Fix #3267: everything sever response with an extra empty SSE event caus

src/everything/README.md

@@ -104,3 +104,32 @@ npx @modelcontextprotocol/server-everything sse
 npx @modelcontextprotocol/server-everything streamableHttp
 ```
 
+## Environment Variables
+
+### DISABLE_SSE_RESUMABILITY
+
+Set to `true` to disable SSE resumability (eventStore). This prevents the server from sending the priming event (empty SSE event with an ID) that is required by [SEP-1699](https://modelcontextprotocol.io/community/seps/1699-support-sse-polling-via-server-side-disconnect) for protocol version 2025-11-25+.
+
+**Note**: This is a workaround for clients that don't properly handle empty SSE data events as specified by the [SSE standard](https://html.spec.whatwg.org/multipage/server-sent-events.html). The proper fix is to update the client to handle empty SSE events correctly.
+
+When resumability is disabled:
+- SSE streams cannot be resumed after network failures
+- Server cannot use polling mode (must keep connections open)
+- Event replay is not available
+
+```shell
+# Disable SSE resumability
+DISABLE_SSE_RESUMABILITY=true npx @modelcontextprotocol/server-everything streamableHttp
+
+# Or with Docker
+docker run -e DISABLE_SSE_RESUMABILITY=true -p 3001:3001 mcp/everything streamableHttp
+```
+
+### PORT
+
+Set the port for the HTTP servers (SSE and Streamable HTTP). Default: `3001`
+
+```shell
+PORT=8080 npx @modelcontextprotocol/server-everything streamableHttp
+```
+

src/everything/transports/streamableHttp.ts

@@ -38,6 +38,13 @@ class InMemoryEventStore implements EventStore {
 
 console.log("Starting Streamable HTTP server...");
 
+// Check if SSE resumability should be disabled (workaround for clients that don't handle empty SSE events)
+const DISABLE_SSE_RESUMABILITY = process.env.DISABLE_SSE_RESUMABILITY === 'true';
+if (DISABLE_SSE_RESUMABILITY) {
+  console.log("SSE resumability is DISABLED - eventStore will not be used");
+  console.log("This is a workaround for clients that don't properly handle empty SSE data events");
+}
+
 // Express app with permissive CORS for testing with Inspector direct connect mode
 const app = express();
 app.use(
@@ -72,10 +79,13 @@ app.post("/mcp", async (req: Request, res: Response) => {
       const { server, cleanup } = createServer();
 
       // New initialization request
-      const eventStore = new InMemoryEventStore();
+      // Only enable eventStore if resumability is not disabled
+      // Note: Disabling resumability is a workaround for clients that don't properly
+      // handle empty SSE data events (required by SEP-1699 for protocol >= 2025-11-25)
+      const eventStore = DISABLE_SSE_RESUMABILITY ? undefined : new InMemoryEventStore();
       transport = new StreamableHTTPServerTransport({
         sessionIdGenerator: () => randomUUID(),
-        eventStore, // Enable resumability
+        eventStore, // Enable resumability (unless disabled)
         onsessioninitialized: (sessionId: string) => {
           // Store the transport by session ID when a session is initialized
           // This avoids race conditions where requests might come in before the session is stored