Client Hints

chrome/browser/net/client_hints.cc

+// 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.
+
+#include "chrome/browser/net/client_hints.h"
+
+#include <locale>
+
+#include "base/bind.h"
+#include "base/strings/stringprintf.h"
+#include "base/task_runner_util.h"
+#include "content/public/browser/browser_thread.h"
+#include "ui/gfx/screen.h"
+
+namespace {
+
+float FetchScreenInfoOnUIThread() {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  // TODO(bengr): Consider multi-display scenarios.
+  gfx::Display display = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay();
+  return display.device_scale_factor();
+}
+
+}  // namespace
+
+const char ClientHints::kDevicePixelRatioHeader[] = "CH-DPR";
+
+ClientHints::ClientHints()
+    : weak_ptr_factory_(this) {
+}
+
+ClientHints::~ClientHints() {
+}
+
+void ClientHints::Init() {
+  // TODO(bengr): Observe the device pixel ratio in case it changes during
+  // the Chrome session.
+  RetrieveScreenInfo();
+}
+
+bool ClientHints::RetrieveScreenInfo() {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::IO));
+  return content::BrowserThread::PostTaskAndReplyWithResult(
+      content::BrowserThread::UI,
+      FROM_HERE,
+      base::Bind(&FetchScreenInfoOnUIThread),
+      base::Bind(
+          &ClientHints::UpdateScreenInfo, weak_ptr_factory_.GetWeakPtr()));
+}
+
+const std::string& ClientHints::GetDevicePixelRatioHeader() const {
+  return screen_hints_;
+}
+
+void ClientHints::UpdateScreenInfo(float device_pixel_ratio_value) {
+  if (device_pixel_ratio_value <= 0.0)
+    return;
+  std::string device_pixel_ratio = base::StringPrintf("%.2f",
+      device_pixel_ratio_value);
+  // Make sure the Client Hints value doesn't change
+  // according to the machine's locale
+  std::locale locale;
+  for (std::string::iterator it = device_pixel_ratio.begin();
+       it != device_pixel_ratio.end(); ++it) {
+    if (!std::isdigit(*it, locale))
+      *it = '.';

[Avi (use Gerrit), 2013/10/04 21:59:01]

:( I wish we could StringPrintf according to a provided locale rather than have
to do a decimal point switch afterwards.

+  }
+  screen_hints_ = device_pixel_ratio;
+}
+