종량제 API 구축

step 1. Client: GET /weather (지불 없음)
        Server: 402 Payment Required
                PAYMENT-REQUIRED: { amount: "1000", asset: USDT0, network: eip155:988 }

step 2. 클라이언트가 ERC-3009 승인에 서명합니다.

step 3. Client: GET /weather + PAYMENT-SIGNATURE 헤더
        Server: 촉진자로 포워딩 → transferWithAuthorization 온체인 결제
                (~700ms 블록 확인)
        Server: 200 OK { weather: "sunny", temperature: 70 }
                PAYMENT-SETTLE-RESPONSE: { txHash: "0x8f3a...", paid: "0.001 USDT0" }

step 4. Stablescan에서 결제 확인
        https://stablescan.xyz/tx/0x8f3a...

// --- 서버 ---
app.use(paymentMiddleware({
  "GET /weather": {
    price: { amount: "1000", asset: USDT0 },
    payTo: sellerAddress,
  },
  "POST /inference": {
    price: { amount: "50000", asset: USDT0 },
    payTo: sellerAddress,
  },
}, resourceServer));
 
// 구성에 나열되지 않은 경로는 게이트되지 않습니다.

// --- 클라이언트 ---
account = new WalletAccountEvm(seedPhrase, { provider: RPC });
client = new x402Client();
fetchWithPayment = wrapFetchWithPayment(fetch, client);
 
weatherResponse = fetchWithPayment("https://api.example.com/weather");
inferenceResponse = fetchWithPayment("https://api.example.com/inference", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ prompt: "Hello" }),
});
 
// 각 유료 요청에 대해:
// 1. 초기 요청은 PAYMENT-REQUIRED 헤더와 함께 402를 반환합니다.
// 2. 클라이언트는 지갑으로 ERC-3009 승인에 서명합니다.
// 3. 클라이언트는 PAYMENT-SIGNATURE 헤더로 재시도합니다.
// 4. 촉진자가 온체인으로 결제하고, 서버는 응답을 반환합니다.

npm install express @x402/express @x402/evm @x402/core

price: {
  amount: "1000",                                      // 기본 단위 (6 소수점)
  asset: USDT0_STABLE,                                 // USDT0 계약 주소
  extra: { name: "USDT0", version: "1", decimals: 6 }, // EIP-712 도메인 정보
}

// server.ts
import express from "express";
import { paymentMiddleware, x402ResourceServer } from "@x402/express";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { HTTPFacilitatorClient } from "@x402/core/server";
 
const PAY_TO = process.env.PAY_TO_ADDRESS as `0x${string}`;
const FACILITATOR_URL = "https://x402.semanticpay.io/";
const STABLE_NETWORK = "eip155:988"; // Stable Mainnet CAIP-2 ID
const USDT0_STABLE = "0x779Ded0c9e1022225f8E0630b35a9b54bE713736";
 
const facilitatorClient = new HTTPFacilitatorClient({ url: FACILITATOR_URL });
const resourceServer = new x402ResourceServer(facilitatorClient)
  .register(STABLE_NETWORK, new ExactEvmScheme());
 
const app = express();
 
app.use(
  paymentMiddleware(
    {
      // 예제 1: 유료 GET 경로 구성
      "GET /weather": {
        accepts: [
          {
            scheme: "exact",
            network: STABLE_NETWORK,
            price: {
              amount: "1000", // $0.001
              asset: USDT0_STABLE,
              extra: { name: "USDT0", version: "1", decimals: 6 },
            },
            payTo: PAY_TO,
          },
        ],
        description: "날씨 데이터",
        mimeType: "application/json",
      },
      // 예제 2: 유료 POST 경로 구성
      "POST /inference": {
        accepts: [
          {
            scheme: "exact",
            network: STABLE_NETWORK,
            price: {
              amount: "50000", // $0.05
              asset: USDT0_STABLE,
              extra: { name: "USDT0", version: "1", decimals: 6 },
            },
            payTo: PAY_TO,
          },
        ],
        description: "AI 추론 엔드포인트",
        mimeType: "application/json",
      },
    },
    resourceServer,
  ),
);
 
app.get("/weather", (req, res) => {
  res.json({ weather: "sunny", temperature: 70 });
});
 
app.post("/inference", (req, res) => {
  const { prompt } = req.body;
  res.json({ result: `Inference result for: ${prompt}` });
});
 
// 구성에 나열되지 않아 지불이 필요하지 않습니다.
app.get("/health", (req, res) => {
  res.json({ status: "ok", payTo: PAY_TO });
});
 
const PORT = process.env.PORT || 4021;
app.listen(PORT, () => {
  console.log(`서버가 http://localhost:${PORT}에서 수신 중입니다.`);
  console.log(`GET  /health    - 무료`);
  console.log(`GET  /weather   - 요청당 $0.001`);
  console.log(`POST /inference - 요청당 $0.05`);
});

npm install @x402/fetch @x402/evm @tetherto/wdk-wallet-evm

// client.ts
import WalletManagerEvm from "@tetherto/wdk-wallet-evm";
 
const account = await new WalletManagerEvm(process.env.SEED_PHRASE!, {
  provider: "https://rpc.stable.xyz",
}).getAccount(0);
 
console.log("구매자 주소:", account.address);
 
// USDT0은 6 소수점을 사용합니다. 1000000의 잔액은 1.00 USDT0과 같습니다.
const USDT0_STABLE = "0x779Ded0c9e1022225f8E0630b35a9b54bE713736";
const balance = await account.getTokenBalance(USDT0_STABLE);
console.log("USDT0 잔액:", Number(balance) / 1e6, "USDT0");

import { x402Client, wrapFetchWithPayment } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
 
const client = new x402Client();
registerExactEvmScheme(client, { signer: account });
const fetchWithPayment = wrapFetchWithPayment(fetch, client);
 
const response = await fetchWithPayment("http://localhost:4021/weather");
const data = await response.json();
console.log("응답:", data);

curl -i http://localhost:4021/weather

npx tsx client.ts

// (계속) client.ts
import { x402HTTPClient } from "@x402/fetch";
 
const httpClient = new x402HTTPClient(client);
const receipt = httpClient.getPaymentSettleResponse(
  (name) => response.headers.get(name),
);
console.log("결제 영수증:", JSON.stringify(receipt, null, 2));

// server.test.ts
import { x402ResourceServer } from "@x402/express";
import { ExactEvmScheme } from "@x402/evm/exact/server";
 
// 스텁 촉진자: 모든 서명을 수락하고 가짜 결제를 반환합니다.
const stubFacilitatorClient = {
  verify: async () => ({ isValid: true, payer: "0xMockPayer" }),
  settle: async () => ({
    success: true,
    txHash: "0xMOCK000000000000000000000000000000000000000000000000000000000001",
    networkId: "eip155:988",
  }),
};
 
export const testResourceServer = new x402ResourceServer(stubFacilitatorClient as any)
  .register("eip155:988", new ExactEvmScheme());