proton_ros2

proton_ros2 is a ROS 2 adapter for Proton. It runs both a ROS 2 node and a protoncpp node in the same process, and bridges Proton bundles to ROS 2 topics for publishers and subscribers, or services for servers and clients.

note

The proton_ros2 package is only released in ROS 2 Jazzy, but can be built from source in other ROS 2 distros.

Converting from Proton to ROS 2

Bundles are dynamic enough that they can support the message structure of most ROS 2 messages. ROS 2 primitives can be mapped to an equivalent Proton Signal primitive, and a Proton Bundle structure can be defined based on the ROS 2 message fields.

Primitive Scalar mapping

ROS 2	Proton
float32	float
float64	double
int8	int32
int16	int32
int32	int32
int64	int64
uint8	uint32
uint16	uint32
uint32	uint32
uint64	uint64
bool	bool
char	uint32
byte	uint32
string	string

Primitive List mapping

ROS 2	Proton
float32[]	list_float
float64[]	list_double
int32[]	list_int32
int64[]	list_int64
uint8[]	bytes
uint32[]	list_uint32
uint64[]	list_uint64
bool[]	list_bool
byte[]	bytes
string[]	list_string

note

Types outside of these tables are not currently supported

Type Adapters

Using the rclcpp::TypeAdapter struct, conversion functions can be created to convert back and forth between Bundles and ROS 2 messages. proton_ros2 implements a similar ServiceTypeAdapter for ROS 2 service request and response messages.

proton_ros2 implements a Python-based code generated that will generate templated C++ code for all supported ROS 2 messages and services. Each message will have a convert_to_ros and convert_to_custom function generated which implements the logic for converting from Proton to ROS 2. Because ROS 2 messages have the ability to contain nested submessages, the generator will attempt to flatten the message into a format that can be mapped to a Proton Bundle. Flattening is done by recursing through a field in a ROS 2 message until the primitive data type is reached, then creating a signal with an equivalent Proton primitive type. The name of the signal will be the name of each field in the path joined by an underscore.

For example, the sensor_msgs/IMU has a geometry_msgs/Quaternion field called orientation. Within Quaternion are the fields x, y, z, and w of type float64. The Bundle that would be used for this message would then have to have the signals orientation_x, orientation_y, orientation_z, and orientation_w of type double, which would be mapped to the ROS 2 message fields.

Configuration

In the Proton configuration file, a ros2 section can be added to map Proton Bundles to ROS 2 topics or services.

Topics

Topic publishers or subscribers can be configured with the following keys:

Key	Type	Description	Required
topic	string	Topic name	Yes
message	string	ROS 2 message type	Yes
bundle	string	The Proton Bundle for this topic	Yes
qos	string or Map	The QoS profile for this topic	No

Bundles that the target consumes will create a ROS 2 publisher, while Bundles that the target produces will create a ROS 2 subscriber. The Bundle must have a signal with a name matching the path of the ROS 2 message field, as well as the same equivalent type.

Example

To create a publisher to the topic /my_string of type std_msgs/msg/String, the following configuration can be used:

nodes:
  - name: pc
    transport:
      type: udp4
      ip: 127.0.0.1
      port: 11416
  - name: mcu
    transport:
      type: udp4
      ip: 127.0.0.1
      port: 11417

connections:
  - first: {node: pc, id: 0}
    second: {node: mcu, id: 0}

bundles:
  - name: my_string
    id: 0x100
    producer: mcu
    consumer: pc
    signals:
      - {name: data, type: string, capacity: 64}

ros2:
  topics:
    - {topic: /my_string, message: std_msgs/msg/String, bundle: my_string}

When the node is launched with pc as the target, it will know that pc consumes the my_string bundle, and so it will create a publisher that will convert the bundle to a std_msgs/msg/String and publish the message as soon as the bundle is consumed.

Note that the signal is named data to match the equivalent ROS 2 field.

