Implement MCP 2026-07-28 (#2286)

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>

examples/sse-polling/server.ts

@@ -0,0 +1,133 @@
+/**
+ * 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
+ *
+ * HTTP-only, sessionful 2025 by definition — `closeSSE`/`eventStore`/`retryInterval`
+ * live on `NodeStreamableHTTPServerTransport`, so this story wires that transport
+ * directly instead of the canonical `createMcpHandler` entry.
+ */
+import { randomUUID } from 'node:crypto';
+
+import { parseExampleArgs } from '@mcp-examples/shared';
+import { InMemoryEventStore } from '@mcp-examples/shared/auth';
+import { createMcpExpressApp } from '@modelcontextprotocol/express';
+import { NodeStreamableHTTPServerTransport } from '@modelcontextprotocol/node';
+import type { CallToolResult } from '@modelcontextprotocol/server';
+import { isInitializeRequest, McpServer } from '@modelcontextprotocol/server';
+import cors from 'cors';
+import type { Request, Response } from 'express';
+
+function buildServer(): McpServer {
+    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.error(`[${ctx.sessionId}] Starting long-operation...`);
+
+            // Send first progress notification
+            await ctx.mcpReq.log('info', 'Progress: 25% - Starting work...');
+            await sleep(200);
+
+            // Send second progress notification
+            await ctx.mcpReq.log('info', 'Progress: 50% - Halfway there...');
+            await sleep(200);
+
+            // Server decides to disconnect the client to free resources
+            // Client will reconnect via GET with Last-Event-ID after the transport's retryInterval
+            // Use ctx.http?.closeSSE callback - available when eventStore is configured
+            if (ctx.http?.closeSSE) {
+                console.error(`[${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(200);
+            await ctx.mcpReq.log('info', 'Progress: 75% - Almost done (sent while client disconnected)...');
+
+            await sleep(200);
+            await ctx.mcpReq.log('info', 'Progress: 100% - Complete!');
+
+            console.error(`[${ctx.sessionId}] Operation complete`);
+
+            return {
+                content: [
+                    {
+                        type: 'text',
+                        text: 'Long operation completed successfully!'
+                    }
+                ]
+            };
+        }
+    );
+
+    return server;
+}
+
+// Set up Express app
+const app = createMcpExpressApp();
+app.use(cors());
+
+// Create event store for resumability
+const eventStore = new InMemoryEventStore();
+
+// Track transports by session ID for session reuse
+const transports = new Map<string, NodeStreamableHTTPServerTransport>();
+
+// Handle all MCP requests (standard sessionful routing: known sid → reuse;
+// no sid + initialize → new session; unknown sid → 404; otherwise → 400).
+app.all('/mcp', async (req: Request, res: Response) => {
+    const sid = req.headers['mcp-session-id'] as string | undefined;
+    if (sid && transports.has(sid)) {
+        await transports.get(sid)!.handleRequest(req, res, req.body);
+    } else if (!sid && isInitializeRequest(req.body)) {
+        const transport = new NodeStreamableHTTPServerTransport({
+            sessionIdGenerator: () => randomUUID(),
+            eventStore,
+            retryInterval: 300, // Default retry interval for priming events
+            onsessioninitialized: id => {
+                console.error(`[${id}] Session initialized`);
+                transports.set(id, transport);
+            }
+        });
+        transport.onclose = () => transport.sessionId && transports.delete(transport.sessionId);
+        await buildServer().connect(transport);
+        await transport.handleRequest(req, res, req.body);
+    } else if (sid) {
+        // Unknown/expired session ID → 404 so the client knows to re-initialize.
+        res.status(404).json({ jsonrpc: '2.0', error: { code: -32_001, message: 'Session not found' }, id: null });
+    } else {
+        res.status(400).json({ jsonrpc: '2.0', error: { code: -32_000, message: 'Bad Request: Session ID required' }, id: null });
+    }
+});
+
+const { port } = parseExampleArgs();
+app.listen(port, () => {
+    console.error(`[server] listening on http://127.0.0.1:${port}/mcp`);
+    console.error('This server demonstrates SEP-1699 SSE polling:');
+    console.error('- retryInterval: 300ms (client waits before reconnecting)');
+    console.error('- eventStore: InMemoryEventStore (events are persisted for replay)');
+    console.error('Try calling the "long-operation" tool to see server-initiated disconnect in action.');
+});