Robot Operating System (ROS)

Snapcraft builds on top of the catkin tool, familiar to any ROS developer, to create snaps for people to install on Linux.

What problems do snaps solve for ROS applications?

ROS itself is distributed via the OSRF’s own Debian archive, along with many community-supported tools. It’s possible to get your own application into their archive as well, but it requires that the application is open-source. You’re also left with the question of how to update ROS and your application on a robotic platform that has already been shipped. With snapcraft it’s just one command to bundle a specific ROS version along with your application into a snap that works anywhere and can be automatically updated.

Here are some snap advantages that will benefit many ROS projects:

  • Bundle all the runtime requirements, including the exact version of ROS, system libraries, etc.
  • Expand the distributions supported beyond just Ubuntu.
  • Directly control the delivery of application updates.
  • Extremely simple creation of daemons.

Getting started

Let’s take a look at the talker and listener out of the ROS tutorials, and show how simple that system is to snap.

ROS Tutorials

Snaps are defined in a single yaml file placed in the root of your project. Here is the entire snapcraft.yaml for this project. Let’s break it down.

name: ros-talker-listener
version: 0.1
summary: ROS Talker/Listener Example
description: |
  This example requires roscore as well as a talker and listener.

grade: devel
confinement: devmode

parts:
  ros-tutorials:
    source: https://github.com/ros/ros_tutorials.git
    source-branch: kinetic-devel
    plugin: catkin
    rosdistro: kinetic
    source-space: roscpp_tutorials/
    catkin-packages: [roscpp_tutorials]

apps:
  run:
    command: roslaunch roscpp_tutorials talker_listener.launch

Metadata

The snapcraft.yaml starts with a small amount of human-readable metadata, which usually can be lifted from the GitHub description or project README.md. This data is used in the presentation of your app in the Snap Store. The summary: can not exceed 79 characters. You can use a pipe in the description: key to declare a multi-line description.

name: ros-talker-listener
version: 0.1
summary: ROS Talker/Listener Example
description: |
  This example requires roscore as well as a talker and listener.

Confinement

To get started we won’t confine this application. Unconfined applications, specified with devmode, can only be released to the hidden “edge” channel where you and other developers can install them.

confinement: devmode

Parts

Parts define how to build your app. Parts can be anything: programs, libraries, or other assets needed to create and run your application. In this case we have one: ros-tutorials. Parts can point to local directories, remote git repositories, or tarballs.

The Catkin plugin will bundle roscore in the snap. It will also use rosdep to determine the dependencies of the catkin-packages provided, download them from the ROS archive, and unpack them into the snap. Finally, it will build the catkin-packages specified.

Important note: Most ROS developers run out of the devel space. As a result, it’s easy to forget the importance of good install rules, i.e. rules for installing every component of the package necessary to run, or every component necessary to use a given library. The Catkin packages you’re building must have good install rules, or Snapcraft won’t know which components to place into the snap. Make sure you install binaries, libraries, header files, launch files, etc.

parts:
  ros-tutorials:
    source: https://github.com/ros/ros_tutorials.git
    source-branch: kinetic-devel
    plugin: catkin
    rosdistro: kinetic
    source-space: roscpp_tutorials/
    catkin-packages: [roscpp_tutorials]

Apps

Apps are the commands and services exposed to end users. If your command name matches the snap name, users will be able run the command directly. If the names differ, then apps are prefixed with the snap name (ros-talker-listener.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.

If you don’t want your command prefixed you can request an alias for it on the Snapcraft forum. These are set up automatically when your snap is installed from the Snap Store.

Here we simply run a launch file that brings up roscore along with the talker and listener.

apps:
  run:
    command: roslaunch roscpp_tutorials talker_listener.launch

If your application is intended to run as a service you simply add the line daemon: simple after the command keyword. This will automatically keep the service running on install, update, and reboot.

