Added defer support.

include/mqtt/null_strand.hpp

@@ -49,7 +49,12 @@ struct null_strand {
     }
     template <typename Func, typename Allocator>
     void dispatch(Func&& f, Allocator) const {
-        std::forward<Func>(f)();
+        as::dispatch(
+            ioc_,
+            [f = std::forward<Func>(f)] () mutable {
+                std::move(f)();
+            }
+        );
     }
     void on_work_started() const noexcept {}
     void on_work_finished() const noexcept {}

include/mqtt/tcp_endpoint.hpp

@@ -83,6 +83,13 @@ class tcp_endpoint : public socket {
         );
     }
 
+    MQTT_ALWAYS_INLINE void defer(std::function<void()> handler) override final {
+        as::defer(
+            strand_,
+            force_move(handler)
+        );
+    }
+
     MQTT_ALWAYS_INLINE as::ip::tcp::socket::lowest_layer_type& lowest_layer() override final {
         return tcp_.lowest_layer();
     }

include/mqtt/type_erased_socket.hpp

@@ -27,6 +27,7 @@ class socket {
     virtual std::size_t write(std::vector<as::const_buffer>, boost::system::error_code&) = 0;
     virtual void post(std::function<void()>) = 0;
     virtual void dispatch(std::function<void()>) = 0;
+    virtual void defer(std::function<void()>) = 0;
     virtual as::ip::tcp::socket::lowest_layer_type& lowest_layer() = 0;
     virtual any native_handle() = 0;
     virtual void clean_shutdown_and_close(boost::system::error_code&) = 0;

include/mqtt/ws_endpoint.hpp

@@ -144,6 +144,13 @@ class ws_endpoint : public socket {
         );
     }
 
+    MQTT_ALWAYS_INLINE void defer(std::function<void()> handler) override final {
+        as::defer(
+            strand_,
+            force_move(handler)
+        );
+    }
+
 #if BOOST_VERSION >= 107000
 
     MQTT_ALWAYS_INLINE as::ip::tcp::socket::lowest_layer_type& lowest_layer() override final {