ReadSize++;

    } while (!bFound);

    if (!bFound)
      // we reached the maximum we could read without a proper ID
      return NULL;

    SizeIdx = ReadIndex;
    ReadIndex -= PossibleID_Length;

    // read the data size
    uint32 _SizeLength;
    PossibleSizeLength = ReadIndex;
    while (1) {
      _SizeLength = PossibleSizeLength;
      SizeFound = ReadCodedSizeValue(&PossibleIdNSize[PossibleID_Length], _SizeLength, SizeUnknown);
      if (_SizeLength != 0) {
        bFound = true;
        break;
      }
      if (PossibleSizeLength >= 8) {
        bFound = false;
        break;
      }
      if (MaxDataSize <= ReadSize) {
        bFound = false;
        break;
      }
      if( DataStream.read( &PossibleIdNSize[SizeIdx++], 1 ) == 0 ) {
        return NULL; // no more data ?
      }
      ReadSize++;
      PossibleSizeLength++;
    }

    if (bFound) {
      // find the element in the context and use the correct creator
      EbmlId PossibleID(PossibleIdNSize, PossibleID_Length);
      EbmlElement * Result = CreateElementUsingContext(PossibleID, Context, UpperLevel, false, AllowDummyElt, MaxLowerLevel);
      ///< \todo continue is misplaced
      if (Result != NULL) {
        if (AllowDummyElt || !Result->IsDummy()) {
          Result->SetSizeLength(_SizeLength);

          Result->Size = SizeFound;
          // UpperLevel values
          // -1 : global element
          //  0 : child
          //  1 : same level
          //  + : further parent
          if (Result->ValidateSize() && (SizeFound == SizeUnknown || UpperLevel > 0 || MaxDataSize == 0 || MaxDataSize >= (PossibleID_Length + PossibleSizeLength + SizeFound))) {
            if (SizeFound != SizeUnknown || Result->SetSizeInfinite()) {
              Result->SizePosition = DataStream.getFilePointer() - SizeIdx + EBML_ID_LENGTH(PossibleID);
              Result->ElementPosition = Result->SizePosition - EBML_ID_LENGTH(PossibleID);
              // place the file at the beggining of the data
              DataStream.setFilePointer(Result->SizePosition + _SizeLength);
              return Result;
            }
          }
        }
        delete Result;
      }
    }

    // recover all the data in the buffer minus one byte
    ReadIndex = SizeIdx - 1;
    memmove(&PossibleIdNSize[0], &PossibleIdNSize[1], ReadIndex);
    UpperLevel = UpperLevel_original;
  } while ( MaxDataSize >= ReadSize );

  return NULL;
}

/*!
  \todo what happens if we are in a upper element with a known size ?
*/
EbmlElement * EbmlElement::SkipData(EbmlStream & DataStream, const EbmlSemanticContext & Context, EbmlElement * TestReadElt, bool AllowDummyElt)
{
  EbmlElement * Result = NULL;
  if (bSizeIsFinite) {
    assert(TestReadElt == NULL);
    assert(ElementPosition < SizePosition);
    DataStream.I_O().setFilePointer(SizePosition + CodedSizeLength(Size, SizeLength, bSizeIsFinite) + Size, seek_beginning);
    //    DataStream.I_O().setFilePointer(Size, seek_current);
  } else {
    /////////////////////////////////////////////////
    // read elements until an upper element is found
    /////////////////////////////////////////////////
    bool bEndFound = false;
    while (!bEndFound && Result == NULL) {
      // read an element
      /// \todo 0xFF... and true should be configurable
      //      EbmlElement * NewElt;
      if (TestReadElt == NULL) {
        int bUpperElement = 0; // trick to call FindNextID correctly
        Result = DataStream.FindNextElement(Context, bUpperElement, 0xFFFFFFFFL, AllowDummyElt);
      } else {
        Result = TestReadElt;
        TestReadElt = NULL;
      }

