chrome/browser/net/client_hints.h

// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CHROME_BROWSER_NET_CLIENT_HINTS_H_
#define CHROME_BROWSER_NET_CLIENT_HINTS_H_

#include <string>

#include "base/basictypes.h"
#include "base/memory/weak_ptr.h"

// ClientHints is a repository in Chrome for information used
// to create the Client-Hints request header. For more information, see:
// https://github.com/igrigorik/http-client-hints/blob/draft2/draft-grigorik-http-client-hints-01.txt
class ClientHints {
 public:
  static const char kDevicePixelRatioHeader[];

  ClientHints();
  ~ClientHints();

  void Init();

  // Returns the device pixel ratio as a string.  Its value is the same as
  // window.devicePixelRatio in Javascript.
  const std::string& GetDevicePixelRatioHeader() const;

 private:
  friend class ClientHintsTest;

  // Retrieves and updates screen information for use on the IO thread.
  bool RetrieveScreenInfo();

  void UpdateScreenInfo(float device_pixel_ratio_value);

  std::string screen_hints_;

  base::WeakPtrFactory<ClientHints> weak_ptr_factory_;

  DISALLOW_COPY_AND_ASSIGN(ClientHints);
};

#endif  // CHROME_BROWSER_NET_CLIENT_HINTS_H_