Add type cast definitions for CPDF_Dictionary.

This CL adds ToCPDFDictionary type definitions and updates one file to use
instead of straight casts. I had to fix two places where we'd casted off the
constness of the original pointer.

BUG=pdfium:201
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1399233003 .

14 files changed, 98 insertions, 92 deletions

diff --git a/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp b/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp
index 4e6c72355d..054cf10c22 100644
--- a/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp
+++ b/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp
@@ -110,7 +110,7 @@ int32_t PDF_CreatorAppendObject(const CPDF_Object* pObj,
         return -1;
       }
       offset += 2;
-      CPDF_Dictionary* p = (CPDF_Dictionary*)pObj;
+      const CPDF_Dictionary* p = pObj->AsDictionary();
       FX_POSITION pos = p->GetStartPos();
       while (pos) {
         CFX_ByteString key;
@@ -334,7 +334,8 @@ CPDF_FlateEncoder::CPDF_FlateEncoder() {
 }
 void CPDF_FlateEncoder::CloneDict() {
   if (!m_bCloned) {
-    m_pDict = (CPDF_Dictionary*)m_pDict->Clone();
+    m_pDict = ToDictionary(m_pDict->Clone());
+    ASSERT(m_pDict);
     m_bCloned = TRUE;
   }
 }
@@ -349,7 +350,7 @@ FX_BOOL CPDF_FlateEncoder::Initialize(CPDF_Stream* pStream,
       destAcc.LoadAllData(pStream);
       m_dwSize = destAcc.GetSize();
       m_pData = (uint8_t*)destAcc.DetachData();
-      m_pDict = (CPDF_Dictionary*)pStream->GetDict()->Clone();
+      m_pDict = ToDictionary(pStream->GetDict()->Clone());
       m_pDict->RemoveAt(FX_BSTRC("Filter"));
       m_bNewData = TRUE;
       m_bCloned = TRUE;
@@ -365,7 +366,7 @@ FX_BOOL CPDF_FlateEncoder::Initialize(CPDF_Stream* pStream,
   m_bNewData = TRUE;
   m_bCloned = TRUE;
   ::FlateEncode(m_Acc.GetData(), m_Acc.GetSize(), m_pData, m_dwSize);
-  m_pDict = (CPDF_Dictionary*)pStream->GetDict()->Clone();
+  m_pDict = ToDictionary(pStream->GetDict()->Clone());
   m_pDict->SetAtInteger("Length", m_dwSize);
   m_pDict->SetAtName("Filter", "FlateDecode");
   m_pDict->RemoveAt("DecodeParms");
@@ -1227,7 +1228,7 @@ int32_t CPDF_Creator::WriteDirectObj(FX_DWORD objnum,
         return -1;
       }
       m_Offset += 2;
-      CPDF_Dictionary* p = (CPDF_Dictionary*)pObj;
+      const CPDF_Dictionary* p = pObj->AsDictionary();
       FX_BOOL bSignDict = IsSignatureDict(p);
       FX_POSITION pos = p->GetStartPos();
       while (pos) {
diff --git a/core/src/fpdfapi/fpdf_font/fpdf_font.cpp b/core/src/fpdfapi/fpdf_font/fpdf_font.cpp
index 7a57889a35..10ca3113e3 100644
--- a/core/src/fpdfapi/fpdf_font/fpdf_font.cpp
+++ b/core/src/fpdfapi/fpdf_font/fpdf_font.cpp
@@ -746,10 +746,11 @@ void CPDF_Font::LoadPDFEncoding(CPDF_Object* pEncoding,
     GetPredefinedEncoding(iBaseEncoding, bsEncoding);
     return;
   }
-  if (pEncoding->GetType() != PDFOBJ_DICTIONARY) {
+
+  CPDF_Dictionary* pDict = pEncoding->AsDictionary();
+  if (!pDict)
     return;
-  }
-  CPDF_Dictionary* pDict = (CPDF_Dictionary*)pEncoding;
+
   if (iBaseEncoding != PDFFONT_ENCODING_ADOBE_SYMBOL &&
       iBaseEncoding != PDFFONT_ENCODING_ZAPFDINGBATS) {
     CFX_ByteString bsEncoding = pDict->GetString(FX_BSTRC("BaseEncoding"));
