Allow ros2 topic echo output to be used in ros2 topic pub

[Ryanf55]

Feature request

Feature description

I want to use ros2 topic echo, copy the contents of a message in CLI, and run ros2 topic pub to publish the data without having to reformat it.

Currently, you can echo a topic like this:

$ ros2 topic echo /geo_path --once
header:
  stamp:
    sec: 0
    nanosec: 0
  frame_id: ''
poses:
- header:
    stamp:
      sec: 0
      nanosec: 0
    frame_id: ''
  pose:
    position:
      latitude: 1.0
      longitude: 2.0
      altitude: 3.0
    orientation:
      x: 0.0
      y: 0.0
      z: 0.0
      w: 1.0
- header:
    stamp:
      sec: 0
      nanosec: 0
    frame_id: ''
  pose:
    position:
      latitude: 4.0
      longitude: 5.0
      altitude: 6.0
    orientation:
      x: 0.0
      y: 0.0
      z: 0.0
      w: 1.0
---

Then, you need to tediously reformat it like this to publish:

$ ros2 topic pub /geo_path geographic_msgs/msg/GeoPath '{poses: [{pose: {position: {latitude: 1.0, longitude: 2.0, altitude: 3.0}}}, {pose: {position: {latitude: 4.0, longitude: 5.0, altitude: 6.0}}}]}'

Implementation considerations

Proposal: Allow publishing by yaml file like so: ros2 topic pub /geo_path geographic_msgs/msg/GeoPath --yaml my_message.yaml

Where my_message.yaml is the direct YAML from ros2 topic echo.

I'm open to other alternatives such as cat operation on the yaml file and piping it to xargs. cat my_message.yaml | xargs -I{} ros2 topic pub /geo_path geographic_msgs/msg/GeoPath {}

[clalancette]

Does the --flow-style parameter to ros2 topic echo do what you want?

[Ryanf55]

Yea, looks like it does.

ros2 topic echo /geo_path --flow-style
header:
  stamp:
    sec: 0
    nanosec: 0
  frame_id: ''
poses: [{header: {stamp: {sec: 0, nanosec: 0}, frame_id: ''}, pose: {position: {latitude: 1.0, longitude: 2.0, altitude: 3.0}, orientation: {x: 0.0, y: 0.0, z: 0.0, w: 1.0}}}, {header: {stamp: {sec: 0, nanosec: 0}, frame_id: ''}, pose: {position: {latitude: 4.0, longitude: 5.0, altitude: 6.0}, orientation: {x: 0.0, y: 0.0, z: 0.0, w: 1.0}}}]
---

Then, copy the content, type the command, add quotes for the message, and paste it in.

ros2 topic pub /geo_path geographic_msgs/msg/GeoPath "header:
  stamp:
    sec: 0
    nanosec: 0
  frame_id: ''
poses: [{header: {stamp: {sec: 0, nanosec: 0}, frame_id: ''}, pose: {position: {latitude: 1.0, longitude: 2.0, altitude: 3.0}, orientation: {x: 0.0, y: 0.0, z: 0.0, w: 1.0}}}, {header: {stamp: {sec: 0, nanosec: 0}, frame_id: ''}, pose: {position: {latitude: 4.0, longitude: 5.0, altitude: 6.0}, orientation: {x: 0.0, y: 0.0, z: 0.0, w: 1.0}}}]"

If this is the intent of flow-style, perhaps the docs could make that clearer?

[clalancette]

If this is the intent of flow-style, perhaps the docs could make that clearer?

I'm not totally sure what the original intent of it was, but certainly an update to the documentation would be welcome.

[fujitatomoya]

i think --flow-stype only helps the collection arrays in the block style,

root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 topic pub /tf_static tf2_msgs/msg/TFMessage "transforms: [{header: {stamp: {sec: 1721935886, nanosec: 528868866}, frame_id: foo}, child_frame_id: bar, transform: {translation: {x: 1.0, y: 2.0, z: 3.0}, rotation: {x: -0.4747921762038255, y: -0.07596622270177095, z: 0.24006245183344296, w: 0.8433098728485138}}}]"

root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 topic echo --once /tf_static
transforms:
- header:
    stamp:
      sec: 1721935886
      nanosec: 528868866
    frame_id: foo
  child_frame_id: bar
  transform:
    translation:
      x: 1.0
      y: 2.0
      z: 3.0
    rotation:
      x: -0.4747921762038255
      y: -0.07596622270177095
      z: 0.24006245183344296
      w: 0.8433098728485138
---
root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 topic echo --once --flow-style /tf_static
transforms: [{header: {stamp: {sec: 1721935886, nanosec: 528868866}, frame_id: foo}, child_frame_id: bar, transform: {translation: {x: 1.0, y: 2.0, z: 3.0}, rotation: {x: -0.4747921762038255, y: -0.07596622270177095, z: 0.24006245183344296, w: 0.8433098728485138}}}]
---

but it does not help if that is not the collection arrays,

root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 topic pub /turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 1.8}}"

root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 topic echo --once /turtle1/cmd_vel
linear:
  x: 2.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 1.8
---
root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 topic echo --once --flow-style /turtle1/cmd_vel
linear:
  x: 2.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 1.8
---

If this is the intent of flow-style, perhaps the docs could make that clearer?

so probably not for this use case...

Then, copy the content, type the command, add quotes for the message, and paste it in.

this works even without --flow-style is specified,

root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 topic pub /turtle1/cmd_vel geometry_msgs/msg/Twist "linear:
  x: 2.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 1.8
"
publisher: beginning loop
publishing #1: geometry_msgs.msg.Twist(linear=geometry_msgs.msg.Vector3(x=2.0, y=0.0, z=0.0), angular=geometry_msgs.msg.Vector3(x=0.0, y=0.0, z=1.8))

publishing #2: geometry_msgs.msg.Twist(linear=geometry_msgs.msg.Vector3(x=2.0, y=0.0, z=0.0), angular=geometry_msgs.msg.Vector3(x=0.0, y=0.0, z=1.8))

maybe we can add some suggestion about --flow-style for collection data,

Proposal: Allow publishing by yaml file like so: ros2 topic pub /geo_path geographic_msgs/msg/GeoPath --yaml my_message.yaml

i think this is useful new feature during development and debugging, we can easily modify the certain data amount to play back by yaml file. we could use rosbag2 but that requires us to modify the backend data base to modify the data contents.

[mjcarroll]

Discussion from maintenance triage: It was agreed that --flow-style is insufficient for what you are trying to accomplish. This would be a very helpful feature for the reasons that you stated above. There isn't any maintainer bandwidth to support creating these changes, but a PR would be happily accepted/reviewed.

[fujitatomoya]

@Ryanf55 i got some spare time to develop this, if you can try https://github.com/ros2/ros2cli/pull/925, that would be appreciated!

[Ryanf55]

Neat, I'm off on holiday weekend, but will review this when I get back Tuesday. Thanks for working on it!