updated based on feedback from slackapi#380/slackapi#381

README.md

@@ -256,7 +256,6 @@ async function authWithAcme({ payload, context, say, next }) {
     // When the user lookup is successful, add the user details to the context
     context.user = user;
   } catch (error) {
-    // middleware/listeners continue
     if (error.message === 'Not Found') {
         // In the real world, you would need to check if the say function was defined, falling back to the respond
         // function if not, and then falling back to only logging the error as a last resort.
@@ -327,7 +326,7 @@ In general, a middleware can run both before and after the remaining middleware
 How you use `next` can
 have four different effects:
 
-* **To both preprocess and post-process events** - You can choose to do work going _before_ listener functions by putting code
+* **To both preprocess and post-process events** - You can choose to do work both _before_ listener functions by putting code
   before `await next()` and _after_ by putting code after `await next()`. `await next()` passes control down the middleware
   stack in the order it was defined, then back up it in reverse order.
 

docs/_advanced/middleware_global.md

@@ -6,7 +6,7 @@ order: 4
 ---
 
 <div class="section-content">
-Global middleware is run for all incoming events before any listener middleware. You can add any number of global middleware to your app by utilizing `app.use(fn({payload,...,next}))`.
+Global middleware is run for all incoming events before any listener middleware. You can add any number of global middleware to your app by utilizing `app.use(fn)`. The middleware function `fn` is called with the same arguments as listeners and an additional `next` function.
 
 Both global and listener middleware must call `await next()` to pass control of the execution chain to the next middleware, or call `throw` to pass an error back up the previously-executed middleware chain.
 

docs/_advanced/receiver.md

@@ -15,11 +15,11 @@ A receiver is responsible for handling and parsing any incoming events from Slac
 | `stop()`     | None                             | `Promise`   |
 
 `init()` is called after Bolt for JavaScript app is created. This method gives the receiver a reference to an `App` to store so that it can call:
-* `await app.processEvent(event)` whenever your app receives an event from Slack. It will reject if there is an unhandled error.
+* `await app.processEvent(event)` whenever your app receives an event from Slack. It will throw if there is an unhandled error.
 
 To use a custom receiver, you can pass it into the constructor when initializing your Bolt for JavaScript app. Here is what a basic custom receiver might look like.
 
-For a more in-depth look at a receiver, [read the source code for the built-in Express receiver](https://github.com/slackapi/bolt/blob/master/src/ExpressReceiver.ts)
+For a more in-depth look at a receiver, [read the source code for the built-in `ExpressReceiver`](https://github.com/slackapi/bolt/blob/master/src/ExpressReceiver.ts)
 </div>
 
 ```javascript

docs/_basic/listening_responding_shortcuts.md

@@ -82,7 +82,7 @@ app.shortcut('open_modal', async ({ shortcut, ack, context, client }) => {
 
   ```javascript
   // Your middleware will only be called when the callback_id matches 'open_modal' AND the type matches 'message_action'
-  app.shortcut({ callback_id: 'open_modal', type: 'message_action' }, async ({ action, ack, context, client }) => {
+  app.shortcut({ callback_id: 'open_modal', type: 'message_action' }, async ({ shortcut, ack, context, client }) => {
     try {
       // Acknowledge shortcut request
       await ack();

src/App.spec.ts

@@ -440,7 +440,6 @@ describe('App', () => {
         app.error(async (actualError) => {
           assert.instanceOf(actualError, UnknownError);
           assert.equal(actualError.message, error.message);
-          await delay(); // Make this async to make sure error handlers can be tested
         });
 
         await fakeReceiver.sendEvent(dummyReceiverEvent);

src/ExpressReceiver.ts

@@ -1,12 +1,12 @@
 import { AnyMiddlewareArgs, Receiver, ReceiverEvent } from './types';
 import { createServer, Server } from 'http';
-import express, { Request, Response, Application, RequestHandler, NextFunction } from 'express';
+import express, { Request, Response, Application, RequestHandler } from 'express';
 import rawBody from 'raw-body';
 import querystring from 'querystring';
 import crypto from 'crypto';
 import tsscmp from 'tsscmp';
 import App from './App';
-import { ReceiverAuthenticityError, ReceiverAckTimeoutError, ReceiverMultipleAckError } from './errors';
+import { ReceiverAuthenticityError, ReceiverMultipleAckError } from './errors';
 import { Logger, ConsoleLogger } from '@slack/logger';
 
 // TODO: we throw away the key names for endpoints, so maybe we should use this interface. is it better for migrations?
@@ -29,14 +29,14 @@ export default class ExpressReceiver implements Receiver {
 
   private server: Server;
   private bolt: App | undefined;
+  private logger: Logger;
 
   constructor({
     signingSecret = '',
     logger = new ConsoleLogger(),
     endpoints = { events: '/slack/events' },
   }: ExpressReceiverOptions) {
     this.app = express();
-    this.app.use(this.errorHandler.bind(this));
     // TODO: what about starting an https server instead of http? what about other options to create the server?
     this.server = createServer(this.app);
 
