added processBeforeResponse flag to ExpressReceiver for FaaS use case

src/App.ts

@@ -62,6 +62,7 @@ const packageJson = require('../package.json'); // tslint:disable-line:no-requir
 export interface AppOptions {
  signingSecret?: ExpressReceiverOptions['signingSecret'];
  endpoints?: ExpressReceiverOptions['endpoints'];
+ processBeforeResponse?: ExpressReceiverOptions['processBeforeResponse'];
  agent?: Agent;
  clientTls?: Pick<SecureContextOptions, 'pfx' | 'key' | 'passphrase' | 'cert' | 'ca'>;
  convoStore?: ConversationStore | false;
@@ -184,6 +185,7 @@ export default class App {
  logLevel = undefined,
  ignoreSelf = true,
  clientOptions = undefined,
+ processBeforeResponse = false,
  }: AppOptions = {}) {
 
  if (typeof logger === 'undefined') {
@@ -249,6 +251,7 @@ export default class App {
  this.receiver = new ExpressReceiver({
  signingSecret,
  endpoints,
+ processBeforeResponse,
  logger: this.logger,
  });
  }

src/ExpressReceiver.spec.ts

@@ -40,6 +40,7 @@ describe('ExpressReceiver', () => {
  signingSecret: 'my-secret',
  logger: noopLogger,
  endpoints: { events: '/custom-endpoint' },
+ processBeforeResponse: true,
  });
  assert.isNotNull(receiver);
  });
@@ -58,7 +59,7 @@ describe('ExpressReceiver', () => {
  });
 
  describe('built-in middleware', () => {
- describe('ssl_check requset handler', () => {
+ describe('ssl_check request handler', () => {
  it('should handle valid requests', async () => {
  // Arrange
  // tslint:disable-next-line: no-object-literal-type-assertion

src/ExpressReceiver.ts

@@ -17,6 +17,7 @@ export interface ExpressReceiverOptions {
  endpoints?: string | {
  [endpointType: string]: string;
  };
+ processBeforeResponse?: boolean;
 }
 
 /**
@@ -30,11 +31,13 @@ export default class ExpressReceiver implements Receiver {
  private server: Server;
  private bolt: App | undefined;
  private logger: Logger;
+ private processBeforeResponse: boolean;
 
  constructor({
  signingSecret = '',
  logger = new ConsoleLogger(),
  endpoints = { events: '/slack/events' },
+ processBeforeResponse = false,
  }: ExpressReceiverOptions) {
  this.app = express();
  // TODO: what about starting an https server instead of http? what about other options to create the server?
@@ -47,6 +50,7 @@ export default class ExpressReceiver implements Receiver {
  this.requestHandler.bind(this),
  ];
 
+ this.processBeforeResponse = processBeforeResponse;
  this.logger = logger;
  const endpointList: string[] = typeof endpoints === 'string' ? [endpoints] : Object.values(endpoints);
  for (const endpoint of endpointList) {
@@ -64,25 +68,41 @@ export default class ExpressReceiver implements Receiver {
  // tslint:disable-next-line: align
  }, 3001);
 
+ let storedResponse = undefined;
  const event: ReceiverEvent = {
  body: req.body,
- ack: async (response: any): Promise<void> => {
+ ack: async (response): Promise<void> => {
  if (isAcknowledged) {
  throw new ReceiverMultipleAckError();
  }
  isAcknowledged = true;
- if (!response) {
- res.send('');
- } else if (typeof response === 'string') {
- res.send(response);
+ if (this.processBeforeResponse) {
+ if (!response) {
+ storedResponse = '';
+ } else {
+ storedResponse = response;
+ }
  } else {
- res.json(response);
+ if (!response) {
+ res.send('');
+ } else if (typeof response === 'string') {
+ res.send(response);
+ } else {
+ res.json(response);
+ }
  }
  },
  };
 
  try {
  await this.bolt?.processEvent(event);
+ if (storedResponse !== undefined) {
+ if (typeof storedResponse === 'string') {
+ res.send(storedResponse);
+ } else {
+ res.json(storedResponse);
+ }
+ }
  } catch (err) {
  res.send(500);
  throw err;