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* AgentKits — A2A (Agent-to-Agent) Protocol Support
*
* Implements Google's A2A protocol basics for agent interop.
* - Agent Card discovery
* - Task management (create, get, cancel)
* - Streaming via SSE
*
* Spec: https://google.github.io/A2A/
*
* Usage:
* import { createA2AClient, createA2AServer } from 'agentkits/a2a';
*/
// ── Types ──────────────────────────────────────────────────────────
export interface AgentSkill {
id: string;
name: string;
description: string;
tags?: string[];
examples?: string[];
}
export interface AgentCard {
name: string;
description: string;
url: string;
version: string;
capabilities: {
streaming?: boolean;
pushNotifications?: boolean;
stateTransitionHistory?: boolean;
};
skills: AgentSkill[];
defaultInputModes?: string[];
defaultOutputModes?: string[];
}
export type TaskState = 'submitted' | 'working' | 'input-required' | 'completed' | 'canceled' | 'failed';
export interface TextPart {
type: 'text';
text: string;
}
export interface FilePart {
type: 'file';
file: { name?: string; mimeType?: string; bytes?: string; uri?: string };
}
export interface DataPart {
type: 'data';
data: Record<string, any>;
}
export type Part = TextPart | FilePart | DataPart;
export interface Message {
role: 'user' | 'agent';
parts: Part[];
metadata?: Record<string, any>;
}
export interface Artifact {
name?: string;
description?: string;
parts: Part[];
index: number;
append?: boolean;
lastChunk?: boolean;
}
export interface Task {
id: string;
sessionId?: string;
status: { state: TaskState; message?: Message; timestamp?: string };
artifacts?: Artifact[];
history?: Message[];
metadata?: Record<string, any>;
}
export interface TaskSendParams {
id: string;
sessionId?: string;
message: Message;
historyLength?: number;
metadata?: Record<string, any>;
}
export interface TaskStatusUpdateEvent {
type: 'status';
id: string;
status: Task['status'];
final: boolean;
}
export interface TaskArtifactUpdateEvent {
type: 'artifact';
id: string;
artifact: Artifact;
}
export type TaskStreamEvent = TaskStatusUpdateEvent | TaskArtifactUpdateEvent;
// ── A2A Client ─────────────────────────────────────────────────────
export interface A2AClientConfig {
/** Base URL of the A2A agent (e.g. http://localhost:8080) */
baseUrl: string;
/** Request timeout in ms */
timeout?: number;
}
export interface A2AClient {
/** Fetch the agent's card from /.well-known/agent.json */
getAgentCard(): Promise<AgentCard>;
/** Send a task (tasks/send) */
sendTask(params: TaskSendParams): Promise<Task>;
/** Get task status (tasks/get) */
getTask(id: string): Promise<Task>;
/** Cancel a task (tasks/cancel) */
cancelTask(id: string): Promise<Task>;
/** Stream task updates via SSE (tasks/sendSubscribe) */
streamTask(params: TaskSendParams): AsyncIterable<TaskStreamEvent>;
}
interface JsonRpcResponse {
jsonrpc: '2.0';
id: number;
result?: any;
error?: { code: number; message: string; data?: any };
}
let _rpcId = 1;
export function createA2AClient(config: A2AClientConfig): A2AClient {
const timeout = config.timeout ?? 30000;
const baseUrl = config.baseUrl.replace(/\/$/, '');
async function rpc(method: string, params: any): Promise<any> {
const controller = new AbortController();
const timer = setTimeout(() => controller.abort(), timeout);
try {
const resp = await fetch(baseUrl, {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({ jsonrpc: '2.0', id: _rpcId++, method, params }),
signal: controller.signal,
});
if (!resp.ok) throw new Error(`A2A request failed: ${resp.status}`);
const data: JsonRpcResponse = await resp.json() as any;
if (data.error) throw new Error(`A2A error ${data.error.code}: ${data.error.message}`);
return data.result;
} finally {
clearTimeout(timer);
}
}
return {
async getAgentCard(): Promise<AgentCard> {
const resp = await fetch(`${baseUrl}/.well-known/agent.json`, {
signal: AbortSignal.timeout(timeout),
});
if (!resp.ok) throw new Error(`Failed to fetch agent card: ${resp.status}`);
return await resp.json() as AgentCard;
},
async sendTask(params: TaskSendParams): Promise<Task> {
return rpc('tasks/send', params);
},
async getTask(id: string): Promise<Task> {
