How to enable CORS for subscriptions when mounted under Starlette/FastAPI ?

[AlexMili]

Hello everyone, does anybody succeeded in using subscriptions this way ?

The doc's example works fine but I need to encapsulate Ariadne with Starlette or FastAPI. I tried several ways but every time, CORS does not work for subscriptions, I get a HTTP 403. Here are my attempts:

Attempt 1:

graphqlapp = CORSMiddleware(
                GraphQL(schema, debug=True, introspection=True),
                allow_origins=["*"],
                allow_methods=["*"],
                allow_headers=["*"])

app = Starlette(debug=True)
app.mount("/graphql", graphqlapp)

Attempt 2:

graphqlapp = GraphQL(schema, debug=True, introspection=True)

app = Starlette(debug=True, middleware=[Middleware(CORSMiddleware,
                allow_origins=["*"], allow_methods=["*"], allow_headers=["*"])])
app.mount("/graphql", graphqlapp)

Both attempts were tested with the subscription counter example using uvicorn and websockets without success. However, CORS works perfectly fine for queries and mutations.

[rafalp]

Hey!

This isn't documented anywhere on Starlette's site but you are supposed to mount WebSocket app separately:

app.mount("/graphql/", graphql)
app.add_websocket_route("/graphql/", graphql.websocket_server)

Your error 403 in fact is not caused by CORS (because those don't apply to the Websocket connections!) - its refusal of protocol by the server that gives 403 here.

[AlexMili]

Thank you very much !! It works perfectly now !
Here is the full working code if someone have the same problem :

import asyncio
from ariadne import SubscriptionType, make_executable_schema
from ariadne.asgi import GraphQL
from starlette.applications import Starlette
from starlette.middleware import Middleware
from starlette.middleware.cors import CORSMiddleware



type_def = """
    type Query {
        _unused: Boolean
    }

    type Subscription {
        counter: Int!
    }
"""

subscription = SubscriptionType()

@subscription.source("counter")
async def counter_generator(obj, info):
    for i in range(5):
        await asyncio.sleep(1)
        yield i


@subscription.field("counter")
def counter_resolver(count, info):
    return count + 1


schema = make_executable_schema(type_def, subscription)
graphqlapp = GraphQL(schema, debug=True)

app = Starlette(debug=True, middleware=[Middleware(CORSMiddleware,
                allow_origins=["*"], allow_methods=["*"], allow_headers=["*"])])

app.mount("/graphql", graphqlapp)
app.add_websocket_route("/graphql", graphqlapp.websocket_server)