Add Slack Socket Mode support by haydenbleasel · Pull Request #162 · vercel/chat

haydenbleasel · 2026-03-02T23:53:43Z

Summary

Adds serverless-compatible Socket Mode forwarding to the Slack adapter, mirroring the Discord gateway pattern
A cron-invoked listener maintains the WebSocket, acks events, and forwards them via HTTP POST to the existing webhook endpoint using an x-slack-socket-token header
The adapter stays in mode: "webhook" (default) — socket mode listener is a separate external concern
routeSocketEvent() now accepts WebhookOptions and uses waitUntil for async handlers
New startSocketModeListener() / runSocketModeListener() / forwardSocketEvent() methods
Example cron route at /api/slack/socket-mode with createPersistentListener for Redis-based cross-instance coordination
Cron runs every 9 min, listener duration 10 min (same as Discord)

Test plan

Closes #123

vercel · 2026-03-02T23:53:49Z

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
chat	Ready	Preview, Comment, Open in v0	Mar 16, 2026 8:29pm
chat-sdk-nextjs-chat	Ready	Preview, Comment, Open in v0	Mar 16, 2026 8:29pm

socket-security · 2026-03-02T23:54:26Z

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Package	Supply Chain Security	Quality	Maintenance
@streamdown/code@1.0.3 ⏵ 1.1.0	⁺¹	⁺¹	⁺³
remend@1.2.1 ⏵ 1.2.2	⁺¹	⁺¹	^-1
@slack/socket-mode@2.0.5
streamdown@2.3.0 ⏵ 2.4.0	⁺¹		^-1
@slack/web-api@7.14.1 ⏵ 7.15.0	⁺¹

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packages/adapter-slack/src/index.ts

…nteractive payloads can cause unhandled promise rejections that crash the Node.js process. This commit fixes the issue reported at packages/adapter-slack/src/index.ts:1152 **Bug Analysis:** In `routeSocketEvent` (line 1150), which is a synchronous `void` method, two async operations produce floating promises: 1. `this.handleSlashCommand(params)` (line 1165) - `handleSlashCommand` is `async` and always returns a `Promise<Response>`. It calls `await this.lookupUser(userId)` which internally calls `await this.chat.getState().get()` (before the try/catch around the API call), and `this.chat.processSlashCommand()`. Any of these could throw. 2. `this.dispatchInteractivePayload(payload)` (line 1172) - Returns `Response | Promise<Response>`. When the payload type is `view_submission`, it delegates to `async handleViewSubmission()`, which calls `await this.chat.processModalSubmit()` and accesses `payload.view.state.values` (which could throw on malformed payloads). Since `routeSocketEvent` is synchronous (`void` return type) and called from a sync context within the socket mode event handler (after `await ack()` has already completed), these returned promises are fire-and-forget. If any reject, it triggers an unhandled promise rejection, which in Node.js 15+ terminates the process by default. In contrast, in the webhook code path (`handleWebhook`), these same methods are always `return`-ed from async functions, so their promises are properly chained to the caller. **Fix:** Added `.catch()` handlers to both floating promises: 1. For `handleSlashCommand`: Added `.catch()` that logs the error via `this.logger.error`. 2. For `dispatchInteractivePayload`: Since it returns `Response | Promise<Response>` (only a Promise for `view_submission`), used `instanceof Promise` to conditionally attach a `.catch()` handler only when the result is a Promise. This approach was chosen over making `routeSocketEvent` async because: (a) it doesn't change the method signature, (b) the caller doesn't need to await it (the ack has already been sent), and (c) errors are logged rather than silently swallowed. Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com> Co-authored-by: haydenbleasel <hello@haydenbleasel.com>

- Export SlackForwardedSocketEvent type - Add x-slack-socket-token check at top of handleWebhook() for forwarded events - Update routeSocketEvent() to accept WebhookOptions and use waitUntil - Add startSocketModeListener(), runSocketModeListener(), forwardSocketEvent() Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- Forwarded event accepted/rejected based on appToken - Bypasses signature verification for forwarded events - Options passthrough to handlers - startSocketModeListener returns 200/500 appropriately Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- New /api/slack/socket-mode route using createPersistentListener - Mirrors Discord gateway pattern (CRON_SECRET auth, Redis coordination) - Cron runs every 9 min, listener duration 10 min Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Make signingSecret optional (string | undefined) instead of falling back to "". verifySignature now returns false when no secret is configured, preventing HMAC with an empty key from silently passing. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Sync errors from processEventPayload were silently dropped in socket mode. Wrap with try-catch for parity with slash_commands and interactive cases. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Stop using the Slack app-level token (xapp-...) as the bearer token for HTTP forwarding. Adds socketForwardingSecret config option (auto-detected from SLACK_SOCKET_FORWARDING_SECRET) with fallback to appToken for backwards compatibility. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Validate body.event exists and construct a properly typed SlackWebhookPayload instead of using `as unknown as`. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Remove export — only used internally by the forwarding mechanism. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

reaganmcf · 2026-03-30T17:18:24Z

@haydenbleasel this looks incredibly promising and useful for us. Any update on when this might get pushed over the finish line?

