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Implement MCP 2026-07-28 (#2286)

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Co-authored-by: Matt <77928207+mattzcarey@users.noreply.github.com>
Co-authored-by: Konstantin Konstantinov <KKonstantinov@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
This commit is contained in:
Felix Weinberger 2026-06-26 14:01:10 +01:00 • committed by GitHub
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135
examples/server/src/ssePollingExample.ts
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/**
* SSE Polling Example Server (SEP-1699)
*
* This example demonstrates server-initiated SSE stream disconnection
* and client reconnection with Last-Event-ID for resumability.
*
* Key features:
* - Configures `retryInterval` to tell clients how long to wait before reconnecting
* - Uses `eventStore` to persist events for replay after reconnection
* - Uses `ctx.http?.closeSSE()` callback to gracefully disconnect clients mid-operation
*
* Run with: pnpm tsx src/ssePollingExample.ts
* Test with: curl or the MCP Inspector
*/
import { randomUUID } from 'node:crypto';
import { createMcpExpressApp } from '@modelcontextprotocol/express';
import { NodeStreamableHTTPServerTransport } from '@modelcontextprotocol/node';
import type { CallToolResult } from '@modelcontextprotocol/server';
import { McpServer } from '@modelcontextprotocol/server';
import cors from 'cors';
import type { Request, Response } from 'express';
import { InMemoryEventStore } from './inMemoryEventStore';
// Create a fresh MCP server per client connection to avoid shared state between clients
const getServer = () => {
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.registerTool(
'long-operation',
{
description: 'A long-running operation that sends progress updates. Server will disconnect mid-stream to demonstrate polling.'
},
async (ctx): Promise<CallToolResult> => {
const sleep = (ms: number) => new Promise(resolve => setTimeout(resolve, ms));
console.log(`[${ctx.sessionId}] Starting long-operation...`);
// Send first progress notification
await ctx.mcpReq.log('info', 'Progress: 25% - Starting work...');
await sleep(1000);
// Send second progress notification
await ctx.mcpReq.log('info', 'Progress: 50% - Halfway there...');
await sleep(1000);
// Server decides to disconnect the client to free resources
// Client will reconnect via GET with Last-Event-ID after the transport's retryInterval
// Use ctx.http?.closeSSE callback - available when eventStore is configured
if (ctx.http?.closeSSE) {
console.log(`[${ctx.sessionId}] Closing SSE stream to trigger client polling...`);
ctx.http?.closeSSE();
}
// Continue processing while client is disconnected
// Events are stored in eventStore and will be replayed on reconnect
await sleep(500);
await ctx.mcpReq.log('info', 'Progress: 75% - Almost done (sent while client disconnected)...');
await sleep(500);
await ctx.mcpReq.log('info', 'Progress: 100% - Complete!');
console.log(`[${ctx.sessionId}] Operation complete`);
return {
content: [
{
type: 'text',
text: 'Long operation completed successfully!'
}
]
};
}
);
return server;
};
// Set up Express app
const app = createMcpExpressApp();
app.use(cors());
// Create event store for resumability
const eventStore = new InMemoryEventStore();
// Track transports by session ID for session reuse
const transports = new Map<string, NodeStreamableHTTPServerTransport>();
// Handle all MCP requests
app.all('/mcp', async (req: Request, res: Response) => {
const sessionId = req.headers['mcp-session-id'] as string | undefined;
// Reuse existing transport or create new one
let transport = sessionId ? transports.get(sessionId) : undefined;
if (!transport) {
transport = new NodeStreamableHTTPServerTransport({
sessionIdGenerator: () => randomUUID(),
eventStore,
retryInterval: 2000, // Default retry interval for priming events
onsessioninitialized: id => {
console.log(`[${id}] Session initialized`);
transports.set(id, transport!);
}
});
// Connect a fresh MCP server to the transport
const server = getServer();
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-operation" tool to see server-initiated disconnect in action.');
});