Issue 4931 - add possibility to not send data depending on connection properties

include/AdblockPlus/FilterEngine.h

Index: include/AdblockPlus/FilterEngine.h
diff --git a/include/AdblockPlus/FilterEngine.h b/include/AdblockPlus/FilterEngine.h
index ab35fa2e10530fe6cc64e46166536bc86f1d5d26..f1c779b367c5efb176890ac96764d582aec5db34 100644
--- a/include/AdblockPlus/FilterEngine.h
+++ b/include/AdblockPlus/FilterEngine.h
@@ -214,6 +214,12 @@ namespace AdblockPlus
     typedef std::function<void(const NotificationPtr&)> ShowNotificationCallback;
 
     /**
+     * Callback function returning false when current connection is not
+     * allowedConnectionType, e.g. because it is a metered connection.
+     */
+    typedef std::function<bool(const std::string* allowedConnectionType)> IsConnectionAllowedCallback;
+
+    /**
      * FilterEngine creation parameters.
      */
     struct CreationParameters
@@ -223,6 +229,12 @@ namespace AdblockPlus
        * prefs.
        */
       Prefs preconfiguredPrefs;
+      /**
+       * `AdblockPlus::FilterEngine::IsConnectionAllowedCallback` a callback
+       * checking whether the request from Adblock Plus should be blocked on
+       * the current connection.
+       */
+      IsConnectionAllowedCallback isConnectionAllowedCallback;
     };
 
     /**
@@ -439,6 +451,20 @@ namespace AdblockPlus
     void RemoveFilterChangeCallback();
 
     /**
+     * Stores the value indicating what connection types are allowed, it is
+     * passed to CreateParameters::isConnectionAllowed callback.
+     * @param value Stored value. nullptr means removing of any previously
+     *        stored value.
+     */
+    void SetAllowedConnectionType(const std::string* value);
+
+    /**
+      * Retrieves previously stored allowed connection type.
+      * @return Preference value, or `nullptr` if it doesn't exist.
+      */
+    std::unique_ptr<std::string> GetAllowedConnectionType();
+
+    /**
      * Compares two version strings in
      * [Mozilla toolkit version format](https://developer.mozilla.org/en/docs/Toolkit_version_format).
      * @param v1 First version string.