feat: introduce sd-event integration

include/sdbus-c++/IConnection.h

@@ -35,6 +35,7 @@
 #include <optional>
 
 struct sd_bus;
+struct sd_event;
 
 namespace sdbus {
 
@@ -107,6 +108,32 @@ namespace sdbus {
          */
         virtual void leaveEventLoop() = 0;
 
+        /*!
+         * @brief Attaches the bus connection to an sd-event event loop
+         *
+         * @param[in] event sd-event event loop object
+         * @param[in] priority Specified priority
+         *
+         * @throws sdbus::Error in case of failure
+         *
+         * See `man sd_bus_attach_event'.
+         */
+        virtual void attachSdEventLoop(sd_event *event, int priority = 0) = 0;
+
+        /*!
+         * @brief Detaches the bus connection from an sd-event event loop
+         *
+         * @throws sdbus::Error in case of failure
+         */
+        virtual void detachSdEventLoop() = 0;
+
+        /*!
+         * @brief Gets current sd-event event loop for the bus connection
+         *
+         * @return Pointer to event loop object if attached, nullptr otherwise
+         */
+        virtual sd_event *getSdEventLoop() = 0;
+
         /*!
          * @brief Adds an ObjectManager at the specified D-Bus object path
          *
@@ -150,6 +177,10 @@ namespace sdbus {
          * Use PollData::getPollTimeout() to have the timeout value converted
          * in a form that can be passed to poll(2).
          *
+         * The bus connection conveniently integrates sd-event event loop.
+         * To attach the bus connection to an sd-event event loop, use
+         * attachSdEventLoop() function.
+         *
          * @throws sdbus::Error in case of failure
          */
         [[nodiscard]] virtual PollData getEventLoopPollData() const = 0;
@@ -170,7 +201,8 @@ namespace sdbus {
          *
          * You don't need to directly call this method or getEventLoopPollData() method
          * when using convenient, internal bus connection event loops through
-         * enterEventLoop() or enterEventLoopAsync() calls.
+         * enterEventLoop() or enterEventLoopAsync() calls, or when the bus is
+         * connected to an sd-event event loop through attachSdEventLoop().
          * It is invoked automatically when necessary.
          *
          * @throws sdbus::Error in case of failure