Nestjs 错误：将标头发送到客户端后无法设置标头

Question

I have a global middleware and a global guard, when request goes into the guard it apparently sends a response(the request doesn't get to the controllers), which is strange because the client gets 404, and nestjs throws an error "Cannot set headers after they are sent to the client". If I disable the middleware everything works fine. How can i fix this?

Middleware:

@Injectable()
export class AuthMiddleware implements NestMiddleware {
  @Inject()
  private readonly usersService: UsersService;
  @Inject()
  private readonly tokenService: TokenService;



  async use(req: Request, res: Response, next: NextFunction): Promise<void> {
    if (!req.cookies.token) {
      req.user = {
        userId: null,
        personId: null,
        role: null,
      };

      next();
    }

    try {
      const result = this.tokenService.verifyToken(req.cookies.token);
      const user = await this.usersService.findOne(result.userId);

      if (!user) {
        req.user = {
          userId: null,
          personId: null,
          role: null,
        };

        next();
      }

      req.user = {
        userId: result.userId,
        personId: result.personId,
        role: result.role,
      };
    } catch {
      req.user = {
        userId: null,
        personId: null,
        role: null,
      };
    }

    next();
  }
}

Guard:

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

  async canActivate(context: ExecutionContext): Promise<boolean> {
    const req: Request = await context.switchToHttp().getRequest();

    const requiredRole = this.reflector.get<Roles | null>(
      'requiredRole',
      context.getHandler(),
    );

    if (!requiredRole) {
      return true; // everything breaks here
    }

    if (
      requiredRole !== req.body.user.role &&
      req.body.user.role !== Roles.ADMIN
    ) {
      return false;
    }

    return true;
  }
}

main.ts:

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.use(cookieParser());
  app.use(urlencoded({ extended: true }));
  app.useGlobalPipes(
    new ValidationPipe({
      transform: true,
    }),
  );
  app.useGlobalGuards(new RoleGuard(new Reflector()));

  await app.listen(3000);
}
bootstrap();

app.module.ts:

@Module({
  imports: [
    ConfigModule.forRoot({
      envFilePath: '.env',
    }),
    TypeOrmModule.forRoot(getOrmConfig()),
    UserModule,
    EventModule,
  ],
  controllers: [],
  providers: [RoleGuard],
})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer.apply(AuthMiddleware).forRoutes({
      path: '*',
      method: RequestMethod.ALL,
    });
  }
}

Answer 1

Somehow I managed to fix it by deleting this from AuthGuard:

if (!req.cookies.token) {
    req.user = {
    userId: null,
    personId: null,
    role: null,
  };

  next();
}

Maybe someone knows why it worked?

Answer 2

I suppose it happens due to inappropriate next() function call implementation.

The error you are getting is because after calling next() , you have some additional code to run which will call next() which will cause your controller to send a response back to the client, but it was already sent by your first call.

To fix current realisation simple change next() - > to return next() here more info about it