ext-apps/examples/simple-server/server.ts

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import express, { Request, Response } from "express";
import { randomUUID } from "node:crypto";
import { z } from "zod";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import {
  CallToolResult,
  isInitializeRequest,
  ReadResourceResult,
  Resource,
} from "@modelcontextprotocol/sdk/types.js";
import { InMemoryEventStore } from "@modelcontextprotocol/sdk/examples/shared/inMemoryEventStore.js";
import cors from "cors";
import path from "node:path";
import fs from "node:fs/promises";
import { fileURLToPath } from "node:url";

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

// Load both UI HTML files from dist/
const distDir = path.join(__dirname, "dist");
const loadHtml = async (name: string) => {
  const htmlPath = path.join(distDir, `${name}.html`);
  return fs.readFile(htmlPath, "utf-8");
};

// Create an MCP server with both UI tools
const getServer = async () => {
  const server = new McpServer(
    {
      name: "simple-mcp-server",
      version: "1.0.0",
    },
    { capabilities: { logging: {} } },
  );

  // Load HTML for both UIs
  const [vanillaHtml, reactHtml] = await Promise.all([
    loadHtml("ui-vanilla"),
    loadHtml("ui-react"),
  ]);

  // --- Vanilla UI Resource & Tool ---
  const vanillaResource: Resource = {
    name: "ui-vanilla-template",
    uri: "ui://vanilla",
    title: "Vanilla UI Template",
    description: "A simple vanilla JS UI",
    mimeType: "text/html+mcp",
  };

  server.registerResource(
    vanillaResource.name,
    vanillaResource.uri,
    vanillaResource,
    async (): Promise<ReadResourceResult> => ({
      contents: [
        {
          uri: vanillaResource.uri,
          mimeType: vanillaResource.mimeType,
          text: vanillaHtml,
        },
      ],
    }),
  );

  server.registerTool(
    "create-ui-vanilla",
    {
      title: "Vanilla UI",
      description: "A tool that returns a simple vanilla JS UI",
      inputSchema: {
        message: z.string().describe("Message to display"),
      },
      _meta: {
        "ui/resourceUri": vanillaResource.uri,
      },
    },
    async ({ message }): Promise<CallToolResult> => ({
      content: [{ type: "text", text: JSON.stringify({ message }) }],
      structuredContent: { message },
    }),
  );

  // --- React UI Resource & Tool ---
  const reactResource: Resource = {
    name: "ui-react-template",
    uri: "ui://react",
    title: "React UI Template",
    description: "A React-based UI",
    mimeType: "text/html+mcp",
  };

  server.registerResource(
    reactResource.name,
    reactResource.uri,
    reactResource,
    async (): Promise<ReadResourceResult> => ({
      contents: [
        {
          uri: reactResource.uri,
          mimeType: reactResource.mimeType,
          text: reactHtml,
        },
      ],
    }),
  );

  server.registerTool(
    "create-ui-react",
    {
      title: "React UI",
      description: "A tool that returns a React-based UI",
      inputSchema: {
        message: z.string().describe("Message to display"),
      },
      _meta: {
        "ui/resourceUri": reactResource.uri,
      },
    },
    async ({ message }): Promise<CallToolResult> => ({
      content: [{ type: "text", text: JSON.stringify({ message }) }],
      structuredContent: { message },
    }),
  );

  // --- Common tool: get-weather ---
  server.registerTool(
    "get-weather",
    {
      title: "Get Weather",
      description: "Returns current weather for a location",
      inputSchema: {
        location: z.string().describe("Location to get weather for"),
      },
    },
    async ({ location }): Promise<CallToolResult> => {
      const temperature = 25;
      const condition = "sunny";
      return {
        content: [
          {
            type: "text",
            text: `The weather in ${location} is ${condition}, ${temperature}°C.`,
          },
        ],
        structuredContent: { temperature, condition },
      };
    },
  );

  return server;
};

const MCP_PORT = process.env.MCP_PORT
  ? parseInt(process.env.MCP_PORT, 10)
  : 3001;

const app = express();
app.use(express.json());
app.use(
  cors({
    origin: "*",
    exposedHeaders: ["Mcp-Session-Id"],
  }),
);

// Map to store transports by session ID
const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {};

const mcpPostHandler = async (req: Request, res: Response) => {
  const sessionId = req.headers["mcp-session-id"] as string | undefined;

  try {
    let transport: StreamableHTTPServerTransport;
    if (sessionId && transports[sessionId]) {
      transport = transports[sessionId];
    } else if (!sessionId && isInitializeRequest(req.body)) {
      const eventStore = new InMemoryEventStore();
      transport = new StreamableHTTPServerTransport({
        sessionIdGenerator: () => randomUUID(),
        eventStore,
        onsessioninitialized: (sessionId) => {
          console.log(`Session initialized: ${sessionId}`);
          transports[sessionId] = transport;
        },
      });

      transport.onclose = () => {
        const sid = transport.sessionId;
        if (sid && transports[sid]) {
          console.log(`Session closed: ${sid}`);
          delete transports[sid];
        }
      };

      const server = await getServer();
      await server.connect(transport);
      await transport.handleRequest(req, res, req.body);
      return;
    } else {
      res.status(400).json({
        jsonrpc: "2.0",
        error: { code: -32000, message: "Bad Request: No valid session ID" },
        id: null,
      });
      return;
    }

    await transport.handleRequest(req, res, req.body);
  } catch (error) {
    console.error("Error handling MCP request:", error);
    if (!res.headersSent) {
      res.status(500).json({
        jsonrpc: "2.0",
        error: { code: -32603, message: "Internal server error" },
        id: null,
      });
    }
  }
};

app.post("/mcp", mcpPostHandler);

app.get("/mcp", async (req: Request, res: 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);
});

app.delete("/mcp", async (req: Request, res: 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;
  }
  try {
    const transport = transports[sessionId];
    await transport.handleRequest(req, res);
  } catch (error) {
    console.error("Error handling session termination:", error);
    if (!res.headersSent) {
      res.status(500).send("Error processing session termination");
    }
  }
});

app.listen(MCP_PORT, () => {
  console.log(`MCP Server listening on http://localhost:${MCP_PORT}/mcp`);
  console.log(`  Tools: create-ui-vanilla, create-ui-react, get-weather`);
});

process.on("SIGINT", async () => {
  console.log("Shutting down...");
  for (const sessionId in transports) {
    try {
      await transports[sessionId].close();
      delete transports[sessionId];
    } catch (error) {
      console.error(`Error closing session ${sessionId}:`, error);
    }
  }
  process.exit(0);
});