Fix auto-registration of child device op dirs thin-edge#2389

If the child device directory the child device operation directories
follow the default external id naming scheme, they are auto-registered
with the right topic id and name derived from that external id.

crates/extensions/c8y_mapper_ext/src/converter.rs

@@ -752,14 +752,15 @@ impl CumulocityConverter {
                     continue;
                 }
             };
-            let child_topic_id =
-                EntityTopicId::default_child_device(child_external_id.as_ref()).unwrap();
+
+            let child_name = self.default_device_name_from_external_id(&child_external_id);
+            let child_topic_id = EntityTopicId::default_child_device(&child_name).unwrap();
             let child_device_reg_msg = EntityRegistrationMessage {
                 topic_id: child_topic_id,
                 external_id: Some(child_external_id.clone()),
                 r#type: EntityType::ChildDevice,
                 parent: None,
-                other: json!({ "name": child_external_id.as_ref() })
+                other: json!({ "name": child_name })
                     .as_object()
                     .unwrap()
                     .to_owned(),

crates/extensions/c8y_mapper_ext/src/tests.rs

@@ -1384,6 +1384,43 @@ async fn mapper_publishes_child_device_create_message() {
     .await;
 }
 
+#[tokio::test]
+async fn mapper_publishes_child_device_create_message_default_naming_scheme() {
+    let cfg_dir = TempTedgeDir::new();
+    create_thin_edge_child_devices(&cfg_dir, vec!["test-device:device:child1"]);
+
+    let (mqtt, _http, _fs, _timer, _dl) = spawn_c8y_mapper_actor(&cfg_dir, false).await;
+    let mut mqtt = mqtt.with_timeout(TEST_TIMEOUT_MS);
+    skip_init_messages(&mut mqtt).await;
+
+    mqtt.send(MqttMessage::new(
+        &C8yTopic::downstream_topic(),
+        "106,child-one",
+    ))
+    .await
+    .expect("Send failed");
+
+    // Expect auto-registration message
+    assert_received_includes_json(
+        &mut mqtt,
+        [(
+            "te/device/child1//",
+            json!({"@type":"child-device", "name": "child1"}),
+        )],
+    )
+    .await;
+
+    // Expect smartrest message on `c8y/s/us` with expected payload "101,child1,child1,thin-edge.io-child".
+    assert_received_contains_str(
+        &mut mqtt,
+        [(
+            "c8y/s/us",
+            "101,test-device:device:child1,child1,thin-edge.io-child",
+        )],
+    )
+    .await;
+}
+
 #[tokio::test]
 async fn mapper_publishes_supported_operations_for_child_device() {
     // The test assures tedge-mapper checks if there is a directory for operations for child devices, then it reads and