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

xfa/fgas/crt/fgas_stream.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 "xfa/fgas/crt/fgas_stream.h"
 
 #if _FX_OS_ == _FX_WIN32_DESKTOP_ || _FX_OS_ == _FX_WIN32_MOBILE_ || \
     _FX_OS_ == _FX_WIN64_
@@ skipping 264 matching lines @@
   void InitStream();
 };
 
 class CFGAS_FileRead : public IFX_SeekableReadStream {
  public:
   CFGAS_FileRead(IFX_Stream* pStream, bool bReleaseStream);
   ~CFGAS_FileRead() override;
 
   // 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) {
   ASSERT(file);
 #if _FX_OS_ == _FX_WIN32_DESKTOP_ || _FX_OS_ == _FX_WIN64_
   return _filelength(_fileno(file));
 #else
   int32_t iPos = FXSYS_ftell(file);
   FXSYS_fseek(file, 0, FXSYS_SEEK_END);
   int32_t iLen = FXSYS_ftell(file);
@@ skipping 268 matching lines @@
 }
 bool CFX_FileReadStreamImp::IsEOF() const {
   return m_iPosition >= m_iLength;
 }
 int32_t CFX_FileReadStreamImp::ReadData(uint8_t* pBuffer, int32_t iBufferSize) {
   ASSERT(m_pFileRead);
   ASSERT(pBuffer && iBufferSize > 0);
   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;
 }
 int32_t CFX_FileReadStreamImp::ReadString(FX_WCHAR* pStr,
                                           int32_t iMaxLength,
                                           bool& bEOS) {
   ASSERT(m_pFileRead);
   ASSERT(pStr && iMaxLength > 0);
   iMaxLength = ReadData((uint8_t*)pStr, iMaxLength * 2) / 2;
   if (iMaxLength <= 0) {
@@ skipping 860 matching lines @@
   return pShared;
 }
 
 IFX_SeekableReadStream* FX_CreateFileRead(IFX_Stream* pBaseStream,
                                           bool bReleaseStream) {
   ASSERT(pBaseStream);
   return new CFGAS_FileRead(pBaseStream, bReleaseStream);
 }
 
 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() {
   if (m_bReleaseStream) {
     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() {
   delete this;
 }