Defined in: activities/chat/stream/processor.ts:128

StreamProcessor - State machine for processing AI response streams

Manages the full UIMessage[] conversation and emits events on changes. Trusts the adapter contract: adapters emit clean AG-UI events in the correct order.

State tracking:

• Full message array
• Per-message stream state (text, tool calls, thinking)
• Multiple concurrent message streams
• Tool call completion via TOOL_CALL_END events

• docs/chat-architecture.md#streamprocessor-internal-state — State field reference
• docs/chat-architecture.md#adapter-contract — What this class expects from adapters

new StreamProcessor(options): StreamProcessor;

Defined in: activities/chat/stream/processor.ts:155

StreamProcessorOptions = {}

StreamProcessor

addToolApprovalResponse(approvalId, approved): void;

Defined in: activities/chat/stream/processor.ts:313

Add an approval response (called by client after handling onApprovalRequest)

string

boolean

void

addToolResult(
   toolCallId, 
   output, 
   error?): void;

Defined in: activities/chat/stream/processor.ts:269

Add a tool result (called by client after handling onToolCall)

string

any

string

void

addUserMessage(content, id?): UIMessage;

Defined in: activities/chat/stream/processor.ts:202

Add a user message to the conversation. Supports both simple string content and multimodal content arrays.

The message content (string or array of content parts)

string | ContentPart[]

string

Optional custom message ID (generated if not provided)

UIMessage

The created UIMessage

// Simple text message
processor.addUserMessage('Hello!')

// Multimodal message with image
processor.addUserMessage([
  { type: 'text', content: 'What is in this image?' },
  { type: 'image', source: { type: 'url', value: 'https://example.com/photo.jpg' } }
])

// With custom ID
processor.addUserMessage('Hello!', 'custom-id-123')

areAllToolsComplete(): boolean;

Defined in: activities/chat/stream/processor.ts:344

Check if all tool calls in the last assistant message are complete Useful for auto-continue logic

boolean

clearMessages(): void;

Defined in: activities/chat/stream/processor.ts:388

Clear all messages

void

finalizeStream(): void;

Defined in: activities/chat/stream/processor.ts:1310

Finalize the stream — complete all pending operations.

Called when the async iterable ends (stream closed). Acts as the final safety net: completes any remaining tool calls, flushes un-emitted text, and fires onStreamEnd.

void

docs/chat-architecture.md#single-shot-text-response — Finalization step

getCurrentAssistantMessageId(): string | null;

Defined in: activities/chat/stream/processor.ts:253

Get the current assistant message ID (if one has been created). Returns null if prepareAssistantMessage() was called but no content has arrived yet.

string | null

getMessages(): UIMessage[];

Defined in: activities/chat/stream/processor.ts:336

Get current messages

UIMessage[]

getRecording(): ChunkRecording | null;

Defined in: activities/chat/stream/processor.ts:1442

Get the current recording

ChunkRecording | null

getState(): ProcessorState;

Defined in: activities/chat/stream/processor.ts:1401

Get current processor state (aggregated across all messages)

ProcessorState

prepareAssistantMessage(): void;

Defined in: activities/chat/stream/processor.ts:232

Prepare for a new assistant message stream. Does NOT create the message immediately -- the message is created lazily when the first content-bearing chunk arrives via ensureAssistantMessage(). This prevents empty assistant messages from flickering in the UI when auto-continuation produces no content.

void

process(stream): Promise<ProcessorResult>;

Defined in: activities/chat/stream/processor.ts:404

Process a stream and emit events through handlers

AsyncIterable<any>

Promise<ProcessorResult>

processChunk(chunk): void;

Defined in: activities/chat/stream/processor.ts:438

Process a single chunk from the stream.

Central dispatch for all AG-UI events. Each event type maps to a specific handler. Events not listed in the switch are intentionally ignored (RUN_STARTED, STEP_STARTED, STATE_DELTA).

AGUIEvent

void

docs/chat-architecture.md#adapter-contract — Expected event types and ordering

removeMessagesAfter(index): void;

Defined in: activities/chat/stream/processor.ts:380

Remove messages after a certain index (for reload/retry)

number

void

reset(): void;

Defined in: activities/chat/stream/processor.ts:1464

Full reset (including messages)

void

setMessages(messages): void;

Defined in: activities/chat/stream/processor.ts:174

Set the messages array (e.g., from persisted state)

UIMessage[]

void

startAssistantMessage(messageId?): string;

Defined in: activities/chat/stream/processor.ts:241

string

string

Use prepareAssistantMessage() instead. This eagerly creates an assistant message which can cause empty message flicker.

startRecording(): void;

Defined in: activities/chat/stream/processor.ts:1429

Start recording chunks

void

toModelMessages(): ModelMessage<
  | string
  | ContentPart<unknown, unknown, unknown, unknown, unknown>[]
  | null>[];

Defined in: activities/chat/stream/processor.ts:325

Get the conversation as ModelMessages (for sending to LLM)

ModelMessage< | string | ContentPart<unknown, unknown, unknown, unknown, unknown>[] | null>[]

static replay(recording, options?): Promise<ProcessorResult>;

Defined in: activities/chat/stream/processor.ts:1483

Replay a recording through the processor

ChunkRecording

StreamProcessorOptions

Promise<ProcessorResult>