How to perform incremental save in pdfium?

[Suhas Chintala]

I have tried the FPDF_INCREMENTAL flag to 1. The code currently does not even update the m_newobjnumarray array, hence  the WriteNewObjs function in the cpdf_creator.cpp does not work. The new xref tables are not populated because of that. Have I not missed something? Does calling FPDF_SaveAsCopy() with incremental save flag set work? Or do I need to some preprocessing to get it working?

A small code snippet demonstrating incremental save if at all it is possible in current code would be very helpful. Thanks.

[Lei Zhang]

Do you have a code snippet of your own to show what you are trying to
do? It is certainly possible that FPDF_INCREMENTAL is broken.

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[Ankit Kumar]

FPDF_INCREMENTAL can't actually do anything since the code below for adding new objects is no-op in case of incremental as on incremental it doesn't add any new objects, it just continues the for loop. Even on removing that part the changed objects are the Appearance streams in cases of form annnotations not the form object itself and we need to rewrite that too since we need to update the AP reference in the object.

https://pdfium.googlesource.com/pdfium/+/master/core/fpdfapi/edit/cpdf_creator.cpp (Line 213)

void CPDF_Creator::InitNewObjNumOffsets() {

  for (const auto& pair : *m_pDocument) {

    const uint32_t objnum = pair.first;

    if (m_IsIncremental ||

        pair.second->GetObjNum() == CPDF_Object::kInvalidObjNum) {

      continue;

    }

    if (m_pParser && m_pParser->IsValidObjectNumber(objnum) &&

        !m_pParser->IsObjectFree(objnum)) {

      continue;

    }

    m_NewObjNumArray.insert(std::lower_bound(m_NewObjNumArray.begin(),

                                             m_NewObjNumArray.end(), objnum),

                            objnum);