Launch python transformation engine as subprocess of nodejs?

[joeriexelmans]

Hi,

I see that the "launch" script starts both a nodejs process and a python process in parallel. From what I understand, the nodejs process, which is the "main" process, needs the python process, but not the other way around, so wouldn't it be better to launch the python process as a child process from nodejs? In this way, the AToMPM backend can be understood as a single nodejs process, and killing it will also kill the python process. It will also make it unnecessary to have a complex launch script.

Best regards,
Joeri

[BentleyJOakes]

Hi Joeri. Thanks for the idea! I think that's its a good one, and I'll try to find some time to implement it, unless you want to make a pull request. The only two concerns would be:

• To make sure that the output from the Python process is routed to the output of the NodeJS server, as this contains important debugging information. For reference: https://www.freecodecamp.org/news/node-js-child-processes-everything-you-need-to-know-e69498fe970a/
• To allow the user to not launch it through NodeJS, in case a custom Python version is needed, or flags need to be passed to the Python process.

[joeriexelmans]

Hi Bentley,

A very basic (not addressing your concerns), and usable implementation can be achieved by adding the following 2 lines at the end of httpwsd.js:

const childProcess = require('node:child_process');
childProcess.spawn('python', ['mt/main.py']);

About your concerns:

• Your first concern is valid, and this should indeed be implemented. Output of NodeJS and Python will be interleaved, so maybe we could give Python's output a different color?
• About your second concern: I agree that the NodeJS script must have the option not to launch the Python child process. For debugging, I imagine it is useful to run NodeJS and Python in different shells.

Anyway, when I look at the source code of the Python script, I don't see any flags that can be set. So the only remaining concern is selecting a specific Python version. This can also be achieved by passing a modified PATH environment variable to NodeJS, containing the right python version.

If you agree with these points, I'm willing to implement this feature and create a pull request.