NestJS
Lifecycle

@Injectable()
export class RequestIdMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: NextFunction) {
    const id = req.header('x-request-id') ?? randomUUID();
    req.headers['x-request-id'] = id;
    res.setHeader('x-request-id', id);
    next(); // forget this and the request hangs forever
  }
}

@Module({ controllers: [GamesController] })
export class GamesModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer
      .apply(RequestIdMiddleware)
      .exclude({ path: 'health', method: RequestMethod.GET })
      .forRoutes(GamesController);
  }
}

export const Roles = Reflector.createDecorator<string[]>();

@Injectable()
export class RolesGuard implements CanActivate {
  constructor(private readonly reflector: Reflector) {}

  canActivate(ctx: ExecutionContext): boolean {
    const roles = this.reflector.getAllAndOverride(Roles, [ctx.getHandler(), ctx.getClass()]);
    if (!roles) return true; // no roles on the route: open
    const user = ctx.switchToHttp().getRequest().user;
    if (!user) throw new UnauthorizedException();
    return roles.some((r) => user.roles.includes(r));
  }
}

@Roles(['admin'])
@Delete(':id')
remove(@Param('id', ParseIntPipe) id: number) {}

@Injectable()
export class TimingInterceptor implements NestInterceptor {
  private readonly log = new Logger('HTTP');

  intercept(ctx: ExecutionContext, next: CallHandler): Observable<unknown> {
    const start = performance.now();
    const { method, url } = ctx.switchToHttp().getRequest();
    return next.handle().pipe(
      map((data) => ({ data })), // wrap every body in one envelope
      tap(() => this.log.log(`${method} ${url} ${Math.round(performance.now() - start)}ms`)),
    );
  }
}

export class CreateGameDto {
  @IsIn(['classic', 'ranked']) mode: string;
  @IsInt() @Min(2) @Max(8) players: number;
  @IsOptional() @IsString() @MaxLength(40) name?: string;
}

// main.ts
app.useGlobalPipes(new ValidationPipe({
  whitelist: true,            // strip fields the DTO does not declare
  forbidNonWhitelisted: true, // or reject them with a 400
  transform: true,            // plain JSON becomes a CreateGameDto instance
}));

@Catch()
export class ProblemFilter implements ExceptionFilter {
  catch(err: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const req = ctx.getRequest<Request>();
    const status = err instanceof HttpException ? err.getStatus() : 500;
    ctx.getResponse<Response>().status(status).json({
      status,
      error: err instanceof HttpException ? err.message : 'Internal error',
      path: req.url,
      requestId: req.headers['x-request-id'],
    });
  }
}

const trail = [];
const say = (s) => trail.push(s);
const fail = (msg, status) => Object.assign(new Error(msg), { status });

const middleware = [() => say('middleware  requestId'), () => say('middleware  parse token')];
const guards = [() => (say('guard       throttle'), true), (req) => (say('guard       roles'), req.role === 'admin')];
const interceptors = ['global timing', 'route transform'];
const pipes = [(v) => (say('pipe        ParseIntPipe'), Number(v))];
const filters = [
  (e) => (e.status === 404 ? 'route filter    404 ' + e.message : null),
  (e) => 'global filter   ' + (e.status || 500) + ' ' + e.message,
];

function handle(req, handler) {
  trail.length = 0;
  try {
    middleware.forEach((m) => m(req));
    for (const g of guards) if (!g(req)) throw fail('Forbidden resource', 403);
    const call = interceptors.reduceRight((next, name) => () => {
      say('before      ' + name);
      const out = next();
      say('after       ' + name);
      return out;
    }, () => handler(pipes.reduce((v, p) => p(v), req.id)));
    call();
    say('response    200');
  } catch (e) {
    for (const f of filters) { const r = f(e); if (r) { say(r); break; } }
  }
  return trail.join('\n');
}

const findGame = (id) => {
  say('handler     findGame(' + id + ')');
  if (id !== 42) throw fail('Game not found', 404);
};

console.log('# admin asks for game 42');
console.log(handle({ role: 'admin', id: '42' }, findGame));
console.log('# player asks for game 42');
console.log(handle({ role: 'player', id: '42' }, findGame));
console.log('# admin asks for game 7');
console.log(handle({ role: 'admin', id: '7' }, findGame));