Bug 983502 - navigator.getFeature implementation (support hardware.memory). r=bz

dom/apps/src/PermissionsTable.jsm

@@ -326,6 +326,11 @@ this.PermissionsTable =  { geolocation: {
                              privileged: PROMPT_ACTION,
                              certified: PROMPT_ACTION
                            },
+                           "feature-detection": {
+                             app: DENY_ACTION,
+                             privileged: ALLOW_ACTION,
+                             certified: ALLOW_ACTION
+                           },
                          };
 
 /**

dom/base/Navigator.cpp

@@ -1471,6 +1471,52 @@ Navigator::GetDataStores(const nsAString& aName, ErrorResult& aRv)
   return GetDataStores(mWindow, aName, aRv);
 }
 
+already_AddRefed<Promise>
+Navigator::GetFeature(const nsAString& aName)
+{
+  nsCOMPtr<nsIGlobalObject> go = do_QueryInterface(mWindow);
+  nsRefPtr<Promise> p = new Promise(go);
+
+#if defined(XP_LINUX)
+  if (aName.EqualsLiteral("hardware.memory")) {
+    static int memLevel = 1;
+    if (memLevel == 1) {
+      FILE* f = fopen("/proc/meminfo", "r");
+      if (!f) {
+        p->MaybeReject(NS_LITERAL_STRING("CannotOpenMeminfo"));
+        return p.forget();
+      }
+
+      int memTotal;
+      int n = fscanf(f, "MemTotal: %d kB\n", &memTotal);
+      fclose(f);
+
+      if (memTotal == 0 || n != 1) {
+        p->MaybeReject(NS_LITERAL_STRING("Abnormal"));
+        return p.forget();
+      }
+      // From KB to MB
+      memTotal /= 1024;
+
+      // round the value up to the next power of two
+      while (memLevel <= memTotal) {
+        memLevel *= 2;
+      }
+    }
+    p->MaybeResolve(memLevel);
+  } // hardware.memory
+  else
+#endif
+  {
+    // resolve with <undefined> because the feature name is not supported
+    p->MaybeResolve(JS::UndefinedHandleValue);
+  }
+
+  return p.forget();
+
+}
+
+
 PowerManager*
 Navigator::GetMozPower(ErrorResult& aRv)
 {
@@ -2444,6 +2490,15 @@ Navigator::HasNetworkStatsSupport(JSContext* /* unused */, JSObject* aGlobal)
   return CheckPermission(win, "networkstats-manage");
 }
 
+/* static */
+bool
+Navigator::HasFeatureDetectionSupport(JSContext* /* unused */, JSObject* aGlobal)
+{
+  nsCOMPtr<nsPIDOMWindow> win = GetWindowFromGlobal(aGlobal);
+  return CheckPermission(win, "feature-detection");
+}
+
+
 /* static */
 already_AddRefed<nsPIDOMWindow>
 Navigator::GetWindowFromGlobal(JSObject* aGlobal)

dom/base/Navigator.h

@@ -164,6 +164,10 @@ public:
 
   already_AddRefed<Promise> GetDataStores(const nsAString &aName,
                                           ErrorResult& aRv);
+
+  // Feature Detection API
+  already_AddRefed<Promise> GetFeature(const nsAString &aName);
+
   bool Vibrate(uint32_t aDuration);
   bool Vibrate(const nsTArray<uint32_t>& aDuration);
   uint32_t MaxTouchPoints();
@@ -317,6 +321,8 @@ public:
 
   static bool HasNetworkStatsSupport(JSContext* aCx, JSObject* aGlobal);
 
+  static bool HasFeatureDetectionSupport(JSContext* aCx, JSObject* aGlobal);
+
   nsPIDOMWindow* GetParentObject() const
   {
     return GetWindow();

dom/webidl/Navigator.webidl

@@ -28,6 +28,7 @@ Navigator implements NavigatorLanguage;
 Navigator implements NavigatorOnLine;
 Navigator implements NavigatorContentUtils;
 Navigator implements NavigatorStorageUtils;
+Navigator implements NavigatorFeatures;
 
 [NoInterfaceObject]
 interface NavigatorID {
@@ -80,6 +81,12 @@ interface NavigatorStorageUtils {
   //void yieldForStorageUpdates();
 };
 
+[NoInterfaceObject]
+interface NavigatorFeatures {
+  [Func="Navigator::HasFeatureDetectionSupport"]
+  Promise getFeature(DOMString name);
+};
+
 // Things that definitely need to be in the spec and and are not for some
 // reason.  See https://www.w3.org/Bugs/Public/show_bug.cgi?id=22406
 partial interface Navigator {