@gsb-core/backend-mcp/bin/server-sse.js

GSB MCP Server CLI for AI editors - supports environment variables and -y flag to skip prompts

import express from 'express';
import { randomUUID } from 'node:crypto';
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
import { InMemoryEventStore } from '@modelcontextprotocol/sdk/examples/shared/inMemoryEventStore.js';
import { toolHelper } from '@gsb-core/mcp-tools'; 
import {  isInitializeRequest } from '@modelcontextprotocol/sdk/types.js';

  // Initialize environment variables
process.env.GSB_API_URL = process.env.GSB_API_URL || '';
process.env.GSB_API_KEY = process.env.GSB_API_KEY || '';
process.env.GSB_TENANT_CODE = process.env.GSB_TENANT_CODE || '';

// Helper functions for token and tenant code
const getToken = function(input) { let resp = input ?? process.env.GSB_API_KEY; console.log('getToken', resp); return resp};
const getTenantCode = function(input) { let resp = input ?? process.env.GSB_TENANT_CODE; console.log('getTenantCode', resp); return resp};

// Create an MCP server with implementation details
const getServer = () => {
  const server = new McpServer({
    name: 'simple-streamable-http-server',
    version: '1.0.0',
  }, { capabilities: { logging: {} } });


  toolHelper.applyToMcp({ server,  getToken,  getTenantCode });

  return server;
};

const app = express();
app.use(express.json());

// Map to store transports by session ID
const transports= {};

app.post('/mcp', async (req, res) => {
  console.log('Received MCP request:', req.body);
  try {
    // Check for existing session ID
    const sessionId = req.headers['mcp-session-id'];
    let transport;

    if (sessionId && transports[sessionId]) {
      // Reuse existing transport
      transport = transports[sessionId];
    } else if (!sessionId && isInitializeRequest(req.body)) {
      // New initialization request
      const eventStore = new InMemoryEventStore();
      transport = new StreamableHTTPServerTransport({
        sessionIdGenerator: () => randomUUID(),
        eventStore, // Enable resumability
        onsessioninitialized: (sessionId) => {
          // Store the transport by session ID when session is initialized
          // This avoids race conditions where requests might come in before the session is stored
          console.log(`Session initialized with ID: ${sessionId}`);
          transports[sessionId] = transport;
        }
      });

      // Set up onclose handler to clean up transport when closed
      transport.onclose = () => {
        const sid = transport.sessionId;
        if (sid && transports[sid]) {
          console.log(`Transport closed for session ${sid}, removing from transports map`);
          delete transports[sid];
        }
      };

      // Connect the transport to the MCP server BEFORE handling the request
      // so responses can flow back through the same transport
      const server = getServer();
      await server.connect(transport);

      await transport.handleRequest(req, res, req.body);
      return; // Already handled
    } else {
      // Invalid request - no session ID or not initialization 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 with existing transport - no need to reconnect
    // The existing transport is already connected to the server
    await transport.handleRequest(req, res, req.body);
  } catch (error) {
    console.error('Error handling MCP request:', error);
    if (!res.headersSent) {
      res.status(500).json({
        jsonrpc: '2.0',
        error: {
          code: -32603,
          message: 'Internal server error',
        },
        id: null,
      });
    }
  }
});

// Handle GET requests for SSE streams (using built-in support from StreamableHTTP)
app.get('/mcp', async (req, res) => {
  const sessionId = req.headers['mcp-session-id'] ;
  if (!sessionId || !transports[sessionId]) {
    res.status(400).send('Invalid or missing session ID');
    return;
  }

  // Check for Last-Event-ID header for resumability
  const lastEventId = req.headers['last-event-id'] ;
  if (lastEventId) {
    console.log(`Client reconnecting with Last-Event-ID: ${lastEventId}`);
  } else {
    console.log(`Establishing new SSE stream for session ${sessionId}`);
  }

  const transport = transports[sessionId];
  await transport.handleRequest(req, res);
});

// Handle DELETE requests for session termination (according to MCP spec)
app.delete('/mcp', async (req, res) => {
  const sessionId = req.headers['mcp-session-id'] ;
  if (!sessionId || !transports[sessionId]) {
    res.status(400).send('Invalid or missing session ID');
    return;
  }

  console.log(`Received session termination request for session ${sessionId}`);

  try {
    const transport = transports[sessionId];
    await transport.handleRequest(req, res);
  } catch (error) {
    console.error('Error handling session termination:', error);
    if (!res.headersSent) {
      res.status(500).send('Error processing session termination');
    }
  }
});

// Start the server
const PORT = 6278;
app.listen(PORT, () => {
  console.log(`MCP Streamable HTTP Server 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);
});