implement demo mode

server/demo/demo-ws.js

@@ -0,0 +1,41 @@
+// Vault prefix translation for WebSocket upgrades.
+//
+// ws.js validates the upgrade's `?vault=` against config.vaults.
+// We translate to the storage-prefixed name before it sees the request, otherwise the handshake fails and the client reconnect-loops.
+
+const url = require("url");
+
+const {
+  COOKIE_NAME,
+  sessions,
+  parseCookies,
+  makeStorageName,
+  touchSession,
+} = require("./demo-sessions");
+
+function wireWebSocket(server) {
+  const origEmit = server.emit.bind(server);
+
+  server.emit = function (event, req, ...rest) {
+    if (event === "upgrade") {
+      const cookies = parseCookies(req);
+      const sessionId = cookies[COOKIE_NAME];
+
+      if (sessionId && sessions.has(sessionId)) {
+        const u = new url.URL(req.url, "http://localhost");
+        const userVault = u.searchParams.get("vault");
+
+        if (userVault && !userVault.startsWith("demo-")) {
+          u.searchParams.set("vault", makeStorageName(sessionId, userVault));
+          req.url = u.pathname + u.search;
+        }
+
+        touchSession(sessionId);
+      }
+    }
+
+    return origEmit(event, req, ...rest);
+  };
+}
+
+module.exports = { wireWebSocket };