@@ -782,6 +783,7 @@ void CPDF_Font::LoadPDFEncoding(CPDF_Object* pEncoding,
     }
   }
 }
+
 FX_BOOL CPDF_Font::IsStandardFont() const {
   if (m_FontType != PDFFONT_TYPE1)
     return FALSE;
diff --git a/core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp b/core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp
index 224c99bb69..d66a9efdaa 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_func.cpp
@@ -818,8 +818,8 @@ CPDF_Function* CPDF_Function::Load(CPDF_Object* pFuncObj) {
     type = ((CPDF_Stream*)pFuncObj)
                ->GetDict()
                ->GetInteger(FX_BSTRC("FunctionType"));
-  } else if (pFuncObj->GetType() == PDFOBJ_DICTIONARY) {
-    type = ((CPDF_Dictionary*)pFuncObj)->GetInteger(FX_BSTRC("FunctionType"));
+  } else if (CPDF_Dictionary* pDict = pFuncObj->AsDictionary()) {
+    type = pDict->GetInteger(FX_BSTRC("FunctionType"));
   } else {
     return NULL;
   }
@@ -853,7 +853,7 @@ FX_BOOL CPDF_Function::Init(CPDF_Object* pObj) {
   if (pObj->GetType() == PDFOBJ_STREAM) {
     pDict = ((CPDF_Stream*)pObj)->GetDict();
   } else {
-    pDict = (CPDF_Dictionary*)pObj;
+    pDict = pObj->AsDictionary();
   }
   CPDF_Array* pDomains = pDict->GetArray(FX_BSTRC("Domain"));
   if (pDomains == NULL) {
diff --git a/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp b/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp
index f11a2bb8d1..6d071f3ae0 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp
@@ -530,7 +530,7 @@ void CPDF_AllStates::ProcessExtGS(CPDF_Dictionary* pGS,
         break;
       }
       case FXBSTR_ID('S', 'M', 'a', 's'):
-        if (pObject && pObject->GetType() == PDFOBJ_DICTIONARY) {
+        if (ToDictionary(pObject)) {
           pGeneralState->m_pSoftMask = pObject;
           FXSYS_memcpy(pGeneralState->m_SMaskMatrix,
                        &pParser->GetCurStates()->m_CTM, sizeof(CPDF_Matrix));
@@ -599,20 +599,21 @@ CPDF_ContentMarkItem::CPDF_ContentMarkItem(const CPDF_ContentMarkItem& src) {
   m_MarkName = src.m_MarkName;
   m_ParamType = src.m_ParamType;
   if (m_ParamType == DirectDict) {
-    m_pParam = ((CPDF_Dictionary*)src.m_pParam)->Clone();
+    m_pParam = ToDictionary(static_cast<CPDF_Object*>(src.m_pParam))->Clone();
   } else {
     m_pParam = src.m_pParam;
   }
 }
 CPDF_ContentMarkItem::~CPDF_ContentMarkItem() {
   if (m_ParamType == DirectDict && m_pParam) {
-    ((CPDF_Dictionary*)m_pParam)->Release();
+    ToDictionary(static_cast<CPDF_Object*>(m_pParam))->Release();
   }
 }
 FX_BOOL CPDF_ContentMarkItem::HasMCID() const {
   if (m_pParam &&
       (m_ParamType == DirectDict || m_ParamType == PropertiesDict)) {
-    return ((CPDF_Dictionary*)m_pParam)->KeyExist(FX_BSTRC("MCID"));
+    return ToDictionary(static_cast<CPDF_Object*>(m_pParam))
+        ->KeyExist(FX_BSTRC("MCID"));
   }
   return FALSE;
 }
@@ -627,7 +628,8 @@ int CPDF_ContentMarkData::GetMCID() const {
     type = m_Marks[i].GetParamType();
     if (type == CPDF_ContentMarkItem::PropertiesDict ||
         type == CPDF_ContentMarkItem::DirectDict) {
-      CPDF_Dictionary* pDict = (CPDF_Dictionary*)m_Marks[i].GetParam();
+      CPDF_Dictionary* pDict =
+          ToDictionary(static_cast<CPDF_Object*>(m_Marks[i].GetParam()));
       if (pDict->KeyExist(FX_BSTRC("MCID"))) {
