api: Don't allow connecting to servers <2.0

src/api/apiErrors.js

@@ -1,6 +1,7 @@
 /* @flow strict-local */
 import { ExtendableError } from '../utils/logging';
 import type { ApiErrorCode, ApiResponseErrorData } from './transportTypes';
+import { ZulipVersion } from '../utils/zulipVersion';
 
 /**
  * Some kind of error from a Zulip API network request.
@@ -168,3 +169,26 @@ export const interpretApiResponse = (httpStatus: number, data: mixed): mixed =>
   // the API says that shouldn't happen.
   throw new UnexpectedHttpStatusError(httpStatus, data);
 };
+
+/**
+ * The Zulip Server version below which we should just refuse to connect.
+ */
+// Currently chosen to affect a truly tiny fraction of users, as we test the
+// feature of refusing to connect, to keep the risk small; see
+//   https://github.com/zulip/zulip-mobile/issues/5102#issuecomment-1233446360
+// In steady state, this should lag a bit behind the threshold version for
+// ServerCompatBanner (kMinSupportedVersion), to give users time to see and
+// act on the banner.
+export const kMinAllowedServerVersion: ZulipVersion = new ZulipVersion('2.0');
+
+/**
+ * An error we throw in API bindings on finding a server is too old.
+ */
+export class ServerTooOldError extends ExtendableError {
+  version: ZulipVersion;
+
+  constructor(version: ZulipVersion) {
+    super(`Unsupported Zulip Server version: ${version.raw()}`);
+    this.version = version;
+  }
+}

src/api/pollForEvents.js

@@ -9,6 +9,9 @@ type ApiResponsePollEvents = {|
 |};
 
 /** See https://zulip.com/api/get-events */
+// TODO: Handle downgrading server across kThresholdVersion, which we'd hear
+//   about in `restart` events, by throwing a ServerTooOldError. This case
+//   seems pretty rare but is possible.
 export default (auth: Auth, queueId: string, lastEventId: number): Promise<ApiResponsePollEvents> =>
   apiGet(
     auth,

src/api/registerForEvents.js

@@ -7,6 +7,7 @@ import type { CrossRealmBot, User } from './modelTypes';
 import { apiPost } from './apiFetch';
 import { AvatarURL } from '../utils/avatar';
 import { ZulipVersion } from '../utils/zulipVersion';
+import { ServerTooOldError, kMinAllowedServerVersion } from './apiErrors';
 
 const transformUser = (rawUser: {| ...User, avatar_url?: string | null |}, realm: URL): User => {
   const { avatar_url: rawAvatarUrl, email } = rawUser;
@@ -34,71 +35,82 @@ const transformCrossRealmBot = (
   };
 };
 
