feat: update SEP-1699 conformance tests for POST stream priming events

- Rewrite server tests to validate priming events on POST SSE streams
- Update client tests for POST→GET reconnection flow with retry timing
- Add eventStore and retryInterval to example server
- All 3 server conformance checks now pass

Author: felixweinberger

examples/clients/typescript/sse-retry-test.ts

@@ -56,17 +56,20 @@ async function main(): Promise<void> {
     console.log('Connected to MCP server');
 
     // Keep connection alive to observe reconnection behavior
-    // The server will disconnect and the client should reconnect
+    // The server will close the POST SSE stream and the client should reconnect via GET
     console.log('Waiting for reconnection cycle...');
     console.log(
-      'Server will close connection and client should wait for retry field timing'
+      'Server will send priming event with retry field, then close POST SSE stream'
+    );
+    console.log(
+      'Client should wait for retry period (2000ms) then reconnect via GET with Last-Event-ID'
     );
 
     // Wait long enough for:
-    // 1. Server to send retry field and close (100ms)
-    // 2. Client to wait for retry period (2000ms expected)
-    // 3. Client to reconnect (100ms)
-    // 4. Second disconnect cycle (optional)
+    // 1. Server to send priming event with retry field on POST SSE stream (100ms)
+    // 2. Server closes POST stream to trigger reconnection
+    // 3. Client waits for retry period (2000ms expected)
+    // 4. Client reconnects via GET with Last-Event-ID header
     await new Promise((resolve) => setTimeout(resolve, 6000));
 
     console.log('Test duration complete');

examples/servers/typescript/everything-server.ts

@@ -12,7 +12,12 @@ import {
   McpServer,
   ResourceTemplate
 } from '@modelcontextprotocol/sdk/server/mcp.js';
-import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
+import {
+  StreamableHTTPServerTransport,
+  EventStore,
+  EventId,
+  StreamId
+} from '@modelcontextprotocol/sdk/server/streamableHttp.js';
 import { z } from 'zod';
 import express from 'express';
 import cors from 'cors';
@@ -26,6 +31,41 @@ const watchedResourceContent = 'Watched resource content';
 const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {};
 const servers: { [sessionId: string]: McpServer } = {};
 
+// In-memory event store for SEP-1699 resumability
+const eventStoreData = new Map<
+  string,
+  { eventId: string; message: any; streamId: string }
+>();
+
+function createEventStore(): EventStore {
+  return {
+    async storeEvent(streamId: StreamId, message: any): Promise<EventId> {
+      const eventId = `${streamId}::${Date.now()}_${randomUUID()}`;
+      eventStoreData.set(eventId, { eventId, message, streamId });
+      return eventId;
+    },
+    async replayEventsAfter(
+      lastEventId: EventId,
+      { send }: { send: (eventId: EventId, message: any) => Promise<void> }
+    ): Promise<StreamId> {
+      const streamId = lastEventId.split('::')[0];
+      const eventsToReplay: Array<[string, { message: any }]> = [];
+      for (const [eventId, data] of eventStoreData.entries()) {
+        if (data.streamId === streamId && eventId > lastEventId) {
+          eventsToReplay.push([eventId, data]);
+        }
+      }
+      eventsToReplay.sort(([a], [b]) => a.localeCompare(b));
+      for (const [eventId, { message }] of eventsToReplay) {
+        if (Object.keys(message).length > 0) {
+          await send(eventId, message);
+        }
+      }
+      return streamId;
+    }
+  };
+}
+
 // Sample base64 encoded 1x1 red PNG pixel for testing
 const TEST_IMAGE_BASE64 =
   'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8DwHwAFBQIAX8jx0gAAAABJRU5ErkJggg==';
@@ -872,6 +912,8 @@ app.post('/mcp', async (req, res) => {
 
       transport = new StreamableHTTPServerTransport({
         sessionIdGenerator: () => randomUUID(),
+        eventStore: createEventStore(),
+        retryInterval: 5000, // 5 second retry interval for SEP-1699
         onsessioninitialized: (newSessionId) => {
           transports[newSessionId] = transport;
           servers[newSessionId] = mcpServer;