How to integrate flask and ariadne to allow subscriptions?

[Draqun]

Hi everyone.

I have a question. I've created Flask app with ariadne to test GraphQL. Everything works fine except Subscriptions. When I run app and setn subscription request I've got in response "error": "Could not connect to websocket endpoint ws://127.0.0.1:5000/graphql. Please check if the endpoint url is correct." like on the screen below.

My schema looks like this

schema {
    query: Query
    mutation: Mutation
    subscription: Subscription
}

...

type Query {
...
}

type Mutation {
...
}

type Subscription {
    subscribeActors: Actor!
}

And part of source code:
Endpoints

web = Blueprint('gql', __name__)

config = AppConfig.read_config()
type_defs = load_schema_from_path(config.schema_path)
schema = make_executable_schema(type_defs, snake_case_fallback_resolvers, *types)


@web.route('/graphql', methods=['GET'])
def graphql_playground():
    return PLAYGROUND_HTML, 200


@web.route('/graphql', methods=['POST'])
def graphql_server():
    data = request.get_json()
    success, result = graphql_sync(
        schema,
        data,
        context_value=request,
        debug=config.debug,
    )
    return json.dumps(result), 200 if success else 400

Resolvers

@convert_kwargs_to_snake_case
async def actors_source() -> AsyncGenerator[Dict[str, Any], None]:
    while True:
        actor = await queue.get()
        queue.task_done()
        yield actor


@convert_kwargs_to_snake_case
async def actor_field(actor, info) -> Dict[str, Any]:
    del info
    return actor


ResolverRegistry.register_subscription_resolver(
    SubscriptionResolverRecord('subscribeActors', actors_source, actor_field)
)

Registering types
(types variable is used in first snippet)

...
subscription = SubscriptionType()
for record in ResolverRegistry.get_subscription_resolvers():
    subscription.set_field(record.name, record.field)
    subscription.set_source(record.name, record.source)

...
types = ( 
    mutation,
    query,
    subscription,
    search_result,
)

and creating flask app

...
app = Flask(config.app_name)
CORS(app)
app.register_blueprint(web)
app.run(
    host=config.host,
    port=config.port,
    debug=config.debug,
)

I saw few examples/tutorial with subscriptions (including this one https://ariadnegraphql.org/docs/0.5.0/subscriptions) but none of them was working with Flask.

Any help will be appreciated.
Best regards.
Draqun

[rafalp]

Key take-away from subscriptions documentation is in big yellow box at its beginning:

Because of their nature, subscriptions are only possible to implement in asynchronous servers that implement the WebSockets protocol.

WSGI-based servers (including Django) are synchronous in nature and unable to handle WebSockets which makes them incapable of implementing subscriptions.

Flask is synchronous and WSGI based, which means it won't support subscriptions. graphql_sync() doesn't support them, and so does @web.route because subscriptions are made over the websocket protocol, which is different from regular HTTP.

[Draqun]

I missed that. Thanks a lot. Maybe Quart (https://gitlab.com/pgjones/quart) will be solution.
Best regards.