webfinger/webfinger/__init__.py

from fastapi import FastAPI
from fastapi.responses import PlainTextResponse, JSONResponse
from fastapi.params import Query
import json
from pathlib import Path
from os import environ as env

app = FastAPI()

@app.get("/")
def lookup(
	resource: str = Query(None),
	rel: list[str] = Query(None)
	):
	"""
	Respond to a WebFinger query.
	"""

	# Basic info as a hint, if no resource given
	if not resource:
		return PlainTextResponse(
			content="Query ?resource= for more information.",
			status_code=400,
		)
	
	# otherwise, load that resource and return its data
	dir = env.get("RESOURCE_DIR") or "resource"
	filename = f"{dir}/{resource}.json"
	path = Path(filename)

	# TODO redirect to upstream webfinger server(s) if resource not found locally
	#       and if there is an upstream to try
	if not path.is_file():
		return PlainTextResponse(
			content=f"{resource} not found",
			status_code=404,
		)

	# open the local file
	with open(filename, "r") as file:
		data: dict = json.loads(file.read())

	# filter links if rel is provided
	links = [link for link in data.get('links', [])]
	if rel:
		links = [link for link in links if link.get('rel', '') in rel]

	# construct json response
	content = {
		"subject": resource,
		"aliases": [alias for alias in data.get('aliases')],
		"properties": data.get('properties'),
		"links": links,
	}
	content = {k: v for k, v in content.items() if v} # remove null values
	headers = {
		"Content-Type": "application/jrd+json"
	}
	return JSONResponse(content=content, headers=headers)

if __name__ == "__main__":
	import uvicorn
	uvicorn.run(app="webfinger:app", port=7033)