Switching tRPC httpLink to httpBatchLink changes expired credential enforcement

Answer

Switching from httpLink to httpBatchLink does not change where credential validation belongs; it only changes how often createContext runs.

Confirmed facts (based on tRPC design)

• httpBatchLink sends a single HTTP request containing an array of procedure calls.
• The server executes createContext once per HTTP request, so all procedures in the same batch share the same context object.
• Each procedure is then processed by the router and its middleware independently; the response is a JSON array where each element corresponds to the procedure’s result or error.

Likely explanation for credential expiry

If your credential check lives in per‑procedure middleware (e.g., a trpc.middleware that throws TRPCError.UNAUTHORIZED), an expired credential will cause only that procedure’s array entry to contain an error object, while other procedures in the same batch succeed.

If the check is placed inside createContext (or any middleware that runs before the router and throws on the shared context), the entire batch will fail because the shared context is invalid for every procedure.

Steps to achieve per‑procedure UNAUTHORIZED while keeping valid procedures

1. Move credential validation into a procedure‑level middleware (or directly into each procedure) rather than createContext.
2. Ensure the middleware throws TRPCError.UNAUTHORIZED (or a custom error with code UNAUTHORIZED) when the token is expired.
3. Keep using httpBatchLink on the client; no client‑side change is required beyond handling the batch response.
4. On the client, iterate over the response array and treat any entry with error.code === 'UNAUTHORIZED' as a signal to refresh credentials before retrying that specific procedure.

Missing diagnostic detail

Please confirm which major version of @trpc/server you are using (e.g., v10.x). The exact timing of createContext execution is stable across recent major versions, but older versions may differ and could affect the recommendation.