Client doesn't report the server abruptly going away in the middle of event emission (only in NodeJS)

[enisdenjo]

Kudos, and big thanks, to @brentmjohnson for discovering this bug over at #21!

As per #22 (comment), this issue seems to be exclusive to NodeJS environments.

Expected Behaviour

If the server goes away abruptly during event emission, the client reports the error to the sink.

Actual Behaviour

If the server goes away abruptly during event emission, the client gets stuck and the sink is never finalised.

[enisdenjo]

Hmm, seems like this bug is exclusive to NodeJS. I've tried replicating the same behaviour in the browser, but it fails immediately when the server gets killed. Here are my repro steps:

1. Write up a test.mjs server:

import { GraphQLSchema, GraphQLObjectType, GraphQLString } from 'graphql';
import http from 'http';
import { createHandler } from 'graphql-sse';

const schema = new GraphQLSchema({
  query: new GraphQLObjectType({
    name: 'Query',
    fields: {
      hello: {
        type: GraphQLString,
        resolve: () => 'world',
      },
    },
  }),
  subscription: new GraphQLObjectType({
    name: 'Subscription',
    fields: {
      greetings: {
        type: GraphQLString,
        subscribe: async function* () {
          for (const hi of ['Hi', 'Bonjour', 'Hola', 'Ciao', 'Zdravo']) {
            yield { greetings: hi };
            await new Promise((resolve) => setTimeout(resolve, 3000));
          }
        },
      },
    },
  }),
});

const handler = createHandler({ schema });

const server = http.createServer(async (req, res) => {
  if (!req.url.startsWith('/graphql/stream')) {
    return res.writeHead(404).end();
  }

  try {
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Access-Control-Allow-Methods', '*');
    res.setHeader('Access-Control-Allow-Headers', '*');
    if (req.method === 'OPTIONS') {
      // preflight
      return res.writeHead(204).end();
    }

    return await handler(req, res);
  } catch (err) {
    console.error(err);
    if (!res.headersSent) {
      res.writeHead(500);
    }
    return res.end();
  }
});

server.listen(4000);
console.log('Listening to port 4000');

2. node test.mjs
3. Load GraphiQL in the browser using this gist
4. Subscribe to greetings:

subscription {
  greetings
}

5. Kill the server whenever after the 1st event emission
6. The browser immediately reports POST http://localhost:4000/graphql/stream net::ERR_INCOMPLETE_CHUNKED_ENCODING 200 (OK) to the console (also when running the client in "single connection mode")

I've Googled around but couldn't find any clues about why this test fails:

graphql-sse/src/__tests__/client.ts

Lines 176 to 194 in 72d284a

	it('should report error to sink if server goes away during generator emission', async () => {
	const server = await startTServer();
	const client = createClient({
	url: server.url,
	fetchFn: fetch,
	retryAttempts: 0,
	});
	const sub = tsubscribe(client, {
	query: 'subscription { slowGreetings }',
	});
	await sub.waitForNext();
	await server.dispose();
	// TODO: should waitForError; but for debugging purposes, we wait for either
	await Promise.race([sub.waitForError(), sub.waitForComplete()]);
	});

Could it be node-fetch or just Node itself? Any ideas @brentmjohnson?

[brentmjohnson]

Sure I'll take a look @enisdenjo - will let you know what I find.

[enisdenjo]

I am closing this issue with 8f002f1 because the issue stems from v2 of node-fetch and is fixed with v3.

See node-fetch/node-fetch#1604.

[brentmjohnson]

I am closing this issue with 8f002f1 because the issue stems from v2 of node-fetch and is fixed with v3.

See node-fetch/node-fetch#1604.

@enisdenjo what a great find. Thank you so much for your persistence in identifying the resolution!