Host MCP Servers

npm install express @modelcontextprotocol/sdk @faremeter/middleware @faremeter/info

import express from "express";
import { randomUUID } from "node:crypto";
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import { express as faremeter } from "@faremeter/middleware";
import { solana } from "@faremeter/info";

const app = express();
app.use(express.json());

const sessions = new Map();

// Create payment middleware
const paywalledMiddleware = await faremeter.createMiddleware({
  facilitatorURL: "https://facilitator.corbits.dev",
  accepts: [
    {
      ...solana.x402Exact({
        network: "devnet",
        asset: "USDC",
        amount: 100, // $0.0001 per request
        payTo: "YOUR_WALLET_ADDRESS",
      }),
      resource: "http://localhost:3000/mcp/premium",
      description: "Premium MCP tools",
    },
  ],
});

// Premium MCP endpoint with payment
app.post(
  "/mcp/premium",
  (req, res, next) => {
    // Bypass payment for MCP protocol methods
    const bypassMethods = [
      "initialize",
      "initialized",
      "notifications/initialized",
      "tools/list",
      "prompts/list",
      "resources/list",
    ];
    if (req.body?.method && bypassMethods.includes(req.body.method)) {
      next();
    } else {
      paywalledMiddleware(req, res, next);
    }
  },
  async (req, res) => {
    const sessionId = req.headers["mcp-session-id"];
    let transport = sessionId ? sessions.get(sessionId) : undefined;

    // Create new session on initialize
    if (!transport && req.body?.method === "initialize") {
      transport = new StreamableHTTPServerTransport({
        sessionIdGenerator: () => randomUUID(),
        onsessioninitialized: (sessionId) => {
          sessions.set(sessionId, transport);
        },
        enableDnsRebindingProtection: true,
        allowedHosts: ["127.0.0.1", "localhost", "localhost:3000"],
      });

      transport.onclose = () => {
        if (transport.sessionId) sessions.delete(transport.sessionId);
      };

      const server = new McpServer({
        name: "my-premium-server",
        version: "1.0.0",
      });

      // Register your tools
      server.registerTool(
        "get_data",
        {
          title: "Get premium data",
          description: "Returns premium data",
          inputSchema: {
            type: "object",
            properties: {
              query: { type: "string" },
            },
          },
        },
        async ({ query }) => {
          return {
            content: [{ type: "text", text: `Premium result for: ${query}` }],
          };
        }
      );

      await server.connect(transport);
    } else if (!transport) {
      res.status(400).json({ error: "Invalid session" });
      return;
    }

    await transport.handleRequest(req, res, req.body);
  }
);

// Session management
const handleSession = async (req, res) => {
  const sessionId = req.headers["mcp-session-id"];
  const transport = sessionId ? sessions.get(sessionId) : undefined;
  if (!transport) {
    res.status(400).send("Invalid session");
    return;
  }
  await transport.handleRequest(req, res);
};

app.get("/mcp/premium", handleSession);
app.delete("/mcp/premium", handleSession);

app.listen(3000, () => {
  console.log("Paywalled MCP server running on http://localhost:3000/mcp/premium");
});