// Copyright 2016 PDFium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com

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

#include <algorithm>
#include <sstream>
#include <utility>
#include <vector>

#include "core/fpdfapi/cpdf_modulemgr.h"
#include "core/fpdfapi/parser/cpdf_array.h"
#include "core/fpdfapi/parser/cpdf_boolean.h"
#include "core/fpdfapi/parser/cpdf_crypto_handler.h"
#include "core/fpdfapi/parser/cpdf_dictionary.h"
#include "core/fpdfapi/parser/cpdf_name.h"
#include "core/fpdfapi/parser/cpdf_null.h"
#include "core/fpdfapi/parser/cpdf_number.h"
#include "core/fpdfapi/parser/cpdf_read_validator.h"
#include "core/fpdfapi/parser/cpdf_reference.h"
#include "core/fpdfapi/parser/cpdf_stream.h"
#include "core/fpdfapi/parser/cpdf_string.h"
#include "core/fpdfapi/parser/fpdf_parser_decode.h"
#include "core/fpdfapi/parser/fpdf_parser_utility.h"
#include "core/fxcrt/fx_extension.h"
#include "third_party/base/numerics/safe_math.h"
#include "third_party/base/ptr_util.h"

namespace {

enum class ReadStatus { Normal, Backslash, Octal, FinishOctal, CarriageReturn };

}  // namespace

// static
int CPDF_SyntaxParser::s_CurrentRecursionDepth = 0;

CPDF_SyntaxParser::CPDF_SyntaxParser()
    : CPDF_SyntaxParser(CFX_WeakPtr<CFX_ByteStringPool>()) {}

CPDF_SyntaxParser::CPDF_SyntaxParser(
    const CFX_WeakPtr<CFX_ByteStringPool>& pPool)
    : m_MetadataObjnum(0),
      m_pFileAccess(nullptr),
      m_pFileBuf(nullptr),
      m_BufSize(CPDF_ModuleMgr::kFileBufSize),
      m_pPool(pPool) {}

CPDF_SyntaxParser::~CPDF_SyntaxParser() {
  FX_Free(m_pFileBuf);
}

bool CPDF_SyntaxParser::GetCharAt(FX_FILESIZE pos, uint8_t& ch) {
  CFX_AutoRestorer<FX_FILESIZE> save_pos(&m_Pos);
  m_Pos = pos;
  return GetNextChar(ch);
}

bool CPDF_SyntaxParser::ReadChar(FX_FILESIZE read_pos, uint32_t read_size) {
  if (static_cast<FX_FILESIZE>(read_pos + read_size) > m_FileLen) {
    if (m_FileLen < static_cast<FX_FILESIZE>(read_size)) {
      read_pos = 0;
      read_size = static_cast<uint32_t>(m_FileLen);
    } else {
      read_pos = m_FileLen - read_size;
    }
  }
  if (!m_pFileAccess->ReadBlock(m_pFileBuf, read_pos, read_size))
    return false;

  m_BufOffset = read_pos;
  return true;
}

bool CPDF_SyntaxParser::GetNextChar(uint8_t& ch) {
  FX_FILESIZE pos = m_Pos + m_HeaderOffset;
  if (pos >= m_FileLen)
    return false;

  if (CheckPosition(pos)) {
    FX_FILESIZE read_pos = pos;
    uint32_t read_size = m_BufSize;
    read_size = std::min(read_size, static_cast<uint32_t>(m_FileLen));
    if (!ReadChar(read_pos, read_size))
      return false;
  }
  ch = m_pFileBuf[pos - m_BufOffset];
  m_Pos++;
  return true;
}

bool CPDF_SyntaxParser::GetCharAtBackward(FX_FILESIZE pos, uint8_t* ch) {
  pos += m_HeaderOffset;
  if (pos >= m_FileLen)
    return false;