-const transform = (rawInitialData: RawInitialData, auth: Auth): InitialData => ({
-  ...rawInitialData,
-
-  zulip_feature_level: rawInitialData.zulip_feature_level ?? 0,
-  zulip_version: new ZulipVersion(rawInitialData.zulip_version),
-
-  // Transform the newer `realm_linkifiers` format, if present, to the
-  // older `realm_filters` format. We do the same transformation on
-  // 'realm_linkifiers' events.
-  // TODO(server-4.0): Switch to new format, if we haven't already;
-  //   and drop conversion.
-  realm_filters: rawInitialData.realm_linkifiers
-    ? rawInitialData.realm_linkifiers.map(({ pattern, url_format, id }) => [
-        pattern,
-        url_format,
-        id,
-      ])
-    : rawInitialData.realm_filters,
-
-  // In 5.0 (feature level 100), the representation the server sends for "no
-  // limit" changed from 0 to `null`.
-  //
-  // It's convenient to emulate Server 5.0's representation in our own data
-  // structures. To get a correct initial value, it's sufficient to coerce
-  // `0` to null here, without even looking at the server feature level.
-  // That's because, in addition to the documented change in 5.0, there was
-  // another: 0 became an invalid value, which means we don't have to
-  // anticipate servers 5.0+ using it to mean anything, such as "0 seconds":
-  //   https://github.com/zulip/zulip/blob/b13bfa09c/zerver/lib/message.py#L1482.
-  //
-  // TODO(server-5.0) Remove this conditional.
-  realm_message_content_delete_limit_seconds:
-    rawInitialData.realm_message_content_delete_limit_seconds === 0
-      ? null
-      : rawInitialData.realm_message_content_delete_limit_seconds,
-
-  realm_users: rawInitialData.realm_users.map(rawUser => transformUser(rawUser, auth.realm)),
-  realm_non_active_users: rawInitialData.realm_non_active_users.map(rawNonActiveUser =>
-    transformUser(rawNonActiveUser, auth.realm),
-  ),
-  cross_realm_bots: rawInitialData.cross_realm_bots.map(rawCrossRealmBot =>
-    transformCrossRealmBot(rawCrossRealmBot, auth.realm),
-  ),
-
-  // The doc says the field will be removed in a future release. So, while
-  // we're still consuming it, fill it in if missing, with instructions from
-  // the doc:
-  //
-  // > Its value will always equal
-  // >   `can_create_public_streams || can_create_private_streams`.
-  //
-  // TODO(server-5.0): Only use `can_create_public_streams` and
-  //   `can_create_private_streams`, and simplify this away.
-  can_create_streams:
-    rawInitialData.can_create_streams
-    ?? (() => {
-      const canCreatePublicStreams = rawInitialData.can_create_public_streams;
-      const canCreatePrivateStreams = rawInitialData.can_create_private_streams;
-      invariant(
-        canCreatePublicStreams != null && canCreatePrivateStreams != null,
-        'these are both present if can_create_streams is missing; see doc',
-      );
-      return canCreatePublicStreams || canCreatePrivateStreams;
-    })(),
-});
+const transform = (rawInitialData: RawInitialData, auth: Auth): InitialData => {
+  // (Even ancient servers have `zulip_version` in the initial data.)
+  const zulipVersion = new ZulipVersion(rawInitialData.zulip_version);
+
+  // Do this at the top, before we can accidentally trip on some later code
+  // that's insensitive to ancient servers' behavior.
+  if (!zulipVersion.isAtLeast(kMinAllowedServerVersion)) {
+    throw new ServerTooOldError(zulipVersion);
+  }
+
+  return {
+    ...rawInitialData,
+
+    zulip_feature_level: rawInitialData.zulip_feature_level ?? 0,
+    zulip_version: zulipVersion,
+
+    // Transform the newer `realm_linkifiers` format, if present, to the
+    // older `realm_filters` format. We do the same transformation on
+    // 'realm_linkifiers' events.
+    // TODO(server-4.0): Switch to new format, if we haven't already;
+    //   and drop conversion.
+    realm_filters: rawInitialData.realm_linkifiers
+      ? rawInitialData.realm_linkifiers.map(({ pattern, url_format, id }) => [
+          pattern,
+          url_format,
+          id,
+        ])
+      : rawInitialData.realm_filters,
+
+    // In 5.0 (feature level 100), the representation the server sends for "no
+    // limit" changed from 0 to `null`.
+    //
+    // It's convenient to emulate Server 5.0's representation in our own data
+    // structures. To get a correct initial value, it's sufficient to coerce
+    // `0` to null here, without even looking at the server feature level.
+    // That's because, in addition to the documented change in 5.0, there was
+    // another: 0 became an invalid value, which means we don't have to
+    // anticipate servers 5.0+ using it to mean anything, such as "0 seconds":
+    //   https://github.com/zulip/zulip/blob/b13bfa09c/zerver/lib/message.py#L1482.
+    //
+    // TODO(server-5.0) Remove this conditional.
+    realm_message_content_delete_limit_seconds:
+      rawInitialData.realm_message_content_delete_limit_seconds === 0
+        ? null
+        : rawInitialData.realm_message_content_delete_limit_seconds,
+
+    realm_users: rawInitialData.realm_users.map(rawUser => transformUser(rawUser, auth.realm)),
+    realm_non_active_users: rawInitialData.realm_non_active_users.map(rawNonActiveUser =>
+      transformUser(rawNonActiveUser, auth.realm),
+    ),
+    cross_realm_bots: rawInitialData.cross_realm_bots.map(rawCrossRealmBot =>
+      transformCrossRealmBot(rawCrossRealmBot, auth.realm),
+    ),
+
+    // The doc says the field will be removed in a future release. So, while
+    // we're still consuming it, fill it in if missing, with instructions from
+    // the doc:
+    //
+    // > Its value will always equal
+    // >   `can_create_public_streams || can_create_private_streams`.
+    //
+    // TODO(server-5.0): Only use `can_create_public_streams` and
+    //   `can_create_private_streams`, and simplify this away.
+    can_create_streams:
+      rawInitialData.can_create_streams
+      ?? (() => {
+        const canCreatePublicStreams = rawInitialData.can_create_public_streams;
+        const canCreatePrivateStreams = rawInitialData.can_create_private_streams;
+        invariant(
+          canCreatePublicStreams != null && canCreatePrivateStreams != null,
+          'these are both present if can_create_streams is missing; see doc',
+        );
+        return canCreatePublicStreams || canCreatePrivateStreams;
+      })(),
+  };
+};
 
