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feat: accept chunks as arguments to chat stream helper #2470

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e3d7b9b
feat: accept chunks as arguments to chat.{start,append,stop}Stream me…
srtaalej Jan 11, 2026
2601199
build: update slack/types version in package json
srtaalej Jan 11, 2026
160cfb7
fix: make markdown text optional and add missing chunk type
srtaalej Jan 15, 2026
81140cc
tests: add missing chunk type to tests
srtaalej Jan 16, 2026
dbca9c9
build: use @slack/logger for debugging parsechunks
srtaalej Jan 22, 2026
1d480f6
type narrowing for parseChunks
srtaalej Jan 22, 2026
14c9f36
feat: chunk processing in chat stream helper
srtaalej Jan 16, 2026
35cceed
fix: buffer logic for chunks and markdown
srtaalej Jan 20, 2026
6f5f8f1
bug: handle undefined args in ChatStream append
srtaalej Jan 21, 2026
5e86b29
linter errors
srtaalej Jan 22, 2026
425b897
Merge branch 'feat-ai-apps-thinking-steps' into ale-chunks-stream-helper
srtaalej Jan 23, 2026
076d3a5
Revert "build: use @slack/logger for debugging parsechunks"
mwbrooks Jan 23, 2026
0e553a7
fix: flush logic for chunks
srtaalej Jan 23, 2026
fc5ed1a
test: update charStream tests to support chunks
mwbrooks Jan 24, 2026
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18 changes: 13 additions & 5 deletions packages/web-api/src/WebClient.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1228,7 +1228,11 @@ describe('WebClient', () => {
ok: true,
ts: '123.123',
})
.post('/api/chat.stopStream', { channel: 'C0123456789', ts: '123.123', markdown_text: 'nice!' })
.post('/api/chat.stopStream', {
channel: 'C0123456789',
ts: '123.123',
chunks: JSON.stringify([{ type: 'markdown_text', text: 'nice!' }]),
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@mwbrooks mwbrooks Jan 24, 2026

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note: I made commit fc5ed1a which updates this test to support chunks instead of markdown_text because the streaming helper will now convert all markdown text into a chunk.

})
.reply(200, {
ok: true,
});
Expand Down Expand Up @@ -1279,7 +1283,7 @@ describe('WebClient', () => {
const scope = nock('https://slack.com')
.post('/api/chat.startStream', {
channel: 'C0123456789',
markdown_text: '**this messag',
chunks: JSON.stringify([{ type: 'markdown_text', text: '**this messag' }]),
recipient_team_id: 'T0123456789',
recipient_user_id: 'U0123456789',
thread_ts: '123.000',
Expand All @@ -1290,7 +1294,7 @@ describe('WebClient', () => {
})
.post('/api/chat.appendStream', {
channel: 'C0123456789',
markdown_text: 'e is bold!',
chunks: JSON.stringify([{ type: 'markdown_text', text: 'e is bold!' }]),
token: 'xoxb-updated-1',
ts: '123.123',
})
Expand All @@ -1300,7 +1304,7 @@ describe('WebClient', () => {
.post('/api/chat.stopStream', {
blocks: JSON.stringify([contextActionsBlock]),
channel: 'C0123456789',
markdown_text: '**',
chunks: JSON.stringify([{ type: 'markdown_text', text: '**' }]),
token: 'xoxb-updated-2',
ts: '123.123',
})
Expand Down Expand Up @@ -1370,7 +1374,11 @@ describe('WebClient', () => {
ok: true,
ts: '123.123',
})
.post('/api/chat.stopStream', { channel: 'C0123456789', ts: '123.123', markdown_text: 'nice!' })
.post('/api/chat.stopStream', {
channel: 'C0123456789',
ts: '123.123',
chunks: JSON.stringify([{ type: 'markdown_text', text: 'nice!' }]),
})
.reply(200, {
ok: true,
});
Expand Down
40 changes: 35 additions & 5 deletions packages/web-api/src/chat-stream.ts
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import type { Logger } from '@slack/logger';
import type { AnyChunk } from '@slack/types';
import type { ChatAppendStreamArguments, ChatStartStreamArguments, ChatStopStreamArguments } from './types/request';
import type { ChatAppendStreamResponse, ChatStartStreamResponse, ChatStopStreamResponse } from './types/response';
import type WebClient from './WebClient';
Expand Down Expand Up @@ -89,8 +90,11 @@ export class ChatStreamer {
if (args.token) {
this.token = args.token;
}
this.buffer += args.markdown_text;
if (this.buffer.length >= this.options.buffer_size) {
if (args?.markdown_text) {
this.buffer += args.markdown_text;
args.markdown_text = undefined;
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@mwbrooks mwbrooks Jan 24, 2026

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note: I pushed commit fc5ed1a to unset the args.markdown_text after adding it to the buffer.

