Can I alter the context in a procedure?

Is there a proper way to do this? Mutating the opts.ctx directly seems wrong

2 Replies

NeoBean•12mo ago

I think middlewares are meant for things like this? You define your initial context types when instantiating trpc. Then you use a middleware that appends variables to the context. You can opts.next({ user: user }) and next middlewares/queries/mutations will the ctx.user typed. Is this what you're looking for?

handsaway•12mo ago

I need to keep track of a session id across the lifespan of a websocket connection to correlate messages to users, the client also keeps this in local storage to handle re-connection flows

  registerSession: publicProcedure
    .input(z.object({ sid: z.nullable(z.string()) }))
    .mutation(async (opts) => {
      logger.info('registerSession');
      // Already an sid attached to this websocket
      if (opts.ctx.sid !== undefined) {
        logger.info(
          'registerSession called with existing sessionId on websocket'
        );
        return opts.ctx.sid;
      }

      if (opts.input.sid === undefined) {
        logger.info('Generating new sessionId');
      } else {
        logger.info('Using sessionId supplied by client', {
          sessionId: opts.input.sid,
        });
      }

      const sid = opts.input.sid ?? uuidV4();

      // Not positive that this is the best place to keep the sid,
      // but it's available in the context this way
      opts.ctx.ws['sid'] = sid;
      return sid;
    }),

  registerSession: publicProcedure
    .input(z.object({ sid: z.nullable(z.string()) }))
    .mutation(async (opts) => {
      logger.info('registerSession');
      // Already an sid attached to this websocket
      if (opts.ctx.sid !== undefined) {
        logger.info(
          'registerSession called with existing sessionId on websocket'
        );
        return opts.ctx.sid;
      }

      if (opts.input.sid === undefined) {
        logger.info('Generating new sessionId');
      } else {
        logger.info('Using sessionId supplied by client', {
          sessionId: opts.input.sid,
        });
      }

      const sid = opts.input.sid ?? uuidV4();

      // Not positive that this is the best place to keep the sid,
      // but it's available in the context this way
      opts.ctx.ws['sid'] = sid;
      return sid;
    }),

I have this where I'm kind of shoving the uuid onto the websocket object then

export const createWSContext = async (opts: CreateWSSContextFnOptions) => {
  const sid: string = opts.res['sid'];
  logger.debug('createWSContext', { sid });
  return { sid, ws: opts.res };
};

export const createWSContext = async (opts: CreateWSSContextFnOptions) => {
  const sid: string = opts.res['sid'];
  logger.debug('createWSContext', { sid });
  return { sid, ws: opts.res };
};

But this doesn't seem like the best way to do this like I'm just hijacking the websocket object, but I guess i need something in memory to mutate to retrieve a session id in teh create context