cramforce · 2026-03-30T20:34:30Z

I'm inclined not to ship this, but I can be convinced otherwise. I'm not sure what it really gains us, but it does add complexity.

reaganmcf · 2026-03-30T20:41:51Z

Socket mode is a huge blocker for us to use this, and I know many other people who share the same sentiment.

Without socket mode, your bot has to expose the handlers to the public internet over HTTP. This is a hard no for many of us who work behind corporate firewalls in sensitive industries with strict IP rules.

Socket mode allows us to run these bots behind our firewalls, greatly improving adoption.

cramforce · 2026-03-30T21:28:34Z

That makes sense. Could you give the PR a try?

reaganmcf · 2026-04-01T13:16:35Z

Gave the PR a try, most of the functionality worked out of the box perfectly:

chat messages worked great
rendering Card and other components work great

The main issues that I've faced (and fixed in my local branch - can push it if useful but it's Claude slop haven't verified it yet) revolves around slash commands and modals:

Slash commands arrive without "type" field in socket mode which prevents it routing correctly. Seems like it's trying to route the raw payload
Interactive payloads have this same problem (type: view_submission)
Modal response actions (push, update, and error) ack() with no payload before processing the events, which I don't believe is the correct implementation (should ack(payload))

More than happy to submit the code I have to patch the PR if it would make it easier - or if there is any more information I can provide to help in any capacity let me know.

Really appreciate the work on this so far 😄

cramforce · 2026-04-02T20:19:15Z

@reaganmcf If you could contribute your changes that would be amazing! I'll merge when it is ready

haydenbleasel linked an issue Mar 2, 2026 that may be closed by this pull request

Slack Socket Mode Support #123

Open

1 task

vercel bot deployed to Preview – chat March 2, 2026 23:54 View deployment

haydenbleasel requested a review from cramforce March 2, 2026 23:54

vercel bot deployed to Preview – chat March 2, 2026 23:58 View deployment

vercel bot reviewed Mar 3, 2026

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haydenbleasel marked this pull request as draft March 3, 2026 00:29

vercel bot deployed to Preview – chat-sdk-nextjs-chat March 3, 2026 00:52 View deployment

vercel bot deployed to Preview – chat March 3, 2026 00:52 View deployment

vercel bot deployed to Preview – chat-sdk-nextjs-chat March 3, 2026 01:06 View deployment

vercel bot deployed to Preview – chat March 3, 2026 01:06 View deployment

haydenbleasel requested review from NicolasMontone and removed request for cramforce March 4, 2026 19:43

haydenbleasel and others added 14 commits March 16, 2026 13:20

Add slack/socket mode dependency

38091a5

Update config types and SlackAdapter class

e2887af

Add socket mode methods, extract interactive dispatch

ee31b62

Update createSlackAdapter factory function

ebec0d6

Write tests for socket mode

349eef8

Create slack-socket-mode.md

e64e36c

Run fix

816f971

Fix polynomial regex issues

4795773

Wrap event_callback in try-catch in routeSocketEvent

62f83b5

Sync errors from processEventPayload were silently dropped in socket mode. Wrap with try-catch for parity with slash_commands and interactive cases. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

haydenbleasel and others added 4 commits March 16, 2026 13:23

Replace double cast with type guard for socket event body

d001452

Validate body.event exists and construct a properly typed SlackWebhookPayload instead of using `as unknown as`. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Internalize SlackForwardedSocketEvent type

2a91337

Remove export — only used internally by the forwarding mechanism. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Fix formatting in socketForwardingSecret check

9d8581c

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

haydenbleasel marked this pull request as ready for review March 16, 2026 20:28

Add socket mode documentation to Slack adapter README

e8a3a97

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

haydenbleasel force-pushed the 123-slack-socket-mode-support branch from 5a58d27 to e8a3a97 Compare March 16, 2026 20:28

vercel bot deployed to Preview – chat-sdk-nextjs-chat March 16, 2026 20:29 View deployment

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Add Slack Socket Mode support#162

Add Slack Socket Mode support#162
haydenbleasel wants to merge 19 commits intomainfrom
123-slack-socket-mode-support

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