How would you implement a request-scoped audit log interceptor that captures both the request and response body in NestJS?

Q: How would you implement a request-scoped audit log interceptor that captures both the request and response body in NestJS?

@Injectable({ scope: Scope.REQUEST }) export class AuditInterceptor implements NestInterceptor { constructor( @Inject(REQUEST) private req: Request, private auditService: AuditService, ) {} intercept(ctx: ExecutionContext, next: CallHandler): Observable { const { method, url, body: reqBody } = this.req; const user = (this.req as any).user; const startTime = Date.now(); return next.handle().pipe( tap(responseBody => { this.auditService.log({ userId: user?.id, method, url, requestBody: reqBody, responseBody, durationMs: Date.now() - startTime, timestamp: new Date(), }); }), catchError(err => { this.auditService.logError({ userId: user?.id, method, url, error: err.message, }); throw err; // re-throw so filters still handle it }), ); } } Scope.REQUEST ensures a fresh instance per request — no state leaks between requests. @Inject(REQUEST) gives direct access to the request object including headers, body, and user. tap() logs on success without changing the response value. catchError() logs the error but re-throws — exception filters still format the error response. Register via APP_INTERCEPTOR with useClass so NestJS manages the REQUEST scope correctly.

Difficulty: 6/10

Interceptors, Request-scoped providers, Logging

Use Scope.REQUEST so a new interceptor instance is created per request — safe for storing request-level state. Inject the REQUEST token to access the request object. Use tap() to log the response body after the handler completes and catchError() to log failures before re-throwing.

Request-scoped audit interceptor

Design decisions for this pattern:

1
Scope.REQUEST ensures a fresh instance per request — no state leaks between requests.
2

How would you implement a request-scoped audit log interceptor that captures both the request and response body in NestJS?

Difficulty: 6/10

Interceptors, Request-scoped providers, Logging

Use Scope.REQUEST so a new interceptor instance is created per request — safe for storing request-level state. Inject the REQUEST token to access the request object. Use tap() to log the response body after the handler completes and catchError() to log failures before re-throwing.

Request-scoped audit interceptor

Design decisions for this pattern:

1
Scope.REQUEST ensures a fresh instance per request — no state leaks between requests.
2

How would you implement a request-scoped audit log interceptor that captures both the request and response body in NestJS?

Use Scope.REQUEST so a new interceptor instance is created per request — safe for storing request-level state. Inject the REQUEST token to access the request object. Use tap() to log the response body after the handler completes and catchError() to log failures before re-throwing.

How would you implement a request-scoped audit log interceptor that captures both the request and response body in NestJS?

Use Scope.REQUEST so a new interceptor instance is created per request — safe for storing request-level state. Inject the REQUEST token to access the request object. Use tap() to log the response body after the handler completes and catchError() to log failures before re-throwing.

Scenario Questions

Follow-up Questions