in the attempt to fix 627393, changed IFX_FileRead's readBlock to return the length it reads

fpdfsdk/fpdfview.cpp

Index: fpdfsdk/fpdfview.cpp
diff --git a/fpdfsdk/fpdfview.cpp b/fpdfsdk/fpdfview.cpp
index 334c14cd45f9d1ed834d80b72bc3595c0de775cd..458153a7def2f2a5c4fa06276e819a486ef68bdf 100644
--- a/fpdfsdk/fpdfview.cpp
+++ b/fpdfsdk/fpdfview.cpp
@@ -120,18 +120,18 @@ FX_FILESIZE CFPDF_FileStream::GetPosition() {
   return m_nCurPos;
 }
 
-bool CFPDF_FileStream::ReadBlock(void* buffer,
-                                 FX_FILESIZE offset,
-                                 size_t size) {
+size_t CFPDF_FileStream::ReadBlock(void* buffer,
+                                   FX_FILESIZE offset,
+                                   size_t size) {
   if (!buffer || !size || !m_pFS->ReadBlock)
-    return false;
+    return 0;
 
   if (m_pFS->ReadBlock(m_pFS->clientData, (FPDF_DWORD)offset, buffer,
                        (FPDF_DWORD)size) == 0) {
     m_nCurPos = offset + size;
-    return true;
+    return size;
   }
-  return false;
+  return 0;
 }
 
 size_t CFPDF_FileStream::ReadBlock(void* buffer, size_t size) {
@@ -176,7 +176,7 @@ bool CFPDF_FileStream::Flush() {
 #endif  // PDF_ENABLE_XFA
 
 CPDF_CustomAccess::CPDF_CustomAccess(FPDF_FILEACCESS* pFileAccess)
-    : m_FileAccess(*pFileAccess) {}
+    : m_FileAccess(*pFileAccess), m_nCurPos(0) {}
 
 FX_FILESIZE CPDF_CustomAccess::GetSize() {
   return m_FileAccess.m_FileLen;
@@ -186,20 +186,26 @@ void CPDF_CustomAccess::Release() {
   delete this;
 }
 
-bool CPDF_CustomAccess::ReadBlock(void* buffer,
-                                  FX_FILESIZE offset,
-                                  size_t size) {
-  if (offset < 0)
-    return false;
+bool CPDF_CustomAccess::IsEOF() {
+  return m_nCurPos >= static_cast<FX_FILESIZE>(m_FileAccess.m_FileLen);
+}
 
-  FX_SAFE_FILESIZE newPos = pdfium::base::checked_cast<FX_FILESIZE>(size);
+size_t CPDF_CustomAccess::ReadBlock(void* buffer,
+                                    FX_FILESIZE offset,
+                                    size_t size) {
+  if (offset < 0) {
+    return 0;
+  }
+  FX_SAFE_FILESIZE newPos =
+      pdfium::base::checked_cast<FX_FILESIZE, size_t>(size);
   newPos += offset;
   if (!newPos.IsValid() ||
       newPos.ValueOrDie() > static_cast<FX_FILESIZE>(m_FileAccess.m_FileLen)) {
-    return false;
+    return 0;
   }
-  return !!m_FileAccess.m_GetBlock(m_FileAccess.m_Param, offset,
-                                   reinterpret_cast<uint8_t*>(buffer), size);
+  m_FileAccess.m_GetBlock(m_FileAccess.m_Param, offset, (uint8_t*)buffer, size);
+  m_nCurPos = newPos.ValueOrDie();
+  return size;
 }
 
 // 0 bit: FPDF_POLICY_MACHINETIME_ACCESS
@@ -379,21 +385,24 @@ DLLEXPORT FPDF_BOOL STDCALL FPDF_LoadXFA(FPDF_DOCUMENT document) {
 
 class CMemFile final : public IFX_SeekableReadStream {
  public:
-  CMemFile(uint8_t* pBuf, FX_FILESIZE size) : m_pBuf(pBuf), m_size(size) {}
+  CMemFile(uint8_t* pBuf, FX_FILESIZE size)
+      : m_pBuf(pBuf), m_size(size), m_nCurPos(0) {}
 
   void Release() override { delete this; }
+  bool IsEOF() override { return m_nCurPos >= m_size; }
   FX_FILESIZE GetSize() override { return m_size; }
-  bool ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override {
+  size_t ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override {
     if (offset < 0) {
-      return false;
+      return 0;
     }
     FX_SAFE_FILESIZE newPos = pdfium::base::checked_cast<FX_FILESIZE>(size);
     newPos += offset;
     if (!newPos.IsValid() || newPos.ValueOrDie() > m_size) {
-      return false;
+      return 0;
     }
     FXSYS_memcpy(buffer, m_pBuf + offset, size);
-    return true;
+    m_nCurPos = offset + size;
+    return size;
   }
 
  private:
@@ -401,6 +410,7 @@ class CMemFile final : public IFX_SeekableReadStream {
 
   uint8_t* const m_pBuf;
   const FX_FILESIZE m_size;
+  FX_FILESIZE m_nCurPos;
 };
 
 DLLEXPORT FPDF_DOCUMENT STDCALL FPDF_LoadMemDocument(const void* data_buf,