Dedupe Middleware

Optimize middleware for fast and efficient repeated execution.

Problem

When a procedure calls another procedure, overlapping middleware may run in both. Similarly, .use(auth).router(router) may run auth multiple times.

Solution

Track middleware execution via context to prevent duplication:

const dbProvider = os
  .$context<{ db?: Awaited<ReturnType<typeof connectDb>> }>()
  .middleware(async ({ context, next }) => {
    const db = context.db ?? await connectDb()
    return next({ context: { db } })
  })

Now dbProvider can be safely applied multiple times without duplicating the connection:

const foo = os.use(dbProvider).handler(({ context }) => 'Hello World')

const bar = os.use(dbProvider).handler(({ context }) => {
  const result = call(foo, 'input', { context })
  return 'Hello World'
})

const router = os
  .use(dbProvider)
  .use(({ next }) => next())
  .router({ foo, bar })

Built-in Dedupe

oRPC auto-dedupes middleware when the router's middlewares are a subset of the leading procedure middlewares and appear in the same order.

const router = os.use(logging).use(dbProvider).router({
  // ✅ Deduplicated:
  ping: os.use(logging).use(dbProvider).use(auth).handler(() => 'ping'),
  pong: os.use(logging).use(dbProvider).handler(() => 'pong'),

  // ⛔ Not deduplicated:
  diff_subset: os.use(logging).handler(() => 'ping'),
  diff_order: os.use(dbProvider).use(logging).handler(() => 'pong'),
  diff_leading: os.use(monitor).use(logging).use(dbProvider).handler(() => 'bar'),
})

Configuration

Disable with .$config:

const base = os.$config({ dedupeLeadingMiddlewares: false })