Resolve promise before registering middleware and exposing routes

[matt-mcdaniel]

I need to fetch a secret from a secrets manager using an async request to use for my middleware, but I find that I get no response or a timed out one when I try and wrap my middleware and routes in a promise chain.

getSecret().then(secret => {
  const strategy = new OAuth2Strategy({
    secret: secret
  }, function (accessToken, refreshToken, params, profile, done) {
    done(null,{data: 'some user data'});
  })


  passport.use('oauth2', strategy);
  refresh.use('oauth2', strategy);

  app.get('/my_route', async function (req, res) {
    ...
  })
})

What is the best way to deal with async code that needs to be resolved before I expose my routes?

[brettstack]

I'll need a more complete example to help with this. What's your lambda handler look like? You'll need something like:

let serverlessExpressHandler

const getAppPromise = getApp().then(app => {
  serverlessExpressHandler = serverlessExpress({ app }).handler
})

exports.handler = async (event, context) => {
  if (!serverlessExpressHandler) {
    await getAppPromise 
  }

  return serverlessExpressHandler(event, context)
}

[matt-mcdaniel]

Thanks @brettstack, I'm trying to understand how to return the app as a promise so that I can fetch my secret. Take the following for example:

If I have, as you suggested, for my lambda.js

const getApp = require('./app');

let serverlessExpressHandler

const getAppPromise = getApp().then(app => {
  serverlessExpressHandler = serverlessExpress({ app }).handler
})

exports.handler = async (event, context) => {
  if (!serverlessExpressHandler) {
    await getAppPromise 
  }

  return serverlessExpressHandler 
}

and for my app.js I have exported a function that returns a promise

module.exports = () => {
    return new Promise((resolve, reject) => {
        const app = express();

        app.get('/', (req, res) => {...})
        
        resolve(app)
    })
}

This configuration gives me the following error:

{
    "errorType": "TypeError",
    "errorMessage": "Wrong arguments",
    "stack": [
        "TypeError: Wrong arguments",
        "    at RAPIDClient.postInvocationResponse (/var/runtime/RAPIDClient.js:46:23)",
        "    at complete (/var/runtime/CallbackContext.js:33:12)",
        "    at done (/var/runtime/CallbackContext.js:58:7)",
        "    at succeed (/var/runtime/CallbackContext.js:62:5)",
        "    at /var/runtime/CallbackContext.js:104:16"
    ]
}

What am I missing here? Are there any examples that show a full example of what you posted above?

[brettstack]

Sorry, that should be return serverlessExpressHandler(event, context). I don't have any complete examples though I recall seeing some Issues here with comments doing similar things. Definitely a common/valid use case that I should add an example for.

[smasilamani-cfins]

May I know how do we use this new version with NestJS. Please note that I am in no hurry to use latest version but I would like to give it a try but facing issue.

import { createServer, proxy } from '@vendia/serverless-express';
import { Handler } from 'aws-lambda';
import Express from 'express';
import { Server } from 'http';

import { INestApplication } from '@nestjs/common';
import { ExpressAdapter } from '@nestjs/platform-express';

const bootstrapServer: () => Promise<Server> = async () => {
	try {
		const expressApp: any = Express();
		const expAdapter: ExpressAdapter = new ExpressAdapter(expressApp);
		const app: INestApplication = await bootstrap(expAdapter);
		return createServer(app.getHttpAdapter().getInstance(), null, binaryMimeTypes);
	} catch (error) {
		// eslint-disable-next-line no-console
		console.error(error);
		throw error;
	}
};

export const handler: Handler = async (event, context) => {
	context.callbackWaitsForEmptyEventLoop = true;

	if (event.path === `/${DSServerConstants.GLOBAL_PATH_PREFIX}`) {
		event.path = `/${DSServerConstants.GLOBAL_PATH_PREFIX}/`;
	}

	event.path = event.path?.includes('swagger-ui') ? `/${DSServerConstants.GLOBAL_PATH_PREFIX}${event.path}` : event.path;
	if (!cachedServer) {
		cachedServer = await bootstrapServer();
	}
	if (event.source === 'serverless-plugin-warmup') {
		const response: {
			statusCode: number;
			body: any;
			headers: any;
		} = {
			statusCode: 200,
			body: null,
			headers: null
		};
		response.body = 'WarmUP - Lambda is warm!';
		// eslint-disable-next-line no-console
		console.log('index - Lambda is warm!');
		return response;
	}

	if (process.env.APP_ENV?.toUpperCase() !== DSServerConstants.LOCAL_ENV) {
		handleCustomDomanin(event);
	}
	return proxy(cachedServer, event, context, 'PROMISE').promise;
};

But now I am getting errors as below

Module '"../node_modules/@vendia/serverless-express/src"' has no exported member 'createServer'

Module '"../node_modules/@vendia/serverless-express/src"' has no exported member 'proxy'

This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.ts(2497)

[brettstack]

Please see https://github.com/vendia/serverless-express/blob/mainline/UPGRADE.md for info on upgrading. I haven't tested with Nest. Let me know if you hit any issues. If you could send a PR with a minimum Nest example, that'd be great!

[smasilamani-cfins]

Please see https://github.com/vendia/serverless-express/blob/mainline/UPGRADE.md for info on upgrading. I haven't tested with Nest. Let me know if you hit any issues. If you could send a PR with a minimum Nest example, that'd be great!

Will definitely do by end of this week.

[smasilamani-cfins]

Please see https://github.com/vendia/serverless-express/blob/mainline/UPGRADE.md for info on upgrading. I haven't tested with Nest. Let me know if you hit any issues. If you could send a PR with a minimum Nest example, that'd be great!

Will definitely do by end of this week.

I see that you already have NestJS example.

[brettstack]

Yes we just merged this a few days ago. Let me know if you have any other issues. I'll close this issue for now.