simpleSseServer.ts

import { Request, Response } from 'express';
import { McpServer } from '../../server/mcp.js';
import { SSEServerTransport } from '../../server/sse.js';
import * as z from 'zod/v4';
import { CallToolResult } from '../../types.js';
import { createMcpExpressApp } from '../../server/express.js';

/**
 * This example server demonstrates the deprecated HTTP+SSE transport
 * (protocol version 2024-11-05). It mainly used for testing backward compatible clients.
 *
 * The server exposes two endpoints:
 * - /mcp: For establishing the SSE stream (GET)
 * - /messages: For receiving client messages (POST)
 *
 */

// Create an MCP server instance
const getServer = () => {
    const server = new McpServer(
        {
            name: 'simple-sse-server',
            version: '1.0.0'
        },
        { capabilities: { logging: {} } }
    );

    server.tool(
        'start-notification-stream',
        'Starts sending periodic notifications',
        {
            interval: z.number().describe('Interval in milliseconds between notifications').default(1000),
            count: z.number().describe('Number of notifications to send').default(10)
        },
        async ({ interval, count }, extra): Promise<CallToolResult> => {
            const sleep = (ms: number) => new Promise(resolve => setTimeout(resolve, ms));
            let counter = 0;

            // Send the initial notification
            await server.sendLoggingMessage(
                {
                    level: 'info',
                    data: `Starting notification stream with ${count} messages every ${interval}ms`
                },
                extra.sessionId
            );

            // Send periodic notifications
            while (counter < count) {
                counter++;
                await sleep(interval);

                try {
                    await server.sendLoggingMessage(
                        {
                            level: 'info',
                            data: `Notification #${counter} at ${new Date().toISOString()}`
                        },
                        extra.sessionId
                    );
                } catch (error) {
                    console.error('Error sending notification:', error);
                }
            }

            return {
                content: [
                    {
                        type: 'text',
                        text: `Completed sending ${count} notifications every ${interval}ms`
                    }
                ]
            };
        }
    );
    return server;
};

const app = createMcpExpressApp();

// Store transports by session ID
const transports: Record<string, SSEServerTransport> = {};

// SSE endpoint for establishing the stream
app.get('/mcp', async (req: Request, res: Response) => {
    console.log('Received GET request to /sse (establishing SSE stream)');

    try {
        // Create a new SSE transport for the client
        // The endpoint for POST messages is '/messages'
        const transport = new SSEServerTransport('/messages', res);

        // Store the transport by session ID
        const sessionId = transport.sessionId;
        transports[sessionId] = transport;

        // Set up onclose handler to clean up transport when closed
        transport.onclose = () => {
            console.log(`SSE transport closed for session ${sessionId}`);
            delete transports[sessionId];
        };

        // Connect the transport to the MCP server
        const server = getServer();
        await server.connect(transport);

        console.log(`Established SSE stream with session ID: ${sessionId}`);
    } catch (error) {
        console.error('Error establishing SSE stream:', error);
        if (!res.headersSent) {
            res.status(500).send('Error establishing SSE stream');
        }
    }
});

// Messages endpoint for receiving client JSON-RPC requests
app.post('/messages', async (req: Request, res: Response) => {
    console.log('Received POST request to /messages');

    // Extract session ID from URL query parameter
    // In the SSE protocol, this is added by the client based on the endpoint event
    const sessionId = req.query.sessionId as string | undefined;

    if (!sessionId) {
        console.error('No session ID provided in request URL');
        res.status(400).send('Missing sessionId parameter');
        return;
    }

    const transport = transports[sessionId];
    if (!transport) {
        console.error(`No active transport found for session ID: ${sessionId}`);
        res.status(404).send('Session not found');
        return;
    }

    try {
        // Handle the POST message with the transport
        await transport.handlePostMessage(req, res, req.body);
    } catch (error) {
        console.error('Error handling request:', error);
        if (!res.headersSent) {
            res.status(500).send('Error handling request');
        }
    }
});

// Start the server
const PORT = 3000;
app.listen(PORT, error => {
    if (error) {
        console.error('Failed to start server:', error);
        process.exit(1);
    }
    console.log(`Simple SSE Server (deprecated protocol version 2024-11-05) listening on port ${PORT}`);
});

// Handle server shutdown
process.on('SIGINT', async () => {
    console.log('Shutting down server...');

    // Close all active transports to properly clean up resources
    for (const sessionId in transports) {
        try {
            console.log(`Closing transport for session ${sessionId}`);
            await transports[sessionId].close();
            delete transports[sessionId];
        } catch (error) {
            console.error(`Error closing transport for session ${sessionId}:`, error);
        }
    }
    console.log('Server shutdown complete');
    process.exit(0);
});