Building the snap

You’ll first need to install snap support, and then install the snapcraft tool:

sudo snap install --beta --classic snapcraft

If you have just installed snap support, start a new shell so your PATH is updated to include /snap/bin. You can then build this example yourself:

git clone https://github.com/snapcraft-docs/ros-talker-listener
cd ros-talker-listener
snapcraft

The resulting snap can be installed locally. This requires the --dangerous flag because the snap is not signed by the Snap Store. The --devmode flag acknowledges that you are installing an unconfined application:

sudo snap install ros-talker-listener_*.snap --devmode --dangerous

You can then try it out:

$ ros-talker-listener.run 
<snip>

SUMMARY
========

PARAMETERS
 * /rosdistro: kinetic
 * /rosversion: 1.12.7

NODES
  /
    listener (roscpp_tutorials/listener)
    talker (roscpp_tutorials/talker)

auto-starting new master
process[master]: started with pid [919]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to a2132f48-a959-11e7-a19a-346895ed0f23
process[rosout-1]: started with pid [932]
started core service [/rosout]
process[listener-2]: started with pid [935]
process[talker-3]: started with pid [936]
[ INFO] [1507158810.260508402]: hello world 0
[ INFO] [1507158810.360553002]: hello world 1
[ INFO] [1507158810.460584229]: hello world 2
[ INFO] [1507158810.460985451]: I heard: [hello world 2]
[ INFO] [1507158810.560586692]: hello world 3
[ INFO] [1507158810.560894817]: I heard: [hello world 3]
[ INFO] [1507158810.660587011]: hello world 4

Removing the snap is simple too:

sudo snap remove ros-talker-listener

Share with your friends

To share your snaps you need to publish them in the Snap Store. First, create an account on the dashboard. Here you can customize how your snaps are presented, review your uploads and control publishing.

You’ll need to choose a unique “developer namespace” as part of the account creation process. This name will be visible by users and associated with your published snaps.

Make sure the snapcraft command is authenticated using the email address attached to your Snap Store account:

snapcraft login

Reserve a name for your snap

You can publish your own version of a snap, provided you do so under a name you have registered.

snapcraft register myrossnap

Be sure to update the name: in your snapcraft.yaml to match this registered name, then run snapcraft again.

Upload your snap

Use snapcraft to push the snap to the Snap Store.

snapcraft push --release=edge myrossnap_*.snap

If you’re happy with the result, you can commit the snapcraft.yaml to your GitHub repo and turn on automatic builds so any further commits automatically get released to edge, without requiring you to manually build locally.

Further customisations

Here are all the Catkin plugin-specific keywords:

    - catkin-packages:
      (list of strings)
      List of catkin packages to build.
      
    - source-space:
      (string)
      The source space containing Catkin packages. By default this is 'src'.
      
    - rosdistro:
      (string)
      The ROS distro required by this system. Defaults to 'indigo'.
      
    - include-roscore:
      (boolean)
      Whether or not to include roscore with the part. Defaults to true.
    
    - rosinstall-files:
      (list of strings)
      List of rosinstall files to merge while pulling. Paths are relative to
      the source.
   
    - catkin-cmake-args:
      (list of strings)
      Configure flags to pass onto the cmake invocation from catkin.
  
    - underlay:
      (object)
      Used to inform Snapcraft that this snap isn't standalone, and is actually
      overlaying a workspace from another snap via content sharing. Made up of
      two properties:
    
      - build-path:
        (string)
        Build-time path to existing workspace to underlay the one being built,
        for example '$SNAPCRAFT_STAGE/opt/ros/kinetic'.
   
      - run-path:
        (string)
        Run-time path of the underlay workspace (e.g. a subdirectory of the
        content interface's 'target' attribute.)

You can view them locally by running:

snapcraft help catkin

Extending and overriding behaviour

You can extend the behaviour of any part in your snapcraft.yaml with shell commands. These can be run after pulling the source code but before building by using the prepare keyword. The build process can be overridden entirely using the build keyword and shell commands. The install keyword is used to run shell commands after building your code, useful for making post build modifications such as relocating build assets.

For example, while the ros_tutorials have proper install rules, say you were creating a snap of an upstream ROS application that didn’t, and you wanted a launch file out of it. You could make use of the install keyword to get around the lack of install rules:

parts:
  ros-tutorials:
    source: https://url/to/bad/workspace
    plugin: catkin
    rosdistro: kinetic
    catkin-packages: [no_install_rules]
    install: |
      mkdir -p "$SNAPCRAFT_PART_INSTALL/opt/ros/kinetic/share/no_install_rules"
      cp -r no_install_rules/launch "$SNAPCRAFT_PART_INSTALL/opt/ros/kinetic/share/no_install_rules/"