Stop event-polling for an account when it's logged out

src/chat/ChatScreen.js

@@ -86,11 +86,12 @@ const useMessagesWithFetch = args => {
     }
   }, [dispatch, narrow]);
 
-  // When the event queue changes, schedule a fetch. (Currently, we never
-  // set this to null from a non-null value, so this really does mean the
-  // event queue has changed; it can't mean that we had a queue ID and
-  // dropped it.)
-  React.useEffect(scheduleFetch, [eventQueueId]);
+  // When we have a new event queue, schedule a fetch.
+  React.useEffect(() => {
+    if (eventQueueId !== null) {
+      scheduleFetch();
+    }
+  }, [eventQueueId]);
 
   // If we stop having any data at all about the messages in this narrow --
   // we don't know any, and nor do we know if there are some -- then

src/events/eventActions.js

@@ -1,14 +1,16 @@
 /* @flow strict-local */
 import { addBreadcrumb } from '@sentry/react-native';
+// $FlowFixMe[untyped-import]
+import isEqual from 'lodash.isequal';
 
 import type { GeneralEvent, ThunkAction } from '../types';
-import { assumeSecretlyGlobalState } from '../reduxTypes';
 import * as api from '../api';
 import { logout } from '../account/accountActions';
 import { deadQueue } from '../session/sessionActions';
 import eventToAction from './eventToAction';
 import doEventActionSideEffects from './doEventActionSideEffects';
-import { tryGetActiveAccountState, tryGetAuth } from '../selectors';
+import { tryGetAuth, getIdentity } from '../selectors';
+import { identityOfAuth } from '../account/accountMisc';
 import { BackoffMachine } from '../utils/async';
 import { ApiError } from '../api/apiErrors';
 import * as logging from '../utils/logging';
@@ -61,11 +63,9 @@ export const startEventPolling = (
 
   // eslint-disable-next-line no-constant-condition
   while (true) {
-    const globalState = assumeSecretlyGlobalState(getState());
-    const state = tryGetActiveAccountState(globalState);
-    const auth = state ? tryGetAuth(state) : undefined;
+    const auth = tryGetAuth(getState());
     if (!auth) {
-      // There is no logged-in active account.
+      // This account is not logged in.
       break;
     }
     // `auth` represents the active account.  It might be different from
@@ -77,10 +77,28 @@ export const startEventPolling = (
       const response = await api.pollForEvents(auth, queueId, lastEventId);
       events = response.events;
 
-      if (queueId !== getState().session.eventQueueId) {
-        // The user switched accounts or logged out.
-        // TODO(#5022): TODO(#5009): This doesn't seem like an adequate
-        //   check for that; it looks like it only detects a new REGISTER_COMPLETE.
+      if (getState().session.eventQueueId === null) {
+        // We don't want to keep polling, e.g., because we've logged out;
+        // see `PerAccountSessionState.eventQueueId` for other cases.
+        break;
+      } else if (!isEqual(getIdentity(getState()), identityOfAuth(auth))) {
+        // During the last poll, the active account changed. Stop polling
+        // for the previous one.
+        // TODO(#5005): Remove this conditional as unreachable, once `auth`
+        //   represents the current account (instead of secretly
+        //   representing the global "active account" which can change.)
+        break;
+      } else if (queueId !== getState().session.eventQueueId) {
+        // While the most recent poll was happening, another queue was
+        // established for this account, and we've started polling on that
+        // one. Stop polling on this one.
+        //
+        // In theory this could happen if you logged out of this account and
+        // logged back in again.
+        //
+        // TODO(#5009): Instead of this conditional, abort the
+        //   `api.pollForEvents` immediately when `eventQueueId` becomes
+        //   `null`, then break at that time?
         break;
       }
     } catch (e) {

src/session/sessionReducer.js

@@ -24,6 +24,15 @@ import { getHasAuth } from '../account/accountsSelectors';
  * See {@link SessionState} for discussion of what "non-persistent" means.
  */
 export type PerAccountSessionState = $ReadOnly<{
+  /**
+   * The event queue ID that we're currently polling on, if any.
+   *
+   * Null when we're not polling on any event queue:
+   * - Between startup and registering a queue
+   * - After the server tells us our old queue was invalid, and before we've
+   *   registered a new one
+   * - While this account is logged out
+   */
   eventQueueId: string | null,
 
   /**
@@ -162,26 +171,43 @@ export default (state: SessionState = initialState, action: Action): SessionStat
         ...state,
         needsInitialFetch: true,
         loading: false,
+
+        // The server told us that the old queue ID is invalid. Forget it,
+        // so we don't try to use it.
+        eventQueueId: null,
       };
 
     case LOGIN_SUCCESS:
       return {
         ...state,
         needsInitialFetch: true,
+
+        // We're about to request a new event queue; no use hanging on to
+        // any old one we might have.
+        eventQueueId: null,
       };
 
     case LOGOUT:
       return {
         ...state,
         needsInitialFetch: false,
         loading: false,
+
+        // Stop polling this event queue.
+        eventQueueId: null,
       };
 
     case ACCOUNT_SWITCH:
       return {
         ...state,
         needsInitialFetch: true,
         loading: false,
+
+        // Stop polling this event queue.  (We'll request a new one soon,
+        // for the new account.)
+        // TODO(#5005): Keep polling on accounts other than the active
+        //   account.
+        eventQueueId: null,
       };
 
     case REHYDRATE: