fix: replace a browser subscription the push service gave up on

lib/__tests__/web-push.test.ts

@@ -741,6 +741,80 @@ describe('what enabling and disabling say when they fail', () => {
   });
 });
 
+describe('an endpoint the push service gave up on', () => {
+  const ENDPOINT_KEY = `bulwark.push.endpoint.v1.${ACCOUNT_ID}`;
+
+  function registered() {
+    localStorage.setItem(DEVICE_KEY, THIS_DEVICE);
+    localStorage.setItem(SUB_KEY, 'push-mine');
+    localStorage.setItem(RELAY_BASE_KEY, RELAY);
+    localStorage.setItem(ENDPOINT_KEY, 'https://fcm.example/endpoint');
+    return makeClient([sub('push-mine', THIS_DEVICE)]);
+  }
+
+  it('gets a new subscription when the relay dropped the record for the very endpoint this browser still holds', async () => {
+    const { browserSub, registration } = installPushBrowser();
+    const client = registered();
+    installFetch({}); // The relay answers 404 for this device.
+
+    await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false });
+
+    expect(browserSub.unsubscribe).toHaveBeenCalledTimes(1);
+    expect(registration.pushManager.subscribe).toHaveBeenCalledTimes(1);
+  });
+
+  it('keeps the subscription while the relay knows the record', async () => {
+    const { browserSub } = installPushBrowser();
+    const client = registered();
+    installFetch({ [THIS_DEVICE]: true });
+
+    await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false });
+
+    expect(browserSub.unsubscribe).not.toHaveBeenCalled();
+  });
+
+  it('keeps it when the relay cannot be asked', async () => {
+    const { browserSub } = installPushBrowser();
+    const client = registered();
+    const calls: string[] = [];
+    vi.stubGlobal('fetch', vi.fn(async (input: RequestInfo | URL) => {
+      const url = String(input);
+      calls.push(url);
+      if (url.includes('/api/push/active/')) throw new TypeError('blip');
+      const json = (body: unknown) => ({ ok: true, status: 200, json: async () => body }) as Response;
+      return url.endsWith('/vapid-public-key') ? json({ publicKey: 'QUJD' }) : json({});
+    }));
+
+    await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false });
+
+    expect(calls.some((url) => url.includes('/api/push/active/'))).toBe(true);
+    expect(browserSub.unsubscribe).not.toHaveBeenCalled();
+  });
+
+  it('only registers when another account already moved the browser to a new endpoint', async () => {
+    const { browserSub } = installPushBrowser();
+    const client = registered();
+    localStorage.setItem(ENDPOINT_KEY, 'https://fcm.example/older');
+    installFetch({});
+
+    await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false });
+
+    expect(browserSub.unsubscribe).not.toHaveBeenCalled();
+    expect(localStorage.getItem(ENDPOINT_KEY)).toBe('https://fcm.example/endpoint');
+  });
+
+  it('does not mistake a move to another relay for a dead endpoint', async () => {
+    const { browserSub } = installPushBrowser();
+    const client = registered();
+    localStorage.setItem(RELAY_BASE_KEY, 'https://old-relay.example');
+    installFetch({});
+
+    await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false });
+
+    expect(browserSub.unsubscribe).not.toHaveBeenCalled();
+  });
+});
+
 describe('resyncWebPush when the relay changed (#903)', () => {
   afterEach(() => setNoThirdPartyTraffic(false));
 

lib/web-push.ts

@@ -53,6 +53,12 @@ function relayBaseKey(accountId: string): string {
   return RELAY_BASE_PREFIX + accountId;
 }
 
+/** The browser endpoint this account last gave the relay: see relayDroppedOurEndpoint. */
+const ENDPOINT_PREFIX = 'bulwark.push.endpoint.v1.';
+function endpointKey(accountId: string): string {
+  return ENDPOINT_PREFIX + accountId;
+}
+
 function emailPushRefusedKey(accountId: string): string {
   return EMAIL_PUSH_REFUSED_PREFIX + accountId;
 }
@@ -642,6 +648,28 @@ async function relayReportsDead(
 const VERIFICATION_RESEND_AFTER_MS = 62_000;
 const VERIFICATION_TIMEOUT_MS = 80_000;
 
+/**
+ * The relay deletes a record when the push service answers 404 or 410. The browser
+ * doesn't get told: it keeps the subscription, and registering that endpoint again
+ * only lasts until the next push. Only for the endpoint this account registered:
+ * after another account moved the browser on, a missing record means nothing.
+ */
+async function relayDroppedOurEndpoint(
+  accountId: string,
+  relayBaseUrl: string,
+  subscriptionId: string,
+  endpoint: string,
+): Promise<boolean> {
+  if (localStorage.getItem(relayBaseKey(accountId)) !== relayBaseUrl) return false;
+  if (localStorage.getItem(endpointKey(accountId)) !== endpoint) return false;
+  try {
+    const res = await fetch(buildRelayUrl(relayBaseUrl, `/api/push/active/${encodeURIComponent(subscriptionId)}`));
+    return res.status === 404;
+  } catch {
+    return false;
+  }
+}
+
 async function pollVerificationCode(
   relayBaseUrl: string,
   subscriptionId: string,
@@ -785,6 +813,14 @@ async function enableWebPushForThisTab(
     await pushSubscription.unsubscribe().catch(() => undefined);
     pushSubscription = null;
   }
+  const accountId = params.client.getAccountId();
+  const deviceClientId = getOrCreateDeviceClientId(accountId);
+  if (pushSubscription && await relayDroppedOurEndpoint(accountId, relayBaseUrl, deviceClientId, pushSubscription.endpoint)) {
+    await pushSubscription.unsubscribe().catch(() => undefined);
+    pushSubscription = null;
+    // The other accounts' records point at the old endpoint: their turn comes too.
+    lastResync.clear();
+  }
   if (!pushSubscription) {
     pushSubscription = await registration.pushManager.subscribe({
       userVisibleOnly: true,
@@ -792,9 +828,6 @@ async function enableWebPushForThisTab(
     });
   }
 
-  const accountId = params.client.getAccountId();
-  const deviceClientId = getOrCreateDeviceClientId(accountId);
-
   await registerWithRelay({
     relayBaseUrl,
     subscriptionId: deviceClientId,
@@ -807,6 +840,7 @@ async function enableWebPushForThisTab(
     },
     accountLabel: params.accountLabel,
   });
+  localStorage.setItem(endpointKey(accountId), pushSubscription.endpoint);
   await keepRelayRegistration(accountId, {
     relay: relayBaseUrl,
     subscriptionId: deviceClientId,
@@ -1001,6 +1035,7 @@ async function disableWebPushForThisTab(params: DisableWebPushParams): Promise<v
   }
   localStorage.removeItem(subIdKey);
   localStorage.removeItem(relayBaseKey(accountId));
+  localStorage.removeItem(endpointKey(accountId));
   await forgetRelayRegistration(accountId);
   // Enabling again starts from the full emailPush map.
   localStorage.removeItem(emailPushRefusedKey(accountId));