Elevator state is not being publish on the ground floor

[Voldivh]

Environment

• OS Version: Ubuntu Jammy
• Source and Binary

Description

• Expected behavior: The elevator should publish a message to it's state topic on each floor it is in.
• Actual behavior: The elevator publish a message for all floors except the ground floor.

Steps to reproduce

1. Run the elevator.sdf file:

gz sim elevator.sdf

2. Subscribe to the elevator state:

gz topic -e -t /model/elevator/state

3. Publish a floor for the elevator to go. Example:

gz topic -t "/model/elevator/cmd" -m gz.msgs.Int32 -p "data: 2"

Output

We get the expected behavior when we send the elevator to any of the upper floors:

However, when we send the elevator to the ground floor (gz topic -t "/model/elevator/cmd" -m gz.msgs.Int32 -p "data: 0"), we stop receiving information on the console:

[mjcarroll]

This is an artifact of using protobuf. A field with a default value is also interpreted as a field that hasn't been set. In this case, the message is still being received, but the mechanism that turns it into a string assumes that field is uninitialized and doesn't output it.

There should be no impact on using the message as part of a callback (the field will still be set to zero), but if echoing on the command line is critical, we could add another field like "is set" to guarantee some output.

[Voldivh]

Interesting. I don't think it is critical to be able to echo it as long as the we still get the correct value on the subscription. My only concern is that it may confuse users that are not aware of that specific behavior. Maybe we could add a little comment at the top of the .sdf file? I can go ahead and create the appropriate PR if you agree on the "solution".

[mjcarroll]

I think a comment would be helpful.

Or we can 1-index all of our arrays from now on. 😉

[Voldivh]

I agree, let's go with the comment for now and keep it in mind from now on.