  if (CheckPosition(pos)) {
    FX_FILESIZE read_pos;
    if (pos < static_cast<FX_FILESIZE>(m_BufSize))
      read_pos = 0;
    else
      read_pos = pos - m_BufSize + 1;
    uint32_t read_size = m_BufSize;
    if (!ReadChar(read_pos, read_size))
      return false;
  }
  *ch = m_pFileBuf[pos - m_BufOffset];
  return true;
}

bool CPDF_SyntaxParser::ReadBlock(uint8_t* pBuf, uint32_t size) {
  if (!m_pFileAccess->ReadBlock(pBuf, m_Pos + m_HeaderOffset, size))
    return false;
  m_Pos += size;
  return true;
}

void CPDF_SyntaxParser::GetNextWordInternal(bool* bIsNumber) {
  m_WordSize = 0;
  if (bIsNumber)
    *bIsNumber = true;

  uint8_t ch;
  if (!GetNextChar(ch))
    return;

  while (1) {
    while (PDFCharIsWhitespace(ch)) {
      if (!GetNextChar(ch))
        return;
    }

    if (ch != '%')
      break;

    while (1) {
      if (!GetNextChar(ch))
        return;
      if (PDFCharIsLineEnding(ch))
        break;
    }
  }

  if (PDFCharIsDelimiter(ch)) {
    if (bIsNumber)
      *bIsNumber = false;

    m_WordBuffer[m_WordSize++] = ch;
    if (ch == '/') {
      while (1) {
        if (!GetNextChar(ch))
          return;

        if (!PDFCharIsOther(ch) && !PDFCharIsNumeric(ch)) {
          m_Pos--;
          return;
        }

        if (m_WordSize < sizeof(m_WordBuffer) - 1)
          m_WordBuffer[m_WordSize++] = ch;
      }
    } else if (ch == '<') {
      if (!GetNextChar(ch))
        return;

      if (ch == '<')
        m_WordBuffer[m_WordSize++] = ch;
      else
        m_Pos--;
    } else if (ch == '>') {
      if (!GetNextChar(ch))
        return;

      if (ch == '>')
        m_WordBuffer[m_WordSize++] = ch;
      else
        m_Pos--;
    }
    return;
  }

  while (1) {
    if (m_WordSize < sizeof(m_WordBuffer) - 1)
      m_WordBuffer[m_WordSize++] = ch;

    if (!PDFCharIsNumeric(ch)) {
      if (bIsNumber)
        *bIsNumber = false;
    }

    if (!GetNextChar(ch))
      return;

    if (PDFCharIsDelimiter(ch) || PDFCharIsWhitespace(ch)) {
      m_Pos--;
      break;
    }
  }
}

CFX_ByteString CPDF_SyntaxParser::ReadString() {
  uint8_t ch;
  if (!GetNextChar(ch))
    return CFX_ByteString();

  std::ostringstream buf;
  int32_t parlevel = 0;
  ReadStatus status = ReadStatus::Normal;
  int32_t iEscCode = 0;
  while (1) {
    switch (status) {
      case ReadStatus::Normal:
        if (ch == ')') {
          if (parlevel == 0)
            return CFX_ByteString(buf);
          parlevel--;
        } else if (ch == '(') {
          parlevel++;
        }
        if (ch == '\\')
          status = ReadStatus::Backslash;
        else
          buf << static_cast<char>(ch);
        break;
      case ReadStatus::Backslash:
        if (ch >= '0' && ch <= '7') {
          iEscCode = FXSYS_DecimalCharToInt(static_cast<wchar_t>(ch));
          status = ReadStatus::Octal;
          break;
        }

