The ros-opt-data interface

doc
1

The ros-opt-data interface creates a read-only mount from within a snap to the standard Robot Operating System (ROS) directory (/opt/ros/*) on the host system, enabling robotics-based snaps to share ROS robot data, such as the URDF.

This interface cannot currently be used on Ubuntu Core. Requires snapd version 2.62+.

To add this interface to a snap, define a plug in the app section of its snapcraft.yaml for the application that requires ROS data access:

apps:
  hello-world:
    command: ./hello.sh
    plugs: [ros-opt-data]   #this is the new interface plug name

Mount location

This interface uses the standard snap location for mounted directories: /var/lib/snapd/hostfs/.

For example, if this interface is used to access /opt/ros/noetic/robot-urdf/models on the host machine, it will be found within the snap at /var/lib/snapd/hostfs/opt/ros/noetic/robot-urdf/models.

Interface documentation:

See Interface management and Supported interfaces for further details on how interfaces are used.

Developer details

Auto-connect: yes

Code examples

The following is a simple hello-world example that includes an additional plug/slot mechanism for enabling the ros-opt-data interface. We’re going to modify this example to show how the interface can access ROS-related data on the host system.

The initial snapcraft.yaml is as follows:

name: hello-world
version: '0.1'
summary: A simple hello world application
description: |
  A simple hello world application.
base: core22

grade: devel
confinement: strict

apps:
  hello-world:
    command: ./hello.sh

parts:
  hello-world:
    plugin: dump
    source: files

When the snap is built, installed and executed, it runs the following hello.sh script (which for now only outputs “hello world”).

#!/bin/bash
echo "hello world"

We now want to change the above script to output the contents of a setup.bash file located in the host’s /opt/ros directory.

The following modification assumes we’re using ROS Noetic Ninjemys, but the file location can be adapted for any other ROS distro:

#!/bin/bash
cat /var/lib/snapd/hostfs/opt/ros/noetic/setup.bash

We now modify the snapcraft.yaml to insert the new plug:

name: hello-world
version: '0.1'
summary: A simple hello world application
description: |
  A simple hello world application.
base: core22

grade: devel # must be 'stable' to release into candidate/stable channels
confinement: strict

apps:
  hello-world:
    command: ./hello.sh
    plugs: [ros-opt-data]

parts:
  hello-world:
    plugin: dump
    source: files

When the new snap is built, installed and executed, the output will now be the contents of /opt/ros/noetic/setup.bash.

The test code can be found in the snapd repository: https://github.com/snapcore/snapd/blob/master/interfaces/builtin/ros_opt_data_test.go

The source code for the interface is in the snapd repository: https://github.com/snapcore/snapd/blob/master/interfaces/builtin/ros_opt_data.go

2