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feat(examples): restore SSE transport support to all servers
Add back the legacy SSE transport endpoints (/sse and /messages) that were lost when server-utils.ts was simplified. This enables older clients like the Kotlin SDK to connect to example servers. Endpoints: - /mcp: Streamable HTTP transport (stateless mode) - /sse: Legacy SSE transport stream endpoint - /messages: Legacy SSE transport message endpoint
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lines changed

13 files changed

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‎examples/basic-server-react/src/server-utils.ts‎

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/**
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* Shared utilities for running MCP servers with various transports.
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*
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* Supports:
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* - Stdio transport (--stdio flag)
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* - Streamable HTTP transport (/mcp) - stateless mode
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* - Legacy SSE transport (/sse, /messages) - for older clients (e.g., Kotlin SDK)
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*/
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import { createMcpExpressApp } from "@modelcontextprotocol/sdk/server/express.js";
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import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
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import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";
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import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
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import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
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import cors from "cors";
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import type { Request, Response } from "express";
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/** Active SSE sessions: sessionId -> { server, transport } */
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const sseSessions = new Map<
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string,
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{ server: McpServer; transport: SSEServerTransport }
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>();
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/**
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* Starts an MCP server using the appropriate transport based on command-line arguments.
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*
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* If `--stdio` is passed, uses stdio transport. Otherwise, uses HTTP transports.
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*
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* @param createServer - Factory function that creates a new McpServer instance.
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*/
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export async function startServer(
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createServer: () => McpServer,
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): Promise<void> {
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try {
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if (process.argv.includes("--stdio")) {
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await startStdioServer(createServer);
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} else {
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await startHttpServer(createServer);
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}
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} catch (e) {
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console.error(e);
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process.exit(1);
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}
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}
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/**
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* Starts an MCP server with stdio transport.
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*
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* @param createServer - Factory function that creates a new McpServer instance.
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*/
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export async function startStdioServer(
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createServer: () => McpServer,
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): Promise<void> {
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await createServer().connect(new StdioServerTransport());
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}
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/**
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* Starts an MCP server with HTTP transports (Streamable HTTP + legacy SSE).
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*
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* Provides:
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* - /mcp (GET/POST/DELETE): Streamable HTTP transport (stateless mode)
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* - /sse (GET) + /messages (POST): Legacy SSE transport for older clients
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*
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* @param createServer - Factory function that creates a new McpServer instance.
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*/
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export async function startHttpServer(
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createServer: () => McpServer,
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): Promise<void> {
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const port = parseInt(process.env.PORT ?? "3001", 10);
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// Express app - bind to all interfaces for development/testing
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const expressApp = createMcpExpressApp({ host: "0.0.0.0" });
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expressApp.use(cors());
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// Streamable HTTP transport (stateless mode)
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expressApp.all("/mcp", async (req: Request, res: Response) => {
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// Create fresh server and transport for each request (stateless mode)
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const server = createServer();
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const transport = new StreamableHTTPServerTransport({
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sessionIdGenerator: undefined,
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});
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// Clean up when response ends
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res.on("close", () => {
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transport.close().catch(() => {});
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server.close().catch(() => {});
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});
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try {
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await server.connect(transport);
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await transport.handleRequest(req, res, req.body);
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} catch (error) {
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console.error("MCP error:", error);
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if (!res.headersSent) {
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res.status(500).json({
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jsonrpc: "2.0",
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error: { code: -32603, message: "Internal server error" },
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id: null,
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});
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}
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}
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});
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// Legacy SSE transport - stream endpoint
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expressApp.get("/sse", async (_req: Request, res: Response) => {
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try {
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const server = createServer();
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const transport = new SSEServerTransport("/messages", res);
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sseSessions.set(transport.sessionId, { server, transport });
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res.on("close", () => {
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sseSessions.delete(transport.sessionId);
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transport.close().catch(() => {});
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server.close().catch(() => {});
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});
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await server.connect(transport);
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} catch (error) {
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console.error("SSE error:", error);
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if (!res.headersSent) res.status(500).end();
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}
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});
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// Legacy SSE transport - message endpoint
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expressApp.post("/messages", async (req: Request, res: Response) => {
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try {
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const sessionId = req.query.sessionId as string;
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const session = sseSessions.get(sessionId);
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if (!session) {
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return res.status(404).json({
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jsonrpc: "2.0",
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error: { code: -32001, message: "Session not found" },
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id: null,
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});
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}
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await session.transport.handlePostMessage(req, res, req.body);
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} catch (error) {
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console.error("Message error:", error);
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if (!res.headersSent) {
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res.status(500).json({
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jsonrpc: "2.0",
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error: { code: -32603, message: "Internal server error" },
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id: null,
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});
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}
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}
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});
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const { promise, resolve, reject } = Promise.withResolvers<void>();
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const httpServer = expressApp.listen(port, (err?: Error) => {
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if (err) return reject(err);
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console.log(`Server listening on http://localhost:${port}/mcp`);
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console.log(` SSE endpoint: http://localhost:${port}/sse`);
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resolve();
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});
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const shutdown = () => {
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console.log("\nShutting down...");
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// Clean up all SSE sessions
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sseSessions.forEach(({ server, transport }) => {
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transport.close().catch(() => {});
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server.close().catch(() => {});
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});
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sseSessions.clear();
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httpServer.close(() => process.exit(0));
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};
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process.on("SIGINT", shutdown);
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process.on("SIGTERM", shutdown);
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return promise;
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}
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/**
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* @deprecated Use startHttpServer instead
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*/
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export const startStreamableHttpServer = startHttpServer;