        if (ch == 'n') {
          buf << '\n';
        } else if (ch == 'r') {
          buf << '\r';
        } else if (ch == 't') {
          buf << '\t';
        } else if (ch == 'b') {
          buf << '\b';
        } else if (ch == 'f') {
          buf << '\f';
        } else if (ch == '\r') {
          status = ReadStatus::CarriageReturn;
          break;
        } else if (ch != '\n') {
          buf << static_cast<char>(ch);
        }
        status = ReadStatus::Normal;
        break;
      case ReadStatus::Octal:
        if (ch >= '0' && ch <= '7') {
          iEscCode =
              iEscCode * 8 + FXSYS_DecimalCharToInt(static_cast<wchar_t>(ch));
          status = ReadStatus::FinishOctal;
        } else {
          buf << static_cast<char>(iEscCode);
          status = ReadStatus::Normal;
          continue;
        }
        break;
      case ReadStatus::FinishOctal:
        status = ReadStatus::Normal;
        if (ch >= '0' && ch <= '7') {
          iEscCode =
              iEscCode * 8 + FXSYS_DecimalCharToInt(static_cast<wchar_t>(ch));
          buf << static_cast<char>(iEscCode);
        } else {
          buf << static_cast<char>(iEscCode);
          continue;
        }
        break;
      case ReadStatus::CarriageReturn:
        status = ReadStatus::Normal;
        if (ch != '\n')
          continue;
        break;
    }

    if (!GetNextChar(ch))
      break;
  }

  GetNextChar(ch);
  return CFX_ByteString(buf);
}

CFX_ByteString CPDF_SyntaxParser::ReadHexString() {
  uint8_t ch;
  if (!GetNextChar(ch))
    return CFX_ByteString();

  std::ostringstream buf;
  bool bFirst = true;
  uint8_t code = 0;
  while (1) {
    if (ch == '>')
      break;

    if (std::isxdigit(ch)) {
      int val = FXSYS_HexCharToInt(ch);
      if (bFirst) {
        code = val * 16;
      } else {
        code += val;
        buf << static_cast<char>(code);
      }
      bFirst = !bFirst;
    }

    if (!GetNextChar(ch))
      break;
  }
  if (!bFirst)
    buf << static_cast<char>(code);

  return CFX_ByteString(buf);
}

void CPDF_SyntaxParser::ToNextLine() {
  uint8_t ch;
  while (GetNextChar(ch)) {
    if (ch == '\n')
      break;

    if (ch == '\r') {
      GetNextChar(ch);
      if (ch != '\n')
        --m_Pos;
      break;
    }
  }
}

void CPDF_SyntaxParser::ToNextWord() {
  uint8_t ch;
  if (!GetNextChar(ch))
    return;

  while (1) {
    while (PDFCharIsWhitespace(ch)) {
      if (!GetNextChar(ch))
        return;
    }

    if (ch != '%')
      break;

    while (1) {
      if (!GetNextChar(ch))
        return;
      if (PDFCharIsLineEnding(ch))
        break;
    }
  }
  m_Pos--;
}

CFX_ByteString CPDF_SyntaxParser::GetNextWord(bool* bIsNumber) {
  const CPDF_ReadValidator::Session read_session(GetValidator().Get());
  GetNextWordInternal(bIsNumber);
  return GetValidator()->has_read_problems()
             ? CFX_ByteString()
             : CFX_ByteString((const char*)m_WordBuffer, m_WordSize);
}

CFX_ByteString CPDF_SyntaxParser::GetKeyword() {
  return GetNextWord(nullptr);
}

std::unique_ptr<CPDF_Object> CPDF_SyntaxParser::GetObject(
    CPDF_IndirectObjectHolder* pObjList,
    uint32_t objnum,
    uint32_t gennum,
    bool bDecrypt) {
  const CPDF_ReadValidator::Session read_session(GetValidator().Get());
  auto result = GetObjectInternal(pObjList, objnum, gennum, bDecrypt);
  if (GetValidator()->has_read_problems())
    return nullptr;
  return result;
}

std::unique_ptr<CPDF_Object> CPDF_SyntaxParser::GetObjectInternal(
    CPDF_IndirectObjectHolder* pObjList,
    uint32_t objnum,
    uint32_t gennum,
    bool bDecrypt) {
  CFX_AutoRestorer<int> restorer(&s_CurrentRecursionDepth);
  if (++s_CurrentRecursionDepth > kParserMaxRecursionDepth)
    return nullptr;