@@ -47,40 +47,36 @@ export default class ExpressReceiver implements Receiver {
       this.requestHandler.bind(this),
     ];
 
+    this.logger = logger;
     const endpointList: string[] = typeof endpoints === 'string' ? [endpoints] : Object.values(endpoints);
     for (const endpoint of endpointList) {
       this.app.post(endpoint, ...expressMiddleware);
     }
   }
 
   private async requestHandler(req: Request, res: Response): Promise<void> {
-    let timer: NodeJS.Timeout | undefined = setTimeout(
-      () => {
-        this.bolt?.handleError(new ReceiverAckTimeoutError(
-          'An incoming event was not acknowledged before the timeout. ' +
-          'Ensure that the ack() argument is called in your listeners.',
-        ));
-        timer = undefined;
-      },
-      2800,
-    );
+    let isAcknowledged = false;
+    setTimeout(() => {
+      if (!isAcknowledged) {
+        this.logger.error('An incoming event was not acknowledged within 3 seconds. ' +
+            'Ensure that the ack() argument is called in a listener.');
+      }
+    // tslint:disable-next-line: align
+    }, 3001);
 
     const event: ReceiverEvent = {
       body: req.body,
-      ack: async (response): Promise<void> => {
-        if (timer !== undefined) {
-          clearTimeout(timer);
-          timer = undefined;
-
-          if (!response) {
-            res.send('');
-          } else if (typeof response === 'string') {
-            res.send(response);
-          } else {
-            res.json(response);
-          }
+      ack: async (response: any): Promise<void> => {
+        if (isAcknowledged) {
+          throw new ReceiverMultipleAckError();
+        }
+        isAcknowledged = true;
+        if (!response) {
+          res.send('');
+        } else if (typeof response === 'string') {
+          res.send(response);
         } else {
-          this.bolt?.handleError(new ReceiverMultipleAckError());
+          res.json(response);
         }
       },
     };
@@ -129,12 +125,6 @@ export default class ExpressReceiver implements Receiver {
       });
     });
   }
-
-  private errorHandler(err: any, _req: Request, _res: Response, next: NextFunction): void {
-    this.bolt?.handleError(err);
-    // Forward to express' default error handler (which knows how to print stack traces in development)
-    next(err);
-  }
 }
 
 export const respondToSslCheck: RequestHandler = (req, res, next) => {

src/errors.spec.ts

@@ -7,8 +7,8 @@ import {
   AppInitializationError,
   AuthorizationError,
   ContextMissingPropertyError,
-  ReceiverAckTimeoutError,
   ReceiverAuthenticityError,
+  ReceiverMultipleAckError,
   UnknownError,
 } from './errors';
 
@@ -19,8 +19,8 @@ describe('Errors', () => {
       [ErrorCode.AppInitializationError]: new AppInitializationError(),
       [ErrorCode.AuthorizationError]: new AuthorizationError('auth failed', new Error('auth failed')),
       [ErrorCode.ContextMissingPropertyError]: new ContextMissingPropertyError('foo', "can't find foo"),
-      [ErrorCode.ReceiverAckTimeoutError]: new ReceiverAckTimeoutError(),
       [ErrorCode.ReceiverAuthenticityError]: new ReceiverAuthenticityError(),
+      [ErrorCode.ReceiverMultipleAckError]: new ReceiverMultipleAckError(),
       [ErrorCode.UnknownError]: new UnknownError(new Error('It errored')),
     };
 

src/errors.ts

@@ -8,8 +8,7 @@ export enum ErrorCode {
 
   ContextMissingPropertyError = 'slack_bolt_context_missing_property_error',
 
-  ReceiverAckTimeoutError = 'slack_bolt_receiver_ack_timeout_error',
-  ReceiverAckTwiceError = 'slack_bolt_receiver_ack_twice_error',
+  ReceiverMultipleAckError = 'slack_bolt_receiver_ack_multiple_error',
   ReceiverAuthenticityError = 'slack_bolt_receiver_authenticity_error',
 
   /**
@@ -52,12 +51,8 @@ export class ContextMissingPropertyError extends Error implements CodedError {
   }
 }
 
-export class ReceiverAckTimeoutError extends Error implements CodedError {
-  public code = ErrorCode.ReceiverAckTimeoutError;
-}
-
 export class ReceiverMultipleAckError extends Error implements CodedError {
-  public code = ErrorCode.ReceiverAckTimeoutError;
+  public code = ErrorCode.ReceiverMultipleAckError;
 
   constructor() {
     super("The receiver's `ack` function was called multiple times.");