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AlemTuzlakAlemTuzlak
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fix: content chunk issue fix (TanStack#272)
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4 files changed

Lines changed: 178 additions & 4 deletions

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‎.changeset/fifty-dingos-mate.md‎

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---
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'@tanstack/ai': patch
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---
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fix issue with delta

‎packages/typescript/ai/src/activities/chat/stream/processor.ts‎

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@@ -483,9 +483,10 @@ export class StreamProcessor {
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let nextText = currentText
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// Prefer delta over content - delta is the incremental change
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if (chunk.delta !== '') {
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// Check for both undefined and empty string to avoid "undefined" string concatenation
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if (chunk.delta !== undefined && chunk.delta !== '') {
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nextText = currentText + chunk.delta
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} else if (chunk.content && chunk.content !== '') {
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} else if (chunk.content !== undefined && chunk.content !== '') {
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// Fallback: use content if delta is not provided
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if (chunk.content.startsWith(currentText)) {
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nextText = chunk.content

‎packages/typescript/ai/src/types.ts‎

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@@ -789,8 +789,8 @@ export interface TextMessageContentEvent extends BaseAGUIEvent {
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type: 'TEXT_MESSAGE_CONTENT'
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/** Message identifier */
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messageId: string
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/** The incremental content token */
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delta: string
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/** The incremental content token (may be undefined if only content is provided) */
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delta?: string
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/** Full accumulated content so far */
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content?: string
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}

‎packages/typescript/ai/tests/stream-processor.test.ts‎

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import { describe, expect, it } from 'vitest'
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import { StreamProcessor } from '../src/activities/chat/stream/processor'
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import type { StreamChunk } from '../src/types'
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describe('StreamProcessor', () => {
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describe('handleTextMessageContentEvent', () => {
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it('should handle TEXT_MESSAGE_CONTENT with delta', () => {
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const processor = new StreamProcessor()
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processor.startAssistantMessage()
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processor.processChunk({
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type: 'TEXT_MESSAGE_CONTENT',
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messageId: 'msg-1',
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delta: 'Hello',
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model: 'test',
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timestamp: Date.now(),
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} as StreamChunk)
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processor.processChunk({
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type: 'TEXT_MESSAGE_CONTENT',
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messageId: 'msg-1',
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delta: ' world',
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model: 'test',
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timestamp: Date.now(),
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} as StreamChunk)
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processor.processChunk({
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type: 'RUN_FINISHED',
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model: 'test',
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timestamp: Date.now(),
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finishReason: 'stop',
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} as StreamChunk)
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const messages = processor.getMessages()
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expect(messages).toHaveLength(1)
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expect(messages[0]?.parts).toHaveLength(1)
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expect(messages[0]?.parts[0]).toEqual({
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type: 'text',
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content: 'Hello world',
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})
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})
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it('should handle TEXT_MESSAGE_CONTENT with undefined delta (issue #257)', () => {
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const processor = new StreamProcessor()
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processor.startAssistantMessage()
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// Simulate a chunk where delta is undefined (which can happen in practice)
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processor.processChunk({
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type: 'TEXT_MESSAGE_CONTENT',
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messageId: 'msg-1',
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delta: undefined,
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content: 'Hello',
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model: 'test',
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timestamp: Date.now(),
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} as unknown as StreamChunk)
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processor.processChunk({
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type: 'TEXT_MESSAGE_CONTENT',
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messageId: 'msg-1',
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delta: undefined,
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content: 'Hello world',
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model: 'test',
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timestamp: Date.now(),
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} as unknown as StreamChunk)
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processor.processChunk({
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type: 'RUN_FINISHED',
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model: 'test',
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timestamp: Date.now(),
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finishReason: 'stop',
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} as StreamChunk)
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const messages = processor.getMessages()
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expect(messages).toHaveLength(1)
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expect(messages[0]?.parts).toHaveLength(1)
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// Should NOT contain "undefined" string
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expect(messages[0]?.parts[0]).toEqual({
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type: 'text',
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content: 'Hello world',
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})
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})
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it('should handle TEXT_MESSAGE_CONTENT with empty delta', () => {
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const processor = new StreamProcessor()
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processor.startAssistantMessage()
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// Empty delta should fall back to content
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processor.processChunk({
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type: 'TEXT_MESSAGE_CONTENT',
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messageId: 'msg-1',
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delta: '',
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content: 'Hello',
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model: 'test',
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timestamp: Date.now(),
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} as StreamChunk)
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processor.processChunk({
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type: 'RUN_FINISHED',
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model: 'test',
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timestamp: Date.now(),
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finishReason: 'stop',
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} as StreamChunk)
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const messages = processor.getMessages()
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expect(messages).toHaveLength(1)
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expect(messages[0]?.parts).toHaveLength(1)
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expect(messages[0]?.parts[0]).toEqual({
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type: 'text',
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content: 'Hello',
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})
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})
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it('should handle TEXT_MESSAGE_CONTENT with only content (no delta)', () => {
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const processor = new StreamProcessor()
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processor.startAssistantMessage()
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// Some servers may only send content without delta
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processor.processChunk({
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type: 'TEXT_MESSAGE_CONTENT',
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messageId: 'msg-1',
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content: 'Hello',
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model: 'test',
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timestamp: Date.now(),
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} as unknown as StreamChunk)
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processor.processChunk({
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type: 'TEXT_MESSAGE_CONTENT',
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messageId: 'msg-1',
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content: 'Hello world',
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model: 'test',
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timestamp: Date.now(),
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} as unknown as StreamChunk)
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processor.processChunk({
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type: 'RUN_FINISHED',
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model: 'test',
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timestamp: Date.now(),
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finishReason: 'stop',
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} as StreamChunk)
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const messages = processor.getMessages()
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expect(messages).toHaveLength(1)
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expect(messages[0]?.parts).toHaveLength(1)
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expect(messages[0]?.parts[0]).toEqual({
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type: 'text',
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content: 'Hello world',
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})
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})
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it('should have empty parts when no TEXT_MESSAGE_CONTENT is received', () => {
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const processor = new StreamProcessor()
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processor.startAssistantMessage()
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// Only RUN_FINISHED without any text content
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processor.processChunk({
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type: 'RUN_FINISHED',
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model: 'test',
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timestamp: Date.now(),
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finishReason: 'stop',
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} as StreamChunk)
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const messages = processor.getMessages()
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expect(messages).toHaveLength(1)
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// Parts should be empty when no content was received
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expect(messages[0]?.parts).toHaveLength(0)
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})
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})
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})

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