         return pDict->GetInteger(FX_BSTRC("MCID"));
       }
@@ -677,7 +679,7 @@ FX_BOOL CPDF_ContentMark::LookupMark(const CFX_ByteStringC& mark,
       pDict = NULL;
       if (item.GetParamType() == CPDF_ContentMarkItem::PropertiesDict ||
           item.GetParamType() == CPDF_ContentMarkItem::DirectDict) {
-        pDict = (CPDF_Dictionary*)item.GetParam();
+        pDict = ToDictionary(static_cast<CPDF_Object*>(item.GetParam()));
       }
       return TRUE;
     }
diff --git a/core/src/fpdfapi/fpdf_page/fpdf_page_image.cpp b/core/src/fpdfapi/fpdf_page/fpdf_page_image.cpp
index e9f70c14db..9cdf00e717 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_image.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_image.cpp
@@ -52,8 +52,7 @@ CPDF_Image* CPDF_Image::Clone() {
   pImage->LoadImageF((CPDF_Stream*)((CPDF_Object*)m_pStream)->Clone(),
                      m_bInline);
   if (m_bInline) {
-    CPDF_Dictionary* pInlineDict = (CPDF_Dictionary*)m_pInlineDict->Clone(TRUE);
-    pImage->SetInlineDict(pInlineDict);
+    pImage->SetInlineDict(ToDictionary(m_pInlineDict->Clone(TRUE)));
   }
   return pImage;
 }
@@ -86,7 +85,7 @@ FX_BOOL CPDF_Image::LoadImageF(CPDF_Stream* pStream, FX_BOOL bInline) {
   m_bInline = bInline;
   CPDF_Dictionary* pDict = pStream->GetDict();
   if (m_bInline) {
-    m_pInlineDict = (CPDF_Dictionary*)pDict->Clone();
+    m_pInlineDict = ToDictionary(pDict->Clone());
   }
   m_pOC = pDict->GetDict(FX_BSTRC("OC"));
   m_bIsMask = !pDict->KeyExist(FX_BSTRC("ColorSpace")) ||
diff --git a/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp b/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp
index 127fb93250..ffa5e62a07 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp
@@ -418,11 +418,9 @@ void CPDF_StreamContentParser::Handle_BeginMarkedContent_Dictionary() {
     }
     bDirect = FALSE;
   }
-  if (pProperty->GetType() != PDFOBJ_DICTIONARY) {
-    return;
+  if (CPDF_Dictionary* pDict = pProperty->AsDictionary()) {
+    m_CurContentMark.GetModify()->AddMark(tag, pDict, bDirect);
   }
-  m_CurContentMark.GetModify()->AddMark(tag, (CPDF_Dictionary*)pProperty,
-                                        bDirect);
 }
 void CPDF_StreamContentParser::Handle_BeginMarkedContent() {
   if (!m_Options.m_bMarkedContent) {
@@ -487,7 +485,7 @@ static CFX_ByteStringC _PDF_FindFullName(const _FX_BSTR* table,
 void _PDF_ReplaceAbbr(CPDF_Object* pObj) {
   switch (pObj->GetType()) {
     case PDFOBJ_DICTIONARY: {
-      CPDF_Dictionary* pDict = (CPDF_Dictionary*)pObj;
+      CPDF_Dictionary* pDict = pObj->AsDictionary();
       FX_POSITION pos = pDict->GetStartPos();
       while (pos) {
         CFX_ByteString key;
@@ -550,7 +548,7 @@ static CFX_ByteStringC _PDF_FindAbbrName(const _FX_BSTR* table,
 void _PDF_ReplaceFull(CPDF_Object* pObj) {
   switch (pObj->GetType()) {
     case PDFOBJ_DICTIONARY: {
-      CPDF_Dictionary* pDict = (CPDF_Dictionary*)pObj;
+      CPDF_Dictionary* pDict = pObj->AsDictionary();
       FX_POSITION pos = pDict->GetStartPos();
       while (pos) {
         CFX_ByteString key;
@@ -886,8 +884,8 @@ void CPDF_StreamContentParser::Handle_SetGray_Stroke() {
 void CPDF_StreamContentParser::Handle_SetExtendGraphState() {
