基于 x402 协议的 AI Agent HTTP 原生微支付方案与实战

┌──────────┐                 GET /api/resource                 ┌──────────┐
│          │──────────────────────────────────────────────────>│          │
│          │  402 Payment Required                             │          │
│          │  X-402-Payment-To: 0xAddress...                   │          │
│          │  X-402-Amount: 10000 (0.01 USDC)                  │          │
│  Agent   │  X-402-Token: 0x833... (USDC)                     │  Service │
│ (客户端) │  X-402-Chain-Id: 8453 (Base)                      │ Provider │
│          │  X-402-Invoice-Id: uuid-123                       │ (服务端) │
│          │<──────────────────────────────────────────────────│          │
│          │                                                   │          │
│          │  ─── 执行 L2 链上转账 (Base) ───                  │          │
│          │                                                   │          │
│          │  GET /api/resource                                │          │
│          │  X-402-Payment-Proof: 0xTxHash...                 │          │
│          │  X-402-Invoice-Id: uuid-123                       │          │
│          │──────────────────────────────────────────────────>│          │
│          │  200 OK + 返回资源数据                            │          │
│          │<──────────────────────────────────────────────────│          │
└──────────┘                                                   └──────────┘

import { createWalletClient, createPublicClient, http, erc20Abi } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { base } from 'viem/chains';

// 配置 Agent 的私钥与账户
const PRIVATE_KEY = process.env.AGENT_PRIVATE_KEY as `0x${string}`;
const account = privateKeyToAccount(PRIVATE_KEY);

const publicClient = createPublicClient({
  chain: base,
  transport: http('https://mainnet.base.org')
});

const walletClient = createWalletClient({
  account,
  chain: base,
  transport: http('https://mainnet.base.org')
});

export async function fetchWithX402(url: string, options: RequestInit = {}): Promise<Response> {
  // 1. 发起第一次常规 HTTP 请求
  let response = await fetch(url, options);

  // 2. 检查是否触发 402 支付挑战
  if (response.status === 402) {
    console.log('[x402] 收到 402 Payment Required 响应，解析支付参数...');

    const recipient = response.headers.get('X-402-Payment-To') as `0x${string}`;
    const amountStr = response.headers.get('X-402-Amount');
    const tokenAddress = response.headers.get('X-402-Token') as `0x${string}`;
    const invoiceId = response.headers.get('X-402-Invoice-Id');

    if (!recipient || !amountStr || !tokenAddress || !invoiceId) {
      throw new Error('[x402] 响应头缺失必要的 402 支付信息。');
    }

    const amount = BigInt(amountStr);
    console.log(`[x402] 执行转账: ${amount.toString()} 单位代币至 ${recipient} (账单 ID: ${invoiceId})`);

    // 3. 在 Base L2 链上执行 ERC-20 代币转账
    const txHash = await walletClient.writeContract({
      address: tokenAddress,
      abi: erc20Abi,
      functionName: 'transfer',
      args: [recipient, amount]
    });

    console.log(`[x402] 交易已提交至链上，Hash: ${txHash}`);

    // 4. 等待 1 个区块确认（Base 链通常 &lt; 2 秒）
    await publicClient.waitForTransactionReceipt({ hash: txHash });

    // 5. 附带支付证明重新发起 HTTP 请求
    const retryHeaders = new Headers(options.headers || {});
    retryHeaders.set('X-402-Payment-Proof', txHash);
    retryHeaders.set('X-402-Invoice-Id', invoiceId);

    response = await fetch(url, {
      ...options,
      headers: retryHeaders
    });
  }

  return response;
}

import express, { Request, Response, NextFunction } from 'express';
import { createPublicClient, http } from 'viem';
import { base } from 'viem/chains';
import crypto from 'crypto';

const app = express();
const PORT = process.env.PORT || 3000;

// 服务端收款配置
const PROVIDER_WALLET = '0xYourWalletAddressHere' as `0x${string}`;
const USDC_BASE_ADDRESS = '0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913' as `0x${string}`;
const COST_PER_CALL = '10000'; // 0.01 USDC (USDC 精度为 6 位)

const publicClient = createPublicClient({
  chain: base,
  transport: http('https://mainnet.base.org')
});

// 防重放攻击的高效缓存
const processedInvoices = new Set<string>();

async function x402Middleware(req: Request, res: Response, next: NextFunction) {
  const paymentProof = req.header('X-402-Payment-Proof') as `0x${string}` | undefined;
  const invoiceId = req.header('X-402-Invoice-Id');

  // 场景 1：未提供支付证明，返回 402 状态码及支付 Header
  if (!paymentProof || !invoiceId) {
    const newInvoiceId = crypto.randomUUID();
    res.setHeader('X-402-Payment-To', PROVIDER_WALLET);
    res.setHeader('X-402-Amount', COST_PER_CALL);
    res.setHeader('X-402-Token', USDC_BASE_ADDRESS);
    res.setHeader('X-402-Chain-Id', '8453');
    res.setHeader('X-402-Invoice-Id', newInvoiceId);
    
    return res.status(402).json({
      error: 'Payment Required',
      message: '访问此 API 接口需要通过 x402 协议进行微支付。'
    });
  }

  // 场景 2：检查是否重放攻击
  if (processedInvoices.has(paymentProof)) {
    return res.status(400).json({ error: '该支付证明已被使用，请勿重复提交。' });
  }

  // 场景 3：链上验证支付证明
  try {
    const txReceipt = await publicClient.getTransactionReceipt({ hash: paymentProof });

    if (!txReceipt || txReceipt.status !== 'success') {
      return res.status(402).json({ error: '链上交易未完成或执行失败。' });
    }

    // 检查日志事件，确保转账合约为 USDC
    const transferLogs = txReceipt.logs.filter(
      (log) => log.address.toLowerCase() === USDC_BASE_ADDRESS.toLowerCase()
    );

    if (transferLogs.length === 0) {
      return res.status(402).json({ error: '未找到有效的 USDC 转账日志。' });
    }

    // 标记凭证已使用并放行
    processedInvoices.add(paymentProof);
    next();
  } catch (error) {
    console.error('[x402 验证失败]:', error);
    return res.status(500).json({ error: '无法在链上验证支付凭证。' });
  }
}

// 受保护的受费资源接口
app.get('/api/data', x402Middleware, (req: Request, res: Response) => {
  res.json({
    status: 'success',
    data: '这是由自主 Agent 成功付费后获取的高价值数据。',
    timestamp: new Date().toISOString()
  });
});

app.listen(PORT, () => console.log(`x402 服务端已启动，监听端口: ${PORT}`));

┌─────────────────────────────────────────────────────────────┐
│                    自主 AI Agent 决策核心                    │
│                                                             │
│  ┌───────────────────────┐       ┌───────────────────────┐  │
│  │     推理思考层        │       │     工具执行层        │  │
│  │ DeepSeek-V3 / Claude  │       │ 动态付费网页抓取      │  │
│  │ 通过 [n1n.ai](https://n1n.ai) 接入  │       │ & 按次计费工具 API   │  │
│  └───────────┬───────────┘       └───────────┬───────────┘  │
└──────────────┼───────────────────────────────┼──────────────┘
               │                               │
               ▼                               ▼
     高并发大模型推理 API API              x402 HTTP 原生微支付
   (由 [n1n.ai](https://n1n.ai) 统一接入)         (链上直接结算)