Implement functions to get publisher and subcription informations like QoS policies from topic name

rclcpp/CMakeLists.txt

@@ -247,6 +247,7 @@ if(BUILD_TESTING)
       "rmw"
       "rosidl_generator_cpp"
       "rosidl_typesupport_cpp"
+      "test_msgs"
     )
     target_link_libraries(test_node ${PROJECT_NAME})
   endif()

rclcpp/include/rclcpp/node.hpp

@@ -867,6 +867,58 @@ class Node : public std::enable_shared_from_this<Node>
   size_t
   count_subscribers(const std::string & topic_name) const;
 
+  /// Return the topic endpoint information about publishers on a given topic.
+  /**
+   * The returned parameter is a list of topic endpoint information, where each item will contain
+   * the node name, node namespace, topic type, endpoint type, topic endpoint's GID, and its QoS
+   * profile.
+   *
+   * When the `no_mangle` parameter is `true`, the provided `topic_name` should be a valid topic
+   * name for the middleware (useful when combining ROS with native middleware (e.g. DDS) apps).
+   * When the `no_mangle` parameter is `false`, the provided `topic_name` should follow
+   * ROS topic name conventions.
+   *
+   * `topic_name` may be a relative, private, or fully qualified topic name.
+   * A relative or private topic will be expanded using this node's namespace and name.
+   * The queried `topic_name` is not remapped.
+   *
+   * \param[in] topic_name the topic_name on which to find the publishers.
+   * \param[in] no_mangle if `true`, `topic_name` needs to be a valid middleware topic name,
+   *   otherwise it should be a valid ROS topic name. Defaults to `false`.
+   * \return a list of TopicEndpointInfo representing all the publishers on this topic.
+   * \throws InvalidTopicNameError if the given topic_name is invalid.
+   * \throws std::runtime_error if internal error happens.
+   */
+  RCLCPP_PUBLIC
+  std::vector<rclcpp::TopicEndpointInfo>
+  get_publishers_info_by_topic(const std::string & topic_name, bool no_mangle = false) const;
+
+  /// Return the topic endpoint information about subscriptions on a given topic.
+  /**
+   * The returned parameter is a list of topic endpoint information, where each item will contain
+   * the node name, node namespace, topic type, endpoint type, topic endpoint's GID, and its QoS
+   * profile.
+   *
+   * When the `no_mangle` parameter is `true`, the provided `topic_name` should be a valid topic
+   * name for the middleware (useful when combining ROS with native middleware (e.g. DDS) apps).
+   * When the `no_mangle` parameter is `false`, the provided `topic_name` should follow
+   * ROS topic name conventions.
+   *
+   * `topic_name` may be a relative, private, or fully qualified topic name.
+   * A relative or private topic will be expanded using this node's namespace and name.
+   * The queried `topic_name` is not remapped.
+   *
+   * \param[in] topic_name the topic_name on which to find the subscriptions.
+   * \param[in] no_mangle if `true`, `topic_name` needs to be a valid middleware topic name,
+   *   otherwise it should be a valid ROS topic name. Defaults to `false`.
+   * \return a list of TopicEndpointInfo representing all the subscriptions on this topic.
+   * \throws InvalidTopicNameError if the given topic_name is invalid.
+   * \throws std::runtime_error if internal error happens.
+   */
+  RCLCPP_PUBLIC
+  std::vector<rclcpp::TopicEndpointInfo>
+  get_subscriptions_info_by_topic(const std::string & topic_name, bool no_mangle = false) const;
+
   /// Return a graph event, which will be set anytime a graph change occurs.
   /* The graph Event object is a loan which must be returned.
    * The Event object is scoped and therefore to return the loan just let it go

rclcpp/include/rclcpp/node_interfaces/node_graph.hpp

@@ -30,6 +30,7 @@
 #include "rclcpp/node_interfaces/node_base_interface.hpp"
 #include "rclcpp/node_interfaces/node_graph_interface.hpp"
 #include "rclcpp/visibility_control.hpp"
+#include "rmw/topic_endpoint_info_array.h"
 
 namespace rclcpp
 {
@@ -117,6 +118,18 @@ class NodeGraph : public NodeGraphInterface
   size_t
   count_graph_users() override;
 
+  RCLCPP_PUBLIC
+  std::vector<rclcpp::TopicEndpointInfo>
+  get_publishers_info_by_topic(
+    const std::string & topic_name,
+    bool no_mangle = false) const override;
+
+  RCLCPP_PUBLIC
+  std::vector<rclcpp::TopicEndpointInfo>
+  get_subscriptions_info_by_topic(
+    const std::string & topic_name,
+    bool no_mangle = false) const override;
+
 private:
   RCLCPP_DISABLE_COPY(NodeGraph)
 

rclcpp/include/rclcpp/node_interfaces/node_graph_interface.hpp

@@ -15,20 +15,120 @@
 #ifndef RCLCPP__NODE_INTERFACES__NODE_GRAPH_INTERFACE_HPP_
 #define RCLCPP__NODE_INTERFACES__NODE_GRAPH_INTERFACE_HPP_
 
+#include <algorithm>
+#include <array>
 #include <chrono>
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
 
+#include "rcl/graph.h"
 #include "rcl/guard_condition.h"
 