  FX_FILESIZE SavedObjPos = m_Pos;
  bool bIsNumber;
  CFX_ByteString word = GetNextWord(&bIsNumber);
  if (word.GetLength() == 0)
    return nullptr;

  if (bIsNumber) {
    FX_FILESIZE SavedPos = m_Pos;
    CFX_ByteString nextword = GetNextWord(&bIsNumber);
    if (bIsNumber) {
      CFX_ByteString nextword2 = GetNextWord(nullptr);
      if (nextword2 == "R") {
        uint32_t refnum = FXSYS_atoui(word.c_str());
        if (refnum == CPDF_Object::kInvalidObjNum)
          return nullptr;
        return pdfium::MakeUnique<CPDF_Reference>(pObjList, refnum);
      }
    }
    m_Pos = SavedPos;
    return pdfium::MakeUnique<CPDF_Number>(word.AsStringC());
  }

  if (word == "true" || word == "false")
    return pdfium::MakeUnique<CPDF_Boolean>(word == "true");

  if (word == "null")
    return pdfium::MakeUnique<CPDF_Null>();

  if (word == "(") {
    CFX_ByteString str = ReadString();
    if (m_pCryptoHandler && bDecrypt)
      str = m_pCryptoHandler->Decrypt(objnum, gennum, str);
    return pdfium::MakeUnique<CPDF_String>(m_pPool, str, false);
  }
  if (word == "<") {
    CFX_ByteString str = ReadHexString();
    if (m_pCryptoHandler && bDecrypt)
      str = m_pCryptoHandler->Decrypt(objnum, gennum, str);
    return pdfium::MakeUnique<CPDF_String>(m_pPool, str, true);
  }
  if (word == "[") {
    std::unique_ptr<CPDF_Array> pArray = pdfium::MakeUnique<CPDF_Array>();
    while (std::unique_ptr<CPDF_Object> pObj =
               GetObject(pObjList, objnum, gennum, true)) {
      pArray->Add(std::move(pObj));
    }
    return std::move(pArray);
  }
  if (word[0] == '/') {
    return pdfium::MakeUnique<CPDF_Name>(
        m_pPool,
        PDF_NameDecode(CFX_ByteStringC(m_WordBuffer + 1, m_WordSize - 1)));
  }
  if (word == "<<") {
    int32_t nKeys = 0;
    FX_FILESIZE dwSignValuePos = 0;
    std::unique_ptr<CPDF_Dictionary> pDict =
        pdfium::MakeUnique<CPDF_Dictionary>(m_pPool);
    while (1) {
      CFX_ByteString key = GetNextWord(nullptr);
      if (key.IsEmpty())
        return nullptr;

      FX_FILESIZE SavedPos = m_Pos - key.GetLength();
      if (key == ">>")
        break;

      if (key == "endobj") {
        m_Pos = SavedPos;
        break;
      }
      if (key[0] != '/')
        continue;

      ++nKeys;
      key = PDF_NameDecode(key);
      if (key.IsEmpty())
        continue;

      if (key == "/Contents")
        dwSignValuePos = m_Pos;

      std::unique_ptr<CPDF_Object> pObj =
          GetObject(pObjList, objnum, gennum, true);
      if (!pObj)
        continue;

      CFX_ByteString keyNoSlash(key.raw_str() + 1, key.GetLength() - 1);
      pDict->SetFor(keyNoSlash, std::move(pObj));
    }

    // Only when this is a signature dictionary and has contents, we reset the
    // contents to the un-decrypted form.
    if (pDict->IsSignatureDict() && dwSignValuePos) {
      CFX_AutoRestorer<FX_FILESIZE> save_pos(&m_Pos);
      m_Pos = dwSignValuePos;
      pDict->SetFor("Contents", GetObject(pObjList, objnum, gennum, false));
    }

