bugfix: #3344 Reconnecting to the same SFU on membership change (#3361)

* bugfix: #3344 Reconnecting to the same SFU on membership change

* fixup! commit error

* Keep useActiveLivekitFocus from changing focus spuriously

* Remove redundant fix for spurious focus changes

We've now fixed it at the source by prohibiting state changes in useActiveLivekitFocus itself.

---------

Co-authored-by: Robin <robin@robin.town>

playwright/sfu-reconnect-bug.spec.ts

@@ -0,0 +1,104 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { expect, test } from "@playwright/test";
+
+test("When creator left, avoid reconnect to the same SFU", async ({
+  browser,
+}) => {
+  // Use reduce motion to disable animations that are making the tests a bit flaky
+  const creatorContext = await browser.newContext({ reducedMotion: "reduce" });
+  const creatorPage = await creatorContext.newPage();
+
+  await creatorPage.goto("/");
+
+  // ========
+  // ARRANGE: The first user creates a call as guest, join it, then click the invite button to copy the invite link
+  // ========
+  await creatorPage.getByTestId("home_callName").click();
+  await creatorPage.getByTestId("home_callName").fill("Welcome");
+  await creatorPage.getByTestId("home_displayName").click();
+  await creatorPage.getByTestId("home_displayName").fill("Inviter");
+  await creatorPage.getByTestId("home_go").click();
+  await expect(creatorPage.locator("video")).toBeVisible();
+
+  // join
+  await creatorPage.getByTestId("lobby_joinCall").click();
+  // Spotlight mode to make checking the test visually clearer
+  await creatorPage.getByRole("radio", { name: "Spotlight" }).check();
+
+  // Get the invite link
+  await creatorPage.getByRole("button", { name: "Invite" }).click();
+  await expect(
+    creatorPage.getByRole("heading", { name: "Invite to this call" }),
+  ).toBeVisible();
+  await expect(creatorPage.getByRole("img", { name: "QR Code" })).toBeVisible();
+  await expect(creatorPage.getByTestId("modal_inviteLink")).toBeVisible();
+  await expect(creatorPage.getByTestId("modal_inviteLink")).toBeVisible();
+  await creatorPage.getByTestId("modal_inviteLink").click();
+
+  const inviteLink = (await creatorPage.evaluate(
+    "navigator.clipboard.readText()",
+  )) as string;
+  expect(inviteLink).toContain("room/#/");
+
+  // ========
+  // ACT: The other user use the invite link to join the call as a guest
+  // ========
+  const guestB = await browser.newContext({
+    reducedMotion: "reduce",
+  });
+  const guestBPage = await guestB.newPage();
+
+  await guestBPage.goto(inviteLink);
+  await guestBPage.getByTestId("joincall_displayName").fill("Invitee");
+  await expect(guestBPage.getByTestId("joincall_joincall")).toBeVisible();
+  await guestBPage.getByTestId("joincall_joincall").click();
+  await guestBPage.getByTestId("lobby_joinCall").click();
+  await guestBPage.getByRole("radio", { name: "Spotlight" }).check();
+
+  // ========
+  // ACT: add a third user to the call to reproduce the bug
+  // ========
+  const guestC = await browser.newContext({
+    reducedMotion: "reduce",
+  });
+  const guestCPage = await guestC.newPage();
+  let sfuGetCallCount = 0;
+  await guestCPage.route("**/livekit/jwt/sfu/get", async (route) => {
+    sfuGetCallCount++;
+    await route.continue();
+  });
+  // Track WebSocket connections
+  let wsConnectionCount = 0;
+  await guestCPage.routeWebSocket("**", (ws) => {
+    // For some reason the interception is not working with the **
+    if (ws.url().includes("livekit/sfu/rtc")) {
+      wsConnectionCount++;
+    }
+    ws.connectToServer();
+  });
+
+  await guestCPage.goto(inviteLink);
+  await guestCPage.getByTestId("joincall_displayName").fill("Invitee");
+  await expect(guestCPage.getByTestId("joincall_joincall")).toBeVisible();
+  await guestCPage.getByTestId("joincall_joincall").click();
+  await guestCPage.getByTestId("lobby_joinCall").click();
+  await guestCPage.getByRole("radio", { name: "Spotlight" }).check();
+
+  await guestCPage.waitForTimeout(1000);
+
+  // ========
+  // the creator leaves the call
+  await creatorPage.getByTestId("incall_leave").click();
+
+  await guestCPage.waitForTimeout(2000);
+  // https://github.com/element-hq/element-call/issues/3344
+  // The app used to request a new jwt token then to reconnect to the SFU
+  expect(wsConnectionCount).toBe(1);
+  expect(sfuGetCallCount).toBe(1);
+});

src/room/useActiveFocus.ts

@@ -9,7 +9,7 @@ import {
   type MatrixRTCSession,
   MatrixRTCSessionEvent,
 } from "matrix-js-sdk/lib/matrixrtc";
-import { useCallback, useEffect, useRef } from "react";
+import { useCallback, useRef } from "react";
 import { deepCompare } from "matrix-js-sdk/lib/utils";
 import { logger } from "matrix-js-sdk/lib/logger";
 import { type LivekitFocus, isLivekitFocus } from "matrix-js-sdk/lib/matrixrtc";
@@ -24,27 +24,22 @@ import { useTypedEventEmitterState } from "../useEvents";
 export function useActiveLivekitFocus(
   rtcSession: MatrixRTCSession,
 ): LivekitFocus | undefined {
-  const activeFocus = useTypedEventEmitterState(
+  const prevActiveFocus = useRef<LivekitFocus | undefined>(undefined);
+  return useTypedEventEmitterState(
     rtcSession,
     MatrixRTCSessionEvent.MembershipsChanged,
     useCallback(() => {
       const f = rtcSession.getActiveFocus();
       // Only handle foci with type="livekit" for now.
-      return !!f && isLivekitFocus(f) ? f : undefined;
+      if (f && isLivekitFocus(f) && !deepCompare(f, prevActiveFocus.current)) {
+        const oldestMembership = rtcSession.getOldestMembership();
+        logger.info(
+          `Got new active focus from membership: ${oldestMembership?.sender}/${oldestMembership?.deviceId}.
+          Updated focus (focus switch) from ${JSON.stringify(prevActiveFocus.current)} to ${JSON.stringify(f)}`,
+        );
+        prevActiveFocus.current = f;
+      }
+      return prevActiveFocus.current;
     }, [rtcSession]),
   );
-
-  const prevActiveFocus = useRef(activeFocus);
-  useEffect(() => {
-    if (!deepCompare(activeFocus, prevActiveFocus.current)) {
-      const oldestMembership = rtcSession.getOldestMembership();
-      logger.warn(
-        `Got new active focus from membership: ${oldestMembership?.sender}/${oldestMembership?.deviceId}.
-        Updated focus (focus switch) from ${JSON.stringify(prevActiveFocus.current)} to ${JSON.stringify(activeFocus)}`,
-      );
-      prevActiveFocus.current = activeFocus;
-    }
-  }, [activeFocus, rtcSession]);
-
-  return activeFocus;
 }