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

core/fxcrt/fx_extension.cpp

Index: core/fxcrt/fx_extension.cpp
diff --git a/core/fxcrt/fx_extension.cpp b/core/fxcrt/fx_extension.cpp
index 0a378f32e5ffaf73184047de79539314064f81f9..4768b1b2f946ac868712127e4c738cd43322a640 100644
--- a/core/fxcrt/fx_extension.cpp
+++ b/core/fxcrt/fx_extension.cpp
@@ -104,31 +104,32 @@ FX_FILESIZE CFX_MemoryStream::GetSize() {
 }
 
 bool CFX_MemoryStream::IsEOF() {
-  return m_nCurPos >= (size_t)GetSize();
+  return m_nCurPos >= pdfium::base::checked_cast<size_t>(GetSize());
 }
 
 FX_FILESIZE CFX_MemoryStream::GetPosition() {
   return (FX_FILESIZE)m_nCurPos;
 }
 
-bool CFX_MemoryStream::ReadBlock(void* buffer,
-                                 FX_FILESIZE offset,
-                                 size_t size) {
+size_t CFX_MemoryStream::ReadBlock(void* buffer,
+                                   FX_FILESIZE offset,
+                                   size_t size) {
   if (!buffer || !size)
-    return false;
+    return 0;
 
   FX_SAFE_SIZE_T newPos = size;
   newPos += offset;
   if (!newPos.IsValid() || newPos.ValueOrDefault(0) == 0 ||
       newPos.ValueOrDie() > m_nCurSize) {
-    return false;
+    return 0;
   }
 
   m_nCurPos = newPos.ValueOrDie();
   if (m_dwFlags & FX_MEMSTREAM_Consecutive) {
     FXSYS_memcpy(buffer, m_Blocks[0] + (size_t)offset, size);
-    return true;
+    return size;
   }
+  size_t readSize = size;
   size_t nStartBlock = (size_t)offset / m_nGrowSize;
   offset -= (FX_FILESIZE)(nStartBlock * m_nGrowSize);
   while (size) {
@@ -142,7 +143,7 @@ bool CFX_MemoryStream::ReadBlock(void* buffer,
     nStartBlock++;
     offset = 0;
   }
-  return true;
+  return readSize;
 }
 
 size_t CFX_MemoryStream::ReadBlock(void* buffer, size_t size) {
@@ -150,7 +151,7 @@ size_t CFX_MemoryStream::ReadBlock(void* buffer, size_t size) {
     return 0;
   }
   size_t nRead = std::min(size, m_nCurSize - m_nCurPos);
-  if (!ReadBlock(buffer, (int32_t)m_nCurPos, nRead)) {
+  if (ReadBlock(buffer, (int32_t)m_nCurPos, nRead) != nRead && !IsEOF()) {
     return 0;
   }
   return nRead;
@@ -305,10 +306,10 @@ FX_FILESIZE CFX_CRTFileStream::GetPosition() {
   return m_pFile->GetPosition();
 }
 
-bool CFX_CRTFileStream::ReadBlock(void* buffer,
-                                  FX_FILESIZE offset,
-                                  size_t size) {
-  return m_pFile->ReadPos(buffer, size, offset) > 0;
+size_t CFX_CRTFileStream::ReadBlock(void* buffer,
+                                    FX_FILESIZE offset,
+                                    size_t size) {
+  return m_pFile->ReadPos(buffer, size, offset);
 }
 
 size_t CFX_CRTFileStream::ReadBlock(void* buffer, size_t size) {