‎examples/basic-server-vanillajs/src/server-utils.ts‎

Lines changed: 180 additions & 0 deletions
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1+
/**
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* Shared utilities for running MCP servers with various transports.
3+
*
4+
* Supports:
5+
* - Stdio transport (--stdio flag)
6+
* - Streamable HTTP transport (/mcp) - stateless mode
7+
* - Legacy SSE transport (/sse, /messages) - for older clients (e.g., Kotlin SDK)
8+
*/
9+
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import { createMcpExpressApp } from "@modelcontextprotocol/sdk/server/express.js";
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import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
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import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";
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import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
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import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
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import cors from "cors";
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import type { Request, Response } from "express";
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/** Active SSE sessions: sessionId -> { server, transport } */
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const sseSessions = new Map<
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string,
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{ server: McpServer; transport: SSEServerTransport }
22+
>();
23+
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/**
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* Starts an MCP server using the appropriate transport based on command-line arguments.
26+
*
27+
* If `--stdio` is passed, uses stdio transport. Otherwise, uses HTTP transports.
28+
*
29+
* @param createServer - Factory function that creates a new McpServer instance.
30+
*/
31+
export async function startServer(
32+
createServer: () => McpServer,
33+
): Promise<void> {
34+
try {
35+
if (process.argv.includes("--stdio")) {
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await startStdioServer(createServer);
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} else {
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await startHttpServer(createServer);
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}
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} catch (e) {
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console.error(e);
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process.exit(1);
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}
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}
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/**
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* Starts an MCP server with stdio transport.
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*
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* @param createServer - Factory function that creates a new McpServer instance.
50+
*/
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export async function startStdioServer(
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createServer: () => McpServer,
53+
): Promise<void> {
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await createServer().connect(new StdioServerTransport());
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}
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57+
/**
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* Starts an MCP server with HTTP transports (Streamable HTTP + legacy SSE).
59+
*
60+
* Provides:
61+
* - /mcp (GET/POST/DELETE): Streamable HTTP transport (stateless mode)
62+
* - /sse (GET) + /messages (POST): Legacy SSE transport for older clients
63+
*
64+
* @param createServer - Factory function that creates a new McpServer instance.
65+
*/
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export async function startHttpServer(
67+
createServer: () => McpServer,
68+
): Promise<void> {
69+
const port = parseInt(process.env.PORT ?? "3001", 10);
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// Express app - bind to all interfaces for development/testing
72+
const expressApp = createMcpExpressApp({ host: "0.0.0.0" });
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expressApp.use(cors());
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// Streamable HTTP transport (stateless mode)
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expressApp.all("/mcp", async (req: Request, res: Response) => {
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// Create fresh server and transport for each request (stateless mode)
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const server = createServer();
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const transport = new StreamableHTTPServerTransport({
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sessionIdGenerator: undefined,
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});
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// Clean up when response ends
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res.on("close", () => {
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transport.close().catch(() => {});
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server.close().catch(() => {});
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});
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try {
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await server.connect(transport);
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await transport.handleRequest(req, res, req.body);
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} catch (error) {
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console.error("MCP error:", error);
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if (!res.headersSent) {
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res.status(500).json({
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jsonrpc: "2.0",
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error: { code: -32603, message: "Internal server error" },
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id: null,
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});
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}
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}
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});
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// Legacy SSE transport - stream endpoint
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expressApp.get("/sse", async (_req: Request, res: Response) => {
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try {
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const server = createServer();
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const transport = new SSEServerTransport("/messages", res);
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sseSessions.set(transport.sessionId, { server, transport });
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res.on("close", () => {
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sseSessions.delete(transport.sessionId);
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transport.close().catch(() => {});
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server.close().catch(() => {});
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});
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await server.connect(transport);
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} catch (error) {
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console.error("SSE error:", error);
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if (!res.headersSent) res.status(500).end();
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}
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});
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// Legacy SSE transport - message endpoint
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expressApp.post("/messages", async (req: Request, res: Response) => {
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try {
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const sessionId = req.query.sessionId as string;
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const session = sseSessions.get(sessionId);
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if (!session) {
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return res.status(404).json({
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jsonrpc: "2.0",
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error: { code: -32001, message: "Session not found" },
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id: null,
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});
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}
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await session.transport.handlePostMessage(req, res, req.body);
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} catch (error) {
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console.error("Message error:", error);
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if (!res.headersSent) {
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res.status(500).json({
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jsonrpc: "2.0",
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error: { code: -32603, message: "Internal server error" },
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id: null,
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});
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}
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}
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});
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const { promise, resolve, reject } = Promise.withResolvers<void>();
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const httpServer = expressApp.listen(port, (err?: Error) => {
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if (err) return reject(err);
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console.log(`Server listening on http://localhost:${port}/mcp`);
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console.log(` SSE endpoint: http://localhost:${port}/sse`);
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resolve();
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});
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const shutdown = () => {
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console.log("\nShutting down...");
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// Clean up all SSE sessions
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sseSessions.forEach(({ server, transport }) => {
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transport.close().catch(() => {});
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server.close().catch(() => {});
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});
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sseSessions.clear();
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httpServer.close(() => process.exit(0));
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};
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process.on("SIGINT", shutdown);
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process.on("SIGTERM", shutdown);
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return promise;
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}
176+
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/**
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* @deprecated Use startHttpServer instead
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*/
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export const startStreamableHttpServer = startHttpServer;

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