Roll forward to cl/314549634

Change-Id: I4d1e7eacd5fa4078a094571ad6d5f51e422535ff

cpp/platform/impl/shared/file_impl.h

@@ -0,0 +1,46 @@
+#ifndef PLATFORM_IMPL_SHARED_FILE_IMPL_H_
+#define PLATFORM_IMPL_SHARED_FILE_IMPL_H_
+
+#include <cstdint>
+#include <fstream>
+
+#include "platform/api/input_file.h"
+#include "platform/api/output_file.h"
+#include "platform/exception.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+
+class InputFileImpl final : public InputFile {
+ public:
+  InputFileImpl(const std::string& path, std::int64_t size);
+  ~InputFileImpl() override {}
+
+  ExceptionOr<ConstPtr<ByteArray>> read(std::int64_t size) override;
+  std::string getFilePath() const override;
+  std::int64_t getTotalSize() const override;
+  void close() override;
+
+ private:
+  std::ifstream file_;
+  const std::string path_;
+  const std::int64_t total_size_;
+};
+
+class OutputFileImpl final : public OutputFile {
+ public:
+  explicit OutputFileImpl(const std::string& path);
+  ~OutputFileImpl() override {}
+
+  Exception::Value write(ConstPtr<ByteArray> data) override;
+  void close() override;
+
+ private:
+  std::ofstream file_;
+};
+
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_IMPL_SHARED_FILE_IMPL_H_