return rpc('tasks/get', { id });
},
async cancelTask(id: string): Promise<Task> {
return rpc('tasks/cancel', { id });
},
async *streamTask(params: TaskSendParams): AsyncIterable<TaskStreamEvent> {
const resp = await fetch(baseUrl, {
method: 'POST',
headers: { 'Content-Type': 'application/json', Accept: 'text/event-stream' },
body: JSON.stringify({ jsonrpc: '2.0', id: _rpcId++, method: 'tasks/sendSubscribe', params }),
});
if (!resp.ok) throw new Error(`A2A stream failed: ${resp.status}`);
if (!resp.body) throw new Error('No response body for streaming');
const reader = resp.body.getReader();
const decoder = new TextDecoder();
let buffer = '';
try {
while (true) {
const { value, done } = await reader.read();
if (done) break;
buffer += decoder.decode(value, { stream: true });
const lines = buffer.split('\n');
buffer = lines.pop() ?? '';
let currentData = '';
for (const line of lines) {
if (line.startsWith('data: ')) {
currentData = line.slice(6);
} else if (line === '' && currentData) {
try {
const msg = JSON.parse(currentData);
if (msg.result) yield msg.result as TaskStreamEvent;
} catch {}
currentData = '';
}
}
}
} finally {
reader.releaseLock();
}
},
};
}
// ── A2A Server (Express-compatible handler) ────────────────────────
export interface A2AServerConfig {
card: AgentCard;
onTask: (params: TaskSendParams) => Promise<Task>;
onTaskGet?: (id: string) => Promise<Task>;
onTaskCancel?: (id: string) => Promise<Task>;
onTaskStream?: (params: TaskSendParams) => AsyncIterable<TaskStreamEvent>;
}
export interface A2AHandler {
/** Handle incoming HTTP request. Returns { status, headers, body }. */
handle(req: { method: string; url: string; body?: any }): Promise<{
status: number;
headers: Record<string, string>;
body: string | ReadableStream<Uint8Array>;
}>;
/** The agent card */
card: AgentCard;
}
export function createA2AServer(config: A2AServerConfig): A2AHandler {
const { card, onTask, onTaskGet, onTaskCancel, onTaskStream } = config;
async function handleRpc(body: any): Promise<any> {
const { method, params, id } = body;
switch (method) {
case 'tasks/send': {
const result = await onTask(params);
return { jsonrpc: '2.0', id, result };
}
case 'tasks/get': {
if (!onTaskGet) return { jsonrpc: '2.0', id, error: { code: -32601, message: 'tasks/get not implemented' } };
const result = await onTaskGet(params.id);
return { jsonrpc: '2.0', id, result };
}
case 'tasks/cancel': {
if (!onTaskCancel) return { jsonrpc: '2.0', id, error: { code: -32601, message: 'tasks/cancel not implemented' } };
const result = await onTaskCancel(params.id);
return { jsonrpc: '2.0', id, result };
}
case 'tasks/sendSubscribe': {
if (!onTaskStream) return { jsonrpc: '2.0', id, error: { code: -32601, message: 'streaming not supported' } };
return { _stream: true, id, params };
}
default:
return { jsonrpc: '2.0', id, error: { code: -32601, message: `Unknown method: ${method}` } };
}
}
return {
card,
async handle(req) {
// Agent card discovery
if (req.method === 'GET' && (req.url === '/.well-known/agent.json' || req.url?.endsWith('/agent.json'))) {
return {
status: 200,
headers: { 'Content-Type': 'application/json' } as Record<string, string>,
body: JSON.stringify(card),
};
}
// JSON-RPC
if (req.method === 'POST') {
const result = await handleRpc(req.body);
// Streaming response
if (result._stream && onTaskStream) {
const encoder = new TextEncoder();
const stream = new ReadableStream({
async start(controller) {
try {
for await (const event of onTaskStream!(result.params)) {
const data = JSON.stringify({ jsonrpc: '2.0', id: result.id, result: event });
controller.enqueue(encoder.encode(`data: ${data}\n\n`));
if (event.type === 'status' && event.final) break;
}
} finally {
controller.close();
}
},
});
return {
status: 200,
headers: { 'Content-Type': 'text/event-stream', 'Cache-Control': 'no-cache', Connection: 'keep-alive' } as Record<string, string>,
body: stream,
};
}
return {
status: 200,
headers: { 'Content-Type': 'application/json' } as Record<string, string>,
body: JSON.stringify(result),
};
}
return { status: 404, headers: {} as Record<string, string>, body: 'Not Found' };
},
};
}
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