Bazel rules for ROS

This repo aims to build ROS (1) from scratch.

Prerequisites

The code is developed and tested on Ubuntu 20.04 with Python 3.8.

You will need to install Bazel, see here. Besides Bazel, you will need a C++ compiler and a Python 3.8 interpreter. If you want to run ROS deployments in Docker containers, install Docker as well.

And no, you don't have to install any ROS packages via apt.

What works?

So far a subset of ros-base packages can be built, including support for

• messages,
• services,
• actions, and
• dynamic reconfiguration.

Here is an example.

Let's begin with starting roscore:

bazel run //:roscore

In a separate terminal, let's start a (C++) talker node:

bazel run //examples/chatter:talker

This single command will compile and run the talker node.

In a yet another terminal we can start a listener node:

bazel run //examples/chatter:listener  # C++ version or
bazel run //examples/chatter:py_listener  # Python version

Rosbag recording & playing works as well:

bazel run //:rosbag_record -- /chatter -o /tmp/foo.bag  # to record a bag or
bazel run //:rosbag_play -- /tmp/foo_<timestamp>.bag  # to play a bag

rostopic, tied to this example (see examples/chatter/BUILD.bazel for more info) can be used as

bazel run //examples/chatter:rostopic -- echo /chatter

Not too shabby.

Next, let's start a deployment with the talker and the listener nodes. You can stop the nodes you started with the above commands. Now execute

bazel run //examples/chatter:chatter

This command will build the necessary nodes and launch them. This is similar to executing good-ol' roslaunch, but, running the chatter ros_launch target using Bazel ensures all necessary dependencies are (re-)built.

How about executing the chatter deployment within a Docker container? Just run

bazel run //examples/chatter:chatter_image

FYI, the size of a compressed image made in release mode (with --config=opt) is less than 50MB -- check here. A very simple base image used for the example chatter image can be found in docker/base.

In //examples/dishwasher you can find another example that demonstrates defining and usage of ROS actions (and actionlib).

Packaging

By running

bazel build //examples/chatter:chatter_pkg

one can create the chatter deployment and package it in an archive. This is interesting for deployment on devices different than the build machine.

Cross-compilation

You can cross-compile the chatter deployment for e.g. NVIDIA's Jetson Nano with

bazel build //examples/chatter:chatter --config=jetson-opt

You don't have to install a cross-compiler, Bazel will download one for you. Neat, right? On it's own, this is not yet super interesting as one has to deploy the cross-compiled binaries to a target device. The binaries can be packaged with

bazel build //examples/chatter:chatter_pkg --config=jetson-opt

All you need to deploy to the target device is in bazel-bin/examples/chatter/chatter_pkg.tar.gz.

After you transfer the archive to the target, you can do the following at the target:

sudo mkdir -p /app  # This is a (configurable) root folder for the deployment.
sudo tar -xvzf chatter_pkg.tar.gz -C /

and then you can start the deployment with

/app/examples/chatter/chatter

Documentation

• C++
  • ros_cc_binary
  • ros_cc_library
• Interfaces (handling messages, services and actions)
  • ros_interface_library
  • cc_ros_interface_library
  • py_ros_interface_library
• Dynamic reconfiguration
  • ros_dynamic_reconfigure_library
  • cc_ros_dynamic_reconfigure_library
• Deployment
  • ros_launch
• Testing
  • ros_test
• Utilities
  • ros_topic

Additional

Optionally you can install pip-tools for resolving/updating Python deps:

sudo python3.8 -m pip install pip-tools

Then you can run the script ./generate_python_requirements.sh to update Python deps.

Background and design decisions

Within this project I want to learn and practice Bazel as well as to learn more about how difficult and/or feasible is to use ROS with Bazel. I started the work for desktop (amd64 architecture) but the real goal is to have cross-compilation for e.g. arm64 architecture working out of the box. Moreover, the number of deps that need to be installed on the target machine should be minimal, e.g. only C++ and Python runtimes.

For C++ this means that the build system needs to cross-compile all ROS and application deps, and for Python packages this means that all of them should be native -- i.e. without compiled extensions. For this project, I tried to find alternatives with Python-only code where possible, otherwise I removed pieces of code that depend on such deps. The end effect is that the core&base ROS packages used in this repo use only native Python deps. In other words, Python deps are handled by Bazel and you don't have to install (almost) any Python packages on the target platform.

It turned out that handling C++ dependencies is not that difficult. Some of the packages, mainly from ros_comm repo, have been fixed along the way. I believe that those changes can be eventually merged into the main ros_comm repo and that is why those changes are at the moment in a fork.

On the Python side, situation was more difficult. I had to refactor roslaunch code to filter out unwanted deps (mainly the ones that require compiled Python extensions in roslaunch). Next, roslib has complex dependencies and I kept only strictly necessary parts. Changes to rosservice are minimal. (Heavily) modified Python ROS packages are stored in //third_party and you can inspect git history to get more info about the changes I made.

Regarding development for embedded platforms, I believe roscpp should be just fine. rospy has some deps that have compiled extensions, so, rospy should not be used for platforms other than amd64 at the moment.

Since plugin functionality depends heavily on roslib and rospack, which I don't intend to touch any more, I won't work on ROS plugin support. Going to a bit more detail: rospack calls Python from C++ which tremendously complicates development for embedded platforms.