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

xfa/fgas/crt/fgas_stream.cpp

Index: xfa/fgas/crt/fgas_stream.cpp
diff --git a/xfa/fgas/crt/fgas_stream.cpp b/xfa/fgas/crt/fgas_stream.cpp
index c3850c00bbe36d7711e113d72c28879aba9d542b..6e3bfa2af94f64543b1593d63c2115a32c4932e5 100644
--- a/xfa/fgas/crt/fgas_stream.cpp
+++ b/xfa/fgas/crt/fgas_stream.cpp
@@ -282,12 +282,14 @@ class CFGAS_FileRead : public IFX_SeekableReadStream {
 
   // IFX_SeekableReadStream
   void Release() override;
+  bool IsEOF() override;
   FX_FILESIZE GetSize() override;
-  bool ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override;
+  size_t ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override;
 
  protected:
   bool m_bReleaseStream;
   IFX_Stream* m_pStream;
+  FX_FILESIZE m_nCurPos;
 };
 
 int32_t FileLength(FXSYS_FILE* file) {
@@ -576,9 +578,11 @@ int32_t CFX_FileReadStreamImp::ReadData(uint8_t* pBuffer, int32_t iBufferSize) {
   if (iBufferSize > m_iLength - m_iPosition) {
     iBufferSize = m_iLength - m_iPosition;
   }
-  if (m_pFileRead->ReadBlock(pBuffer, m_iPosition, iBufferSize)) {
-    m_iPosition += iBufferSize;
-    return iBufferSize;
+  int32_t readSize = pdfium::base::checked_cast<int32_t>(
+      m_pFileRead->ReadBlock(pBuffer, m_iPosition, iBufferSize));
+  if (readSize == iBufferSize || m_pFileRead->IsEOF()) {
+    m_iPosition += readSize;
+    return readSize;
   }
   return 0;
 }
@@ -1459,7 +1463,7 @@ IFX_SeekableReadStream* FX_CreateFileRead(IFX_Stream* pBaseStream,
 }
 
 CFGAS_FileRead::CFGAS_FileRead(IFX_Stream* pStream, bool bReleaseStream)
-    : m_bReleaseStream(bReleaseStream), m_pStream(pStream) {
+    : m_bReleaseStream(bReleaseStream), m_pStream(pStream), m_nCurPos(0) {
   ASSERT(m_pStream);
 }
 CFGAS_FileRead::~CFGAS_FileRead() {
@@ -1467,14 +1471,20 @@ CFGAS_FileRead::~CFGAS_FileRead() {
     m_pStream->Release();
   }
 }
+bool CFGAS_FileRead::IsEOF() {
+  return m_nCurPos >= (FX_FILESIZE)m_pStream->GetLength();
+}
 FX_FILESIZE CFGAS_FileRead::GetSize() {
   return (FX_FILESIZE)m_pStream->GetLength();
 }
 
-bool CFGAS_FileRead::ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) {
+size_t CFGAS_FileRead::ReadBlock(void* buffer,
+                                 FX_FILESIZE offset,
+                                 size_t size) {
   m_pStream->Seek(FX_STREAMSEEK_Begin, (int32_t)offset);
   int32_t iLen = m_pStream->ReadData((uint8_t*)buffer, (int32_t)size);
-  return iLen == (int32_t)size;
+  m_nCurPos = offset + pdfium::base::checked_cast<size_t>(iLen);
+  return pdfium::base::checked_cast<size_t>(iLen);
 }
 
 void CFGAS_FileRead::Release() {