Add function to get publisher actual qos settings (ros2#667)

* Added get_actual_qos method to publisher.

Signed-off-by: ivanpauno <ivanpauno@ekumenlabs.com>

rclcpp/include/rclcpp/publisher.hpp

@@ -128,6 +128,20 @@ class PublisherBase
   size_t
   get_intra_process_subscription_count() const;
 
+  /// Get the actual QoS settings, after the defaults have been determined.
+  /**
+   * The actual configuration applied when using RMW_QOS_POLICY_*_SYSTEM_DEFAULT
+   * can only be resolved after the creation of the publisher, 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_QOS_POLICY_*_UNKNOWN.
+   * May throw runtime_error when an unexpected error occurs.
+   * \return The actual qos settings.
+   */
+  RCLCPP_PUBLIC
+  rmw_qos_profile_t
+  get_actual_qos() const;
+
   /// Compare this publisher to a gid.
   /**
    * Note that this function calls the next function.

rclcpp/src/rclcpp/publisher.cpp

@@ -159,7 +159,7 @@ PublisherBase::get_subscription_count() const
 {
   size_t inter_process_subscription_count = 0;
 
-  rmw_ret_t status = rcl_publisher_get_subscription_count(
+  rcl_ret_t status = rcl_publisher_get_subscription_count(
     &publisher_handle_,
     &inter_process_subscription_count);
 
@@ -197,6 +197,18 @@ PublisherBase::get_intra_process_subscription_count() const
   return ipm->get_subscription_count(intra_process_publisher_id_);
 }
 
+rmw_qos_profile_t
+PublisherBase::get_actual_qos() const
+{
+  const rmw_qos_profile_t * qos = rcl_publisher_get_actual_qos(&publisher_handle_);
+  if (!qos) {
+    auto msg = std::string("failed to get qos settings: ") + rcl_get_error_string().str;
+    rcl_reset_error();
+    throw std::runtime_error(msg);
+  }
+  return *qos;
+}
+
 bool
 PublisherBase::operator==(const rmw_gid_t & gid) const
 {