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

core/fxcodec/codec/fx_codec_tiff.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 "core/fxcodec/codec/codec_int.h"
 #include "core/fxcodec/include/fx_codec.h"
 #include "core/fxge/include/fx_dib.h"
 
@@ skipping 72 matching lines @@
   return op1 > std::numeric_limits<tmsize_t>::max() / op2;
 }
 
 TIFFErrorHandler _TIFFwarningHandler = nullptr;
 TIFFErrorHandler _TIFFerrorHandler = nullptr;
 
 namespace {
 
 tsize_t tiff_read(thandle_t context, tdata_t buf, tsize_t length) {
   CCodec_TiffContext* pTiffContext = (CCodec_TiffContext*)context;
-  if (!pTiffContext->io_in()->ReadBlock(buf, pTiffContext->offset(), length))
+  size_t readSize =
+      pTiffContext->io_in()->ReadBlock(buf, pTiffContext->offset(), length);
+  if (readSize != static_cast<size_t>(length) &&
+      !pTiffContext->io_in()->IsEOF())
     return 0;
 
-  pTiffContext->increment_offset(length);
-  return length;
+  pTiffContext->increment_offset(readSize);
+  return readSize;
 }
 
 tsize_t tiff_write(thandle_t context, tdata_t buf, tsize_t length) {
   ASSERT(false);
   return 0;
 }
 
 toff_t tiff_seek(thandle_t context, toff_t offset, int whence) {
   CCodec_TiffContext* pTiffContext = (CCodec_TiffContext*)context;
   switch (whence) {
@@ skipping 347 matching lines @@
 }
 
 bool CCodec_TiffModule::Decode(CCodec_TiffContext* ctx,
                                class CFX_DIBitmap* pDIBitmap) {
   return ctx->Decode(pDIBitmap);
 }
 
 void CCodec_TiffModule::DestroyDecoder(CCodec_TiffContext* ctx) {
   delete ctx;
 }