   CFX_ByteString name = GetString(0);
   CPDF_Dictionary* pGS =
-      (CPDF_Dictionary*)FindResourceObj(FX_BSTRC("ExtGState"), name);
-  if (pGS == NULL || pGS->GetType() != PDFOBJ_DICTIONARY) {
+      ToDictionary(FindResourceObj(FX_BSTRC("ExtGState"), name));
+  if (!pGS) {
     m_bResourceMissing = TRUE;
     return;
   }
@@ -1217,11 +1215,12 @@ CPDF_Object* CPDF_StreamContentParser::FindResourceObj(
 }
 CPDF_Font* CPDF_StreamContentParser::FindFont(const CFX_ByteString& name) {
   CPDF_Dictionary* pFontDict =
-      (CPDF_Dictionary*)FindResourceObj(FX_BSTRC("Font"), name);
-  if (pFontDict == NULL || pFontDict->GetType() != PDFOBJ_DICTIONARY) {
+      ToDictionary(FindResourceObj(FX_BSTRC("Font"), name));
+  if (!pFontDict) {
     m_bResourceMissing = TRUE;
     return CPDF_Font::GetStockFont(m_pDocument, FX_BSTRC("Helvetica"));
   }
+
   CPDF_Font* pFont = m_pDocument->LoadFont(pFontDict);
   if (pFont && pFont->GetType3Font()) {
     pFont->GetType3Font()->SetPageResources(m_pResources);
@@ -1261,8 +1260,8 @@ CPDF_Pattern* CPDF_StreamContentParser::FindPattern(const CFX_ByteString& name,
                                                     FX_BOOL bShading) {
   CPDF_Object* pPattern = FindResourceObj(
       bShading ? FX_BSTRC("Shading") : FX_BSTRC("Pattern"), name);
-  if (pPattern == NULL || (pPattern->GetType() != PDFOBJ_DICTIONARY &&
-                           pPattern->GetType() != PDFOBJ_STREAM)) {
+  if (pPattern == NULL ||
+      (!pPattern->IsDictionary() && pPattern->GetType() != PDFOBJ_STREAM)) {
     m_bResourceMissing = TRUE;
     return NULL;
   }
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
index 2d6e9f3436..55c62e2878 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
@@ -283,7 +283,7 @@ ICodec_ScanlineDecoder* FPDFAPI_CreateFlateDecoder(
   int predictor = 0;
   int Colors = 0, BitsPerComponent = 0, Columns = 0;
   if (pParams) {
-    predictor = ((CPDF_Dictionary*)pParams)->GetInteger(FX_BSTRC("Predictor"));
+    predictor = pParams->GetInteger(FX_BSTRC("Predictor"));
     Colors = pParams->GetInteger(FX_BSTRC("Colors"), 1);
     BitsPerComponent = pParams->GetInteger(FX_BSTRC("BitsPerComponent"), 8);
     Columns = pParams->GetInteger(FX_BSTRC("Columns"), 1);
@@ -306,9 +306,8 @@ FX_DWORD FPDFAPI_FlateOrLZWDecode(FX_BOOL bLZW,
   FX_BOOL bEarlyChange = TRUE;
   int Colors = 0, BitsPerComponent = 0, Columns = 0;
   if (pParams) {
-    predictor = ((CPDF_Dictionary*)pParams)->GetInteger(FX_BSTRC("Predictor"));
-    bEarlyChange =
-        ((CPDF_Dictionary*)pParams)->GetInteger(FX_BSTRC("EarlyChange"), 1);
+    predictor = pParams->GetInteger(FX_BSTRC("Predictor"));
+    bEarlyChange = pParams->GetInteger(FX_BSTRC("EarlyChange"), 1);
     Colors = pParams->GetInteger(FX_BSTRC("Colors"), 1);
     BitsPerComponent = pParams->GetInteger(FX_BSTRC("BitsPerComponent"), 8);
     Columns = pParams->GetInteger(FX_BSTRC("Columns"), 1);
@@ -365,7 +364,9 @@ FX_BOOL PDF_DataDecode(const uint8_t* src_buf,
     int estimated_size =
         i == DecoderList.GetSize() - 1 ? last_estimated_size : 0;
     CFX_ByteString decoder = DecoderList[i];
-    CPDF_Dictionary* pParam = (CPDF_Dictionary*)ParamList[i];
+    // Use ToDictionary here because we can push NULL into the ParamList.
