From 0234918f304aca89eb98d7ea0a73b0d30e9e2ab2 Mon Sep 17 00:00:00 2001
From: Int32Overflow <frankschmidbc@gmail.com>
Date: Sat, 28 Jan 2023 12:12:20 +0100
Subject: [PATCH] Performance impact fix (#1661)

---
 .../MqttClientSubscriptionsManager.cs         | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/Source/MQTTnet/Server/Internal/MqttClientSubscriptionsManager.cs b/Source/MQTTnet/Server/Internal/MqttClientSubscriptionsManager.cs
index b409d959..70a5df88 100644
--- a/Source/MQTTnet/Server/Internal/MqttClientSubscriptionsManager.cs
+++ b/Source/MQTTnet/Server/Internal/MqttClientSubscriptionsManager.cs
@@ -403,6 +403,18 @@ namespace MQTTnet.Server
             CreateSubscriptionResult createSubscriptionResult,
             SubscribeResult subscribeResult)
         {
+            if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.DoNotSendOnSubscribe)
+            {
+                // This is a MQTT V5+ feature.
+                return;
+                }
+
+            if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.SendAtSubscribeIfNewSubscriptionOnly && !createSubscriptionResult.IsNewSubscription)
+                {
+                    // This is a MQTT V5+ feature.
+                return;
+                }
+
             for (var index = retainedMessages.Count - 1; index >= 0; index--)
             {
                 var retainedMessage = retainedMessages[index];
@@ -411,18 +423,6 @@ namespace MQTTnet.Server
                     continue;
                 }
 
-                if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.DoNotSendOnSubscribe)
-                {
-                    // This is a MQTT V5+ feature.
-                    continue;
-                }
-
-                if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.SendAtSubscribeIfNewSubscriptionOnly && !createSubscriptionResult.IsNewSubscription)
-                {
-                    // This is a MQTT V5+ feature.
-                    continue;
-                }
-
                 if (MqttTopicFilterComparer.Compare(retainedMessage.Topic, createSubscriptionResult.Subscription.Topic) != MqttTopicFilterCompareResult.IsMatch)
                 {
                     continue;