Nestjs拦截器没有被调用

Question

I am using NestJS with a serverless app (deployed to AWS Lambda). I now have a need to use middleware, or Interceptors as they are called in nest, but I'm struggling to get them to work. I have changed from using NestFactory.createApplicationContext to NestFactory.create , as per the docs, that's what wraps Controller methods with enhancers, eg Interceptors

I am registering the Interceptor in a module, so it should be globally available

const loggingInterceptorProvider = {
  provide: APP_INTERCEPTOR,
  useClass: LoggingInterceptor,
};

My bootstrap looks like so

export async function bootstrap(Module: any) {
  if (app) return app;
  app = await NestFactory.createApplicationContext(Module);
 return await app.init();
}

Now the non-standard bit, because I am using a generic "builder" (library code), the builder is passed the controller name as a string, and it is then invoked, as such

// the Module is accessible in the bootstrap via a closure, not shown in this code
const app = await bootstrap();
const appController = app.get(Controller);
// functionName is a string
const controllerFunction = appController[functionName];

const boundControllerFunction = controllerFunction.bind(
  appController,
);

const result = await boundControllerFunction(body);

I am not seeing any of my Interceptor logging output. Am I doing something wrong? Or is it the way I am invoking the Controller that is not working with Interceptors?

EDIT:

For completeness, this is the correct bootstrap function I use

let cachedApp: INestApplication;
export async function bootstrap(Module: any) {
  if (cachedApp) return cachedApp;

  cachedApp = await NestFactory.create(Module, {
    bufferLogs: true,
    logger: ['error', 'warn'],
  });

  await cachedApp.init();

  return cachedApp;
}

Answer 1

It happens because you've called the controller method directly, bypassing the nestjs lifecycle. When nest js server handles the request it applies its internal mechanisms for running interceptors, validation pipes, and exception filters. If you call class method directly it will not be used.

In your case you can follow this section of nestjs documentation:

https://docs.nestjs.com/faq/serverless#example-integration

let server: Handler;

async function bootstrap(): Promise<Handler> {
  const app = await NestFactory.create(AppModule);
  await app.init();

  const expressApp = app.getHttpAdapter().getInstance();
  return serverlessExpress({ app: expressApp });
}

export const handler: Handler = async (
  event: any,
  context: Context,
  callback: Callback,
) => {
  server = server ?? (await bootstrap());
  return server(event, context, callback);
};

The "standalone application feature" from docs is useful if you want to call some service code, not a controller.

---

By the way, in the code snippet, you can see the variable server , they moved it outside of a handler function intentionally. Because in AWS lambdas it can be cached between different requests.

Answer 2

I found a/the way to do it, using the very poorly documented feature ExternalContextCreator . So basically the last code snippet I posted above, would become this

  import { ExternalContextCreator } from '@nestjs/core/helpers/external-context-creator';   

  // the Module is accessible in the bootstrap via a closure, not shown in this code
  const app = await bootstrap();
  const appController = app.get(Controller);
  // functionName is a string
  const controllerFunction = appController[functionName];

  const extContextCreator = app.get(ExternalContextCreator);

  const boundControllerFunction = extContextCreator.create(
    appController,
    controllerFunction,
    String(functionName),
  );

  const result = await boundControllerFunction(body);