Apa iku middleware ing NestJS lan kumaha bedane karo guards/interceptors?

Question

Accepted Answer

**Middleware** yaiku fungsi sing mlaku **sadurunge route handler**, kanthi akses menyang request lan response objects — konsep sing padha karo Express middleware. NestJS uga nduweni guards, interceptors, pipes, lan filters, saben-saben mlaku ing titik spesifik ing request lifecycle kanthi tujuan sing beda. Ngerti endi sing digunakake iku kunci.

## Middleware — mlaku pisma, nduweni req/res

```ts
@Injectable()
export class LoggerMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: NextFunction) {
    console.log(`${req.method} ${req.url}`);   // logging, modifying req
    next();                                      // MUST call next() to continue
  }
}

// register in a module
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(LoggerMiddleware).forRoutes("*");   // apply to routes
  }
}
```

Middleware mlaku paling awal, sadurunge guards/interceptors/pipes, lan gumana karo `req`/`res` mentah — apik kanggo logging, modifikasi request, CORS, lan Express-compatible concerns.

## Urutan request lifecycle lengkap

```text
Request →
  1. Middleware     (req/res; runs first, Express-style)
  2. Guards         (return true/false → AUTHORIZE or block the request)
  3. Interceptors   (BEFORE the handler)
  4. Pipes          (validate/transform the handler's arguments)
  5. → Route Handler ←
  6. Interceptors   (AFTER the handler — transform the response)
  7. Exception Filters (if an error was thrown anywhere)
→ Response
```

## Apa-apa sing digunakake kanggo (milih alat sing tepat)

```text
Middleware  → general pre-processing with req/res (logging, CORS, raw request work)
Guards      → AUTHORIZATION — decide if a request may proceed (auth, roles)
              (return true = allow, false/throw = block)
Interceptors→ wrap the handler — transform request/response, add logging/caching/timing
              (can run logic BEFORE and AFTER the handler)
Pipes       → VALIDATE/TRANSFORM the handler's input arguments (DTO validation)
Filters     → catch and format EXCEPTIONS into responses
```

Distingsi kunci: middleware yaiku pre-processing gaya Express generik; **guards** khusus nangani authorization (tempat sing bersih lan khusus kanggo auth, tinimbang ngumpulake ing middleware); **interceptors** mbungkus handler kanggo transform responses utawa nambahake cross-cutting behavior; **pipes** validasi input; **filters** nangani errors.

## Kapan nggunakake middleware versus guards versus interceptors

```text
Auth check?           → Guard (dedicated, has execution context, returns boolean)
Logging requests?     → Middleware OR an interceptor (interceptor sees the response too)
Transform responses?  → Interceptor (runs after the handler)
Validate a DTO?       → Pipe
Modify raw req early?  → Middleware
```

## Apa iki penting

Ngerti middleware lan bedane karo guards, interceptors, pipes, lan filters yaiku essential kanggo strukturisasi NestJS applications kanthi bener — saben-saben nduweni peran spesifik lan mlaku ing titik spesifik ing request lifecycle, lan nggunakake sing tepat nyebabake kode sing bersih lan idiomatic.

Middleware nangani pre-processing gaya Express umum kanthi raw req/res.

Distingsi krusial yaiku **guards** yaiku tempat khusus lan bener kanggo authorization (auth/roles) — luwih bersih tinimbang middleware kanggo tujuan kasebut — lan **interceptors** mbungkus handler kanggo transform responses lan nambahake cross-cutting concerns (logging, caching, timing) sing middleware ora bisa gampang gawe (amarga mlaku sadurunge handler lan ora natural ndelok response).

Ngerti urutan lifecycle lengkap (middleware → guards → interceptors → pipes → handler → interceptors → filters) lan alat apa sing cocok kanggo saben concern (auth → guard, response transformation → interceptor, validation → pipe, errors → filter) yaiku tanda NestJS competence lan nyegah kesalahan umum nggunakake middleware kanggo kabeh.

Iki yaiku topik sing sering ditest, penting ing arsitektur ing framework.