Implement get_actual_qos() for subscriptions

rcl/include/rcl/subscription.h

@@ -445,6 +445,32 @@ rcl_subscription_get_publisher_count(
   const rcl_subscription_t * subscription,
   size_t * publisher_count);
 
+/// Get the actual qos settings of the subscription.
+/**
+ * Used to get the actual qos settings of the subscription.
+ * The actual configuration applied when using RMW_*_SYSTEM_DEFAULT
+ * can only be resolved after the creation of the subscription, and it
+ * depends on the underlying rmw implementation.
+ * If the underlying setting in use can't be represented in ROS terms,
+ * it will be set to RMW_*_UNKNOWN.
+ * The returned struct is only valid as long as the rcl_subscription_t is valid.
+ *
+ * <hr>
+ * Attribute          | Adherence
+ * ------------------ | -------------
+ * Allocates Memory   | No
+ * Thread-Safe        | Yes
+ * Uses Atomics       | No
+ * Lock-Free          | Yes
+ *
+ * \param[in] subscription pointer to the rcl subscription
+ * \return qos struct if successful, otherwise `NULL`
+ */
+RCL_PUBLIC
+RCL_WARN_UNUSED
+const rmw_qos_profile_t *
+rcl_subscription_get_actual_qos(const rcl_subscription_t * subscription);
+
 #ifdef __cplusplus
 }
 #endif

rcl/src/rcl/subscription.c

@@ -167,6 +167,17 @@ rcl_subscription_init(
     RCL_SET_ERROR_MSG(rmw_get_error_string().str);
     goto fail;
   }
+  // get actual qos, and store it
+  rmw_ret = rmw_subscription_get_actual_qos(
+    subscription->impl->rmw_handle,
+    &subscription->impl->actual_qos);
+  if (RMW_RET_OK != rmw_ret) {
+    RCL_SET_ERROR_MSG(rmw_get_error_string().str);
+    ret = RCL_RET_ERROR;
+    goto fail;
+  }
+  subscription->impl->actual_qos.avoid_ros_namespace_conventions =
+    options->qos.avoid_ros_namespace_conventions;
   // options
   subscription->impl->options = *options;
   RCUTILS_LOG_DEBUG_NAMED(ROS_PACKAGE_NAME, "Subscription initialized");
@@ -359,6 +370,15 @@ rcl_subscription_get_publisher_count(
   return RCL_RET_OK;
 }
 
+const rmw_qos_profile_t *
+rcl_subscription_get_actual_qos(const rcl_subscription_t * subscription)
+{
+  if (!rcl_subscription_is_valid(subscription)) {
+    return NULL;
+  }
+  return &subscription->impl->actual_qos;
+}
+
 #ifdef __cplusplus
 }
 #endif

rcl/src/rcl/subscription_impl.h

@@ -22,6 +22,7 @@
 typedef struct rcl_subscription_impl_t
 {
   rcl_subscription_options_t options;
+  rmw_qos_profile_t actual_qos;
   rmw_subscription_t * rmw_handle;
 } rcl_subscription_impl_t;