login: Reject earlier (at get-server-settings) when server is too old

There's a planned change to make zulipMergeBase required in
GetServerSettingsResult (see #904). When we do that, we'd otherwise
just treat a missing zulipMergeBase on an ancient server the same
way we treat any malformed response. Better to check if the server
is an ancient one we don't support, just like when the /register
response is malformed.

Author: chrisbobbe

lib/model/server_support.dart

@@ -1,17 +1,24 @@
 import '../api/core.dart';
 import '../api/exception.dart';
 import '../api/model/initial_snapshot.dart';
+import '../api/route/realm.dart';
 import 'database.dart';
 
 /// The fields 'zulip_version', 'zulip_merge_base', and 'zulip_feature_level'
-/// from a /register response.
+/// from a /server_settings or /register response.
 class ZulipVersionData {
   const ZulipVersionData({
     required this.zulipVersion,
     required this.zulipMergeBase,
     required this.zulipFeatureLevel,
   });
 
+  factory ZulipVersionData.fromServerSettings(GetServerSettingsResult serverSettings) =>
+    ZulipVersionData(
+      zulipVersion: serverSettings.zulipVersion,
+      zulipMergeBase: serverSettings.zulipMergeBase,
+      zulipFeatureLevel: serverSettings.zulipFeatureLevel);
+
   factory ZulipVersionData.fromInitialSnapshot(InitialSnapshot initialSnapshot) =>
     ZulipVersionData(
       zulipVersion: initialSnapshot.zulipVersion,
@@ -21,6 +28,8 @@ class ZulipVersionData {
   /// Make a [ZulipVersionData] from a [MalformedServerResponseException],
   /// if the body was readable/valid JSON and contained the data, else null.
   ///
+  /// May be used for the /server_settings or the /register response.
+  ///
   /// If there's a zulip_version but no zulip_feature_level,
   /// we infer it's indeed a Zulip server,
   /// just an ancient one before feature levels were introduced in Zulip 3.0,

lib/widgets/login.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:url_launcher/url_launcher.dart';
 
+import '../api/core.dart';
 import '../api/exception.dart';
 import '../api/model/web_auth.dart';
 import '../api/route/account.dart';
@@ -13,6 +14,7 @@ import '../api/route/users.dart';
 import '../generated/l10n/zulip_localizations.dart';
 import '../log.dart';
 import '../model/binding.dart';
+import '../model/server_support.dart';
 import '../model/store.dart';
 import 'dialog.dart';
 import 'home.dart';
@@ -180,17 +182,40 @@ class _AddAccountPageState extends State<AddAccountPage> {
         final connection = globalStore.apiConnection(realmUrl: url!, zulipFeatureLevel: null);
         try {
           serverSettings = await getServerSettings(connection);
+          final zulipVersionData = ZulipVersionData.fromServerSettings(serverSettings);
+          if (zulipVersionData.isUnsupported) {
+            throw ServerVersionUnsupportedException(zulipVersionData);
+          }
+        } on MalformedServerResponseException catch (e) {
+          final zulipVersionData = ZulipVersionData.fromMalformedServerResponseException(e);
+          if (zulipVersionData != null && zulipVersionData.isUnsupported) {
+            throw ServerVersionUnsupportedException(zulipVersionData);
+          }
+          rethrow;
         } finally {
           connection.close();
         }
       } catch (e) {
         if (!context.mounted) return;
 
-        // TODO(#105) give more helpful feedback; see `fetchServerSettings`
-        //   in zulip-mobile's src/message/fetchActions.js.
+        String? message;
+        Uri? learnMoreButtonUrl;
+        switch (e) {
+          case ServerVersionUnsupportedException(:final data):
+            message = zulipLocalizations.errorServerVersionUnsupportedMessage(
+              url.toString(),
+              data.zulipVersion,
+              kMinSupportedZulipVersion);
+            learnMoreButtonUrl = kServerSupportDocUrl;
+          default:
+            // TODO(#105) give more helpful feedback; see `fetchServerSettings`
+            //   in zulip-mobile's src/message/fetchActions.js.
+            message = zulipLocalizations.errorLoginCouldNotConnect(url.toString());
+        }
         showErrorDialog(context: context,
           title: zulipLocalizations.errorCouldNotConnectTitle,
-          message: zulipLocalizations.errorLoginCouldNotConnect(url.toString()));
+          message: message,
+          learnMoreButtonUrl: learnMoreButtonUrl);
         return;
       }
       if (!context.mounted) return;

test/widgets/login_test.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:http/http.dart' as http;
+import 'package:zulip/api/core.dart';
 import 'package:zulip/api/model/web_auth.dart';
 import 'package:zulip/api/route/account.dart';
 import 'package:zulip/api/route/realm.dart';
@@ -120,6 +121,59 @@ void main() {
       check(takePushedRoutes()).single.isA<WidgetRoute>().page.isA<LoginPage>()
         .serverSettings.realmUrl.equals(serverSettings.realmUrl);
     });
+
+    testWidgets('Server too old, well-formed response', (tester) async {
+      await prepare(tester);
+
+      final serverSettings = eg.serverSettings(
+        zulipFeatureLevel: 1, zulipVersion: '3.0');
+
+      await attempt(tester, serverSettings.realmUrl, serverSettings.toJson());
+      checkErrorDialog(tester,
+        expectedTitle: 'Could not connect',
+        expectedMessage: '${serverSettings.realmUrl} is running Zulip Server 3.0, which is unsupported. The minimum supported version is Zulip Server $kMinSupportedZulipVersion.');
+      // i.e., not the login route
+      check(takePushedRoutes()).single.isA<DialogRoute<void>>();
+    });
+
+    testWidgets('Server too old, malformed response', (tester) async {
+      await prepare(tester);
+
+      final serverSettings = eg.serverSettings(
+        zulipFeatureLevel: 1, zulipVersion: '3.0');
+      final serverSettingsMalformedJson =
+        serverSettings.toJson()..['push_notifications_enabled'] = 'abcd';
+      check(() => GetServerSettingsResult.fromJson(serverSettingsMalformedJson))
+        .throws<void>();
+
+      await attempt(tester, serverSettings.realmUrl, serverSettingsMalformedJson);
+      checkErrorDialog(tester,
+        expectedTitle: 'Could not connect',
+        expectedMessage: '${serverSettings.realmUrl} is running Zulip Server 3.0, which is unsupported. The minimum supported version is Zulip Server $kMinSupportedZulipVersion.');
+      // i.e., not the login route
+      check(takePushedRoutes()).single.isA<DialogRoute<void>>();
+    });
+
+    testWidgets('Malformed response, server not too old', (tester) async {
+      await prepare(tester);
+
+      final serverSettings = eg.serverSettings(
+        zulipVersion: eg.recentZulipVersion,
+        zulipFeatureLevel: eg.recentZulipFeatureLevel);
+      final serverSettingsMalformedJson =
+        serverSettings.toJson()..['push_notifications_enabled'] = 'abcd';
+      check(() => GetServerSettingsResult.fromJson(serverSettingsMalformedJson))
+        .throws<void>();
+
+      await attempt(tester, serverSettings.realmUrl, serverSettingsMalformedJson);
+      checkErrorDialog(tester,
+        expectedTitle: 'Could not connect',
+        expectedMessage: 'Failed to connect to server:\n${serverSettings.realmUrl}');
+      // i.e., not the login route
+      check(takePushedRoutes()).single.isA<DialogRoute<void>>();
+    });
+
+    // TODO other errors
   });
 
   group('LoginPage', () {