How to use `localLink` (`unstable_localLink`)

This is more of a guide, rather than a question since I've found no docs on how to use this function to fix SSR related issues.
So, based on https://orpc.unnoq.com/docs/best-practices/optimize-ssr I've managed to cook something that has fixed my issues with the headers not passed to the requests on initial SSR of "use client" components (nextjs).
So, in my

trpc/server/index.ts

trpc/server/index.ts

(usually

server.ts

server.ts

) I added the following:

globalThis.$getTRPCServerSideTerminatingLink = () => unstable_localLink({
  router: appRouter,
  createContext: createContext,
  transformer,
})

globalThis.$getTRPCServerSideTerminatingLink = () => unstable_localLink({
  router: appRouter,
  createContext: createContext,
  transformer,
})

trpc/client.ts

trpc/client.ts

declare global {
  /** HACK: For SSR we wan't to use a `localLink` directly instead of going over HTTP so that headers are properly forwarded (Otherwise auth won't work) */
  var $getTRPCServerSideTerminatingLink: (() => TRPCLink<AppRouter>) | undefined;
}

declare global {
  /** HACK: For SSR we wan't to use a `localLink` directly instead of going over HTTP so that headers are properly forwarded (Otherwise auth won't work) */
  var $getTRPCServerSideTerminatingLink: (() => TRPCLink<AppRouter>) | undefined;
}

and also:

export const TRPCWithReactQueryProvider = ({ children, queryClient }: TRPCWithReactQueryProviderProps) => {
  const qc = queryClient ?? getQueryClient();

  const links: TRPCLink<AppRouter>[] = [];

  /** Add terminating link */
  if (isServer) {
    const link = globalThis.$getTRPCServerSideTerminatingLink?.();
    if (link) {
      links.push(link);
    } else {
      throw new Error('No server-side `terminating link` found on globalThis');
    }
  } else {
    links.push(
      httpBatchLink<AppRouter>({
        url: '/api/trpc',
        transformer,
      }),
    );
  }

  const [trpcClient] = useState(() =>
    createTRPCProxyClient<AppRouter>({
      links
    }),
  );
  
  // ....
};

export const TRPCWithReactQueryProvider = ({ children, queryClient }: TRPCWithReactQueryProviderProps) => {
  const qc = queryClient ?? getQueryClient();

  const links: TRPCLink<AppRouter>[] = [];

  /** Add terminating link */
  if (isServer) {
    const link = globalThis.$getTRPCServerSideTerminatingLink?.();
    if (link) {
      links.push(link);
    } else {
      throw new Error('No server-side `terminating link` found on globalThis');
    }
  } else {
    links.push(
      httpBatchLink<AppRouter>({
        url: '/api/trpc',
        transformer,
      }),
    );
  }

  const [trpcClient] = useState(() =>
    createTRPCProxyClient<AppRouter>({
      links
    }),
  );
  
  // ....
};

I also had to add imports to

instrumentation.ts

instrumentation.ts

(See the orpc docs), and to my very root

layout

layout

(Just make sure it's not

use client

use client

!)

Question:
Is this is safe to do on the server side? (As in, does

localLink

localLink

do any kind of caching or something that could leak data between users?)

Optimize Server-Side Rendering (SSR) for Fullstack Frameworks - oRPC

Optimize SSR performance in Next.js, SvelteKit, and other frameworks by using oRPC to make direct server-side API calls, avoiding unnecessary network requests.

How to use `localLink` (`unstable_localLink`)

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