What are the correct beginsPattern and endsPattern for a background Task in VSCode? - visual-studio-code

Question

I have a static website (i.e. just html and client side JavaScript) that I serve with python while debugging locally. I have a VSCode task that will start python correctly and am trying to set that task as the preLaunchTask on a Debugger for Chrome launch task. The desired behavior is that whenever I start debugging the serve task below ensures the site is being served.
If I understand background tasks correctly one can set a beginsPattern and endsPattern to signal state changes.
I am expecting that when python echos
Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...
to stdout that the problemMatcher below would signal to the launch task that it had started. Instead, the launch task waits forever, and doesn't proceed until the task's shell command is terminated.
Can tasks be configured to achieve this sort of behavior?
Launch Configuration
{
"version": "0.2.0",
"configurations": [
{
"type": "chrome",
"request": "launch",
"name": "Launch Chrome against localhost",
"url": "http://localhost:8000",
"webRoot": "${workspaceFolder}/webroot",
"preLaunchTask": "serve"
}
]
}
Serve Task
{
"version": "2.0.0",
"tasks": [
{
"label": "serve",
"type": "shell",
"command": "python3 -m http.server",
"windows": {
"command": "py -m http.server"
},
"isBackground": true,
"options": {
"cwd": "${workspaceFolder}/webroot"
},
"presentation": {
"echo": true,
"reveal": "always",
"focus": false,
"panel": "dedicated"
},
"problemMatcher": {
"owner": "custom",
"pattern":[
{
"regexp": "^([^\\s].*)$",
"file": 1,
"location": 2,
"message": 3
}
],
"background": {
"activeOnStart": true,
"beginsPattern":"^Serving HTTP (.*)$",
"endsPattern":"^Keyboard interrupt received, exiting(.*)$"
}
}
}
]
}

Answer 1

So we also had a similar problem: wanted to set up a Debugger on a Django app running inside Docker. On my setup, the debugger launched a preLaunchTask which starts the remote interpreter debugger, among other things (like installing ptvsd.
Original Steps:
preLaunchTask calls a script (./run-debug.sh).
This script calls remote debugger with this command:
docker container exec -it my_app python debug.py runserver --noreload --nothreading 0.0.0.0:8000
On the debug.py file, there's a print statement to know that the debugger started.
That didn't work, apparently, VSCode doesn't catch the output of the debugger. Instead, on the run-debug.sh file I added an echo statement: Starting debugger session: which VSCode caught ^_^. That fixed the issue for me.
tasks.json, relevant problem matcher:
"problemMatcher": {
"pattern": [
{
"regexp": ".",
"file": 1,
"location": 2,
"message": 3
}
],
"background": {
"beginsPattern": "^Starting debugger session:",
"endsPattern": ".",
}
}
run-debug.sh script, relevant part:
# Start remote process
echo 'Starting debugger session:' #VSCode beginsPattern will catch this!
docker container exec -it my_app python debug.py runserver --noreload --nothreading 0.0.0.0:8000