+    CPDF_Dictionary* pParam =
+        ToDictionary(static_cast<CPDF_Object*>(ParamList[i]));
     uint8_t* new_buf = NULL;
     FX_DWORD new_size = (FX_DWORD)-1;
     int offset = -1;
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp
index 2dff766187..29c1a007cf 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp
@@ -143,18 +143,15 @@ CPDF_Dictionary* CPDF_Document::GetPage(int iPage) {
     return nullptr;
 
   if (m_bLinearized && (iPage == (int)m_dwFirstPageNo)) {
-    CPDF_Object* pObj = GetIndirectObject(m_dwFirstPageObjNum);
-    if (pObj && pObj->GetType() == PDFOBJ_DICTIONARY) {
-      return static_cast<CPDF_Dictionary*>(pObj);
-    }
+    if (CPDF_Dictionary* pDict =
+            ToDictionary(GetIndirectObject(m_dwFirstPageObjNum)))
+      return pDict;
   }
 
   int objnum = m_PageList.GetAt(iPage);
   if (objnum) {
-    CPDF_Object* pObj = GetIndirectObject(objnum);
-    if (pObj && pObj->GetType() == PDFOBJ_DICTIONARY) {
-      return static_cast<CPDF_Dictionary*>(pObj);
-    }
+    if (CPDF_Dictionary* pDict = ToDictionary(GetIndirectObject(objnum)))
+      return pDict;
   }
 
   CPDF_Dictionary* pRoot = GetRoot();
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp
index 19359ad7cf..82bfbb56eb 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp
@@ -70,13 +70,11 @@ void CFDF_Document::ParseStream(IFX_FileRead* pFile, FX_BOOL bOwnFile) {
       if (word != FX_BSTRC("trailer")) {
         break;
       }
-      CPDF_Dictionary* pMainDict =
-          (CPDF_Dictionary*)parser.GetObject(this, 0, 0, 0);
-      if (pMainDict == NULL || pMainDict->GetType() != PDFOBJ_DICTIONARY) {
-        break;
+      if (CPDF_Dictionary* pMainDict =
+              ToDictionary(parser.GetObject(this, 0, 0, 0))) {
+        m_pRootDict = pMainDict->GetDict(FX_BSTRC("Root"));
+        pMainDict->Release();
       }
-      m_pRootDict = pMainDict->GetDict(FX_BSTRC("Root"));
-      pMainDict->Release();
       break;
     }
   }
@@ -142,18 +140,17 @@ void FPDF_FileSpec_SetWin32Path(CPDF_Object* pFileSpec,
   }
   if (pFileSpec->GetType() == PDFOBJ_STRING) {
     pFileSpec->SetString(CFX_ByteString::FromUnicode(result));
-  } else if (pFileSpec->GetType() == PDFOBJ_DICTIONARY) {
-    ((CPDF_Dictionary*)pFileSpec)
-        ->SetAtString(FX_BSTRC("F"), CFX_ByteString::FromUnicode(result));
-    ((CPDF_Dictionary*)pFileSpec)
-        ->SetAtString(FX_BSTRC("UF"), PDF_EncodeText(result));
-    ((CPDF_Dictionary*)pFileSpec)->RemoveAt(FX_BSTRC("FS"));
+  } else if (CPDF_Dictionary* pFileDict = pFileSpec->AsDictionary()) {
+    pFileDict->SetAtString(FX_BSTRC("F"), CFX_ByteString::FromUnicode(result));
+    pFileDict->SetAtString(FX_BSTRC("UF"), PDF_EncodeText(result));
+    pFileDict->RemoveAt(FX_BSTRC("FS"));
   }
 }
 CFX_WideString FPDF_FileSpec_GetWin32Path(const CPDF_Object* pFileSpec) {
   CFX_WideString wsFileName;
-  if (pFileSpec->GetType() == PDFOBJ_DICTIONARY) {
-    CPDF_Dictionary* pDict = (CPDF_Dictionary*)pFileSpec;
+  if (!pFileSpec) {
+    wsFileName = CFX_WideString();
+  } else if (const CPDF_Dictionary* pDict = pFileSpec->AsDictionary()) {
     wsFileName = pDict->GetUnicodeText(FX_BSTRC("UF"));
     if (wsFileName.IsEmpty()) {
       wsFileName = CFX_WideString::FromLocal(pDict->GetString(FX_BSTRC("F")));
@@ -164,9 +161,7 @@ CFX_WideString FPDF_FileSpec_GetWin32Path(const CPDF_Object* pFileSpec) {
     if (wsFileName.IsEmpty() && pDict->KeyExist(FX_BSTRC("DOS"))) {
       wsFileName = CFX_WideString::FromLocal(pDict->GetString(FX_BSTRC("DOS")));
     }
-  } else if (!pFileSpec)
-    wsFileName = CFX_WideString();
-  else {
+  } else {
     wsFileName = CFX_WideString::FromLocal(pFileSpec->GetString());
   }
   if (wsFileName[0] != '/') {
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
index e1e821c4c5..317f96d1dc 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
@@ -28,7 +28,7 @@ void CPDF_Object::Destroy() {
       delete (CPDF_Array*)this;
       break;
     case PDFOBJ_DICTIONARY:
-      delete (CPDF_Dictionary*)this;
+      delete this->AsDictionary();
       break;
     case PDFOBJ_STREAM:
       delete (CPDF_Stream*)this;
@@ -138,7 +138,9 @@ int CPDF_Object::GetInteger() const {
 CPDF_Dictionary* CPDF_Object::GetDict() const {
   switch (m_Type) {
     case PDFOBJ_DICTIONARY:
-      return (CPDF_Dictionary*)this;
+      // The method should be made non-const if we want to not be const.