 #include "rclcpp/event.hpp"
 #include "rclcpp/macros.hpp"
+#include "rclcpp/qos.hpp"
 #include "rclcpp/visibility_control.hpp"
 
 namespace rclcpp
 {
+
+enum class EndpointType
+{
+  Invalid = RMW_ENDPOINT_INVALID,
+  Publisher = RMW_ENDPOINT_PUBLISHER,
+  Subscription = RMW_ENDPOINT_SUBSCRIPTION
+};
+
+/**
+ * Struct that contains topic endpoint information like the associated node name, node namespace,
+ * topic type, endpoint type, endpoint GID, and its QoS.
+ */
+class TopicEndpointInfo
+{
+public:
+  /// Construct a TopicEndpointInfo from a rcl_topic_endpoint_info_t.
+  RCLCPP_PUBLIC
+  explicit TopicEndpointInfo(const rcl_topic_endpoint_info_t & info)
+  : node_name_(info.node_name),
+    node_namespace_(info.node_namespace),
+    topic_type_(info.topic_type),
+    endpoint_type_(static_cast<rclcpp::EndpointType>(info.endpoint_type)),
+    qos_profile_({info.qos_profile.history, info.qos_profile.depth}, info.qos_profile)
+  {
+    std::copy(info.endpoint_gid, info.endpoint_gid + RMW_GID_STORAGE_SIZE, endpoint_gid_.begin());
+  }
+
+  /// Get a mutable reference to the node name.
+  RCLCPP_PUBLIC
+  std::string &
+  node_name();
+
+  /// Get a const reference to the node name.
+  RCLCPP_PUBLIC
+  const std::string &
+  node_name() const;
+
+  /// Get a mutable reference to the node namespace.
+  RCLCPP_PUBLIC
+  std::string &
+  node_namespace();
+
+  /// Get a const reference to the node namespace.
+  RCLCPP_PUBLIC
+  const std::string &
+  node_namespace() const;
+
+  /// Get a mutable reference to the topic type string.
+  RCLCPP_PUBLIC
+  std::string &
+  topic_type();
+
+  /// Get a const reference to the topic type string.
+  RCLCPP_PUBLIC
+  const std::string &
+  topic_type() const;
+
+  /// Get a mutable reference to the topic endpoint type.
+  RCLCPP_PUBLIC
+  rclcpp::EndpointType &
+  endpoint_type();
+
+  /// Get a const reference to the topic endpoint type.
+  RCLCPP_PUBLIC
+  const rclcpp::EndpointType &
+  endpoint_type() const;
+
+  /// Get a mutable reference to the GID of the topic endpoint.
+  RCLCPP_PUBLIC
+  std::array<uint8_t, RMW_GID_STORAGE_SIZE> &
+  endpoint_gid();
+
+  /// Get a const reference to the GID of the topic endpoint.
+  RCLCPP_PUBLIC
+  const std::array<uint8_t, RMW_GID_STORAGE_SIZE> &
+  endpoint_gid() const;
+
+  /// Get a mutable reference to the QoS profile of the topic endpoint.
+  RCLCPP_PUBLIC
+  rclcpp::QoS &
+  qos_profile();
+
+  /// Get a const reference to the QoS profile of the topic endpoint.
+  RCLCPP_PUBLIC
+  const rclcpp::QoS &
+  qos_profile() const;
+
+private:
+  std::string node_name_;
+  std::string node_namespace_;
+  std::string topic_type_;
+  rclcpp::EndpointType endpoint_type_;
+  std::array<uint8_t, RMW_GID_STORAGE_SIZE> endpoint_gid_;
+  rclcpp::QoS qos_profile_;
+};
+
 namespace node_interfaces
 {
 
@@ -150,6 +250,24 @@ class NodeGraphInterface
   virtual
   size_t
   count_graph_users() = 0;
+
+  /// Return the topic endpoint information about publishers on a given topic.
+  /**
+   * \sa rclcpp::Node::get_publishers_info_by_topic
+   */
+  RCLCPP_PUBLIC
+  virtual
+  std::vector<rclcpp::TopicEndpointInfo>
+  get_publishers_info_by_topic(const std::string & topic_name, bool no_mangle = false) const = 0;
+
+  /// Return the topic endpoint information about subscriptions on a given topic.
+  /**
+   * \sa rclcpp::Node::get_subscriptions_info_by_topic
+   */
+  RCLCPP_PUBLIC
+  virtual
+  std::vector<rclcpp::TopicEndpointInfo>
+  get_subscriptions_info_by_topic(const std::string & topic_name, bool no_mangle = false) const = 0;
 };
 
 }  // namespace node_interfaces

rclcpp/src/rclcpp/node.cpp

@@ -364,6 +364,18 @@ Node::count_subscribers(const std::string & topic_name) const
   return node_graph_->count_subscribers(topic_name);
 }
 
+std::vector<rclcpp::TopicEndpointInfo>
+Node::get_publishers_info_by_topic(const std::string & topic_name, bool no_mangle) const
+{
+  return node_graph_->get_publishers_info_by_topic(topic_name, no_mangle);
+}
+
+std::vector<rclcpp::TopicEndpointInfo>
+Node::get_subscriptions_info_by_topic(const std::string & topic_name, bool no_mangle) const
+{
+  return node_graph_->get_subscriptions_info_by_topic(topic_name, no_mangle);
+}
+
 const std::vector<rclcpp::callback_group::CallbackGroup::WeakPtr> &
 Node::get_callback_groups() const
 {