receiverAckTimeoutError should not throw if authorization of incoming event fails

Description

When an incoming event fails to authenticate via Bolt’s authorizeFn, the following warning is thrown:

https://github.com/slackapi/bolt/blob/227421b324bcf5548d1263db7b61fc66eb407908/src/App.ts#L395

Then, the following error is thrown that the incoming event is not acknowledged.

https://github.com/slackapi/bolt/blob/6cd88eb3a6246405dee9afe06f793ed7c59958f2/src/ExpressReceiver.ts#L75-L78

Is this the expected design? If listeners are not being called, why do we need to call ack()?

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I’ve read and understood the Contributing guidelines and have done my best effort to follow them.
• I’ve read and agree to the Code of Conduct.
• I’ve searched for any related issues and avoided creating a duplicate issue.

---

Bug Report

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Reproducible in:

package version: >= 1.2.0

node version: v12.12.0

OS version(s): macOS Catalina 10.15.1

Steps to reproduce:

1. With authorizeFn, do not authorize an incoming event.

Expected result:

Incoming event is not sent to listeners. receiverAckTimeoutError is not thrown.

Actual result:

receiverAckTimeoutError is thrown.

Attachments:

   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR { Error: Authorization of incoming event did not succeed.
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR     at Object.errorWithCode (/home/vcap/deps/0/node_modules/@slack/bolt/dist/errors.js:17:19)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR     at authorizationErrorFromOriginal (/home/vcap/deps/0/node_modules/@slack/bolt/dist/App.js:293:28)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR     at authorizeResult.authorize.catch (/home/vcap/deps/0/node_modules/@slack/bolt/dist/App.js:145:32)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR     at process._tickCallback (internal/process/next_tick.js:68:7)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR   code: 'slack_bolt_authorization_error',
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR   original:
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR    Error: No matching authorizations for E27SFGS2W:T0258Q0SG
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at App.module.exports [as authorize] (/home/vcap/app/src/authorizeFn.js:15:15)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at App.onIncomingEvent (/home/vcap/deps/0/node_modules/@slack/bolt/dist/App.js:144:45)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at ExpressReceiver.App.receiver.on.message (/home/vcap/deps/0/node_modules/@slack/bolt/dist/App.js:55:53)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at ExpressReceiver.emit (events.js:198:13)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at ExpressReceiver.requestHandler (/home/vcap/deps/0/node_modules/@slack/bolt/dist/ExpressReceiver.js:70:14)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at Layer.handle [as handle_request] (/home/vcap/deps/0/node_modules/express/lib/router/layer.js:95:5)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at next (/home/vcap/deps/0/node_modules/express/lib/router/route.js:137:13)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at respondToUrlVerification (/home/vcap/deps/0/node_modules/@slack/bolt/dist/ExpressReceiver.js:122:5)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at Layer.handle [as handle_request] (/home/vcap/deps/0/node_modules/express/lib/router/layer.js:95:5)
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR        at next (/home/vcap/deps/0/node_modules/express/lib/router/route.js:137:13) }
   2020-01-02T15:25:13.64-0500 [APP/PROC/WEB/0] ERR [WARN]   Authorization of incoming event did not succeed. No listeners will be called.
   2020-01-02T15:25:16.44-0500 [APP/PROC/WEB/0] ERR { Error: An incoming event was not acknowledged before the timeout. Ensure that the ack() argument is called in your listeners.
   2020-01-02T15:25:16.44-0500 [APP/PROC/WEB/0] ERR     at receiverAckTimeoutError (/home/vcap/deps/0/node_modules/@slack/bolt/dist/ExpressReceiver.js:213:19)
   2020-01-02T15:25:16.44-0500 [APP/PROC/WEB/0] ERR     at Timeout.setTimeout [as _onTimeout] (/home/vcap/deps/0/node_modules/@slack/bolt/dist/ExpressReceiver.js:39:32)
   2020-01-02T15:25:16.44-0500 [APP/PROC/WEB/0] ERR     at ontimeout (timers.js:436:11)
   2020-01-02T15:25:16.44-0500 [APP/PROC/WEB/0] ERR     at tryOnTimeout (timers.js:300:5)
   2020-01-02T15:25:16.44-0500 [APP/PROC/WEB/0] ERR     at listOnTimeout (timers.js:263:5)

[barlock]

@aoberoi ☝️ This is a really good example of why I think App.processEvent in the proposal https://github.com/slackapi/bolt/issues/353#issuecomment-570650203 should reject with an error.

[seratch]

I’ve confirmed that #891 can resolve this issue.

import { App, ExpressReceiver } from '@slack/bolt';
const app = new App({
  receiver: new ExpressReceiver({
    signingSecret: process.env.SLACK_SIGNING_SECRET!!,
  }),
  authorize: async (_) => { throw new Error("Failed!"); }
});

The above example app returns 401 HTTP status and shows the following logs only:

[WARN]  bolt-app Authorization of incoming event did not succeed. No listeners will be called.
[ERROR]  bolt-app Error: Failed!
    at /Users/ksera/github/bolt-js/examples/getting-started-typescript/dist/app.js:25:15
    at Generator.next (<anonymous>)
    at /Users/ksera/github/bolt-js/examples/getting-started-typescript/dist/app.js:8:71
    at new Promise (<anonymous>)
    at __awaiter (/Users/ksera/github/bolt-js/examples/getting-started-typescript/dist/app.js:4:12)
    at App.authorize (/Users/ksera/github/bolt-js/examples/getting-started-typescript/dist/app.js:24:23)
    at App.processEvent (/Users/ksera/github/bolt-js/dist/App.js:375:46)
    at ExpressReceiver.requestHandler (/Users/ksera/github/bolt-js/dist/receivers/ExpressReceiver.js:154:77)
    at Layer.handle [as handle_request] (/Users/ksera/github/bolt-js/node_modules/express/lib/router/layer.js:95:5)
    at next (/Users/ksera/github/bolt-js/node_modules/express/lib/router/route.js:137:13) {
  code: 'slack_bolt_authorization_error'
}