error-handling

Error Hanlding

• use route.get(errors=VioletsAreBlue) to declare a endpoint response

class VioletsAreBlue(HTTPException[str]):
    "how about you?"
    __status__ = 418


@lhl.post(errors=VioletsAreBlue)
async def roses_are_red():
    raise VioletsAreBlue("I am a pythonista")

• use lihil.problems.problem_solver as decorator to register a error handler, error will be parsed as Problem Detail.

from lihil.problems import problem_solver

# NOTE: you can use type union for exc, e.g. UserNotFound | status.NOT_FOUND
@problem_solver
def handle_404(req: Request, exc: Literal[404]):
    return Response("resource not found", status_code=404)

A solver that handles a specific exception type (e.g., UserNotFound) takes precedence over a solver that handles the status code (e.g., 404).

Exception-Problem mapping

lihil automatically generates a response and documentation based on your HTTPException, Here is the generated doc for the endpoint roses_are_red

click url under External documentation tab

we will see the detailed problem page

By default, every endpoint will have at least one response with code 422 for InvalidRequestErrors.

Here is one example response of InvalidRequestErrors.

{
  "type_": "invalid-request-errors",
  "status": 422,
  "title": "Missing",
  "detail": [
    {
      "type": "MissingRequestParam",
      "location": "query",
      "param": "q",
      "message": "Param is Missing"
    },
    {
      "type": "MissingRequestParam",
      "location": "query",
      "param": "r",
      "message": "Param is Missing"
    }
  ],
  "instance": "/users"
}

• To alter the creation of the response, use lihil.problems.problem_solver to register your solver.
• To change the documentation, override DetailBase.__json_example__ and DetailBase.__problem_detail__.
• To extend the error detail, provide typevar when inheriting HTTPException[T].