    FX_FILESIZE SavedPos = m_Pos;
    CFX_ByteString nextword = GetNextWord(nullptr);
    if (nextword != "stream") {
      m_Pos = SavedPos;
      return std::move(pDict);
    }
    return ReadStream(std::move(pDict), objnum, gennum);
  }
  if (word == ">>")
    m_Pos = SavedObjPos;

  return nullptr;
}

std::unique_ptr<CPDF_Object> CPDF_SyntaxParser::GetObjectForStrict(
    CPDF_IndirectObjectHolder* pObjList,
    uint32_t objnum,
    uint32_t gennum) {
  const CPDF_ReadValidator::Session read_session(GetValidator().Get());
  auto result = GetObjectForStrictInternal(pObjList, objnum, gennum);
  if (GetValidator()->has_read_problems())
    return nullptr;
  return result;
}

std::unique_ptr<CPDF_Object> CPDF_SyntaxParser::GetObjectForStrictInternal(
    CPDF_IndirectObjectHolder* pObjList,
    uint32_t objnum,
    uint32_t gennum) {
  CFX_AutoRestorer<int> restorer(&s_CurrentRecursionDepth);
  if (++s_CurrentRecursionDepth > kParserMaxRecursionDepth)
    return nullptr;

  FX_FILESIZE SavedObjPos = m_Pos;
  bool bIsNumber;
  CFX_ByteString word = GetNextWord(&bIsNumber);
  if (word.GetLength() == 0)
    return nullptr;

  if (bIsNumber) {
    FX_FILESIZE SavedPos = m_Pos;
    CFX_ByteString nextword = GetNextWord(&bIsNumber);
    if (bIsNumber) {
      CFX_ByteString nextword2 = GetNextWord(nullptr);
      if (nextword2 == "R") {
        uint32_t refnum = FXSYS_atoui(word.c_str());
        if (refnum == CPDF_Object::kInvalidObjNum)
          return nullptr;
        return pdfium::MakeUnique<CPDF_Reference>(pObjList, refnum);
      }
    }
    m_Pos = SavedPos;
    return pdfium::MakeUnique<CPDF_Number>(word.AsStringC());
  }

  if (word == "true" || word == "false")
    return pdfium::MakeUnique<CPDF_Boolean>(word == "true");

  if (word == "null")
    return pdfium::MakeUnique<CPDF_Null>();

  if (word == "(") {
    CFX_ByteString str = ReadString();
    if (m_pCryptoHandler)
      str = m_pCryptoHandler->Decrypt(objnum, gennum, str);
    return pdfium::MakeUnique<CPDF_String>(m_pPool, str, false);
  }
  if (word == "<") {
    CFX_ByteString str = ReadHexString();
    if (m_pCryptoHandler)
      str = m_pCryptoHandler->Decrypt(objnum, gennum, str);
    return pdfium::MakeUnique<CPDF_String>(m_pPool, str, true);
  }
  if (word == "[") {
    auto pArray = pdfium::MakeUnique<CPDF_Array>();
    while (std::unique_ptr<CPDF_Object> pObj =
               GetObject(pObjList, objnum, gennum, true)) {
      pArray->Add(std::move(pObj));
    }
    return m_WordBuffer[0] == ']' ? std::move(pArray) : nullptr;
  }
  if (word[0] == '/') {
    return pdfium::MakeUnique<CPDF_Name>(
        m_pPool,
        PDF_NameDecode(CFX_ByteStringC(m_WordBuffer + 1, m_WordSize - 1)));
  }
  if (word == "<<") {
    std::unique_ptr<CPDF_Dictionary> pDict =
        pdfium::MakeUnique<CPDF_Dictionary>(m_pPool);
    while (1) {
      FX_FILESIZE SavedPos = m_Pos;
      CFX_ByteString key = GetNextWord(nullptr);
      if (key.IsEmpty())
        return nullptr;

      if (key == ">>")
        break;

      if (key == "endobj") {
        m_Pos = SavedPos;
        break;
      }
      if (key[0] != '/')
        continue;

      key = PDF_NameDecode(key);
      std::unique_ptr<CPDF_Object> obj(
          GetObject(pObjList, objnum, gennum, true));
      if (!obj) {
        uint8_t ch;
        while (GetNextChar(ch) && ch != 0x0A && ch != 0x0D) {
          continue;
        }
        return nullptr;
      }

      if (key.GetLength() > 1) {
        pDict->SetFor(CFX_ByteString(key.c_str() + 1, key.GetLength() - 1),
                      std::move(obj));
      }
    }

