Rate limiting

rateLimit() counts calls with Effect's RateLimiter (effect/persistence). The store is a layer on the handler: layerStoreMemory for one instance, layerStoreRedis for many.

import { RateLimiter } from 'effect/persistence';
import { rateLimit } from '@trpc12/trpc/middleware';

const login = t.procedure
  .use(
    rateLimit<{ ctx: { ip: string } }>({
      key: (opts) => `login:${opts.ctx.ip}`,
      limit: 5,
      window: '1 minute',
    }),
  )
  .mutation(/* … */);

createFetchHandler({
  router,
  layer: RateLimiter.layer.pipe(Layer.provide(RateLimiter.layerStoreMemory)),
});

Past the limit it fails with RateLimited (TOO_MANY_REQUESTS, 429, data: { limit, retryAfter } in milliseconds), and it sets RateLimit-Limit, RateLimit-Remaining, RateLimit-Reset and Retry-After. onExceeded: 'delay' waits for capacity instead.

On the client

RateLimited is a typed error, so the client narrows on its code. retryLink({ retry, delayMs }) gets the error, so it can wait error.data.retryAfter (retryLink).