Services

Service servers or clients can be configured with the following keys:

Key	Type	Description	Required
topic	string	Service topic name	Yes
service	string	ROS 2 service type	Yes
request	string	The Proton Bundle for the request message of this service	Yes
response	string	The Proton Bundle for the response message of this service	No
timeout	uint32	Number of milliseconds to wait for a Proton response or a ROS 2 service server (Default: 1000ms)	No
qos	string or Map	The QoS profile for this service	No

If the target produces the request Bundle, then the node will create a service server. Otherwise, it will create a service client. The response Bundle is optional. Each Bundle must have a signal with a name matching the path of the ROS 2 message field for the corresponding Request or Response message, as well as the equivalent primitive type.

Example

To create a service on the topic /light_switch of type std_srvs/srv/SetBool, the following configuration can be used:

nodes:
  - name: pc
    transport:
      type: udp4
      ip: 127.0.0.1
      port: 11416
  - name: mcu
    transport:
      type: udp4
      ip: 127.0.0.1
      port: 11417

connections:
  - first: {node: pc, id: 0}
    second: {node: mcu, id: 0}

bundles:
  - name: light_switch_request
    id: 0x100
    producer: pc
    consumer: mcu
    signals:
      - {name: data, type: bool}
  - name: light_switch_response
    id: 0x101
    producer: mcu
    consumer: pc
    signals:
      - {name: success, type: bool}
      - {name: message, type: string, capacity: 64}

ros2:
  services:
    - {topic: /light_switch, service: std_srvs/srv/SetBool, request: light_switch_request, response: light_switch_response, timeout: 100}

When the node is launched with pc as the target, it will know that pc produces the request bundle, and so it will create a service that will convert a std_srvs/srv/SetBool request to the light_switch_request Bundle, then send it to the mcu target. It will then wait up to 100ms for a light_switch_response Bundle to be received. If successful, that Bundle will be converted to a std_srvs/srv/SetBool response, and returned to the ROS 2 service client.

QoS

The QoS profiles for both Topics and Services can also be configured. You can either choose a predefined standard profile, or create a custom one. To choose a standard profile, set the value of the qos key to the name of the profile.

Standard profiles

The following standard QoS profiles are supported:

Profile	Description
default	Default topic profile
services	Default services profile
sensor_data	Best Effort sensor data profile
rosout	Transient Local profile for /rosout
system_defaults	Default profile based on middleware

For example, a /rosout topic can be defined like this:

ros2:
  topics:
    - {topic: /rosout, message: rcl_interfaces/msg/Log, qos: rosout, bundle: log}

Custom profiles

A custom QoS profile can be created by defining the value of the qos key as another map. The map can have the following keys:

Key	Type	Required
history	string	No
depth	uint32	No
reliability	string	No
durability	string	No

History

The history value can be one of the following policies:

Policy	Description
keep_last	Keep the last depth messages
keep_all	Keep all messages
system_default	Default based on middleware

The default history is system_default

Depth

If history is set to keep_last, depth will determine how many messages to keep.

The default depth is 10

Reliability

The reliability value can be one of the following policies:

Policy	Description
best_effort	Attempt to deliver samples, but may lose them if the network is not robust
reliable	Guarantee that samples are delivered, may retry multiple times
system_default	Default based on middleware

The default reliability is system_default

Durability

The durability value can be one of the following policies:

Policy	Description
transient_local	The publisher becomes responsible for persisting samples for “late-joining” subscriptions
volatile	No attempt is made to persist samples
system_default	Default based on middleware

The default durability is system_default

For example, a my_string topic can be defined like this:

ros2:
  topics:
    - topic: my_string
      message: std_msgs/msg/String
      qos:
        history: keep_last
        depth: 15
        reliability: best_effort
        durability: volatile
      bundle: my_string

Usage

The executable produced by proton_ros2 is proton_ros2_node.

It takes two ROS parameters:

• config_file (string): path to the Proton YAML configuration file
• target (string): Proton node name this process represents (used to decide which bundles are produced/consumed)

The launch file proton_ros2.launch.py wires these parameters and supports an optional namespace.

Launch the node with ros2 CLI:

ros2 launch proton_ros2 proton_ros2.launch.py config_file:=/path/to/config.yaml target:=target_node namespace:=/my_namespace

The launched node with automatically spin up a ROS 2 and Proton node, connect to Proton peers, and create ROS 2 publishers, subscribers, services, and clients as defined in the configuration file.

