Reland of Initial version of file wrapper

webrtc/base/file.h

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_FILE_H_
+#define WEBRTC_BASE_FILE_H_
+
+#include <stdint.h>
+
+#include <string>
+
+#include "webrtc/base/platform_file.h"
+#include "webrtc/base/constructormagic.h"
+
+namespace rtc {
+
+// This class wraps the platform specific APIs for simple file interactions.
+//
+// The various read and write methods are best effort, i.e. if an underlying
+// call does not manage to read/write all the data more calls will be performed,
+// until an error is detected or all data is read/written.
+class File {
+ public:
+  // Wraps the given PlatformFile. This class is then responsible for closing
+  // the file, which will be done in the destructor if Close is never called.
+  explicit File(PlatformFile);
+  ~File();
+
+  File(File&& other);
+  File& operator=(File&& other);
+
+  static File Open(const std::string& path);
+
+  size_t Write(const uint8_t* data, size_t length);
+  size_t Read(uint8_t* buffer, size_t length);
+
+  // The current position in the file after a call to these methods is platform
+  // dependent (MSVC gives position offset+length, most other
+  // compilers/platforms do not alter the position), i.e. do not depend on it,
+  // do a Seek before any subsequent Read/Write.
+  size_t WriteAt(const uint8_t* data, size_t length, size_t offset);
+  size_t ReadAt(uint8_t* buffer, size_t length, size_t offset);
+
+  // Attempt to position the file at the given offset from the start.
+  // Returns true if successful, false otherwise.
+  bool Seek(size_t offset);
+
+  // Attempt to close the file. Returns true if successful, false otherwise,
+  // most notably when the file is already closed.
+  bool Close();
+
+  bool IsOpen();
+
+ private:
+  PlatformFile file_;
+  RTC_DISALLOW_COPY_AND_ASSIGN(File);
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_FILE_H_