Sample MCP Server

import express from "express"; import { randomUUID } from "crypto"; import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"; import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js"; import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js" import { z } from "zod"; const app = express(); app.use(express.json()); // Map to store transports by session ID const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {}; // Handle POST requests for client-to-server communication app.post('/mcp', async (req, res) => { // Check for existing session ID const sessionId = req.headers['mcp-session-id'] as string | undefined; let transport: StreamableHTTPServerTransport; if (sessionId && transports[sessionId]) { // Reuse existing transport transport = transports[sessionId]; } else if (!sessionId && isInitializeRequest(req.body)) { // New initialization request transport = new StreamableHTTPServerTransport({ sessionIdGenerator: () => randomUUID(), onsessioninitialized: (sessionId) => { // Store the transport by session ID transports[sessionId] = transport; } }); // Clean up transport when closed transport.onclose = () => { if (transport.sessionId) { delete transports[transport.sessionId]; } }; const server = new McpServer({ name: "example-server", version: "1.0.0" }); // ... set up server resources, tools, and prompts ... server.tool( "fetch-weather", { city: z.string() }, async ({ city }) => { const response = await fetch(`https://api.weatherapi.com/v1/current.json?key=${process.env.WEATHER_API_KEY}&q=${city}&aqi=no`); const data = await response.json(); const weather = data.current.condition.text + " " + data.current.temp_c + "°C"; return { content: [{ type: "text", text: weather }] }; } ); // Connect to the MCP server await server.connect(transport); } else { // Invalid request res.status(400).json({ jsonrpc: '2.0', error: { code: -32000, message: 'Bad Request: No valid session ID provided', }, id: null, }); return; } // Handle the request await transport.handleRequest(req, res, req.body); }); // Reusable handler for GET and DELETE requests const handleSessionRequest = async (req: express.Request, res: express.Response) => { const sessionId = req.headers['mcp-session-id'] as string | undefined; if (!sessionId || !transports[sessionId]) { res.status(400).send('Invalid or missing session ID'); return; } const transport = transports[sessionId]; await transport.handleRequest(req, res); }; // Handle GET requests for server-to-client notifications via SSE app.get('/mcp', handleSessionRequest); // Handle DELETE requests for session termination app.delete('/mcp', handleSessionRequest); app.listen(3006);