GraphQL subscription isn't triggered after PubSub publish - websocket

Question

I'm trying to create a basic subscriptions system using WebSockets, TypeGraphQL and Apollo Server. I've created the WS server and it seems to work correctly.
import express from 'express'
import cors from 'cors'
import cookieParser from 'cookie-parser'
import { ApolloServer } from 'apollo-server-express'
import { ApolloServerPluginLandingPageGraphQLPlayground } from 'apollo-server-core'
import { buildSchema } from 'type-graphql'
import { MessageResolver } from './resolvers/messageResolver'
import { appDataSource } from './dataSource'
import { PubSub } from 'graphql-subscriptions'
import http from 'http'
import { WebSocketServer } from 'ws'
const main = async () => {
appDataSource.initialize().then(() => {
console.log("DataSource initialized.")
})
const app = express()
app.set('trust proxy', 1)
app.use(
cors({
origin: process.env.CORS_ORIGIN,
credentials: true,
})
)
app.use(cookieParser())
const schema = await buildSchema({
resolvers: [MessageResolver],
validate: false
})
const pubsub = new PubSub();
const apolloServer = new ApolloServer({
plugins: [
ApolloServerPluginLandingPageGraphQLPlayground(),
],
schema,
context: ({ req, res }) => ({ req, res, pubsub }),
})
await apolloServer.start()
apolloServer.applyMiddleware({ app, cors: false })
const httpServer = http.createServer()
const wss = new WebSocketServer({
server: httpServer
})
httpServer.on('request', app);
httpServer.listen(5000, function () {
console.log(`http/ws server listening on 5000`);
});
wss.on('connection', function connection(ws) {
ws.on('message', function incoming(message) {
console.log(`received: ${message}`);
ws.send(JSON.stringify({
answer: 42
}));
});
});
}
main().catch((err) => {
console.error(err.stack);
})
Here are my subscription and my mutation:
#Subscription({
topics: "NOTIFICATIONS"
})
test(
#Root() message: string,
): string {
return message
}
#Mutation(() => Boolean)
async addNewComment(
#Arg("message") message: string,
#PubSub("NOTIFICATIONS") publish: Publisher<string>
) {
await Message.create({ message }).save()
await publish(message);
return true;
}
The problem I have is that when I use the mutation, the subscription should be triggered. This thing doesn't happen and I don't know why. Do you have any ideas?
Thank you!