import { Request, Response, NextFunction, RequestHandler } from 'express';
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
import { ServerFactory, StatelessHandlerOptions } from './types.js';
/**
* Creates an Express middleware handler for stateless MCP interactions
*
* @param serverFactory - Function to create a new McpServer instance for each request
* @param options - Optional configuration options for the handler
* @returns An Express request handler function
*/
export function statelessHandler(
serverFactory: ServerFactory = () => new McpServer({ name: 'stateless-mcp-server', version: '1.0.0' }),
options: StatelessHandlerOptions = {}
): RequestHandler {
return async (req: Request, res: Response, next: NextFunction) => {
// Only accept POST requests for stateless mode
if (req.method !== 'POST') {
return res.status(405).json({
jsonrpc: '2.0',
error: {
code: -32000,
message: 'Method not allowed',
},
id: null,
});
}
let transport: StreamableHTTPServerTransport | undefined;
let server: McpServer | undefined;
try {
// Create new server and transport instances for this request
server = serverFactory();
transport = new StreamableHTTPServerTransport({
sessionIdGenerator: options.sessionIdGenerator,
});
// Connect to the MCP server
await server.connect(transport);
// Handle the request
await transport.handleRequest(req, res, req.body);
// Set up clean-up on connection close
res.on('close', () => {
if (transport && server) {
// Call user-provided close handler if defined
if (options.onClose) {
options.onClose(req, res);
}
// Clean up resources
transport.close();
server.close();
transport = undefined;
server = undefined;
}
});
} catch (error) {
// Clean up resources on error
if (transport) {
transport.close();
}
if (server) {
server.close();
}
// Call user-provided error handler if defined
if (options.onError) {
options.onError(error as Error);
}
// Only send error response if headers haven't been sent yet
if (!res.headersSent) {
res.status(500).json({
jsonrpc: '2.0',
error: {
code: -32603,
message: 'Internal server error',
},
id: null,
});
}
// Pass to next error handler if available
if (next) {
next(error);
}
}
};
}
