[ISSUE #1775]🤡Simply MQClientInstance#query_assignment method code an…

…d add doc for method🔥 (#1776)

rocketmq-client/src/factory/mq_client_instance.rs

@@ -1151,6 +1151,25 @@ impl MQClientInstance {
         false
     }
 
+    /// Queries the assignment for a given topic.
+    ///
+    /// This function attempts to find the broker address for the specified topic. If the broker
+    /// address is not found, it updates the topic route information from the name server and
+    /// retries. If the broker address is found, it queries the assignment from the broker.
+    ///
+    /// # Arguments
+    ///
+    /// * `topic` - A reference to a `CheetahString` representing the topic to query.
+    /// * `consumer_group` - A reference to a `CheetahString` representing the consumer group.
+    /// * `strategy_name` - A reference to a `CheetahString` representing the allocation strategy
+    ///   name.
+    /// * `message_model` - The message model to use for the query.
+    /// * `timeout` - The timeout duration for the query.
+    ///
+    /// # Returns
+    ///
+    /// A `Result` containing an `Option` with a `HashSet` of `MessageQueueAssignment` if the query
+    /// is successful, or an error if it fails.
     pub async fn query_assignment(
         &mut self,
         topic: &CheetahString,
@@ -1159,27 +1178,33 @@ impl MQClientInstance {
         message_model: MessageModel,
         timeout: u64,
     ) -> Result<Option<HashSet<MessageQueueAssignment>>> {
+        // Try to find broker address
         let mut broker_addr = self.find_broker_addr_by_topic(topic).await;
+
+        // If not found, update and retry
         if broker_addr.is_none() {
             self.update_topic_route_info_from_name_server_topic(topic)
                 .await;
             broker_addr = self.find_broker_addr_by_topic(topic).await;
         }
         if let Some(broker_addr) = broker_addr {
             let client_id = self.client_id.clone();
-            self.mq_client_api_impl
-                .as_mut()
-                .unwrap()
-                .query_assignment(
-                    &broker_addr,
-                    topic.clone(),
-                    consumer_group.clone(),
-                    strategy_name.clone(),
-                    client_id,
-                    message_model,
-                    timeout,
-                )
-                .await
+            match self.mq_client_api_impl.as_mut() {
+                Some(api_impl) => {
+                    api_impl
+                        .query_assignment(
+                            &broker_addr,
+                            topic.clone(),
+                            consumer_group.clone(),
+                            strategy_name.clone(),
+                            client_id,
+                            message_model,
+                            timeout,
+                        )
+                        .await
+                }
+                None => mq_client_err!("mq_client_api_impl is None"),
+            }
         } else {
             Ok(None)
         }