Minimal ros2 node using r2r

This package shows how to use https://github.com/sequenceplanner/r2r to create a minimal ros node. Some custom messages are defined in the ros package r2r_minimal_node_msgs, while r2r_minimal_node implements a node with a simple service that uses the custom messages.

Using colcon to build

mkdir src
cd src
git clone [this repo]
cd ..
colcon build
. install/setup.sh
ros2 run r2r_minimal_node r2r_minimal_node --ros-args -p param1:="a string" -p param2:=5.5 -p param3:=true -r __ns:=/demo -r __node:=my_node
[ctrl-z]
bg
ros2 service call /hello_world r2r_minimal_node_msgs/srv/HelloWorld '{ hello: "Hello" }'

The integration with colcon is just a cmake hack that calls cargo, see CMakeLists.txt. Note the r2r_cargo function call. Note that an empty dummy.c is required in the crate root. To keep builds performed by colcon separate, r2r_cargo expects a custom profile called colcon to exist. See https://github.com/m-dahl/r2r_minimal_node/blob/master/r2r_minimal_node/Cargo.toml for an example.

cargo clean can be invoked by passing -DCARGO_CLEAN=ON to cmake, eg.

colcon build --cmake-args -DCARGO_CLEAN=ON

Note on cmake and Ubuntu 20.04

The r2r_cargo function requires cmake version 3.21 or newer, but ubuntu 20.04 ships with cmake 3.16.3. You can update to a newer cmake version by adding the kitware apt repo: https://apt.kitware.com.

Building using only cargo

Another option is to build the message package first, then sourcing the resulting workspace. When r2r_minimal_node_msgs is sourced, the r2r build script will automatically pick up the custom messages (it defaults to building everything).

To avoid building everything, it is possible to declare only the messages needed using the environment variable IDL_PACKAGE_FILTER. Setting this can be done in .cargo/config.toml for convenience, e.g. https://github.com/m-dahl/r2r_minimal_node/blob/master/r2r_minimal_node/.cargo/config.toml

mkdir src
cd src
git clone [this repo]
cd ..
colcon build --packages-select r2r_minimal_node_msgs # note that we only build the messages here
. install/setup.sh
cd src/r2r_minimal_node/r2r_minimal_node
cargo run -- --ros-args  -p param1:="a string" -p param2:=5.5 -p param3:=true
[ctrl-z]
bg
ros2 service call /hello_world r2r_minimal_node_msgs/srv/HelloWorld '{ hello: "Hello" }'