Use strict types in FPDF API, try #3

Rather than messing with actual inheritence, add type-checking wrappers
and just blatantly cast to incomplete types.  Along the way, this points
out places where we would downcast without checking, which I fix.

Change-Id: Ieb303eb46ad8522dfe082454f1f10f247ffd52d5
Reviewed-on: https://pdfium-review.googlesource.com/32030
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/fpdfsdk/fpdf_attachment.cpp b/fpdfsdk/fpdf_attachment.cpp
index 25957174bc..f2ed684e40 100644
--- a/fpdfsdk/fpdf_attachment.cpp
+++ b/fpdfsdk/fpdf_attachment.cpp
@@ -26,10 +26,6 @@ namespace {
 
 constexpr char kChecksumKey[] = "CheckSum";
 
-CPDF_Object* CPDFObjectFromFPDFAttachment(FPDF_ATTACHMENT attachment) {
-  return static_cast<CPDF_Object*>(attachment);
-}
-
 ByteString CFXByteStringHexDecode(const ByteString& bsHex) {
   uint8_t* result = nullptr;
   uint32_t size = 0;
@@ -101,7 +97,7 @@ FPDFDoc_AddAttachment(FPDF_DOCUMENT document, FPDF_WIDESTRING name) {
     return nullptr;
   }
 
-  return pFile;
+  return FPDFAttachmentFromCPDFObject(pFile);
 }
 
 FPDF_EXPORT FPDF_ATTACHMENT FPDF_CALLCONV
@@ -115,7 +111,8 @@ FPDFDoc_GetAttachment(FPDF_DOCUMENT document, int index) {
     return nullptr;
 
   WideString csName;
-  return nameTree.LookupValueAndName(index, &csName);
+  return FPDFAttachmentFromCPDFObject(
+      nameTree.LookupValueAndName(index, &csName));
 }
 
 FPDF_EXPORT FPDF_BOOL FPDF_CALLCONV