feat: Rate limit streams so that large accounts have a smoother UI

lib/pages/views/chat_list_view.dart

@@ -9,6 +9,7 @@ import 'package:flutter/material.dart';
 import 'package:vrouter/vrouter.dart';
 import '../../widgets/matrix.dart';
 import 'package:flutter_gen/gen_l10n/l10n.dart';
+import '../../utils/stream_extension.dart';
 
 class ChatListView extends StatelessWidget {
   final ChatListController controller;
@@ -161,7 +162,8 @@ class ChatListView extends StatelessWidget {
                             .client
                             .onSync
                             .stream
-                            .where((s) => s.hasRoomUpdate),
+                            .where((s) => s.hasRoomUpdate)
+                            .rateLimit(Duration(seconds: 1)),
                         builder: (context, snapshot) {
                           return FutureBuilder<void>(
                             future: controller.waitForFirstSync(),

lib/pages/views/chat_view.dart

@@ -27,6 +27,8 @@ import 'package:scroll_to_index/scroll_to_index.dart';
 import 'package:swipe_to_action/swipe_to_action.dart';
 import 'package:vrouter/vrouter.dart';
 
+import '../../utils/stream_extension.dart';
+
 class ChatView extends StatelessWidget {
   final ChatController controller;
 
@@ -72,7 +74,8 @@ class ChatView extends StatelessWidget {
             titleSpacing: 0,
             title: controller.selectedEvents.isEmpty
                 ? StreamBuilder(
-                    stream: controller.room.onUpdate.stream,
+                    stream: controller.room.onUpdate.stream
+                        .rateLimit(Duration(milliseconds: 250)),
                     builder: (context, snapshot) => ListTile(
                           leading: Avatar(controller.room.avatar,
                               controller.room.displayname),
@@ -105,7 +108,8 @@ class ChatView extends StatelessWidget {
                                       .stream
                                       .where((p) =>
                                           p.senderId ==
-                                          controller.room.directChatMatrixID),
+                                          controller.room.directChatMatrixID)
+                                      .rateLimit(Duration(seconds: 1)),
                                   builder: (context, snapshot) => Text(
                                         controller.room
                                             .getLocalizedStatus(context),
@@ -283,8 +287,10 @@ class ChatView extends StatelessWidget {
                                             : Container()
                                     : i == 0
                                         ? StreamBuilder(
-                                            stream:
-                                                controller.room.onUpdate.stream,
+                                            stream: controller
+                                                .room.onUpdate.stream
+                                                .rateLimit(Duration(
+                                                    milliseconds: 250)),
                                             builder: (_, __) {
                                               final seenByText = controller.room
                                                   .getLocalizedSeenByText(

lib/utils/stream_extension.dart

@@ -0,0 +1,46 @@
+import 'dart:async';
+
+extension StreamExtension on Stream {
+  /// Returns a new Stream which outputs only `true` for every update of the original
+  /// stream, ratelimited by the Duration t
+  Stream<bool> rateLimit(Duration t) {
+    final controller = StreamController<bool>();
+    Timer timer;
+    var gotMessage = false;
+    // as we call our inline-defined function recursively we need to make sure that the
+    // variable exists prior of creating the function. Silly dart.
+    Function _onMessage;
+    // callback to determine if we should send out an update
+    _onMessage = () {
+      // do nothing if it is already closed
+      if (controller.isClosed) {
+        return;
+      }
+      if (timer == null) {
+        // if we don't have a timer yet, send out the update and start a timer
+        gotMessage = false;
+        controller.add(true);
+        timer = Timer(t, () {
+          // the timer has ended...delete it and, if we got a message, re-run the
+          // method to send out an update!
+          timer = null;
+          if (gotMessage) {
+            _onMessage();
+          }
+        });
+      } else {
+        // set that we got a message
+        gotMessage = true;
+      }
+    };
+    final subscription = listen((_) => _onMessage(),
+        onDone: () => controller.close(),
+        onError: (e, s) => controller.addError(e, s));
+    // add proper cleanup to the subscription and the controller, to not memory leak
+    controller.onCancel = () {
+      subscription.cancel();
+      controller.close();
+    };
+    return controller.stream;
+  }
+}

lib/widgets/list_items/chat_list_item.dart

@@ -289,7 +289,9 @@ class ChatListItem extends StatelessWidget {
                 curve: Curves.bounceInOut,
                 padding: EdgeInsets.symmetric(horizontal: 7),
                 height: unreadBubbleSize,
-                width: room.notificationCount == 0 && !room.isUnread ? 0 : null,
+                width: room.notificationCount == 0 && !room.isUnread
+                    ? 0
+                    : unreadBubbleSize,
                 decoration: BoxDecoration(
                   color: room.highlightCount > 0
                       ? Colors.red