DeltaKitSSE Events
Server-Sent Event types used by the streaming protocol.
SSE events are the wire format between your server and DeltaKit. Each event is a JSON object with a type field, sent as a data: line in the SSE stream.
import type { SSEEvent, TextDeltaEvent, ToolCallEvent, ToolResultEvent } from "@deltakit/core";SSEEvent
Union of all built-in event types:
type SSEEvent = TextDeltaEvent | ToolCallEvent | ToolResultEvent;TextDeltaEvent
A chunk of text to append to the assistant's response. This is the most common event type.
interface TextDeltaEvent {
type: "text_delta";
delta: string;
}Wire format:
data: {"type":"text_delta","delta":"Hello"}When using @deltakit/react, the default event handler in useStreamChat only processes text_delta events. All other event types require a custom onEvent handler. See Custom Event Handling.
ToolCallEvent
The assistant is invoking a tool.
interface ToolCallEvent {
type: "tool_call";
tool_name: string;
argument: string;
call_id?: string;
}| Field | Type | Description |
|---|---|---|
tool_name | string | Name of the tool being invoked |
argument | string | JSON string of arguments |
call_id | string? | ID to match this call with its result |
Wire format:
data: {"type":"tool_call","tool_name":"get_weather","argument":"{\"city\":\"London\"}","call_id":"call_1"}ToolResultEvent
The result of a tool execution.
interface ToolResultEvent {
type: "tool_result";
call_id: string;
output: string;
}| Field | Type | Description |
|---|---|---|
call_id | string | Matches the call_id from the corresponding ToolCallEvent |
output | string | The tool's output |
Wire format:
data: {"type":"tool_result","call_id":"call_1","output":"Sunny, 18°C"}Stream Termination
The stream ends with the [DONE] sentinel:
data: [DONE]This is not a JSON event. parseSSEStream recognizes it as a termination signal and stops the generator.
Custom Event Types
You can define your own event types alongside the built-in ones:
interface ProgressEvent {
type: "progress";
step: string;
percent: number;
}
type MyEvent = SSEEvent | ProgressEvent;Your server can send any JSON as a data: line. parseSSEStream will yield it. Use a union type to handle all cases:
import { parseSSEStream } from "@deltakit/core";
const response = await fetch("/api/chat", {
method: "POST",
body: JSON.stringify({ message: "Hello" }),
});
if (response.body) {
for await (const event of parseSSEStream(response.body) as AsyncGenerator<MyEvent>) {
switch (event.type) {
case "text_delta":
process.stdout.write(event.delta);
break;
case "progress":
// event.step and event.percent are typed
console.log(`${event.step}: ${event.percent}%`);
break;
}
}
}For handling custom events in React, see Custom Event Handling.