Introduce "underlying types" to abstract XFA differences.

fpdfsdk/src/fpdfview.cpp

 // Copyright 2014 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 "public/fpdfview.h"
 
 #include "../include/fpdfxfa/fpdfxfa_app.h"
 #include "../include/fpdfxfa/fpdfxfa_doc.h"
 #include "../include/fpdfxfa/fpdfxfa_page.h"
 #include "../include/fpdfxfa/fpdfxfa_util.h"
 #include "core/include/fpdfapi/fpdf_module.h"
 #include "core/include/fxcodec/fx_codec.h"
 #include "core/include/fxcrt/fx_safe_types.h"
 #include "fpdfsdk/include/fsdk_define.h"
 #include "fpdfsdk/include/fsdk_mgr.h"
 #include "fpdfsdk/include/fsdk_rendercontext.h"
 #include "fpdfsdk/include/javascript/IJavaScript.h"
 #include "public/fpdf_ext.h"
 #include "public/fpdf_formfill.h"
 #include "public/fpdf_progressive.h"
 #include "third_party/base/nonstd_unique_ptr.h"
 #include "third_party/base/numerics/safe_conversions_impl.h"
 
+UnderlyingDocumentType* UnderlyingFromFPDFDocument(FPDF_DOCUMENT doc) {
+  return static_cast<UnderlyingDocumentType*>(doc);
+}
+
+FPDF_DOCUMENT FPDFDocumentFromUnderlying(UnderlyingDocumentType* doc) {
+  return static_cast<FPDF_DOCUMENT>(doc);
+}
+
+UnderlyingPageType* UnderlyingFromFPDFPage(FPDF_PAGE page) {
+  return static_cast<UnderlyingPageType*>(page);
+}
+
 CPDF_Document* CPDFDocumentFromFPDFDocument(FPDF_DOCUMENT doc) {
-  return doc ? static_cast<CPDFXFA_Document*>(doc)->GetPDFDoc() : nullptr;
+  return doc ? UnderlyingFromFPDFDocument(doc)->GetPDFDoc() : nullptr;
 }
 
 FPDF_DOCUMENT FPDFDocumentFromCPDFDocument(CPDF_Document* doc) {
-  return doc ? new CPDFXFA_Document(doc, CPDFXFA_App::GetInstance()) : nullptr;
+  return doc ? FPDFDocumentFromUnderlying(
+                   new CPDFXFA_Document(doc, CPDFXFA_App::GetInstance()))
+             : nullptr;
 }
 
 CPDF_Page* CPDFPageFromFPDFPage(FPDF_PAGE page) {
-  return page ? static_cast<CPDFXFA_Page*>(page)->GetPDFPage() : nullptr;
+  return page ? UnderlyingFromFPDFPage(page)->GetPDFPage() : nullptr;
 }
 
 CFPDF_FileStream::CFPDF_FileStream(FPDF_FILEHANDLER* pFS) {
   m_pFS = pFS;
   m_nCurPos = 0;
 }
 
 IFX_FileStream* CFPDF_FileStream::Retain() {
   return this;
 }
@@ skipping 1010 matching lines @@
   if (!buffer) {
     *buflen = len;
   } else if (*buflen >= len) {
     memcpy(buffer, utf16Name.c_str(), len);
     *buflen = len;
   } else {
     *buflen = -1;
   }
   return (FPDF_DEST)pDestObj;
 }