Built-in middleware

@trpc12/trpc/middleware has middleware for common jobs. Each one is ordinary middleware: apply it with .use() on a procedure or a base procedure, and give the handler the layer it needs, if any.

import { function onError(fn: (error: AnyTrpcError, opts: AnyOpts) => MaybePromise<void>): MiddlewareFunction<unknown, unknown, unknown, {}, never>onError } from '@trpc12/trpc/middleware';

const const logged: ProcedureBuilder<With<RootDef<Context, {}>, {
    ctx: Context;
    ctxAdded: {};
    inputOut: Unset;
    errors: never;
    shorts: never;
}>>logged = const t: TrpcRoot<Context, {}, RootDef<Context, {}>>t.TrpcRoot<Context, {}, RootDef<Context, {}>>.procedure: ProcedureBuilder<RootDef<Context, {}>>procedure.ProcedureBuilder<RootDef<Context, {}>>.use<{}, never, never, Unset, object>(fn: MiddlewareFunction<{
    user: User | null;
} & object, undefined, {}, {}, never, never, Unset>): ProcedureBuilder<With<RootDef<Context, {}>, {
    ctx: Context;
    ctxAdded: {};
    inputOut: Unset;
    errors: never;
    shorts: never;
}>> (+1 overload)use(
  function onError(fn: (error: AnyTrpcError, opts: AnyOpts) => MaybePromise<void>): MiddlewareFunction<unknown, unknown, unknown, {}, never>onError((err: AnyTrpcErrorerr, opts: AnyOptsopts) => var console: Consoleconsole.Console.error(...data: any[]): voiderror(opts: AnyOptsopts.MiddlewareOpts<unknown, unknown, unknown>.path: stringpath, err: AnyTrpcErrorerr.TrpcError<string, any>.code: stringcode)),
);

Middleware	Does	Needs on the handler
Lifecycle hooks	`onStart`, `onSuccess`, `onError` and `onFinish` run code around each call, for logs and metrics	nothing
Rate limiting	`rateLimit()` fails calls past a limit per key, and sets the `RateLimit` headers	a `RateLimiter` layer, in memory or Redis
Locks	`experimental_lock()` runs calls with the same key one at a time, across instances	an `experimental_Locker` layer, in memory, Redis or Durable Objects
Durable calls	`experimental_durable()` keeps a call's result, so a client that lost the response gets it instead of running the mutation twice	a `BackingPersistence` layer

To add middleware, context, meta and errors to every procedure of an app from a package, see Extensions.