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

core/fpdfapi/parser/cpdf_parser.cpp

 // Copyright 2016 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/fpdfapi/parser/cpdf_parser.h"
 
 #include <vector>
 
@@ skipping 580 matching lines @@
   FX_FILESIZE start_pos1 = 0;
   FX_FILESIZE last_obj = -1;
   FX_FILESIZE last_xref = -1;
   FX_FILESIZE last_trailer = -1;
 
   while (pos < m_pSyntax->m_FileLen) {
     const FX_FILESIZE saved_pos = pos;
     bool bOverFlow = false;
     uint32_t size =
         std::min((uint32_t)(m_pSyntax->m_FileLen - pos), kBufferSize);
-    if (!m_pSyntax->m_pFileAccess->ReadBlock(buffer.data(), pos, size))
+    uint32_t readSize =
+        m_pSyntax->m_pFileAccess->ReadBlock(buffer.data(), pos, size);
+    if (readSize != size && !m_pSyntax->m_pFileAccess->IsEOF())
       break;
-
+    size = readSize;
     for (uint32_t i = 0; i < size; i++) {
       uint8_t byte = buffer[i];
       switch (state) {
         case ParserState::kDefault:
           if (PDFCharIsWhitespace(byte)) {
             state = ParserState::kWhitespace;
           } else if (std::isdigit(byte)) {
             --i;
             state = ParserState::kWhitespace;
           } else if (byte == '%') {
@@ skipping 958 matching lines @@
   if (!LoadLinearizedAllCrossRefV4(m_LastXRefOffset, m_dwXrefStartObjNum) &&
       !LoadLinearizedAllCrossRefV5(m_LastXRefOffset)) {
     m_LastXRefOffset = 0;
     m_pSyntax->m_MetadataObjnum = dwSaveMetadataObjnum;
     return FORMAT_ERROR;
   }
 
   m_pSyntax->m_MetadataObjnum = dwSaveMetadataObjnum;
   return SUCCESS;
 }