How to process GET parameters from HTTP endpoint in a flow

[nickyreinert]

Hey

I have problems looping GET parameters through a flow. I know that I must use a pre-processor before the INPUT node (according to https://www.windmill.dev/docs/core_concepts/preprocessors).

But thats it. Doc doesnt really reveal how and where to access GET parameters, vibe coding also doesnt really helped. I don't even know where to start and what to ask, tbh. That's what I got so far:

1. HTTP GET trigger is set up and running (windmill.example.com/api/r/helloworld?foobar=foobar)
2. Pre-Processore is up and running using this code (that's all I could put together from the doc)

def preprocessor(
    # Trigger metadata
    wm_trigger: WmTrigger = None,
    ):
    # Initialize foobar with default value
    foobar = ""

    # Check if wm_trigger exists and then extract foobar from query parameters
    if wm_trigger is not None and wm_trigger.get("kind") in ("http", "webhook"):
        http_data = wm_trigger.get("http")
        if http_data is not None and "query" in http_data:
            foobar = http_data["query"].get("foobar", "")

    return {
        "foobar": foobar
        # return the args to be passed to the runnable
    }

3. INPUT Node looks like this:

{
	"$schema": "https://json-schema.org/draft/2020-12/schema",
	"properties": {
		"foobar": {
			"description": "",
			"type": "object"
		}
	},
	"required": [],
	"type": "object",
	"order": [
		"fooobar"
	]
}

rest of the flow is probably not relevant.. as it seems like the information stuck somewhere between the HTTP endpoint and the INPUT node. (When I test the flow and add dummy content, it's being passed through to the end)

[rubenfiszel]

We are refactoring to preprocessors soon to make it a bit easier, but my advice would be to deploy a flow where preprocessor return the entire wm_trigger and look at your flow_input to find the args you are interested in. Then adjust your preprocessor accordingly.

[nickyreinert]

Good advice, got it. Doc is a little misleading I'd say. There's no "kind" attriibute in the windmill object. In short, one can referer to the query parameters like that (ofc you should buy tests around it):

def preprocessor(
    wm_trigger: WmTrigger = None,
    ):
    return {
        "foobar": wm_trigger["http"]["query"]["foobar"]
        # return the args to be passed to the runnable
    }