 /** See https://zulip.com/api/register-queue */
 export default async (

src/api/settings/getServerSettings.js

@@ -1,7 +1,7 @@
 /* @flow strict-local */
 import type { ApiResponseSuccess } from '../transportTypes';
 import { apiGet } from '../apiFetch';
-import { ApiError } from '../apiErrors';
+import { ApiError, ServerTooOldError, kMinAllowedServerVersion } from '../apiErrors';
 import { ZulipVersion } from '../../utils/zulipVersion';
 
 // This corresponds to AUTHENTICATION_FLAGS in zulip/zulip:zerver/models.py .
@@ -83,6 +83,15 @@ export type ServerSettings = $ReadOnly<{|
  * Make a ServerSettings from a raw API response.
  */
 function transform(raw: ApiResponseServerSettings): ServerSettings {
+  // (Even ancient servers have `zulip_version` in the response.)
+  const zulipVersion = new ZulipVersion(raw.zulip_version);
+
+  // Do this at the top, before we can accidentally trip on some later code
+  // that's insensitive to ancient servers' behavior.
+  if (!zulipVersion.isAtLeast(kMinAllowedServerVersion)) {
+    throw new ServerTooOldError(zulipVersion);
+  }
+
   const { realm_name } = raw;
   if (realm_name == null) {
     // See comment on realm_name in ApiResponseServerSettings.
@@ -101,7 +110,7 @@ function transform(raw: ApiResponseServerSettings): ServerSettings {
   return {
     ...raw,
     zulip_feature_level: raw.zulip_feature_level ?? 0,
-    zulip_version: new ZulipVersion(raw.zulip_version),
+    zulip_version: zulipVersion,
     realm_uri: new URL(raw.realm_uri),
     realm_name,
     realm_web_public_access_enabled: raw.realm_web_public_access_enabled ?? false,

src/common/ServerCompatBanner.js

@@ -18,6 +18,9 @@ import { Role } from '../api/permissionsTypes';
  *
  * Should match what we say at:
  *   https://zulip.readthedocs.io/en/stable/overview/release-lifecycle.html#compatibility-and-upgrading
+ *
+ * See also kMinAllowedServerVersion in apiErrors.js, for the version below
+ * which we just refuse to connect.
  */
 // "2.2.0" is a funny way of saying "3.0", differing in that it accepts
 // versions like 2.2-dev-1234-g08192a3b4c.  Some servers running versions
@@ -96,6 +99,8 @@ export default function ServerCompatBanner(props: Props): Node {
           label: 'Learn more',
           onPress: () => {
             openLinkWithUserPreference(
+              // TODO: Instead, link to new Help Center doc once we have it:
+              //   https://github.com/zulip/zulip/issues/23842
               'https://zulip.readthedocs.io/en/stable/overview/release-lifecycle.html#compatibility-and-upgrading',
               settings,
             );

