fix(liveupdates): add subscription to backlog if failed (#6763)

Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>

tests/src/BasicPubSub.cpp

@@ -80,8 +80,9 @@ class MyManager;
 class MyClient : public BasicPubSubClient<DummySubscription, MyClient>
 {
 public:
-    MyClient(MyManager &manager)
-        : manager(manager)
+    MyClient(MyManager &manager, size_t limit)
+        : BasicPubSubClient(limit)
+        , manager(manager)
     {
     }
 
@@ -94,8 +95,9 @@ private:
 class MyManager : public BasicPubSubManager<MyManager, MyClient>
 {
 public:
-    MyManager(QString host)
+    MyManager(QString host, size_t limit = 100)
         : BasicPubSubManager(std::move(host), "Test")
+        , limit_(limit)
     {
     }
 
@@ -126,12 +128,13 @@ public:
 
     std::shared_ptr<MyClient> makeClient()
     {
-        return std::make_shared<MyClient>(*this);
+        return std::make_shared<MyClient>(*this, this->limit_);
     }
 
 private:
     std::mutex messageMtx_;
     std::deque<QString> messageQueue_;
+    size_t limit_;
 
     friend MyClient;
 };
@@ -177,3 +180,46 @@ TEST(BasicPubSub, SubscriptionCycle)
     ASSERT_EQ(manager.diag.connectionsFailed, 0);
     ASSERT_EQ(manager.messagesReceived, 2);
 }
+
+TEST(BasicPubSub, SubLimits)
+{
+    mock::BaseApplication app;
+    const QString host("wss://127.0.0.1:9050/liveupdates/sub-unsub");
+    MyManager manager(host, 1);
+    manager.sub({.type = 1, .condition = "foo"});
+    manager.sub({.type = 2, .condition = "foo"});
+    manager.sub({.type = 3, .condition = "foo"});
+    manager.sub({.type = 4, .condition = "foo"});
+    manager.sub({.type = 5, .condition = "foo"});
+    QTest::qWait(500);
+    ASSERT_EQ(manager.diag.connectionsOpened, 5);
+    ASSERT_EQ(manager.diag.connectionsClosed, 0);
+    ASSERT_EQ(manager.diag.connectionsFailed, 0);
+    ASSERT_EQ(manager.messagesReceived, 5);
+
+    // The messages come from multiple connections, so they're not necessarily
+    // in order.
+    std::vector<QString> messages;
+    for (size_t i = 0; i < 5; i++)
+    {
+        auto msg = manager.popMessage();
+        ASSERT_TRUE(msg.has_value());
+        messages.push_back(*std::move(msg));
+    }
+    std::ranges::sort(messages);
+    ASSERT_EQ(messages[0], QString("ack-sub-1-foo"));
+    ASSERT_EQ(messages[1], QString("ack-sub-2-foo"));
+    ASSERT_EQ(messages[2], QString("ack-sub-3-foo"));
+    ASSERT_EQ(messages[3], QString("ack-sub-4-foo"));
+    ASSERT_EQ(messages[4], QString("ack-sub-5-foo"));
+
+    manager.stop();
+    // after exactly one event loop iteration, we should see updated counters
+    QCoreApplication::processEvents(QEventLoop::AllEvents);
+    QCoreApplication::sendPostedEvents(nullptr, QEvent::DeferredDelete);
+
+    ASSERT_EQ(manager.diag.connectionsOpened, 5);
+    ASSERT_EQ(manager.diag.connectionsClosed, 5);
+    ASSERT_EQ(manager.diag.connectionsFailed, 0);
+    ASSERT_EQ(manager.messagesReceived, 5);
+}