If this is not done, then the markdown_text will be added to the API request, which is also included in the chunks: [{ type: "markdown_text", "text": "...." }].

@zimeg Does this look correct to you? I noticed this wasn't explicitly done in the Python SDK.

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@zimeg zimeg Jan 24, 2026

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@mwbrooks A change similar to other comments might be useful to destructure markdown_text and chunks from the rest of args before a chance to flush the buffer?

const { markdown_text, chunks, ...opts } = args;

IIRC the arguments alongside **kwargs in the Python implementation do this without added lines!

}
if (this.buffer.length >= this.options.buffer_size || args?.chunks) {
return await this.flushBuffer(args);
}
const details = {
Expand Down Expand Up @@ -132,6 +136,7 @@ export class ChatStreamer {
}
if (args?.markdown_text) {
this.buffer += args.markdown_text;
args.markdown_text = undefined;
}
if (!this.streamTs) {
const response = await this.client.chat.startStream({
Expand All @@ -144,12 +149,25 @@ export class ChatStreamer {
this.streamTs = response.ts;
this.state = 'in_progress';
}

const flushings: AnyChunk[] = [];

if (this.buffer.length > 0) {
flushings.push({
type: 'markdown_text',
text: this.buffer,
});
}
if (args?.chunks) {
flushings.push(...args.chunks);
}

const response = await this.client.chat.stopStream({
token: this.token,
channel: this.streamArgs.channel,
ts: this.streamTs,
chunks: flushings,
...args,
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@mwbrooks mwbrooks Jan 24, 2026

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note: I made commit fc5ed1a which added back ..args,. If we don't have this, then we may drop additional args like token. This also has the side effect of adding markdown_text as an arg, which is why we now must unset it. .cc @zimeg

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@zimeg zimeg Jan 24, 2026

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@mwbrooks Thanks so much for catching this! We might want to consider a "destructured" approach to separate markdown_text and also chunks from the remaining options:

const { markdown_text, chunks, ...opts } = args;

This might help us avoid overriding new chunks with ...args as well, or chunks can be a following parameter?

markdown_text: this.buffer,
});
this.state = 'completed';
return response;
Expand All @@ -158,12 +176,24 @@ export class ChatStreamer {
private async flushBuffer(
args: Omit<ChatStartStreamArguments | ChatAppendStreamArguments, 'channel' | 'ts'>,
): Promise<ChatStartStreamResponse | ChatAppendStreamResponse> {
const flushings: AnyChunk[] = [];

if (this.buffer.length > 0) {
flushings.push({
type: 'markdown_text',
text: this.buffer,
});
}
if (args?.chunks) {
flushings.push(...args.chunks);
}

if (!this.streamTs) {
const response = await this.client.chat.startStream({
...this.streamArgs,
token: this.token,
chunks: flushings,
...args,
markdown_text: this.buffer,
});
this.buffer = '';
this.streamTs = response.ts;
Expand All @@ -174,8 +204,8 @@ export class ChatStreamer {
token: this.token,
channel: this.streamArgs.channel,
ts: this.streamTs,
chunks: flushings,
...args,
markdown_text: this.buffer,
});
this.buffer = '';
return response;
Expand Down
18 changes: 17 additions & 1 deletion packages/web-api/test/types/methods/chat.test-d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -676,7 +676,23 @@ expectAssignable<Parameters<typeof web.chat.startStream>>([
{
channel: 'C1234',
thread_ts: '1234.56',
markdown_text: 'hello',
chunks: [
{
type: 'markdown_text',
text: 'Hello world',
},
{
type: 'plan_update',
title: 'Analyzing request',
},
{
type: 'task_update',
id: 'task-1',
title: 'Processing request',
status: 'in_progress',
details: 'Working on it...',
},
],
recipient_team_id: 'T1234',
recipient_user_id: 'U1234',
},
Expand Down
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