Supported messages

The following message and service packages are currently supported in the proton_ros2 binary. Messages marked with a ✅ are supported and follow the standard Proton to ROS 2 mapping convention. Messages with a ✴️ symbol are supported with a custom mapping from Proton to ROS 2. Messages marked with ❌ are not supported at this time.

Messages

clearpath_platform_msgs

Message
DisplayStatus	✅
Drive	✅
DriveFeedback	✅
Fans	✅
Feedback	✅
Lights	✴️
PinoutCommand	✅
PinoutState	✅
Power	✅
RGB	✅
Status	✅
StopStatus	✅
Temperature	✅

geometry_msgs

Message
Accel	✅
AccelStamped	✅
AccelWithCovariance	✅
AccelWithCovarianceStamped	✅
Inertia	✅
InertiaStamped	✅
Point	✅
Point32	✅
PointStamped	✅
Polygon	✅
PolygonInstance	❌
PolygonInstanceStamped	❌
PolygonStamped	❌
Pose	✅
Pose2D	✅
PoseArray	❌
PoseStamped	✅
PoseWithCovariance	✅
PoseWithCovarianceStamped	✅
Quaternion	✅
QuaternionStamped	✅
Transform	✅
TransformStamped	✅
Twist	✅
TwistStamped	✅
TwistWithCovariance	✅
TwistWithCovarianceStamped	✅
Vector3	✅
Vector3Stamped	✅
VelocityStamped	✅
Wrench	✅
WrenchStamped	✅

nmea_msgs

Message
Gpgga	✅
Gpgsa	✅
Gpgst	✅
Gpgsv	✅
GpgsvSatellite	✅
Gprmc	✅
Gpvtg	✅
Gpzda	✅
Sentence	✅

rcl_interfaces

Message
FloatingPointRange	✅
IntegerRange	✅
ListParametersResult	✅
Log	✅
LoggerLevel	✅
Parameter	✅
ParameterDescriptor	❌
ParameterEvent	❌
ParameterEventDescriptors	❌
ParameterType	✅
ParameterValue	✅
SetParametersResult	✅

sensor_msgs

Message
BatteryState	✅
CameraInfo	✅
ChannelFloat32	✅
CompressedImage	✅
FluidPressure	✅
Illuminance	✅
Image	✅
Imu	✅
JointState	✅
Joy	✅
JoyFeedback	✅
JoyFeedbackArray	✅
LaserEcho	✅
LaserScan	✅
MagneticField	✅
MultiDOFJointState	❌
MultiEchoLaserScan	❌
NavSatFix	✅
NavSatStatus	✅
PointCloud	❌
PointCloud2	✅
PointField	✅
Range	✅
RegionOfInterest	✅
RelativeHumidity	✅
Temperature	✅
TimeReference	✅

std_msgs

Message
Bool	✅
Byte	✅
ByteMultiArray	✴️
Char	✅
ColorRGBA	✅
Empty	✅
Float32	✅
Float32MultiArray	✴️
Float64	✅
Float64MultiArray	✴️
Header	✅
Int16	✅
Int16MultiArray	❌
Int32	✅
Int32MultiArray	✴️
Int64	✅
Int64MultiArray	✴️
Int8	✅
Int8MultiArray	❌
MultiArrayDimension	✅
MultiArrayLayout	✅
String	✅
UInt16	✅
UInt16MultiArray	❌
UInt32	✅
UInt32MultiArray	✴️
UInt64	✅
UInt64MultiArray	✴️
UInt8	✅
UInt8MultiArray	✴️

Services

clearpath_platform_msgs

Message
ConfigureMcu	❌
SetPinout	✅

std_srvs

Message
Empty	✅
SetBool	✅
Trigger	✅

Adding custom message packages

If you wish to add support for additional message or service packages, the proton_ros2 package will have to be built from source.