+      // See bug #234.
+      return const_cast<CPDF_Dictionary*>(this->AsDictionary());
     case PDFOBJ_STREAM:
       return ((CPDF_Stream*)this)->GetDict();
     case PDFOBJ_REFERENCE: {
@@ -215,7 +217,7 @@ FX_BOOL CPDF_Object::IsIdentical(CPDF_Object* pOther) const {
     case PDFOBJ_ARRAY:
       return (((CPDF_Array*)this)->Identical((CPDF_Array*)pOther));
     case PDFOBJ_DICTIONARY:
-      return (((CPDF_Dictionary*)this)->Identical((CPDF_Dictionary*)pOther));
+      return this->AsDictionary()->Identical(pOther->AsDictionary());
     case PDFOBJ_NULL:
       return TRUE;
     case PDFOBJ_STREAM:
@@ -264,7 +266,7 @@ CPDF_Object* CPDF_Object::CloneInternal(FX_BOOL bDirect,
     }
     case PDFOBJ_DICTIONARY: {
       CPDF_Dictionary* pCopy = new CPDF_Dictionary();
-      CPDF_Dictionary* pThis = (CPDF_Dictionary*)this;
+      const CPDF_Dictionary* pThis = this->AsDictionary();
       FX_POSITION pos = pThis->m_Map.GetStartPosition();
       while (pos) {
         CFX_ByteString key;
@@ -283,9 +285,9 @@ CPDF_Object* CPDF_Object::CloneInternal(FX_BOOL bDirect,
       acc.LoadAllData(pThis, TRUE);
       FX_DWORD streamSize = acc.GetSize();
       CPDF_Dictionary* pDict = pThis->GetDict();
-      if (pDict)
-        pDict = (CPDF_Dictionary*)((CPDF_Object*)pDict)
-                    ->CloneInternal(bDirect, visited);
+      if (pDict) {
+        pDict = pDict->CloneInternal(bDirect, visited)->AsDictionary();
+      }
       return new CPDF_Stream(acc.DetachData(), streamSize, pDict);
     }
     case PDFOBJ_REFERENCE: {
@@ -335,6 +337,14 @@ void CPDF_Object::SetUnicodeText(const FX_WCHAR* pUnicodes, int len) {
   }
 }
 
+CPDF_Dictionary* CPDF_Object::AsDictionary() {
+  return IsDictionary() ? static_cast<CPDF_Dictionary*>(this) : nullptr;
+}
+
+const CPDF_Dictionary* CPDF_Object::AsDictionary() const {
+  return IsDictionary() ? static_cast<const CPDF_Dictionary*>(this) : nullptr;
+}
+
 CPDF_Number::CPDF_Number(int value)
     : CPDF_Object(PDFOBJ_NUMBER), m_bInteger(TRUE), m_Integer(value) {}
 
@@ -442,8 +452,8 @@ CPDF_Dictionary* CPDF_Array::GetDict(FX_DWORD i) const {
   if (!p) {
     return NULL;
   }
-  if (p->GetType() == PDFOBJ_DICTIONARY) {
-    return (CPDF_Dictionary*)p;
+  if (CPDF_Dictionary* pDict = p->AsDictionary()) {
+    return pDict;
   }
   if (p->GetType() == PDFOBJ_STREAM) {
     return ((CPDF_Stream*)p)->GetDict();
@@ -663,8 +673,8 @@ CPDF_Dictionary* CPDF_Dictionary::GetDict(const CFX_ByteStringC& key) const {
   if (!p) {
     return nullptr;
   }
-  if (p->GetType() == PDFOBJ_DICTIONARY) {
-    return (CPDF_Dictionary*)p;
+  if (CPDF_Dictionary* pDict = p->AsDictionary()) {
+    return pDict;
   }
   if (p->GetType() == PDFOBJ_STREAM) {
     return ((CPDF_Stream*)p)->GetDict();
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index a36850bc2e..b436ba16f5 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -277,8 +277,8 @@ FX_DWORD CPDF_Parser::SetEncryptHandler() {
   }
   CPDF_Object* pEncryptObj = m_pTrailer->GetElement(FX_BSTRC("Encrypt"));
   if (pEncryptObj) {
-    if (pEncryptObj->GetType() == PDFOBJ_DICTIONARY) {
-      SetEncryptDictionary((CPDF_Dictionary*)pEncryptObj);
