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src/api/index.js

@@ -60,8 +60,11 @@ function corsMiddleware(req, res, next) {
 async function createApi() {
     const app = express();
 
-    app.use((_req, res, next) => {
-        res.setHeader('Cache-Control', 'no-store');
+    app.use((req, res, next) => {
+        // Do not attach no-store to SSE endpoint
+        if (req.path !== '/api/events') {
+            res.setHeader('Cache-Control', 'no-store');
+        }
         next();
     });
     app.use(corsMiddleware);

src/api/routes/events.js

@@ -27,7 +27,7 @@ export function register(app, basePath = '') {
      *       es.addEventListener('article-42000045', () => { refetchArticle('42000045'); });
      *       ```
      *
-     *       Keep-alive comments (`: keepalive`) are sent roughly every 25s.
+     *       Keep-alive comments (`: heartbeat`) are sent roughly every 20s.
      *       Reconnect after changing the selected company (the stream is bound
      *       to the company at connect time).
      *
@@ -76,24 +76,28 @@ export function register(app, basePath = '') {
      *             schema:
      *               $ref: '#/components/schemas/Error'
      */
-    app.get(`${basePath}/events`, (req, res) => {
-        const companyId = req.user.selectedCompanyId;
-        if (companyId == null) {
-            return res.status(400).json({ error: 'No company selected' });
-        }
-
-        req.socket.setTimeout(0);
-        res.setTimeout(0);
-
-        res.status(200);
-        res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
-        res.setHeader('Cache-Control', 'no-cache, no-transform');
-        res.setHeader('Connection', 'keep-alive');
-        res.setHeader('X-Accel-Buffering', 'no');
-        res.flushHeaders?.();
-
-        res.write(': connected\n\n');
-
-        subscribe(res, { companyId, userId: req.user.id });
-    });
+    app.get(`${basePath}/events`, handleSse);
+}
+
+export function handleSse(req, res) {
+    const companyId = req.user?.selectedCompanyId;
+    if (companyId == null) {
+        return res.status(400).json({ error: 'No company selected' });
+    }
+
+    req.socket?.setTimeout(0);
+    res.setTimeout?.(0);
+
+    res.writeHead(200, {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache, no-transform',
+        'Connection': 'keep-alive',
+        'X-Accel-Buffering': 'no' // Instructs NGINX explicitly to disable buffering
+    });
+    res.flushHeaders(); // Ensure headers are sent over HTTP/2 frame immediately
+
+    // Send an initial ping to establish frame
+    res.write(': ping\n\n');
+
+    subscribe(res, { companyId, userId: req.user?.id }, req);
 }

src/api/sse.js

@@ -8,15 +8,16 @@
 /** @type {Set<SseClient>} */
 const clients = new Set();
 
-const KEEP_ALIVE_MS = 25_000;
+const KEEP_ALIVE_MS = 20_000;
 
 /**
  * Register an open SSE response. Caller must write the initial headers.
  * @param {import('express').Response} res
  * @param {{ companyId: number, userId: number }} meta
+ * @param {import('express').Request} [req]
  * @returns {() => void} unsubscribe
  */
-export function subscribe(res, { companyId, userId }) {
+export function subscribe(res, { companyId, userId }, req) {
     /** @type {SseClient} */
     const client = {
         res,
@@ -24,7 +25,7 @@ export function subscribe(res, { companyId, userId }) {
         userId,
         keepAlive: setInterval(() => {
             if (res.writableEnded) return;
-            res.write(': keepalive\n\n');
+            res.write(': heartbeat\n\n');
         }, KEEP_ALIVE_MS),
     };
     clients.add(client);
@@ -35,6 +36,7 @@ export function subscribe(res, { companyId, userId }) {
     };
 
     res.on('close', unsubscribe);
+    req?.on('close', unsubscribe);
     return unsubscribe;
 }