x402 协议 — AI 代理与 LLM API 的 USDC 微支付

npm install @xpaylabs/x402

import { pay } from '@xpaylabs/x402';

const response = await pay('https://api.example.com/weather', {
  amount: '0.001',
  network: 'base-sepolia',
  privateKey: '0x...',
});

console.log(response.data);      // 响应体
console.log(response.paymentId); // 链上交易哈希

import { XPayClient } from '@xpaylabs/x402';

const client = new XPayClient({
  privateKey: '0x...',
  network: 'base-sepolia',
  facilitatorUrl: 'https://x402-facilitator-testnet.vercel.app/api',
});

const res1 = await client.request('https://api.example.com/weather', {
  amount: '0.001',
});
const res2 = await client.request('https://api.example.com/weather', {
  amount: '0.001',
});

import { extractPaymentId } from '@xpaylabs/x402';

const paymentId = extractPaymentId(response.headers);
console.log(paymentId); // "0xabc...123"

npm install @x402/express

import express from 'express';
import { x402Middleware } from '@x402/express';

const app = express();

app.use(x402Middleware({
  network: 'base-sepolia',
  facilitatorUrl: 'https://x402-facilitator-testnet.vercel.app/api',
  evmAddress: '0x...',       // 卖家 USDC 收款地址
}));

// 付费路由
app.get('/api/generate', (req, res) => {
  res.json({ result: 'llm response', paymentId: req.x402.paymentId });
});

// 公共路由
app.get('/health', (req, res) => {
  res.json({ status: 'ok' });
});

AI 代理 (买家)                      AI API (卖家)
      │                                   │
      │  1. POST /api/generate            │
      │     (未支付)                      │
      │                                   │
      │  2. 402 Payment Required          │
      │     { amount: "0.001" }           │
      │                                   │
      │  3. 提交 USDC Transfer (链上)      │
      │     通过 x402 facilitator         │
      │                                   │
      │  4. 重试 + x402 授权头            │
      │                                   │
      │  5. 200 OK + 响应                 │
      │     (paymentId 在 headers 中)     │