How handle errors on AioHttp using Connexion

Question

I'd like to handle errors using AioHttp and Connexion in my python web apis in the same way Flask does through @app.errorhandler(Exception)

In another words, let's say my services raises SomethingAlreadyExists and I want to return 409 Conflict, rather than add the code below in all my apis:

try:
  myservice.create_something(..)
except SomethingAlreadyExists as error:     # Repeated code -> DRY
  return json_response({"message": str(error)}, status=409)

I'd like to just call the myservice.create_something(..) in the API layer and the error handle would return the 409 for SomethingAlreadyExists exceptions or 404 for SomethingNotFound .

Note: In Flask land it would be something like below:

import connexion


def create_api_app(version='api'):
    connexion_app = connexion.FlaskApp(__name__, specification_dir='../api/')
    connexion_app.add_api('openapi.yaml', validate_responses=True)
    app = connexion_app.app

    # It intercepts the specific exception and returns the respective status_code
    @app.errorhandler(InvalidValueException)
    def bad_request_handler(error):
        return 'Bad Request: {}'.format(str(error)), 400

    @app.errorhandler(NotFoundException)
    def not_found_handler(error):
        return 'Not found: {}'.format(str(error)), 404

    @app.errorhandler(AlreadyExistsException)
    def conflict_handler(error):
        return 'Conflict: {}'.format(str(error)), 409


# my_service.py
def get_model(i):

    model = get_model_or_none(id)
    if btask is None:
        raise NotFoundException(f"Model id:{id} not found.")
    ...

# api.py
def get_model(id):
    model = my_service.get_model(id)
    # handle errors not required ;)
    return btask.to_dict()

I'd like to do the same in my AioHttp connexion app:

from connexion import AioHttpApp


def create_app():
    connexion_app = AioHttpApp(__name__, port=8000, specification_dir="../", only_one_api=True)
    connexion_app.add_api("openapi.yaml", pass_context_arg_name="request")

    # Do something here.. like
    # web.Application(middlewares=[handle_already_exists_errors]) --> doesn't work
    # OR
    # connex_app.add_error_handler(
    #       AlreadyExistsException, handle_already_exists_errors) --> doesn't work too 
    return connexion_app

Cheers and I'll appreciate any help!

Roger

Answer 1

I was digging into the connexion and aiohttp code and figured out a way to do it using middlewares:

import json
from aiohttp.web import middleware
from connexion.lifecycle import ConnexionResponse
from connexion import AioHttpApp
from .exceptions import NotFoundException, AlreadyExistsException


def create_app():
    connexion_app = AioHttpApp(
        __name__, port=8000, specification_dir="../", only_one_api=True
    )
    connexion_app.add_api("openapi.yaml", pass_context_arg_name="request")
    connexion_app.app.middlewares.append(errors_handler_middleware)
    return connexion_app


@middleware
async def errors_handler_middleware(request, handler):
    """ Handle standard errors returning response following the connexion style messages"""
    try:
        response = await handler(request)
        return response

    except NotFoundException as error:
        return json_error(message=str(error), title='Not Found', status_code=404)
    except AlreadyExistsException as error:
        return json_error(message=str(error), title='Conflict', status_code=409)


def json_error(message, title, status_code):
    return ConnexionResponse(
        body=json.dumps({
            'title': title,
            'detail': message,
            'status': status_code,
        }).encode('utf-8'),
        status_code=status_code,
        content_type='application/json'
    )