      if (Result != NULL) {
        unsigned int EltIndex;
        // data known in this Master's context
        for (EltIndex = 0; EltIndex < EBML_CTX_SIZE(Context); EltIndex++) {
          if (EbmlId(*Result) == EBML_CTX_IDX_ID(Context,EltIndex)) {
            // skip the data with its own context
            Result = Result->SkipData(DataStream, EBML_SEM_CONTEXT(EBML_CTX_IDX(Context,EltIndex)), NULL);
            break; // let's go to the next ID
          }
        }

        if (EltIndex >= EBML_CTX_SIZE(Context)) {
          if (EBML_CTX_PARENT(Context) != NULL) {
            Result = SkipData(DataStream, *EBML_CTX_PARENT(Context), Result);
          } else {
            assert(Context.GetGlobalContext != NULL);
            if (Context != Context.GetGlobalContext()) {
              Result = SkipData(DataStream, Context.GetGlobalContext(), Result);
            } else {
              bEndFound = true;
            }
          }
        }
      } else {
        bEndFound = true;
      }
    }
  }
  return Result;
}

EbmlElement *EbmlElement::CreateElementUsingContext(const EbmlId & aID, const EbmlSemanticContext & Context,
                                                    int & LowLevel, bool IsGlobalContext, bool bAllowDummy, unsigned int MaxLowerLevel)
{
  unsigned int ContextIndex;
  EbmlElement *Result = NULL;

  // elements at the current level
  for (ContextIndex = 0; ContextIndex < EBML_CTX_SIZE(Context); ContextIndex++) {
    if (aID == EBML_CTX_IDX_ID(Context,ContextIndex)) {
      return &EBML_SEM_CREATE(EBML_CTX_IDX(Context,ContextIndex));
    }
  }

  // global elements
  assert(Context.GetGlobalContext != NULL); // global should always exist, at least the EBML ones
  const EbmlSemanticContext & tstContext = Context.GetGlobalContext();
  if (tstContext != Context) {
    LowLevel--;
    MaxLowerLevel--;
    // recursive is good, but be carefull...
    Result = CreateElementUsingContext(aID, tstContext, LowLevel, true, bAllowDummy, MaxLowerLevel);
    if (Result != NULL) {
      return Result;
    }
    LowLevel++;
    MaxLowerLevel++;
  } else {
    return NULL;
  }

  // parent elements
  if (EBML_CTX_MASTER(Context) != NULL && aID == EBML_INFO_ID(*EBML_CTX_MASTER(Context))) {
    LowLevel++; // already one level up (same as context)
    return &EBML_INFO_CREATE(*EBML_CTX_MASTER(Context));
  }

  // check wether it's not part of an upper context
  if (EBML_CTX_PARENT(Context) != NULL) {
    LowLevel++;
    MaxLowerLevel++;
    return CreateElementUsingContext(aID, *EBML_CTX_PARENT(Context), LowLevel, IsGlobalContext, bAllowDummy, MaxLowerLevel);
  }

  if (!IsGlobalContext && bAllowDummy) {
    LowLevel = 0;
    Result = new (std::nothrow) EbmlDummy(aID);
  }

  return Result;
}

/*!
  \todo verify that the size written is the same as the data written
*/
filepos_t EbmlElement::Render(IOCallback & output, bool bWithDefault, bool bKeepPosition, bool bForceRender)
{
  assert(bValueIsSet || (bWithDefault && DefaultISset())); // an element is been rendered without a value set !!!
  // it may be a mandatory element without a default value
  if (!bWithDefault && IsDefaultValue()) {
    return 0;
  }
#if defined(LIBEBML_DEBUG)
  uint64 SupposedSize = UpdateSize(bWithDefault, bForceRender);
#endif // LIBEBML_DEBUG
  filepos_t result = RenderHead(output, bForceRender, bWithDefault, bKeepPosition);
  uint64 WrittenSize = RenderData(output, bForceRender, bWithDefault);
#if defined(LIBEBML_DEBUG)
  if (static_cast<int64>(SupposedSize) != (0-1))
    assert(WrittenSize == SupposedSize);
#endif // LIBEBML_DEBUG
  result += WrittenSize;
  return result;
}

