Implement GraphQL subscription

[hoangvvo]

This PR builds upon the previous one #94.

I refactor the implementation and update with recent changes in graphql-js.

The test has also been updated to include the latest test cases from graphql-js using graphql/graphql-js@1bd65a3 (3 days ago). For the diff of our test cases and theirs (mainly because we don't support root resolver), see 6c8cfc6.

Close #74

[hoangvvo]

I think, if it is not too breaking, we should change this message to stay up to date with graphql-js. Wdyt?

[oporkka]

Yes, we can change it.

[hoangvvo]

@boopathi I have confirmed that your test case (https://gist.github.com/boopathi/885f41720f258b50a2ba67bed76581af) now works. We are covering it in this case:

graphql-jit/src/__tests__/subscription.test.ts

Lines 203 to 220 in 27c197c

	it("accepts type definition with sync subscribe function", async () => {
	async function* fooGenerator() {
	yield { foo: "FooValue" };
	}
	const schema = new GraphQLSchema({
	query: DummyQueryType,
	subscription: new GraphQLObjectType({
	name: "Subscription",
	fields: {
	foo: {
	type: GraphQLString,
	subscribe: fooGenerator
	}
	}
	})
	});

[hoangvvo]

@ruiaraujo Could you please approve the CI run? Thanks!

[ardatan]

Any updates for this PR?

[hoangvvo]

Any updates for this PR?

On my side, all tests are currently passing, so I'm just waiting for a review actually.

[boopathi]

@hoangvvo

@boopathi I have confirmed that your test case (https://gist.github.com/boopathi/885f41720f258b50a2ba67bed76581af) now works

I'm trying it out without the resolve function mentioned in my test case. It still gives me an error. Looks like when using makeExecutableSchema, a resolve function that does (x) => x is necessary for subscriptions. I don't understand this limitation.

[hoangvvo]

@hoangvvo

@boopathi I have confirmed that your test case (https://gist.github.com/boopathi/885f41720f258b50a2ba67bed76581af) now works

I'm trying it out without the resolve function mentioned in my test case. It still gives me an error. Looks like when using makeExecutableSchema, a resolve function that does (x) => x is necessary for subscriptions. I don't understand this limitation.

Sorry for the late reply, as I mentioned in the other PR, that pattern is not supported by graphql-js either. I think the function can only either be non-async generator function, or a promise that resolved into a async iterator.

import { makeExecutableSchema } from "@graphql-tools/schema";
import { parse, subscribe } from "graphql";

function isAsyncIterable<T>(val: any): val is AsyncIterableIterator<T> {
  return val != null && typeof val[Symbol.asyncIterator] === "function";
}

const schema = makeExecutableSchema({
  typeDefs: `
    type Subscription {
      nodes: Node
    }
    type Node {
      id: ID
    }
    type Query {
      foo: ID
    }
  `,
  resolvers: {
    Query: {
      foo: () => ""
    },
    Subscription: {
      nodes: {
        async *subscribe() {
          for (let i = 0; i < 3; i++) {
            yield {
              id: i.toString()
            };
          }
        },
      }
    }
  }
});

describe("subscription happy case", () => {
  test("nodes and ids", async () => {
    const sub = await subscribe({ document: parse(`
      subscription {
        nodes {
          id
        }
      }
    `) });
    if (isAsyncIterable(sub)) {
      let i = 0;
      for await (const val of sub) {
        expect(val.data?.nodes?.id).toBe((i++).toString());
      }
    }
  });
});

[boopathi]

LGTM 🎉

[boopathi]

👍

[oporkka]

Would it be possible to extend the comment here to explicitly state why we ignore the error?

[oporkka]

👍