src/events/eventActions.js

@@ -14,20 +14,26 @@ import { REGISTER_START, REGISTER_ABORT, REGISTER_COMPLETE, DEAD_QUEUE } from '.
 import { logout } from '../account/logoutActions';
 import eventToAction from './eventToAction';
 import doEventActionSideEffects from './doEventActionSideEffects';
-import { getAuth, tryGetAuth, getIdentity } from '../selectors';
+import { getAccount, tryGetAuth, getIdentity } from '../selectors';
 import { getHaveServerData } from '../haveServerDataSelectors';
 import { getOwnUserRole, roleIsAtLeast } from '../permissionSelectors';
 import { Role } from '../api/permissionsTypes';
-import { identityOfAuth } from '../account/accountMisc';
+import { authOfAccount, identityOfAccount, identityOfAuth } from '../account/accountMisc';
 import { BackoffMachine, TimeoutError } from '../utils/async';
-import { ApiError, RequestError, Server5xxError, NetworkError } from '../api/apiErrors';
+import {
+  ApiError,
+  RequestError,
+  Server5xxError,
+  NetworkError,
+  ServerTooOldError,
+} from '../api/apiErrors';
 import * as logging from '../utils/logging';
 import { showErrorAlert } from '../utils/info';
 import { tryFetch, fetchPrivateMessages } from '../message/fetchActions';
 import { MIN_RECENTPMS_SERVER_VERSION } from '../pm-conversations/pmConversationsModel';
 import { sendOutbox } from '../outbox/outboxActions';
-import { initNotifications } from '../notification/notifTokens';
-import { kNextMinSupportedVersion } from '../common/ServerCompatBanner';
+import { initNotifications, tryStopNotifications } from '../notification/notifTokens';
+import { kMinSupportedVersion, kNextMinSupportedVersion } from '../common/ServerCompatBanner';
 import { maybeRefreshServerEmojiData } from '../emoji/data';
 
 const registerStart = (): PerAccountAction => ({
@@ -115,8 +121,11 @@ const registerComplete = (data: InitialData): PerAccountAction => ({
  * (`SearchMessagesScreen`).
  */
 export const registerAndStartPolling =
-  (): ThunkAction<Promise<void>> => async (dispatch, getState) => {
-    const auth = getAuth(getState());
+  (): ThunkAction<Promise<void>> =>
+  async (dispatch, getState, { getGlobalSettings }) => {
+    const account = getAccount(getState());
+    const identity = identityOfAccount(account);
+    const auth = authOfAccount(account);
 
     const haveServerData = getHaveServerData(getState());
 
@@ -152,6 +161,28 @@ export const registerAndStartPolling =
         // *do* expect that whatever invalidated the auth also caused the
         // server to forget all push tokens.
         dispatch(logout());
+      } else if (e instanceof ServerTooOldError) {
+        showErrorAlert(
+          // TODO(i18n): Set up these user-facing strings for translation
+          //   once callers all have access to a `GetText` function. One
+          //   place we dispatch this action is in StoreProvider, which
+          //   isn't a descendant of `TranslationProvider`.
+          'Could not connect',
+          `${identity.realm.toString()} is running Zulip Server ${e.version.raw()}, which is unsupported. The minimum supported version is Zulip Server ${kMinSupportedVersion.raw()}.`,
+          {
+            url: new URL(
+              // TODO: Instead, link to new Help Center doc once we have it:
+              //   https://github.com/zulip/zulip/issues/23842
+              'https://zulip.readthedocs.io/en/stable/overview/release-lifecycle.html#compatibility-and-upgrading',
+            ),
+            globalSettings: getGlobalSettings(),
+          },
+        );
+        // Don't delay the logout action by awaiting this request: it may
+        // take a long time or never succeed, and we need to kick the user
+        // out immediately.
+        dispatch(tryStopNotifications(account));
+        dispatch(logout());
       } else if (e instanceof Server5xxError) {
         dispatch(registerAbort('server'));
       } else if (e instanceof NetworkError) {

src/haveServerDataSelectors.js

@@ -2,8 +2,13 @@
 
 import type { GlobalState, PerAccountState } from './types';
 import { getUsers } from './directSelectors';
-import { tryGetAuth, tryGetActiveAccountState } from './account/accountsSelectors';
+import {
+  tryGetAuth,
+  tryGetActiveAccountState,
+  getServerVersion,
+} from './account/accountsSelectors';
 import { getUsersById } from './users/userSelectors';
+import { kMinAllowedServerVersion } from './api/apiErrors';
 
 /**
  * Whether we have server data for the active account.
@@ -114,6 +119,12 @@ export const getHaveServerData = (state: PerAccountState): boolean => {
     return false;
   }
 
+  // We may have server data, but it would be from an ancient server that we
+  // don't support, so it might be malformed.
+  if (!getServerVersion(state).isAtLeast(kMinAllowedServerVersion)) {
+    return false;
+  }
+
   // Valid server data must have a user: the self user, at a minimum.
   if (getUsers(state).length === 0) {
     // From `usersReducer`: