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

core/fpdfapi/parser/cpdf_parser_unittest.cpp

Index: core/fpdfapi/parser/cpdf_parser_unittest.cpp
diff --git a/core/fpdfapi/parser/cpdf_parser_unittest.cpp b/core/fpdfapi/parser/cpdf_parser_unittest.cpp
index 7148c54f30d55649cad324ff4a382df7b0a826e4..8aeb9813164397eae21b122216d60662018b24b1 100644
--- a/core/fpdfapi/parser/cpdf_parser_unittest.cpp
+++ b/core/fpdfapi/parser/cpdf_parser_unittest.cpp
@@ -16,25 +16,30 @@
 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.