Part 1 - exercise: Add additional application to the snap

Important

This exercise requires having followed the Tutorial 1: Packaging our first ROS application as a snap.

Let’s do a little exercise. Right now, our talker-listener only has one application. How about you add another one? Having the ROS 2 topic tools inside our snap would be great for some introspection.

Assignment

Modify the snapcraft.yaml file:

• Add a new app entry for ros2topic

• Add the corresponding dependencies

Build and install the new snap.

Outcome

By the end of this exercise, you will have a new command available:

ros2-talker-listener.ros2topic hz /chatter

• Note that the ROS 2 topic tools are only going to work with message types that are included in the snap.

Solution

Click here for the solution

• Add ros2topic as a stage-package to have it available at run time:

  parts:
    ros-demos:
      plugin: colcon
      source: https://github.com/ros2/demos.git
      source-branch: humble
      source-subdir: demo_nodes_cpp
  -   stage-packages: [ros-humble-ros2launch]
  +   stage-packages: [ros-humble-ros2launch, ros-humble-ros2topic]
  

  • We add our dependency (ros-humble-ros2topic) to the stage-packages list. Stage-packages are packages that are required to run the part. Here we decided to add our dependency to our already existing ros-demos part for simplicity. Alternatively, we could have created an additional empty part simply to add our stage-packages dependency.

• Add an additional app:

  apps:
    ros2-talker-listener:
      command: opt/ros/humble/bin/ros2 launch talker-listener talker_listener.launch.py
      daemon: simple
      plugs: [network, network-bind]
      extensions: [ros2-humble]
  
  + ros2topic:
  +   command: opt/ros/humble/bin/ros2 topic
  +   plugs: [network, network-bind]
  +   extensions: [ros2-humble]
  

  • We added another application entry to our snap. We kept the plugs and extensions and simply exposed the ros2 topic command.

• Build and install the new snap:

  snapcraft
  sudo snap install ros2-talker-listener_0.1_*.snap --dangerous
  

• Make sure everything works:

  $ ros2-talker-listener.ros2topic hz /chatter
  average rate: 1.000 min: 0.999s max: 1.000s std dev: 0.00049s window: 3