Improve transport in SSE server example

README.md

@@ -211,7 +211,7 @@ await server.connect(transport);
 For remote servers, start a web server with a Server-Sent Events (SSE) endpoint, and a separate endpoint for the client to send its messages to:
 
 ```typescript
-import express from "express";
+import express, { Request, Response } from "express";
 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
 import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";
 
@@ -224,16 +224,27 @@ const server = new McpServer({
 
 const app = express();
 
-app.get("/sse", async (req, res) => {
-  const transport = new SSEServerTransport("/messages", res);
+// to support multiple simultaneous connections we have a lookup object from
+// sessionId to transport
+const transports: {[sessionId: string]: SSEServerTransport} = {};
+
+app.get("/sse", async (_: Request, res: Response) => {
+  const transport = new SSEServerTransport('/messages', res);
+  transports[transport.sessionId] = transport;
+  res.on("close", () => {
+    delete transports[transport.sessionId];
+  });
   await server.connect(transport);
 });
 
-app.post("/messages", async (req, res) => {
-  // Note: to support multiple simultaneous connections, these messages will
-  // need to be routed to a specific matching transport. (This logic isn't
-  // implemented here, for simplicity.)
-  await transport.handlePostMessage(req, res);
+app.post("/messages", async (req: Request, res: Response) => {
+  const sessionId = req.query.sessionId as string;
+  const transport = transports[sessionId];
+  if (transport) {
+    await transport.handlePostMessage(req, res);
+  } else {
+    res.status(400).send('No transport found for sessionId');
+  }
 });
 
 app.listen(3001);