/*!
  \todo store the position of the Size writing for elements with unknown size
  \todo handle exceptions on errors
  \todo handle CodeSize bigger than 5 bytes
*/
filepos_t EbmlElement::RenderHead(IOCallback & output, bool bForceRender, bool bWithDefault, bool bKeepPosition)
{
  if (EBML_ID_LENGTH((const EbmlId&)*this) <= 0 || EBML_ID_LENGTH((const EbmlId&)*this) > 4)
    return 0;

  UpdateSize(bWithDefault, bForceRender);

  return MakeRenderHead(output, bKeepPosition);
}

filepos_t EbmlElement::MakeRenderHead(IOCallback & output, bool bKeepPosition)
{
  binary FinalHead[4+8]; // Class D + 64 bits coded size
  unsigned int FinalHeadSize;

  FinalHeadSize = EBML_ID_LENGTH((const EbmlId&)*this);
  EbmlId(*this).Fill(FinalHead);

  int CodedSize = CodedSizeLength(Size, SizeLength, bSizeIsFinite);
  CodedValueLength(Size, CodedSize, &FinalHead[FinalHeadSize]);
  FinalHeadSize += CodedSize;

  output.writeFully(FinalHead, FinalHeadSize);
  if (!bKeepPosition) {
    ElementPosition = output.getFilePointer() - FinalHeadSize;
    SizePosition = ElementPosition + EBML_ID_LENGTH((const EbmlId&)*this);
  }

  return FinalHeadSize;
}

uint64 EbmlElement::ElementSize(bool bWithDefault) const
{
  if (!bWithDefault && IsDefaultValue())
    return 0; // won't be saved
  return Size + EBML_ID_LENGTH((const EbmlId&)*this) + CodedSizeLength(Size, SizeLength, bSizeIsFinite);
}

bool EbmlElement::IsSmallerThan(const EbmlElement *Cmp) const
{
  return EbmlId(*this) == EbmlId(*Cmp);
}

bool EbmlElement::CompareElements(const EbmlElement *A, const EbmlElement *B)
{
  if (EbmlId(*A) == EbmlId(*B))
    return A->IsSmallerThan(B);
  else
    return false;
}

void EbmlElement::Read(EbmlStream & inDataStream, const EbmlSemanticContext & /* Context */, int & /* UpperEltFound */, EbmlElement * & /* FoundElt */, bool /* AllowDummyElt */, ScopeMode ReadFully)
{
  ReadData(inDataStream.I_O(), ReadFully);
}

bool EbmlElement::ForceSize(uint64 NewSize)
{
  if (bSizeIsFinite) {
    return false;
  }

  int OldSizeLen = CodedSizeLength(Size, SizeLength, bSizeIsFinite);
  uint64 OldSize = Size;

  Size = NewSize;

  if (CodedSizeLength(Size, SizeLength, bSizeIsFinite) == OldSizeLen) {
    bSizeIsFinite = true;
    return true;
  }
  Size = OldSize;

  return false;
}

filepos_t EbmlElement::OverwriteHead(IOCallback & output, bool bKeepPosition)
{
  if (ElementPosition == 0) {
    return 0; // the element has not been written
  }

  uint64 CurrentPosition = output.getFilePointer();
  output.setFilePointer(GetElementPosition());
  filepos_t Result = MakeRenderHead(output, bKeepPosition);
  output.setFilePointer(CurrentPosition);
  return Result;
}

uint64 EbmlElement::VoidMe(IOCallback & output, bool bWithDefault)
{
  if (ElementPosition == 0) {
    return 0; // the element has not been written
  }

  EbmlVoid Dummy;
  return Dummy.Overwrite(*this, output, bWithDefault);
}

END_LIBEBML_NAMESPACE