Zenoh
=====

Zenoh is an open source communication protocol and middleware designed to facilitate efficient data distribution across heterogeneous systems.
It provides location-transparent abstractions for high performance pub/sub and distributed queries.
See also: https://zenoh.io/docs/getting-started/first-app/

Prerequisites
-------------

Have :doc:`rosdep installed <../../../Tutorials/Intermediate/Rosdep>`.

Installation packages
---------------------

The rmw implementation Zenoh can be installed via binaries, recommended for stable development.

Binary packages for supported ROS 2 distributions (see distro branches) are available on respective Tier-1 platforms for the distributions.
First ensure that your system is set up to install ROS 2 binaries by following the instructions here.

Then install rmw_zenoh binaries using the command

.. code-block:: bash

   sudo apt install ros-{DISTRO}-rmw-zenoh-cpp

Build from source code
----------------------

Building from source is only recommended if latest features are needed.

By default, we vendor and compile ``zenoh-cpp`` with a subset of zenoh features.
The ``ZENOHC_CARGO_FLAGS`` CMake argument may be overwritten with other features included if required.
See `zenoh_cpp_vendor/CMakeLists.txt <https://github.com/ros2/rmw_zenoh/blob/{DISTRO}/zenoh_cpp_vendor/CMakeLists.txt>`__ for more details.

1. Clone the repository

.. code-block:: bash

    mkdir ~/ws_rmw_zenoh/src -p && cd ~/ws_rmw_zenoh/src
    git clone https://github.com/ros2/rmw_zenoh.git -b {DISTRO}

1. Install dependencies:

.. code-block:: bash

    cd ~/ws_rmw_zenoh
    rosdep install --from-paths src --ignore-src --rosdistro {DISTRO} -y

3. Build the workspace using Colcon:

.. code-block:: bash

    source /opt/ros/{DISTRO}/setup.bash
    colcon build --cmake-args -DCMAKE_BUILD_TYPE=Release


Switch to rmw_zenoh_cpp
------------------------

Switch from other rmw to rmw_zenoh_cpp by specifying the environment variable.

.. code-block:: bash

   export RMW_IMPLEMENTATION=rmw_zenoh_cpp

Run the talker and listener
---------------------------

Now run ``talker`` and ``listener`` to test Zenoh.

Start the Zenoh router

.. code-block:: bash

   # terminal 1
   source /opt/ros/{DISTRO}/setup.bash
   ros2 run rmw_zenoh_cpp rmw_zenohd

.. note:: Without the Zenoh router, nodes will not be able to discover each other since multicast discovery is disabled by default in the node's session config.
    Instead, nodes will receive discovery information about other peers via the Zenoh router's gossip functionality.

.. code-block:: bash

   # terminal 2
   export RMW_IMPLEMENTATION=rmw_zenoh_cpp
   source /opt/ros/{DISTRO}/setup.bash
   ros2 run demo_nodes_cpp talker

.. code-block:: bash

   # terminal 3
   export RMW_IMPLEMENTATION=rmw_zenoh_cpp
   source /opt/ros/{DISTRO}/setup.bash
   ros2 run demo_nodes_cpp listener

.. note:: Remember to source your ROS 2 setup script before running these commands.