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

core/fpdfapi/parser/cpdf_parser_unittest.cpp

 // Copyright 2015 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.
 
 #include <limits>
 #include <string>
 
 #include "core/fpdfapi/parser/cpdf_parser.h"
 #include "core/fpdfapi/parser/cpdf_syntax_parser.h"
 #include "core/fxcrt/fx_ext.h"
 #include "core/fxcrt/fx_stream.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/utils/path_service.h"
 
 // Provide a way to read test data from a buffer instead of a file.
 class CFX_TestBufferRead : public IFX_SeekableReadStream {
  public:
   CFX_TestBufferRead(const unsigned char* buffer_in, size_t buf_size)
-      : buffer_(buffer_in), total_size_(buf_size) {}
+      : buffer_(buffer_in), total_size_(buf_size), current_pos_(0) {}
 
   // IFX_Stream
   void Release() override { delete this; }
 
   // IFX_SeekableReadStream
-  bool ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override {
-    if (offset < 0 || offset + size > total_size_)
-      return false;
+  bool IsEOF() override { return current_pos_ >= total_size_; }
 
+  size_t ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override {
+    if (offset < 0 || size > total_size_ ||
+        offset > total_size_ - pdfium::base::checked_cast<FX_FILESIZE>(size)) {
+      return 0;
+    }
     memcpy(buffer, buffer_ + offset, size);
-    return true;
+    current_pos_ = offset + pdfium::base::checked_cast<FX_FILESIZE>(size);
+    return size;
   }
 
-  FX_FILESIZE GetSize() override { return (FX_FILESIZE)total_size_; };
+  FX_FILESIZE GetSize() override { return total_size_; };
 
  protected:
   const unsigned char* buffer_;
-  size_t total_size_;
+  FX_FILESIZE total_size_;
+  FX_FILESIZE current_pos_;
 };
 
 // A wrapper class to help test member functions of CPDF_Parser.
 class CPDF_TestParser : public CPDF_Parser {
  public:
   CPDF_TestParser() {}
   ~CPDF_TestParser() {}
 
   // Setup reading from a file and initial states.
   bool InitTestFromFile(const FX_CHAR* path) {
@@ skipping 145 matching lines @@
 
     ASSERT_TRUE(parser.LoadCrossRefV4(0, 0, false));
     const FX_FILESIZE offsets[] = {0, 23, 0, 0, 0, 45, 179};
     const uint8_t types[] = {0, 1, 0, 0, 0, 1, 1};
     for (size_t i = 0; i < FX_ArraySize(offsets); ++i) {
       EXPECT_EQ(offsets[i], parser.m_ObjectInfo[i].pos);
       EXPECT_EQ(types[i], parser.m_ObjectInfo[i].type);
     }
   }
 }