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+/**
+ * @brief Export DBus property to scalar MIB value
+ *
+ * This file is part of sila-snmp project.
+ *
+ * Copyright (c) 2022 SILA
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+#pragma once
+
+#include "sdbusplus/helper.hpp"
+#include <memory>
+
+namespace phosphor
+{
+namespace snmp
+{
+namespace data
+{
+template <typename T> class Scalar
+{
+ public:
+ using value_t = std::variant<T>;
+
+ /* Define all of the basic class operations:
+ * Not allowed:
+ * - Default constructor to avoid nullptrs.
+ * - Copy operations due to internal unique_ptr.
+ * Allowed:
+ * - Move operations.
+ * - Destructor.
+ */
+ Scalar() = delete;
+ Scalar(const Scalar&) = delete;
+ Scalar& operator=(const Scalar&) = delete;
+ Scalar(Scalar&&) = default;
+ Scalar& operator=(Scalar&&) = default;
+ ~Scalar() = default;
+
+ /**
+ * @brief Object constructor
+ */
+ Scalar(const std::string& path, const std::string& iface,
+ const std::string& prop, const T& initValue) :
+ _value(initValue),
+ _path(path), _iface(iface), _prop(prop),
+ _onChangedMatch(sdbusplus::helper::helper::getBus(),
+ sdbusplus::bus::match::rules::propertiesChanged(
+ path.c_str(), iface.c_str()),
+ std::bind(&Scalar<T>::onPropertyChanged, this,
+ std::placeholders::_1))
+ {
+ }
+
+ /**
+ * @brief Sent request to DBus object and store new value of property
+ */
+ void update()
+ {
+ try
+ {
+ auto service = sdbusplus::helper::helper::getService(_path, _iface);
+ auto r = sdbusplus::helper::helper::callMethod(
+ service, _path, sdbusplus::helper::PROPERTIES_IFACE, "Get",
+ _iface, _prop);
+
+ value_t var;
+ r.read(var);
+ setValue(var);
+ }
+ catch (const sdbusplus::exception::SdBusError&)
+ {
+ // Corresponding service is not started yet.
+ // When service is started, we'll receive data with
+ // `propertiesChanged` signal.
+ // So, this catch block is just for silencing the exception.
+ }
+ }
+
+ const T& getValue() const
+ {
+ return _value;
+ }
+
+ const std::string& getPath() const
+ {
+ return _path;
+ }
+
+ const std::string& getInterface() const
+ {
+ return _iface;
+ }
+
+ const std::string& getProperty() const
+ {
+ return _prop;
+ }
+
+ protected:
+ /**
+ * @brief DBus signal `PropertiesChanged` handler
+ */
+ void onPropertyChanged(sdbusplus::message::message& m)
+ {
+ std::string iface;
+ std::map<std::string, value_t> data;
+ std::vector<std::string> v;
+
+ m.read(iface, data, v);
+
+ if (data.find(_prop) != data.end())
+ {
+ setValue(data[_prop]);
+ }
+ }
+
+ /**
+ * @brief Setter for actual value
+ */
+ virtual void setValue(value_t& var)
+ {
+ auto newValue = std::get<T>(var);
+ std::swap(_value, newValue);
+ }
+
+ private:
+ T _value;
+ std::string _path;
+ std::string _iface;
+ std::string _prop;
+
+ sdbusplus::bus::match::match _onChangedMatch;
+};
+
+} // namespace data
+} // namespace snmp
+} // namespace phosphor