Closed
Description
Describe the bug
State or stateless StreamableHTTPServerTransport gives
{"jsonrpc":"2.0","error":{"code":-32000,"message":"Bad Request: Server not initialized"},"id":null}
To Reproduce
Steps to reproduce the behavior: Code
const express = require("express");
const { randomUUID } = require("node:crypto");
const { McpServer } = require("@modelcontextprotocol/sdk/server/mcp.js");
const { StreamableHTTPServerTransport } = require("@modelcontextprotocol/sdk/server/streamableHttp.js");
const { isInitializeRequest } = require("@modelcontextprotocol/sdk/types.js");
const app = express();
app.use(express.json());
// Map to store transports by session ID
const transports = {};
// 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'] | undefined;
let transport;
console.log(req.body)
if (sessionId && transports[sessionId]) {
// Reuse existing transport
transport = transports[sessionId];
} else if (!sessionId && req.body.method === 'initialize') {
// New initialization request
transport = new StreamableHTTPServerTransport({
sessionIdGenerator: () => 100,
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 ...
// 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, res) => {
const sessionId = req.headers['mcp-session-id'] | 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);
const port = process.env.PORT || 3000;
app.listen(port, () => {
console.log(`MCP Server is running on http://localhost:${port}`);
});
Postman request:
{
"jsonrpc": "2.0",
"method": "initialize",
"params": {},
"id": 1
}
Expected behavior
Initialize session