Waɗansu exception filters?

Question

Accepted Answer

**Exception filters** suna ba ka cikakken iko akan yadda za a kama kuskure da sauya su zuwa amsosai. Suna zaune a ƙarshე na lifecycle na buɗin, suna kama junkuna da aka jefar a duk a cikin buɗin suna ba ka damar gyara tsarin amsowa ta kurakira, matsanancin HTTP, da rubuce-rubucen makiya.

## Ƴan kama exception na asali

```ts
import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from "@nestjs/common";

@Catch(HttpException)                    // catch HttpExceptions specifically
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const request = ctx.getRequest();
    const status = exception.getStatus();

// build a CUSTOM error response shape
    response.status(status).json({
      statusCode: status,
      timestamp: new Date().toISOString(),
      path: request.url,
      message: exception.message,
    });
  }
}
```

`@Catch()` decorator yana bayyana nawa nau'awa na junkuna wannan kama yake jaki, kuma `catch()` hanya tana karba junkuna da halin - ga jiya ka ƙera duk amin amsowar da kake so.

## Kama duk junkuna (da sauyi kuma)

```ts
@Catch()                                 // no argument = catch EVERYTHING
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const status = exception instanceof HttpException
      ? exception.getStatus()
      : 500;                              // unknown errors → 500
    // log the full error internally, return a safe message to the client
    this.logger.error(exception);
    ctx.getResponse().status(status).json({ statusCode: status, message: "..." });
  }
}
```

Kama tare da `@Catch()` (babu hujja) yana jaki kowane junkuna — waje don rubuce-rubucen makiya wajen da ba a sakaci da insure cewa ko non-HTTP junkuna suna dawo da tsabtacciyar amsowar (ba baba ba da stack traces ga abokan ciniki).

## Aiwata kama

```ts
@UseFilters(HttpExceptionFilter)         // method or controller level
export class UsersController {}

app.useGlobalFilters(new AllExceptionsFilter());   // GLOBAL — app-wide, most common
```

Kama ana aiwata **jajajjace** ne don insure matsanancin nau'awa ta kurakira jajajjace a duk API.

## Me ya sa a yi amfani da exception filters?

```text
✓ Consistent error response format across ALL endpoints (a standard shape)
✓ Centralized error LOGGING (log every error in one place)
✓ Handle non-HTTP errors safely (turn unexpected errors into clean 500s)
✓ Hide internal details from clients (no leaked stack traces — security)
✓ Add context (request path, timestamp, correlation IDs) to error responses
```

## Kama da jefar da junkuna

```text
Throwing exceptions (NotFoundException, etc.) → SIGNALS an error with a status
Exception filters → control HOW those errors are FORMATTED/logged into responses
→ You throw exceptions in your code; filters customize the resulting response globally.
```

## Me ya sa ya matuwa

Exception filters abokin buƙatu na NestJS don gina jajajjace, ingantacciyar API tare da **matsanancin, jari shakatawa ta kurakira**.

Sai dai NestJS na gari na kurakira layer yana jiya shi shan junkuna zuwa HTTP amsosai, exception filters suna ba ka cikakken iko don sauya haka halaye — abin da ke da mahimmanci ga wasiku na gida: insure **matsanancin sauyan kurakira-amsowar tsari** a duk gefen endpoint (don abokan ciniki koyaushe suna karba kurakira a tsari iri daya), **tsakiya makiya rubuce-rubuce** (kama duk kurakira a waje gida maimakon watse-watse try/catch), sannu **wajuyi jagun non-HTTP junkuna** (sauya su zuwa tsabtacciyar 500s maimakon kafe ko baba ba da alƙalomi), da **tsaro** (boye ciki stack traces da baba-bakin alƙalomi daga abokan ciniki yayin rubuce-rubucen ciki).

Gajajjaciyar "kama duk" kama ⁇ tare da jefar da takaici HTTP junkuna a cikin nawan ka ce daidai tsarin don gida-matsananci shakatawa ta kurakira.

Dimana lokaci da yadda za a yi amfani da kama (maimakon jefa junkuna kawai), da aiwata su jajajjace don tsari, abokin buƙatu ne na da ingantaccin NestJS aikace-aikace da ya nuna balaga back-end aiki-aiki kewaye da abubuwan da ba a game da su ba amma mahimmanci wasika na kurakira shakatawa.