Would like a way to not run rosmaster

[frankjoshua]

It would be great to have some sort of flag or environmental variable to not start a ROS master. My use case is that I want to use Jupyter lab in an existing system with an already running master. It could be accomplished by adding --wait before roslaunch.

In https://github.com/RoboStack/jupyterlab-ros/blob/70b0582b834fa0ca9b03acc75226696de0758d23/jupyter_ros_server/api/master.py
cls.thread = Thread(target=cls.run, args=([path.join(getEnv(), 'roslaunch'), getMaster()],))
becomes
cls.thread = Thread(target=cls.run, args=([path.join(getEnv(), 'roslaunch --wait'), getMaster()],))

Is this an unusual use case? If so I could also just fork and change for my purpose.

[hbcarlos]

Hi @frankjoshua, actually this behaviour was only to make the binder examples easier, we can change it.
We can also change the frontend to not start ROS master by default if you prefer.

Just modifying this line

jupyterlab-ros/js/src/master/status.tsx

Line 34 in 455c8b3

onOpen = (msg) => { this.ws.send(JSON.stringify({ cmd: "start" })); }

for something like:
onOpen = (msg) => {}

Do you what to open a PR? I'll be happy to merge.

[frankjoshua]

I don't think it should be permanently changed. Probably still want Binder to work. I think maybe an environmental variable to set the behavior? Where would be the best place for that?

[hbcarlos]

A good place would be here

jupyterlab-ros/jupyter_ros_server/api/master.py

Line 38 in 455c8b3

if msg['cmd'] == "start" and cls.proc == None :

to prevent ROS master to start. But the problem is that when starting ROS master, we also run tf2_web_republisher which is necessary for Zethus and also turns on web bridge and sets a variable to allow running roslaunch from the frontend.

Another problem is that you should have ROS master running before starting JupyterLab-ROS because we start Web bridge with the extension and needs ROS master running.

jupyterlab-ros/jupyter_ros_server/api/bridge.py

Line 250 in 455c8b3

while cont < 10 and (not rosgraph.is_master_online()) :

Anyway, the status bar widget is a button to start and stop master. There is no problem at all with binder since we can turn it on later.

The main problem is that if you want to run your own master, you will need to run also tf2_web_republisher and every time you stop master you will probably need to restart jupyterlab, otherwise the extension would not work.