Fix auto_map_topic_alias_send logic

Previously, it would always remove the topic name when adding the alias,
even the first time, so the mapping would not be set on the server, and
the server would reject the packet.

Author: smaeul

src/mqtt/connection/core.rs

@@ -1630,7 +1630,7 @@ where
                     } else {
                         let lru_ta = topic_alias_send.get_lru_alias();
                         topic_alias_send.insert_or_update(packet.topic_name(), lru_ta);
-                        packet = packet.remove_topic_add_topic_alias(lru_ta);
+                        packet = packet.add_topic_alias(lru_ta);
                     }
                 }
             } else if self.auto_replace_topic_alias_send {

src/mqtt/packet/v5_0/publish.rs

@@ -688,6 +688,45 @@ where
         // Set topic name to empty string
         self.topic_name_buf = MqttString::new("").unwrap();
 
+        self.add_topic_alias(topic_alias)
+    }
+
+    /// Add TopicAlias property
+    ///
+    /// This method adds a TopicAlias property to the packet properties. This
+    /// is required to associate a topic alias with a topic name on the server.
+    /// Future messages can use only the topic alias and omit the topic name.
+    /// This is useful for reducing packet size when sending multiple messages
+    /// to the same topic.
+    ///
+    /// The method removes any existing TopicAlias property before adding the new one
+    /// to ensure only one TopicAlias property exists. It automatically recalculates
+    /// the property_length and remaining_length to reflect these changes.
+    ///
+    /// # Parameters
+    ///
+    /// - `topic_alias`: The numeric topic alias to associate with the topic name
+    ///
+    /// # Returns
+    ///
+    /// The modified `GenericPublish` instance with the TopicAlias property
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// use mqtt_protocol_core::mqtt;
+    ///
+    /// let publish_with_topic = mqtt::packet::v5_0::Publish::builder()
+    ///     .topic_name("sensors/temperature/room1")
+    ///     .unwrap()
+    ///     .payload(b"23.5")
+    ///     .build()
+    ///     .unwrap();
+    ///
+    /// let publish_with_alias = publish_with_topic.add_topic_alias(42);
+    /// // props() now contains TopicAlias property with value 42
+    /// ```
+    pub fn add_topic_alias(mut self, topic_alias: TopicAliasType) -> Self {
         // Add TopicAlias property to the end of properties
         let topic_alias_property =
             Property::TopicAlias(crate::mqtt::packet::TopicAlias::new(topic_alias).unwrap());