Vipi HTTP interceptors?

Question

Accepted Answer

**HTTP interceptors** vina katikati ya kila `HttpClient` hoja/jibu, na wakakuruhusu kuchunguza na kubadilisha kwa jumla. Wao ni mahali bora kwa **matatizo yanayokatiza** inayotumika kwa hoja zote — tokens ya uhalali, kurekodi, kushughulikia makosa, viashiria vya kupakia.

## Interceptor inayofanya kazi (Angular ya kisasa)

```ts
import { HttpInterceptorFn } from "@angular/common/http";
import { inject } from "@angular/core";

export const authInterceptor: HttpInterceptorFn = (req, next) => {
  const token = inject(AuthService).getToken();

// requests are immutable — CLONE to modify
  const authReq = req.clone({
    setHeaders: { Authorization: `Bearer ${token}` }, // attach token to EVERY request
  });

return next(authReq); // pass the (modified) request along the chain
};
```

Interceptor inakubali hoja na kazi ya `next` (mhusumaji anayefuata). Muhimu sana, hoja ni **isiyobadilika**, kwa hivyo wewe `.clone()` na mabadiliko badala ya kusonga. Kuandikisha hii mara moja inamaanisha kila hoja inayoenda nje kwa automatic inaburudisha kichwa cha uhalali — bila kurudia katika kila huduma.

## Kuandikisha interceptors

```ts
bootstrapApplication(AppComponent, {
  providers: [
    provideHttpClient(withInterceptors([authInterceptor, errorInterceptor, loggingInterceptor])),
  ],
});
```

Interceptors nyingi huunda **mlolongo**, kila mmoja inapitisha kwa ifuatayo — mpangilio ni muhimu.

## Kushughulikia majibu na makosa kwa jumla

```ts
import { catchError } from "rxjs/operators";
import { throwError } from "rxjs";

export const errorInterceptor: HttpInterceptorFn = (req, next) =>
  next(req).pipe(
    catchError((err) => {
      if (err.status === 401) inject(Router).navigate(["/login"]); // global 401 handling
      inject(NotificationService).showError(err.message);
      return throwError(() => err);
    })
  );
```

Kwa sababu interceptors huzunguka Observable ya jibu pia, unaweza kushughulikia makosa (mfano umelekezaji kwenye 401, kueleza toast) katika **mahali moja** kwa programu nzima.

## Matumizi ya kawaida ya interceptor

```text
✓ Attach auth tokens to requests
✓ Global error handling (401 → login, show notifications)
✓ Logging / analytics of all HTTP traffic
✓ Show/hide a global loading spinner
✓ Add common headers, retry logic, caching
```

## Kwa nini inamatter

Interceptors kuzunguka mantiki ambayo vinginevyo ingetolewa katika hojas za HTTP zote — mahalisi ni kuambatisha tokens ya uhalali na kushughulikia makosa kwa jumla.

Hii inaweka huduma safi (wao hutengeneza tu hojas) na kuhakikisha tabia inayoitikia kwa programu nzima.

Tokens ya uhalali na interceptors ya makosa ya jumla ni karibu na ulimwengu katika programu za Angular za uzalishaji; kujua sheria ya clone-to-modify na mfano wa mlolongo ni muhimu kwa kuandika kwa usahihi.