boneyB
tRPC•3y ago•
5 replies
boney

Unable to get mutation to trigger subscription because EventEmitter not being shared

Hey folks,

Been struggling with this for a few hours now hopelessly and trying random things - read all related posts in this forum, on github issues, and stackoverflow - and still don't understand what is going on.

I have a next app with a custom HTTP server and using tRPC. WSLink etc is all fine - i'm doing everything the proper way.

I have a router with these two functions:
 sendMessage: protectedProcedure
    .input(z.string())
    .mutation(async ({ ctx, input }) => {
      try {
        const chatRepo = new CommunityChatRepository(ctx.prisma);
        const result = await chatRepo.sendMessage(ctx.session!.user.id, input);

        if (!result.ok) throw result.error;
        console.log({ namesSendMsg: wsee.eventNames() });

        wsee.emit('onNewMessage', result.value);

        return result.value;
      } catch (error) {
        if (error instanceof TRPCError) {
          throw error;
        } else {
          console.error(error);
          throw new TRPCError({
            code: 'INTERNAL_SERVER_ERROR',
            message: 'Internal server error',
          });
        }
      }
    }),

  onNewMessage: publicProcedure.subscription(() => {
    return observable<ChatMessageWithSenderInformation>((emit) => {
      const onNewMessage = (data: ChatMessageWithSenderInformation) => {
        emit.next(data);
      };

      console.log({ names: wsee.eventNames() });
      wsee.on('onNewMessage', onNewMessage);
      console.log({ names: wsee.eventNames() });

      console.log(`added listener ${wsee.listenerCount('onNewMessage')}`);

      return () => {
        console.log(`removed listener ${wsee.listenerCount('onNewMessage')}`);
        wsee.off('onNewMessage', onNewMessage);
      };
    });
  }),


I've added a bunch of console logs to help explain.

So, in my logs I see that when the app loads up I get a WS Connection to the server.

On the client side, I have trpc.chat.onNewMessage.useSubscription which console logs {names: []} first and then {names: ['onNewMessage']} as it should based on the code for the router.

But, when I send a message, the mutation fails to trigger the subscription because it logs {namesSendMsg: []} i.e. for some reason it does;n't recognize the attached listener

I thought it was because maybe somehow multiple EventEmitter instances are being created due to HMR - so I did a workaround similar to what we do with Prisma for next dev mode:

src/eventEmitter.ts:
import { EventEmitter } from 'events';

import type { ChatMessageWithSenderInformation } from './server/repositories/CommunityChatRepository';

interface WSEvents {
  // Community Chat
  onNewMessage: (message: ChatMessageWithSenderInformation) => void;

  // Trivia
  join: () => void;
  getQuestions: () => void;
  onRankingUpdate: () => void;
  onChoiceUpdate: () => void;
}

export declare interface WSEventEmitter {
  on<WEv extends keyof WSEvents>(event: WEv, listener: WSEvents[WEv]): this;
  off<WEv extends keyof WSEvents>(event: WEv, listener: WSEvents[WEv]): this;
  once<WEv extends keyof WSEvents>(event: WEv, listener: WSEvents[WEv]): this;
  emit<WEv extends keyof WSEvents>(
    event: WEv,
    ...args: Parameters<WSEvents[WEv]>
  ): boolean;
}

export class WSEventEmitter extends EventEmitter {}

const globalForWSEE = globalThis as unknown as { wsee: WSEventEmitter };
const isDevMode = process.env.NODE_ENV !== 'production';

export const wsee = globalForWSEE.wsee || new WSEventEmitter();

if (isDevMode) globalForWSEE.wsee = wsee;


this did not help either. using this wsee everywhere doesn't change anything. im lost and have no idea WHY there are supposedly two different event emitter instances being used here?
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