core/fpdfapi/parser/cpdf_object_stream.cpp

// Copyright 2018 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "core/fpdfapi/parser/cpdf_object_stream.h"

#include <utility>

#include "core/fpdfapi/parser/cpdf_dictionary.h"
#include "core/fpdfapi/parser/cpdf_number.h"
#include "core/fpdfapi/parser/cpdf_parser.h"
#include "core/fpdfapi/parser/cpdf_reference.h"
#include "core/fpdfapi/parser/cpdf_stream.h"
#include "core/fpdfapi/parser/cpdf_stream_acc.h"
#include "core/fpdfapi/parser/cpdf_syntax_parser.h"
#include "core/fpdfapi/parser/fpdf_parser_utility.h"
#include "core/fxcrt/cfx_read_only_span_stream.h"
#include "core/fxcrt/check.h"
#include "core/fxcrt/fx_safe_types.h"
#include "core/fxcrt/ptr_util.h"

namespace {

bool IsObjectStream(const CPDF_Stream* stream) {
  if (!stream)
    return false;

  // See ISO 32000-1:2008 spec, table 16.
  RetainPtr<const CPDF_Dictionary> stream_dict = stream->GetDict();
  if (!ValidateDictType(stream_dict.Get(), "ObjStm"))
    return false;

  RetainPtr<const CPDF_Number> number_of_objects =
      stream_dict->GetNumberFor("N");
  if (!number_of_objects || !number_of_objects->IsInteger() ||
      number_of_objects->GetInteger() < 0 ||
      number_of_objects->GetInteger() >=
          static_cast<int>(CPDF_Parser::kMaxObjectNumber)) {
    return false;
  }

  RetainPtr<const CPDF_Number> first_object_offset =
      stream_dict->GetNumberFor("First");
  if (!first_object_offset || !first_object_offset->IsInteger() ||
      first_object_offset->GetInteger() < 0) {
    return false;
  }

  return true;
}

}  // namespace

//  static
std::unique_ptr<CPDF_ObjectStream> CPDF_ObjectStream::Create(
    RetainPtr<const CPDF_Stream> stream) {
  if (!IsObjectStream(stream.Get()))
    return nullptr;

  // Protected constructor.
  return pdfium::WrapUnique(new CPDF_ObjectStream(std::move(stream)));
}

CPDF_ObjectStream::CPDF_ObjectStream(RetainPtr<const CPDF_Stream> obj_stream)
    : stream_acc_(pdfium::MakeRetain<CPDF_StreamAcc>(obj_stream)),
      first_object_offset_(obj_stream->GetDict()->GetIntegerFor("First")) {
  DCHECK(IsObjectStream(obj_stream.Get()));
  Init(obj_stream.Get());
}

CPDF_ObjectStream::~CPDF_ObjectStream() = default;

RetainPtr<CPDF_Object> CPDF_ObjectStream::ParseObject(
    CPDF_IndirectObjectHolder* pObjList,
    uint32_t obj_number,
    uint32_t archive_obj_index) const {
  if (archive_obj_index >= object_info_.size())
    return nullptr;

  const auto& info = object_info_[archive_obj_index];
  if (info.obj_num != obj_number)
    return nullptr;

  RetainPtr<CPDF_Object> result =
      ParseObjectAtOffset(pObjList, info.obj_offset);
  if (result)
    result->SetObjNum(obj_number);
  return result;
}

void CPDF_ObjectStream::Init(const CPDF_Stream* stream) {
  stream_acc_->LoadAllDataFiltered();
  data_stream_ =
      pdfium::MakeRetain<CFX_ReadOnlySpanStream>(stream_acc_->GetSpan());

  CPDF_SyntaxParser syntax(data_stream_);
  const int object_count = stream->GetDict()->GetIntegerFor("N");
  for (int32_t i = object_count; i > 0; --i) {
    if (syntax.GetPos() >= data_stream_->GetSize())
      break;

    const uint32_t obj_num = syntax.GetDirectNum();
    const uint32_t obj_offset = syntax.GetDirectNum();
    if (!obj_num)
      continue;

    object_info_.emplace_back(obj_num, obj_offset);
  }
}

RetainPtr<CPDF_Object> CPDF_ObjectStream::ParseObjectAtOffset(
    CPDF_IndirectObjectHolder* pObjList,
    uint32_t object_offset) const {
  FX_SAFE_FILESIZE offset_in_stream = first_object_offset_;
  offset_in_stream += object_offset;

  if (!offset_in_stream.IsValid())
    return nullptr;

  if (offset_in_stream.ValueOrDie() >= data_stream_->GetSize())
    return nullptr;

  CPDF_SyntaxParser syntax(data_stream_);
  syntax.SetPos(offset_in_stream.ValueOrDie());
  return syntax.GetObjectBody(pObjList);
}