@modelcontextprotocol/sdk
Version:
Model Context Protocol implementation for TypeScript
97 lines • 3.97 kB
JavaScript
import { randomUUID } from 'node:crypto';
import { McpServer } from '../../server/mcp.js';
import { createMcpExpressApp } from '../../server/express.js';
import { StreamableHTTPServerTransport } from '../../server/streamableHttp.js';
import { InMemoryEventStore } from '../shared/inMemoryEventStore.js';
import cors from 'cors';
// Create the MCP server
const server = new McpServer({
name: 'sse-polling-example',
version: '1.0.0'
}, {
capabilities: { logging: {} }
});
// Register a long-running tool that demonstrates server-initiated disconnect
server.tool('long-task', 'A long-running task that sends progress updates. Server will disconnect mid-task to demonstrate polling.', {}, async (_args, extra) => {
const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));
console.log(`[${extra.sessionId}] Starting long-task...`);
// Send first progress notification
await server.sendLoggingMessage({
level: 'info',
data: 'Progress: 25% - Starting work...'
}, extra.sessionId);
await sleep(1000);
// Send second progress notification
await server.sendLoggingMessage({
level: 'info',
data: 'Progress: 50% - Halfway there...'
}, extra.sessionId);
await sleep(1000);
// Server decides to disconnect the client to free resources
// Client will reconnect via GET with Last-Event-ID after the transport's retryInterval
// Use extra.closeSSEStream callback - available when eventStore is configured
if (extra.closeSSEStream) {
console.log(`[${extra.sessionId}] Closing SSE stream to trigger client polling...`);
extra.closeSSEStream();
}
// Continue processing while client is disconnected
// Events are stored in eventStore and will be replayed on reconnect
await sleep(500);
await server.sendLoggingMessage({
level: 'info',
data: 'Progress: 75% - Almost done (sent while client disconnected)...'
}, extra.sessionId);
await sleep(500);
await server.sendLoggingMessage({
level: 'info',
data: 'Progress: 100% - Complete!'
}, extra.sessionId);
console.log(`[${extra.sessionId}] Task complete`);
return {
content: [
{
type: 'text',
text: 'Long task completed successfully!'
}
]
};
});
// Set up Express app
const app = createMcpExpressApp();
app.use(cors());
// Create event store for resumability
const eventStore = new InMemoryEventStore();
// Track transports by session ID for session reuse
const transports = new Map();
// Handle all MCP requests
app.all('/mcp', async (req, res) => {
const sessionId = req.headers['mcp-session-id'];
// Reuse existing transport or create new one
let transport = sessionId ? transports.get(sessionId) : undefined;
if (!transport) {
transport = new StreamableHTTPServerTransport({
sessionIdGenerator: () => randomUUID(),
eventStore,
retryInterval: 2000, // Default retry interval for priming events
onsessioninitialized: id => {
console.log(`[${id}] Session initialized`);
transports.set(id, transport);
}
});
// Connect the MCP server to the transport
await server.connect(transport);
}
await transport.handleRequest(req, res, req.body);
});
// Start the server
const PORT = 3001;
app.listen(PORT, () => {
console.log(`SSE Polling Example Server running on http://localhost:${PORT}/mcp`);
console.log('');
console.log('This server demonstrates SEP-1699 SSE polling:');
console.log('- retryInterval: 2000ms (client waits 2s before reconnecting)');
console.log('- eventStore: InMemoryEventStore (events are persisted for replay)');
console.log('');
console.log('Try calling the "long-task" tool to see server-initiated disconnect in action.');
});
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