feat: Prevent sending messages if other party has no encryption keys

assets/l10n/intl_en.arb

@@ -2821,5 +2821,6 @@
   "invalidUrl": "Invalid url",
   "addLink": "Add link",
   "unableToJoinChat": "Unable to join chat. Maybe the other party has already closed the conversation.",
-  "previous": "Previous"
+  "previous": "Previous",
+  "otherPartyNotLoggedIn": "The other party is currently not logged in and therefore cannot receive messages!"
 }

lib/pages/chat/chat.dart

@@ -30,6 +30,7 @@ import 'package:fluffychat/utils/file_selector.dart';
 import 'package:fluffychat/utils/matrix_sdk_extensions/event_extension.dart';
 import 'package:fluffychat/utils/matrix_sdk_extensions/filtered_timeline_extension.dart';
 import 'package:fluffychat/utils/matrix_sdk_extensions/matrix_locals.dart';
+import 'package:fluffychat/utils/other_party_can_receive.dart';
 import 'package:fluffychat/utils/platform_infos.dart';
 import 'package:fluffychat/utils/show_scaffold_dialog.dart';
 import 'package:fluffychat/widgets/adaptive_dialogs/show_modal_action_popup.dart';
@@ -237,6 +238,23 @@ class ChatController extends State<ChatPageWithRoom>
   void _shareItems([_]) {
     final shareItems = widget.shareItems;
     if (shareItems == null || shareItems.isEmpty) return;
+    if (!room.otherPartyCanReceiveMessages) {
+      final theme = Theme.of(context);
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(
+          backgroundColor: theme.colorScheme.errorContainer,
+          closeIconColor: theme.colorScheme.onErrorContainer,
+          content: Text(
+            L10n.of(context).otherPartyNotLoggedIn,
+            style: TextStyle(
+              color: theme.colorScheme.onErrorContainer,
+            ),
+          ),
+          showCloseIcon: true,
+        ),
+      );
+      return;
+    }
     for (final item in shareItems) {
       if (item is FileShareItem) continue;
       if (item is TextShareItem) room.sendTextEvent(item.value);

lib/pages/chat/chat_input_row.dart

@@ -5,6 +5,7 @@ import 'package:flutter_gen/gen_l10n/l10n.dart';
 import 'package:matrix/matrix.dart';
 
 import 'package:fluffychat/config/app_config.dart';
+import 'package:fluffychat/utils/other_party_can_receive.dart';
 import 'package:fluffychat/utils/platform_infos.dart';
 import 'package:fluffychat/widgets/avatar.dart';
 import 'package:fluffychat/widgets/matrix.dart';
@@ -25,6 +26,20 @@ class ChatInputRow extends StatelessWidget {
       return const SizedBox.shrink();
     }
     const height = 48.0;
+
+    if (!controller.room.otherPartyCanReceiveMessages) {
+      return Center(
+        child: Padding(
+          padding: const EdgeInsets.all(12.0),
+          child: Text(
+            L10n.of(context).otherPartyNotLoggedIn,
+            style: theme.textTheme.bodySmall,
+            textAlign: TextAlign.center,
+          ),
+        ),
+      );
+    }
+
     return Row(
       crossAxisAlignment: CrossAxisAlignment.end,
       mainAxisAlignment: MainAxisAlignment.spaceBetween,

lib/pages/chat/send_file_dialog.dart

@@ -12,6 +12,7 @@ import 'package:mime/mime.dart';
 import 'package:fluffychat/config/app_config.dart';
 import 'package:fluffychat/utils/localized_exception_extension.dart';
 import 'package:fluffychat/utils/matrix_sdk_extensions/matrix_file_extension.dart';
+import 'package:fluffychat/utils/other_party_can_receive.dart';
 import 'package:fluffychat/utils/platform_infos.dart';
 import 'package:fluffychat/utils/size_string.dart';
 import 'package:fluffychat/widgets/adaptive_dialogs/adaptive_dialog_action.dart';
@@ -44,6 +45,9 @@ class SendFileDialogState extends State<SendFileDialog> {
     final l10n = L10n.of(context);
 
     try {
+      if (!widget.room.otherPartyCanReceiveMessages) {
+        throw OtherPartyCanNotReceiveMessages();
+      }
       scaffoldMessenger.showLoadingSnackBar(l10n.prepareSendingAttachment);
       Navigator.of(context, rootNavigator: false).pop();
       final clientConfig = await widget.room.client.getConfig();

lib/utils/other_party_can_receive.dart

@@ -0,0 +1,21 @@
+import 'package:matrix/matrix.dart';
+
+extension OtherPartyCanReceiveExtension on Room {
+  bool get otherPartyCanReceiveMessages {
+    if (!encrypted) return true;
+    final users = getParticipants()
+        .map((u) => u.id)
+        .where((userId) => userId != client.userID)
+        .toSet();
+    if (users.isEmpty) return true;
+
+    for (final userId in users) {
+      if (client.userDeviceKeys[userId]?.deviceKeys.values.isNotEmpty == true) {
+        return true;
+      }
+    }
+    return false;
+  }
+}
+
+class OtherPartyCanNotReceiveMessages implements Exception {}