    FX_FILESIZE SavedPos = m_Pos;
    CFX_ByteString nextword = GetNextWord(nullptr);
    if (nextword != "stream") {
      m_Pos = SavedPos;
      return std::move(pDict);
    }
    return ReadStream(std::move(pDict), objnum, gennum);
  }
  if (word == ">>")
    m_Pos = SavedObjPos;

  return nullptr;
}

unsigned int CPDF_SyntaxParser::ReadEOLMarkers(FX_FILESIZE pos) {
  unsigned char byte1 = 0;
  unsigned char byte2 = 0;

  GetCharAt(pos, byte1);
  GetCharAt(pos + 1, byte2);

  if (byte1 == '\r' && byte2 == '\n')
    return 2;

  if (byte1 == '\r' || byte1 == '\n')
    return 1;

  return 0;
}

std::unique_ptr<CPDF_Stream> CPDF_SyntaxParser::ReadStream(
    std::unique_ptr<CPDF_Dictionary> pDict,
    uint32_t objnum,
    uint32_t gennum) {
  CPDF_Object* pLenObj = pDict->GetObjectFor("Length");
  FX_FILESIZE len = -1;
  CPDF_Reference* pLenObjRef = ToReference(pLenObj);

  bool differingObjNum = !pLenObjRef || (pLenObjRef->GetObjList() &&
                                         pLenObjRef->GetRefObjNum() != objnum);
  if (pLenObj && differingObjNum)
    len = pLenObj->GetInteger();

  // Locate the start of stream.
  ToNextLine();
  FX_FILESIZE streamStartPos = m_Pos;

  const CFX_ByteStringC kEndStreamStr("endstream");
  const CFX_ByteStringC kEndObjStr("endobj");

  CPDF_CryptoHandler* pCryptoHandler =
      objnum == m_MetadataObjnum ? nullptr : m_pCryptoHandler.Get();
  if (!pCryptoHandler) {
    bool bSearchForKeyword = true;
    if (len >= 0) {
      pdfium::base::CheckedNumeric<FX_FILESIZE> pos = m_Pos;
      pos += len;
      if (pos.IsValid() && pos.ValueOrDie() < m_FileLen)
        m_Pos = pos.ValueOrDie();

      m_Pos += ReadEOLMarkers(m_Pos);
      memset(m_WordBuffer, 0, kEndStreamStr.GetLength() + 1);
      GetNextWordInternal(nullptr);
      // Earlier version of PDF specification doesn't require EOL marker before
      // 'endstream' keyword. If keyword 'endstream' follows the bytes in
      // specified length, it signals the end of stream.
      if (memcmp(m_WordBuffer, kEndStreamStr.raw_str(),
                 kEndStreamStr.GetLength()) == 0) {
        bSearchForKeyword = false;
      }
    }

    if (bSearchForKeyword) {
      // If len is not available, len needs to be calculated
      // by searching the keywords "endstream" or "endobj".
      m_Pos = streamStartPos;
      FX_FILESIZE endStreamOffset = 0;
      while (endStreamOffset >= 0) {
        endStreamOffset = FindTag(kEndStreamStr, 0);

        // Can't find "endstream".
        if (endStreamOffset < 0)
          break;