+    if (CPDF_Dictionary* pEncryptDict = pEncryptObj->AsDictionary()) {
+      SetEncryptDictionary(pEncryptDict);
     } else if (pEncryptObj->GetType() == PDFOBJ_REFERENCE) {
       pEncryptObj = m_pDocument->GetIndirectObject(
           ((CPDF_Reference*)pEncryptObj)->GetRefObjNum());
@@ -804,7 +804,7 @@ FX_BOOL CPDF_Parser::RebuildCrossRef() {
                             if (m_pTrailer) {
                               m_pTrailer->Release();
                             }
-                            m_pTrailer = (CPDF_Dictionary*)pDict->Clone();
+                            m_pTrailer = ToDictionary(pDict->Clone());
                           }
                         }
                       }
@@ -857,15 +857,14 @@ FX_BOOL CPDF_Parser::RebuildCrossRef() {
               m_Syntax.RestorePos(pos + i - m_Syntax.m_HeaderOffset);
               CPDF_Object* pObj = m_Syntax.GetObject(m_pDocument, 0, 0, 0);
               if (pObj) {
-                if (pObj->GetType() != PDFOBJ_DICTIONARY &&
-                    pObj->GetType() != PDFOBJ_STREAM) {
+                if (!pObj->IsDictionary() && pObj->GetType() != PDFOBJ_STREAM) {
                   pObj->Release();
                 } else {
                   CPDF_Dictionary* pTrailer = NULL;
                   if (pObj->GetType() == PDFOBJ_STREAM) {
                     pTrailer = ((CPDF_Stream*)pObj)->GetDict();
                   } else {
-                    pTrailer = (CPDF_Dictionary*)pObj;
+                    pTrailer = pObj->AsDictionary();
                   }
                   if (pTrailer) {
                     if (m_pTrailer) {
@@ -890,7 +889,7 @@ FX_BOOL CPDF_Parser::RebuildCrossRef() {
                       }
                     } else {
                       if (pObj->GetType() == PDFOBJ_STREAM) {
-                        m_pTrailer = (CPDF_Dictionary*)pTrailer->Clone();
+                        m_pTrailer = ToDictionary(pTrailer->Clone());
                         pObj->Release();
                       } else {
                         m_pTrailer = pTrailer;
@@ -1034,13 +1033,13 @@ FX_BOOL CPDF_Parser::LoadCrossRefV5(FX_FILESIZE pos,
     return FALSE;
   }
   if (bMainXRef) {
-    m_pTrailer = (CPDF_Dictionary*)pStream->GetDict()->Clone();
+    m_pTrailer = ToDictionary(pStream->GetDict()->Clone());
     m_CrossRef.SetSize(size);
     if (m_V5Type.SetSize(size)) {
       FXSYS_memset(m_V5Type.GetData(), 0, size);
     }
   } else {
-    m_Trailers.Add((CPDF_Dictionary*)pStream->GetDict()->Clone());
+    m_Trailers.Add(ToDictionary(pStream->GetDict()->Clone()));
   }
   std::vector<std::pair<int32_t, int32_t> > arrIndex;
   CPDF_Array* pArray = pStream->GetDict()->GetArray(FX_BSTRC("Index"));
@@ -1490,9 +1489,9 @@ CPDF_Dictionary* CPDF_Parser::LoadTrailerV4() {
 
   nonstd::unique_ptr<CPDF_Object, ReleaseDeleter<CPDF_Object>> pObj(
       m_Syntax.GetObject(m_pDocument, 0, 0, 0));
-  if (!pObj || pObj->GetType() != PDFOBJ_DICTIONARY)
+  if (!ToDictionary(pObj.get()))
     return nullptr;
-  return static_cast<CPDF_Dictionary*>(pObj.release());
+  return pObj.release()->AsDictionary();
 }
 
 FX_DWORD CPDF_Parser::GetPermissions(FX_BOOL bCheckRevision) {
@@ -3490,7 +3489,7 @@ FX_BOOL CPDF_DataAvail::CheckPage(IFX_DownloadHints* pHints) {
