149 lines
6.2 KiB
Plaintext
149 lines
6.2 KiB
Plaintext
import { randomUUID } from 'node:crypto';
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import { McpServer } from '../../server/mcp.js';
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import { createMcpExpressApp } from '../../server/express.js';
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import { StreamableHTTPServerTransport } from '../../server/streamableHttp.js';
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import { isInitializeRequest } from '../../types.js';
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import { InMemoryEventStore } from '../shared/inMemoryEventStore.js';
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import cors from 'cors';
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// Factory to create a new MCP server per session.
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// Each session needs its own server+transport pair to avoid cross-session contamination.
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const getServer = () => {
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const server = new McpServer({
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name: 'sse-polling-example',
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version: '1.0.0'
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}, {
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capabilities: { logging: {} }
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});
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// Register a long-running tool that demonstrates server-initiated disconnect
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server.tool('long-task', 'A long-running task that sends progress updates. Server will disconnect mid-task to demonstrate polling.', {}, async (_args, extra) => {
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const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));
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console.log(`[${extra.sessionId}] Starting long-task...`);
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// Send first progress notification
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await server.sendLoggingMessage({
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level: 'info',
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data: 'Progress: 25% - Starting work...'
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}, extra.sessionId);
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await sleep(1000);
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// Send second progress notification
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await server.sendLoggingMessage({
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level: 'info',
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data: 'Progress: 50% - Halfway there...'
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}, extra.sessionId);
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await sleep(1000);
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// Server decides to disconnect the client to free resources
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// Client will reconnect via GET with Last-Event-ID after the transport's retryInterval
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// Use extra.closeSSEStream callback - available when eventStore is configured
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if (extra.closeSSEStream) {
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console.log(`[${extra.sessionId}] Closing SSE stream to trigger client polling...`);
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extra.closeSSEStream();
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}
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// Continue processing while client is disconnected
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// Events are stored in eventStore and will be replayed on reconnect
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await sleep(500);
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await server.sendLoggingMessage({
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level: 'info',
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data: 'Progress: 75% - Almost done (sent while client disconnected)...'
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}, extra.sessionId);
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await sleep(500);
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await server.sendLoggingMessage({
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level: 'info',
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data: 'Progress: 100% - Complete!'
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}, extra.sessionId);
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console.log(`[${extra.sessionId}] Task complete`);
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return {
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content: [
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{
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type: 'text',
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text: 'Long task completed successfully!'
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}
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]
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};
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});
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return server;
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};
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// Set up Express app
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const app = createMcpExpressApp();
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app.use(cors());
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// Create event store for resumability
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const eventStore = new InMemoryEventStore();
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// Close sessions that have been idle for IDLE_MS, and keep at most MAX_SESSIONS open
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const IDLE_MS = 30 * 60000;
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const MAX_SESSIONS = 1000;
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const sessions = new Map();
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// Count open responses so a long-running request or a listening SSE stream is not treated as idle
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const trackResponse = (session, res) => {
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if (!res.socket || res.destroyed)
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return;
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session.open++;
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res.on('close', () => {
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session.open--;
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session.lastActive = Date.now();
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});
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};
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// Close sessions with nothing open and no activity for IDLE_MS
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setInterval(() => {
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const cutoff = Date.now() - IDLE_MS;
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for (const { transport, open, lastActive } of sessions.values()) {
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if (open === 0 && lastActive < cutoff)
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transport.close().catch(console.error);
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}
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}, 60000).unref();
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// Handle all MCP requests
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app.all('/mcp', async (req, res) => {
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const sessionId = req.headers['mcp-session-id'];
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// Reuse the existing transport for a known session
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const session = sessionId ? sessions.get(sessionId) : undefined;
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if (session) {
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trackResponse(session, res);
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await session.transport.handleRequest(req, res, req.body);
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return;
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}
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if (sessionId) {
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// Unknown or expired session ID - the client should start a new session
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res.status(404).json({ jsonrpc: '2.0', error: { code: -32001, message: 'Session not found' }, id: null });
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return;
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}
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if (!isInitializeRequest(req.body)) {
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// Invalid request - no session ID and not an initialization request
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res.status(400).json({ jsonrpc: '2.0', error: { code: -32000, message: 'Bad Request: No valid session ID provided' }, id: null });
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return;
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}
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if (sessions.size >= MAX_SESSIONS) {
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res.status(503).json({ jsonrpc: '2.0', error: { code: -32000, message: 'Too many open sessions' }, id: null });
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return;
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}
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// New initialization request - create a transport for the session
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const transport = new StreamableHTTPServerTransport({
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sessionIdGenerator: () => randomUUID(),
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eventStore,
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retryInterval: 2000, // Default retry interval for priming events
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onsessioninitialized: id => {
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console.log(`[${id}] Session initialized`);
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sessions.set(id, { transport, open: 0, lastActive: Date.now() });
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}
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});
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// Set up onclose handler to clean up transport when closed
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transport.onclose = () => {
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const sid = transport.sessionId;
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if (sid && sessions.has(sid)) {
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console.log(`[${sid}] Transport closed, removing from sessions map`);
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sessions.delete(sid);
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}
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};
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// Create a new server per session and connect it to the transport
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const server = getServer();
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await server.connect(transport);
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await transport.handleRequest(req, res, req.body);
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});
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// Start the server
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const PORT = 3001;
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app.listen(PORT, () => {
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console.log(`SSE Polling Example Server running on http://localhost:${PORT}/mcp`);
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console.log('');
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console.log('This server demonstrates SEP-1699 SSE polling:');
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console.log('- retryInterval: 2000ms (client waits 2s before reconnecting)');
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console.log('- eventStore: InMemoryEventStore (events are persisted for replay)');
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console.log('');
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console.log('Try calling the "long-task" tool to see server-initiated disconnect in action.');
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});
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//# sourceMappingURL=ssePollingExample.js.map |