        // Stop searching when "endstream" is found.
        if (IsWholeWord(m_Pos - kEndStreamStr.GetLength(), m_FileLen,
                        kEndStreamStr, true)) {
          endStreamOffset = m_Pos - streamStartPos - kEndStreamStr.GetLength();
          break;
        }
      }

      m_Pos = streamStartPos;
      FX_FILESIZE endObjOffset = 0;
      while (endObjOffset >= 0) {
        endObjOffset = FindTag(kEndObjStr, 0);

        // Can't find "endobj".
        if (endObjOffset < 0)
          break;

        // Stop searching when "endobj" is found.
        if (IsWholeWord(m_Pos - kEndObjStr.GetLength(), m_FileLen, kEndObjStr,
                        true)) {
          endObjOffset = m_Pos - streamStartPos - kEndObjStr.GetLength();
          break;
        }
      }

      // Can't find "endstream" or "endobj".
      if (endStreamOffset < 0 && endObjOffset < 0)
        return nullptr;

      if (endStreamOffset < 0 && endObjOffset >= 0) {
        // Correct the position of end stream.
        endStreamOffset = endObjOffset;
      } else if (endStreamOffset >= 0 && endObjOffset < 0) {
        // Correct the position of end obj.
        endObjOffset = endStreamOffset;
      } else if (endStreamOffset > endObjOffset) {
        endStreamOffset = endObjOffset;
      }
      len = endStreamOffset;

      int numMarkers = ReadEOLMarkers(streamStartPos + endStreamOffset - 2);
      if (numMarkers == 2) {
        len -= 2;
      } else {
        numMarkers = ReadEOLMarkers(streamStartPos + endStreamOffset - 1);
        if (numMarkers == 1) {
          len -= 1;
        }
      }
      if (len < 0)
        return nullptr;

      pDict->SetNewFor<CPDF_Number>("Length", static_cast<int>(len));
    }
    m_Pos = streamStartPos;
  }
  // Read up to the end of the buffer. Note, we allow zero length streams as
  // we need to pass them through when we are importing pages into a new
  // document.
  len = std::min(len, m_FileLen - m_Pos - m_HeaderOffset);
  if (len < 0)
    return nullptr;

  std::unique_ptr<uint8_t, FxFreeDeleter> pData;
  if (len > 0) {
    pData.reset(FX_Alloc(uint8_t, len));
    ReadBlock(pData.get(), len);
    if (pCryptoHandler) {
      CFX_BinaryBuf dest_buf;
      dest_buf.EstimateSize(pCryptoHandler->DecryptGetSize(len));

      void* context = pCryptoHandler->DecryptStart(objnum, gennum);
      pCryptoHandler->DecryptStream(context, pData.get(), len, dest_buf);
      pCryptoHandler->DecryptFinish(context, dest_buf);
      len = dest_buf.GetSize();
      pData = dest_buf.DetachBuffer();
    }
  }
  auto pStream =
      pdfium::MakeUnique<CPDF_Stream>(std::move(pData), len, std::move(pDict));
  streamStartPos = m_Pos;
  memset(m_WordBuffer, 0, kEndObjStr.GetLength() + 1);
  GetNextWordInternal(nullptr);

  int numMarkers = ReadEOLMarkers(m_Pos);
  if (m_WordSize == static_cast<unsigned int>(kEndObjStr.GetLength()) &&
      numMarkers != 0 &&
      memcmp(m_WordBuffer, kEndObjStr.raw_str(), kEndObjStr.GetLength()) == 0) {
    m_Pos = streamStartPos;
  }
  return pStream;
}

void CPDF_SyntaxParser::InitParser(
    const CFX_RetainPtr<IFX_SeekableReadStream>& pFileAccess,
    uint32_t HeaderOffset) {
  ASSERT(pFileAccess);
  return InitParserWithValidator(
      pdfium::MakeRetain<CPDF_ReadValidator>(pFileAccess, nullptr),
      HeaderOffset);
}