First, create a workspace and clone the proton_ros2 package:

mkdir ~/proton_ws/src -p
cd ~/proton_ws/src
git clone https://github.com/clearpathrobotics/proton_ros2.git

Then, modify the CMakelists.txt file to find your package:

find_package(my_msgs REQUIRED)

Finally, add your package to the PROTON_ROS2_MESSAGES list (or PROTON_ROS2_SERVICES for a service package) and build the package.

set(PROTON_ROS2_MESSAGES
  clearpath_platform_msgs
  geometry_msgs
  nmea_msgs
  rcl_interfaces
  sensor_msgs
  std_msgs
  my_msgs
)

source /opt/ros/jazzy/setup.bash
cd ~/proton_ws
colcon build
source ~/proton_ws/install/setup.bash

If you encounter errors while building, it may suggest that the generator was not able to flatten a message in your message package. In that case, you may need to create a configuration file to either customize how that message is mapped to a Proton Bundle, or disable that message entirely.

Custom mapping

Generator mappings can be customized through a configuration YAML file specific to the message or service package. To create a configuration file, create a .yaml file with the same name as your message package underneat the config/messages or config/services folder in proton_ros2. Inside the file, add a package: entry with the name of your package. Then, add a messages: or services: entry. Under this section, you will add a list of each message that you want to modify:

package: clearpath_platform_msgs
messages:
  - name: Lights
    path: msg
    mapping:
      - {ros2.path: lights, ros2.length: 0, ros2.subpath: red, proton.signal: lights, proton.subindex: 0, type: list_bytes}
      - {ros2.path: lights, ros2.length: 0, ros2.subpath: green, proton.signal: lights, proton.subindex: 1, type: list_bytes}
      - {ros2.path: lights, ros2.length: 0, ros2.subpath: blue, proton.signal: lights, proton.subindex: 2, type: list_bytes}

In this example, the clearpath_platform_msgs/msg/Lights message is being modified to have a custom mapping. The default generator mapping would have created three Signals called lights_red, lights_green and lights_blue, each of type bytes. Instead, this custom mapping creates a single Signal called lights which is a list_bytes type and maps the indices of the list_bytes to each colour.

Mapping rules

A mapping rule can be created for each ROS 2 field and equivalent Proton Signal. There are several mapping types:

• Scalar: ros_msg.field = proton.signal
• Proton Indexed: ros_msg.field = proton.signal[proton_index]
• ROS Indexed: ros_msg.field[ros_index] = proton.signal
• Both Indexed: ros_msg.field[ros_index] = proton.signal[proton_index]
• Fixed List: ros_msg.field[n] = proton.signal[n]
• Dynamic List: ros_msg.field[] = proton.signal[]
• Fixed Submessage: ros_msg.field[n].subfield = proton.signal[n]
• Dynamic Submessage: ros_msg.field[].subfield = proton.signal[]
• Fixed Subindex: ros_msg.field[n].subfield = proton.signal[n][proton_subindex] (list_bytes only)
• Dynamic Subindex: ros_msg.field[].subfield = proton.signal[n][proton_subindex] (list_bytes only)

These rules are defined in the YAML file with these parameters:

• ros2.path: ROS field path (dot-separated, e.g. layout.data_offset)
• ros2.index: fixed index into a ROS array/vector
• ros2.length: list length behavior
  • > 0 indicates fixed-size array length
  • 0 indicates dynamic list (resize destination on Proton->ROS)
• ros2.subpath: field name inside a nested message element (used for arrays of nested messages)
• proton.signal: Proton Signal name
• proton.index: fixed index into a Proton list signal
• proton.subindex: subindex inside a list_bytes element
• type: Proton signal type string (e.g. uint32, list_float, bytes, list_bytes)

note

Signals do not support dynamically sized arrays, so dynamic arrays in ROS 2 will be limited to the length of the Signal array

Diagnostics

proton_ros2 registers diagnostics stats via diagnostic_updater:

• Per-connection RX/TX rates (KB/s) from the embedded protoncpp node
• Per-bundle frequency (Hz) depending on whether target produces or consumes the bundle
• Heartbeat frequency checks for peers that have heartbeat enabled in the Proton config

Diagnostics are published through the standard ROS 2 diagnostics pipeline.