         }
       }
     }
-    if (pObj->GetType() != PDFOBJ_DICTIONARY) {
+    if (!pObj->IsDictionary()) {
       pObj->Release();
       continue;
     }
@@ -4043,7 +4042,7 @@ FX_BOOL CPDF_DataAvail::CheckTrailer(IFX_DownloadHints* pHints) {
       pHints->AddSegment(m_Pos, iTrailerSize);
       return FALSE;
     }
-    if (pTrailer->GetType() != PDFOBJ_DICTIONARY)
+    if (!pTrailer->IsDictionary())
       return FALSE;
 
     CPDF_Dictionary* pTrailerDict = pTrailer->GetDict();
@@ -4158,7 +4157,7 @@ FX_BOOL CPDF_DataAvail::CheckUnkownPageNode(FX_DWORD dwPageNo,
     pPage->Release();
     return TRUE;
   }
-  if (pPage->GetType() != PDFOBJ_DICTIONARY) {
+  if (!pPage->IsDictionary()) {
     pPage->Release();
     m_docStatus = PDF_DATAAVAIL_ERROR;
     return FALSE;
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp
index 63454d2cb5..c34d8122f8 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp
@@ -403,7 +403,7 @@ CFX_ByteTextBuf& operator<<(CFX_ByteTextBuf& buf, const CPDF_Object* pObj) {
       break;
     }
     case PDFOBJ_DICTIONARY: {
-      CPDF_Dictionary* p = (CPDF_Dictionary*)pObj;
+      const CPDF_Dictionary* p = pObj->AsDictionary();
       buf << FX_BSTRC("<<");
       FX_POSITION pos = p->GetStartPos();
       while (pos) {
diff --git a/core/src/fpdfapi/fpdf_render/fpdf_render.cpp b/core/src/fpdfapi/fpdf_render/fpdf_render.cpp
index 5b2158f17d..cf37f0c6f4 100644
--- a/core/src/fpdfapi/fpdf_render/fpdf_render.cpp
+++ b/core/src/fpdfapi/fpdf_render/fpdf_render.cpp
@@ -738,7 +738,7 @@ FX_BOOL CPDF_RenderStatus::ProcessTransparency(
     return TRUE;
   }
   CPDF_Dictionary* pSMaskDict =
-      pGeneralState ? (CPDF_Dictionary*)pGeneralState->m_pSoftMask : NULL;
+      pGeneralState ? pGeneralState->m_pSoftMask->AsDictionary() : NULL;
   if (pSMaskDict) {
     if (pPageObj->m_Type == PDFPAGE_IMAGE &&
         ((CPDF_ImageObject*)pPageObj)
@@ -1437,7 +1437,8 @@ FX_BOOL IPDF_OCContext::CheckObjectVisible(const CPDF_PageObject* pObj) {
     CPDF_ContentMarkItem& item = pData->GetItem(i);
     if (item.GetName() == FX_BSTRC("OC") &&
         item.GetParamType() == CPDF_ContentMarkItem::PropertiesDict) {
-      CPDF_Dictionary* pOCG = (CPDF_Dictionary*)item.GetParam();
+      CPDF_Dictionary* pOCG =
+          ToDictionary(static_cast<CPDF_Object*>(item.GetParam()));
       if (!CheckOCGVisible(pOCG)) {
         return FALSE;
       }
diff --git a/core/src/fpdfapi/fpdf_render/fpdf_render_image.cpp b/core/src/fpdfapi/fpdf_render/fpdf_render_image.cpp
index 222f58c088..e4afdd80c2 100644
--- a/core/src/fpdfapi/fpdf_render/fpdf_render_image.cpp
+++ b/core/src/fpdfapi/fpdf_render/fpdf_render_image.cpp
@@ -1056,8 +1056,8 @@ CFX_DIBitmap* CPDF_RenderStatus::LoadSMask(CPDF_Dictionary* pSMaskDict,
   }
   CPDF_Function* pFunc = NULL;
   CPDF_Object* pFuncObj = pSMaskDict->GetElementValue(FX_BSTRC("TR"));
-  if (pFuncObj && (pFuncObj->GetType() == PDFOBJ_DICTIONARY ||
-                   pFuncObj->GetType() == PDFOBJ_STREAM)) {
+  if (pFuncObj &&
+      (pFuncObj->IsDictionary() || pFuncObj->GetType() == PDFOBJ_STREAM)) {
     pFunc = CPDF_Function::Load(pFuncObj);
   }
   CFX_AffineMatrix matrix = *pMatrix;