.. _getting-started-connext:

**************************************************
Interoperating Connext 7.3.0 or Earlier with ROS 2
**************************************************

The following describes a quick way to get started with ROS 2 and |CONNEXT|,
for |CONNEXT| versions 7.3.0 or earlier. (Interoperating |CONNEXT| 7.5.0 or later
with ROS 2 is even easier. See :numref:`enable-connext750-index`.)

.. note::

    These instructions are for using standalone |CONNEXT| applications
    with ROS 2 applications, regardless of the RMW used. This approach is ideal if you have an
    existing ROS 2 system that you cannot change, but you want to utilize the many
    features of *Connext* in additional applications. 

Ensure these prerequisites:

* **ROS 2 (any LTS version)**

  It is recommended to use Ubuntu 24.04 (LTS) and
  `Debian packages <https://docs.ros.org/en/kilted/Installation.html>`__ for
  installation, since this platform is referenced throughout the examples.
  Substitute your platform for “x64Linux4gcc7.3.0” throughout the examples if you are using another architecture.

* **Existing ROS 2 application**

  The examples throughout this document are based on the 
  `Creating custom msg and serv files <https://docs.ros.org/en/kilted/Tutorials/Beginner-Client-Libraries/Custom-ROS2-Interfaces.html>`__
  and `Writing a simple publisher and subscriber (C++) <https://docs.ros.org/en/kilted/Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Cpp-Publisher-And-Subscriber.html>`__
  ROS 2 tutorials. If you have your own existing application, you should
  substitute your own types and topic names throughout the examples.

* **Connext (any version at/before 7.3.0)**


In these getting started steps, your ROS 2 application will publish to
your |CONNEXT| subscribing application:

1.  Create a new directory (outside of your ROS 2 workspace) called ``connext_ws``.

2.  Copy the IDL file for your ROS 2 type into the newly created directory:

    .. code-block:: bash

        cp <ros2_ws>/src/tutorial_interfaces/tutorial_interfaces/share/tutorial_interfaces/msg/Num.idl .

3.  Configure your *Connext* environment (note: it is recommended to do this
    in a separate terminal from the one where you have configured your ROS 2
    environment):

    .. code-block:: bash

        source <rti_connext_install_directory>/resource/scripts/rtisetenv_x64Linux4gcc7.3.0.bash

4.  Modify your IDL to follow ROS 2 naming conventions. ROS 2 DDS types
    include an additional ``dds_`` namespace before the underlying typename,
    and the typenames are appended with ``_``. We must manually modify this
    typename before generating the type, in order to allow communication to
    take place.

    .. code-block:: idl

        module tutorial_interfaces {
            module msg {
                module dds_ {
                    struct Num_ {
                        int64 num;
                    };
                };
            };
        };

5.  Generate your *Connext* example application:

    .. code-block:: bash

        rtiddsgen -example x64Linux4gcc7.3.0 -language c++11 Num.idl

6.  Edit `Num_publisher.cpp` and `Num_subscriber.cpp` to set the topic name to
    ``rt/topic``:

    .. code-block:: c++

        dds::topic::Topic< ::tutorial_interfaces::msg::dds_::Num_> topic(participant, "rt/topic");

    .. note:: 
        
        This is not the same topic name that is used in your ROS 2 application.
        Your ROS 2 application should be using the topic name "topic". The RMW
        automatically adds "rt/" to the topic name at runtime.

7.  Compile your *Connext* application:

    .. code-block:: bash

        make -f makefile_x64Linux4gcc7.3.0

8.  In one terminal, run the *Connext* subscriber:

    .. code-block:: bash

        ./objs/x64Linux4gcc7.3.0/Num_subscriber

9.  In another terminal, run the ROS 2 publisher:

    .. code-block:: bash

        ros2 run cpp_pubsub talker

10. Verify that the *Connext* subscriber application now starts receiving data
    from the ROS 2 publisher application:

    .. code-block:: text

        ::tutorial_interfaces::msg::Num subscriber sleeping up to 1 sec...
        [num: 0]
        ::tutorial_interfaces::msg::Num subscriber sleeping up to 1 sec...
        [num: 1]
        ::tutorial_interfaces::msg::Num subscriber sleeping up to 1 sec...
        [num: 2]
        ::tutorial_interfaces::msg::Num subscriber sleeping up to 1 sec...
        [num: 3]