void CPDF_SyntaxParser::InitParserWithValidator(
    const CFX_RetainPtr<CPDF_ReadValidator>& validator,
    uint32_t HeaderOffset) {
  ASSERT(validator);
  FX_Free(m_pFileBuf);
  m_pFileBuf = FX_Alloc(uint8_t, m_BufSize);
  m_HeaderOffset = HeaderOffset;
  m_FileLen = validator->GetSize();
  m_Pos = 0;
  m_pFileAccess = validator;
  m_BufOffset = 0;
  validator->ReadBlock(m_pFileBuf, 0,
                       std::min(m_BufSize, static_cast<uint32_t>(m_FileLen)));
}

uint32_t CPDF_SyntaxParser::GetDirectNum() {
  bool bIsNumber;
  GetNextWordInternal(&bIsNumber);
  if (!bIsNumber)
    return 0;

  m_WordBuffer[m_WordSize] = 0;
  return FXSYS_atoui(reinterpret_cast<const char*>(m_WordBuffer));
}

bool CPDF_SyntaxParser::IsWholeWord(FX_FILESIZE startpos,
                                    FX_FILESIZE limit,
                                    const CFX_ByteStringC& tag,
                                    bool checkKeyword) {
  const uint32_t taglen = tag.GetLength();

  bool bCheckLeft = !PDFCharIsDelimiter(tag[0]) && !PDFCharIsWhitespace(tag[0]);
  bool bCheckRight = !PDFCharIsDelimiter(tag[taglen - 1]) &&
                     !PDFCharIsWhitespace(tag[taglen - 1]);

  uint8_t ch;
  if (bCheckRight && startpos + (int32_t)taglen <= limit &&
      GetCharAt(startpos + (int32_t)taglen, ch)) {
    if (PDFCharIsNumeric(ch) || PDFCharIsOther(ch) ||
        (checkKeyword && PDFCharIsDelimiter(ch))) {
      return false;
    }
  }

  if (bCheckLeft && startpos > 0 && GetCharAt(startpos - 1, ch)) {
    if (PDFCharIsNumeric(ch) || PDFCharIsOther(ch) ||
        (checkKeyword && PDFCharIsDelimiter(ch))) {
      return false;
    }
  }
  return true;
}

bool CPDF_SyntaxParser::BackwardsSearchToWord(const CFX_ByteStringC& tag,
                                              FX_FILESIZE limit) {
  int32_t taglen = tag.GetLength();
  if (taglen == 0)
    return false;

  FX_FILESIZE pos = m_Pos;
  int32_t offset = taglen - 1;
  while (1) {
    if (limit && pos <= m_Pos - limit)
      return false;

    uint8_t byte;
    if (!GetCharAtBackward(pos, &byte))
      return false;

    if (byte == tag[offset]) {
      offset--;
      if (offset >= 0) {
        pos--;
        continue;
      }
      if (IsWholeWord(pos, limit, tag, false)) {
        m_Pos = pos;
        return true;
      }
    }
    offset = byte == tag[taglen - 1] ? taglen - 2 : taglen - 1;
    pos--;
    if (pos < 0)
      return false;
  }
}

FX_FILESIZE CPDF_SyntaxParser::FindTag(const CFX_ByteStringC& tag,
                                       FX_FILESIZE limit) {
  int32_t taglen = tag.GetLength();
  int32_t match = 0;
  limit += m_Pos;
  FX_FILESIZE startpos = m_Pos;

  while (1) {
    uint8_t ch;
    if (!GetNextChar(ch))
      return -1;

    if (ch == tag[match]) {
      match++;
      if (match == taglen)
        return m_Pos - startpos - taglen;
    } else {
      match = ch == tag[0] ? 1 : 0;
    }

    if (limit && m_Pos == limit)
      return -1;
  }
  return -1;
}

void CPDF_SyntaxParser::SetEncrypt(
    const CFX_RetainPtr<CPDF_CryptoHandler>& pCryptoHandler) {
  m_pCryptoHandler = pCryptoHandler;
}

CFX_RetainPtr<IFX_SeekableReadStream> CPDF_SyntaxParser::GetFileAccess() const {
  return m_pFileAccess;
}