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

xfa/fxfa/app/xfa_ffapp.cpp

Index: xfa/fxfa/app/xfa_ffapp.cpp
diff --git a/xfa/fxfa/app/xfa_ffapp.cpp b/xfa/fxfa/app/xfa_ffapp.cpp
index c5dcad848cd7ca9752401c053c2669ec4fe52287..0910326f27e6d4d97e747fed725c0bfc48b35bd1 100644
--- a/xfa/fxfa/app/xfa_ffapp.cpp
+++ b/xfa/fxfa/app/xfa_ffapp.cpp
@@ -20,25 +20,31 @@
 #include "xfa/fxfa/xfa_fontmgr.h"
 
 CXFA_FileRead::CXFA_FileRead(const std::vector<CPDF_Stream*>& streams) {
+  m_FileSize = 0;
+  m_nCurPos = 0;
   for (CPDF_Stream* pStream : streams) {
     CPDF_StreamAcc& acc = m_Data.Add();
     acc.LoadAllData(pStream);
+    m_FileSize += pdfium::base::checked_cast<FX_FILESIZE>(acc.GetSize());
   }
 }
 
 CXFA_FileRead::~CXFA_FileRead() {}
 
+bool CXFA_FileRead::IsEOF() {
+  return m_nCurPos >= GetSize();
+}
+
 FX_FILESIZE CXFA_FileRead::GetSize() {
-  uint32_t dwSize = 0;
-  int32_t iCount = m_Data.GetSize();
-  for (int32_t i = 0; i < iCount; i++) {
-    CPDF_StreamAcc& acc = m_Data[i];
-    dwSize += acc.GetSize();
-  }
-  return dwSize;
+  return m_FileSize;
 }
 
-bool CXFA_FileRead::ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) {
+size_t CXFA_FileRead::ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) {
+  if (offset < 0 || GetSize() < offset) {
+    return 0;
+  }
+  size_t readSize =
+      std::min(pdfium::base::checked_cast<size_t>(GetSize() - offset), size);
   int32_t iCount = m_Data.GetSize();
   int32_t index = 0;
   while (index < iCount) {
@@ -57,13 +63,13 @@ bool CXFA_FileRead::ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) {
     FXSYS_memcpy(buffer, acc.GetData() + offset, dwRead);
     size -= dwRead;
     if (size == 0) {
-      return true;
+      break;
     }
     buffer = (uint8_t*)buffer + dwRead;
     offset = 0;
     index++;
   }
-  return false;
+  return readSize;
 }
 
 void CXFA_FileRead::Release() {