TypeError: Cannot read properties of undefined (reading 'type') at SocketModeClient.onWebSocketMessage

[levenleven]

Sometimes we get an error due to event.payload.event being undefined

node-slack-sdk/packages/socket-mode/src/SocketModeClient.ts

Line 344 in 039bd05

this.emit(event.payload.event.type, {

TypeError: Cannot read properties of undefined (reading 'type')
    at SocketModeClient.onWebSocketMessage (/app/node_modules/@slack/socket-mode/dist/SocketModeClient.js:620:43)
    at WebSocket.onMessage (/app/node_modules/ws/lib/event-target.js:132:16)
    at WebSocket.emit (node:events:514:28)
    at Receiver.receiverOnMessage (/app/node_modules/ws/lib/websocket.js:1070:20)
    at Receiver.emit (node:events:514:28)
    at Receiver.dataMessage (/app/node_modules/ws/lib/receiver.js:517:14)
    at Receiver.getData (/app/node_modules/ws/lib/receiver.js:435:17)
    at Receiver.startLoop (/app/node_modules/ws/lib/receiver.js:143:22)
    at Receiver._write (/app/node_modules/ws/lib/receiver.js:78:10)
    at writeOrBuffer (node:internal/streams/writable:447:12)
    at _write (node:internal/streams/writable:389:10)
    at Receiver.Writable.write (node:internal/streams/writable:393:10)
    at TLSSocket.socketOnData (/app/node_modules/ws/lib/websocket.js:1164:35)
    at TLSSocket.emit (node:events:514:28)

Packages:

Select all that apply:

• @slack/web-api
• @slack/rtm-api
• @slack/webhooks
• @slack/oauth
• @slack/socket-mode
• @slack/types
• I don't know

Reproducible in:

The Slack SDK version

"@slack/socket-mode": "1.3.6"

Node.js runtime version

v20.9.0

OS info

#141~20.04.1-Ubuntu SMP Thu Jan 16 18:38:51 UTC 2025

Steps to reproduce:

N/A

Expected result:

Missing payload handled gracefully

Actual result:

Unhandled error

Requirements

For general questions/issues about Slack API platform or its server-side, could you submit questions at https://my.slack.com/help/requests/new instead. 🙇

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to those rules.

[misscoded]

HI @levenleven! Thanks for bringing this to our attention. Unfortunately, we'll need more information in order to begin to debug and remedy what is going on here. If you're able to provide which event(s) that this error is occurring for, that'd be a great start.

[levenleven]

@misscoded thanks for looking into this. We subscribe to message events using bolt sdk (e.g. app.message(...)).

[misscoded]

Are message events the only events that your app listens for/subscribes to then? On your end and with your own logs, are you able to narrow down which specific message event type is causing the issue?

[levenleven]

Sorry, missed we also have app.action subscription. So only these two, message and action.

This is not reproducible (at least now), we've got ~ 20 such errors between Mar 5, 2025 10:40:00 PM UTC and Mar 6, 2025 10:51:30 PM UTC

On your end and with your own logs, are you able to narrow down which specific message event type is causing the issue

No, as this is happening not in application but in framework code.

[misscoded]

No worries! If you provide us your app ID, we might be able to look into the logs and figure out what the event in question is.

[levenleven]

Thanks! App id is A02V1ADGH5F

[levenleven]

Few other occasions

• Mar 12, 2025 9:42:02 PM UTC - Mar 12, 2025 9:49:31 PM UTC
• Mar 15, 2025 9:48:01 PM UTC - Mar 15, 2025 9:50:30 PM UTC
• Mar 17, 2025 9:30:01 PM UTC - Mar 17, 2025 9:36:31 PM UTC

[levenleven]

@misscoded Is there anything else I can do to help with the investigation?