StreamProcessor

Defined in: packages/ai/src/activities/chat/stream/processor.ts:265

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

See#

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

Constructors#

Constructor#

new StreamProcessor(options?): StreamProcessor;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:325

Parameters#

options?#

StreamProcessorOptions = {}

Returns#

StreamProcessor

Methods#

addToolApprovalResponse()#

addToolApprovalResponse(approvalId, approved): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:529

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

Parameters#

approvalId#

string

approved#

boolean

Returns#

void

addToolResult()#

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

Defined in: packages/ai/src/activities/chat/stream/processor.ts:478

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

Parameters#

toolCallId#

string

output#

any

error?#

string

Returns#

void

addUserMessage()#

addUserMessage(
   content, 
   id?, 
   metadata?): UIMessage;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:405

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

Parameters#

content#

string | ContentPart[]

The message content (string or array of content parts)

id?#

string

Optional custom message ID (generated if not provided)

metadata?#

Record<string, any>

Optional AG-UI metadata bag

Returns#

UIMessage

The created UIMessage

Example#

// 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()#

areAllToolsComplete(): boolean;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:569

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

Returns#

boolean

clearMessages()#

clearMessages(): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:654

Clear all messages

Returns#

void

finalizeStream()#

finalizeStream(): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:3536

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.

Returns#

void

See#

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

getCurrentAssistantMessageId()#

getCurrentAssistantMessageId(): string | null;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:462

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

Returns#

string | null

getMessages()#

getMessages(): UIMessage<unknown>[];

Defined in: packages/ai/src/activities/chat/stream/processor.ts:561

Get current messages

Returns#

UIMessage<unknown>[]

getRecording()#

getRecording(): ChunkRecording | null;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:3704

Get the current recording

Returns#

ChunkRecording | null

getState()#

getState(): ProcessorState;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:3661

Get current processor state (aggregated across all messages)

Returns#

ProcessorState

prepareAssistantMessage()#

prepareAssistantMessage(): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:440

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.

Returns#

void

prependMessages()#

prependMessages(messages): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:366

Put older UI messages at the front of the conversation.

Skip a message if its id is already in the list. Keep the existing message. Then emit the same messages-change event as setMessages.

Use this for older history pages. The first hydrate window uses setMessages.

Parameters#

messages#

UIMessage<unknown>[]

Older UI messages in insertion order. The first item is the oldest.

Returns#

void

Example#

processor.setMessages([newest])
processor.prependMessages([oldest])

process()#

process(stream): Promise<ProcessorResult>;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:679

Process a stream and emit events through handlers

Parameters#

stream#

AsyncIterable<any>

Returns#

Promise<ProcessorResult>

processChunk()#

processChunk(chunk): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:713

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 (STATE_SNAPSHOT, STATE_DELTA).

Parameters#

chunk#

AGUIEvent

Returns#

void

See#

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

removeMessagesAfter()#

removeMessagesAfter(index): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:609

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

Parameters#

index#

number

Returns#

void

reset()#

reset(): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:3734

Full reset (including messages)

Returns#

void

setMessages()#

setMessages(messages): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:345

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

Parameters#

messages#

UIMessage<unknown>[]

Returns#

void

startAssistantMessage()#

startAssistantMessage(messageId?): string;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:449

Parameters#

messageId?#

string

Returns#

string

Deprecated#

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

startRecording()#

startRecording(): void;

Defined in: packages/ai/src/activities/chat/stream/processor.ts:3691

Start recording chunks

Returns#

void

toModelMessages()#

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

Defined in: packages/ai/src/activities/chat/stream/processor.ts:550

Get the conversation as ModelMessages (for sending to LLM)

Returns#

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

replay()#

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

Defined in: packages/ai/src/activities/chat/stream/processor.ts:3755

Replay a recording through the processor

Parameters#

recording#

ChunkRecording

options?#

StreamProcessorOptions

Returns#

Promise<ProcessorResult>