[xswiftbus] Replace QtDBus with a libevent driven C++ wrapper on top of libdbus

QtDBus was the main component of xswiftbus' Qt dependency. This is the
first preparation step to get xswiftbus Qt free.
The new implementation is based on the low level libdbus library, which
was also in use by QtDBus itself. But instead of QtDBus, we use now a thin
C++ wrapper. To keep DBus handling async, libevent is used to monitor
timeouts and fds.

src/xswiftbus/dbusmessage.h

@@ -0,0 +1,99 @@
+/* Copyright (C) 2018
+ * swift project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
+ * including this file, may be copied, modified, propagated, or distributed except according to the terms
+ * contained in the LICENSE file.
+ */
+
+#ifndef BLACKSIM_XSWIFTBUS_DBUSMESSAGE_H
+#define BLACKSIM_XSWIFTBUS_DBUSMESSAGE_H
+
+#include "dbus/dbus.h"
+#include <string>
+#include <vector>
+
+namespace XSwiftBus
+{
+
+    //! DBus Message
+    class CDBusMessage
+    {
+    public:
+        //! Constructor
+        //! @{
+        CDBusMessage(DBusMessage *message);
+        CDBusMessage(const CDBusMessage &other);
+        //! @}
+
+        //! Destructor
+        ~CDBusMessage();
+
+        //! Assignment operator
+        CDBusMessage &operator=(CDBusMessage other);
+
+        //! Is this message a method call?
+        bool isMethodCall() const;
+
+        //! Does this message want a reply?
+        bool wantsReply() const;
+
+        //! Get the message sender
+        std::string getSender() const;
+
+        //! Get the message serial. This is usally required for reply message.
+        dbus_uint32_t getSerial() const;
+
+        //! Get the called interface name
+        std::string getInterfaceName() const;
+
+        //! Get the called object path
+        std::string getObjectPath() const;
+
+        //! Get the called method name
+        std::string getMethodName() const;
+
+        //! Begin writing argument
+        void beginArgumentWrite();
+
+        //! Append argument. Make sure to call \sa beginArgumentWrite() before.
+        //! @{
+        void appendArgument(bool value);
+        void appendArgument(const char *value);
+        void appendArgument(const std::string &value);
+        void appendArgument(int value);
+        void appendArgument(double value);
+        void appendArgument(const std::vector<double> &array);
+        void appendArgument(const std::vector<std::string> &array);
+        //! @}
+
+        //! Begin reading arguments
+        void beginArgumentRead();
+
+        //! Read single argument. Make sure to call \sa beginArgumentRead() before.
+        //! @{
+        void getArgument(int &value);
+        void getArgument(bool &value);
+        void getArgument(double &value);
+        void getArgument(std::string &value);
+        //! @}
+
+        //! Creates a DBus message containing a DBus signal
+        static CDBusMessage createSignal(const std::string &path, const std::string &interfaceName, const std::string &signalName);
+
+        //! Creates a DBus message containing a DBus reply
+        static CDBusMessage createReply(const std::string &destination, dbus_uint32_t serial);
+
+    private:
+        friend class CDBusConnection;
+
+        DBusMessage *m_message = nullptr;
+        DBusMessageIter m_messageIterator;
+        CDBusMessage(DBusMessage *message, dbus_uint32_t serial);
+        dbus_uint32_t m_serial = 0;
+    };
+
+}
+
+#endif // guard