Add free function for creating service clients (ros2#788)

Equivalent to the free function for creating a service.
Resolves ros2#768

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

rclcpp/include/rclcpp/create_client.hpp

@@ -0,0 +1,56 @@
+// Copyright 2019 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef RCLCPP__CREATE_CLIENT_HPP_
+#define RCLCPP__CREATE_CLIENT_HPP_
+
+#include <memory>
+#include <string>
+
+#include "rclcpp/node_interfaces/node_base_interface.hpp"
+#include "rclcpp/node_interfaces/node_services_interface.hpp"
+#include "rmw/rmw.h"
+
+namespace rclcpp
+{
+
+/// Create a service client with a given type.
+/// \internal
+template<typename ServiceT>
+typename rclcpp::Client<ServiceT>::SharedPtr
+create_client(
+  std::shared_ptr<node_interfaces::NodeBaseInterface> node_base,
+  std::shared_ptr<node_interfaces::NodeGraphInterface> node_graph,
+  std::shared_ptr<node_interfaces::NodeServicesInterface> node_services,
+  const std::string & service_name,
+  const rmw_qos_profile_t & qos_profile,
+  rclcpp::callback_group::CallbackGroup::SharedPtr group)
+{
+  rcl_client_options_t options = rcl_client_get_default_options();
+  options.qos = qos_profile;
+
+  auto cli = rclcpp::Client<ServiceT>::make_shared(
+    node_base.get(),
+    node_graph,
+    service_name,
+    options);
+
+  auto cli_base_ptr = std::dynamic_pointer_cast<rclcpp::ClientBase>(cli);
+  node_services->add_client(cli_base_ptr, group);
+  return cli;
+}
+
+}  // namespace rclcpp
+
+#endif  // RCLCPP__CREATE_CLIENT_HPP_

rclcpp/include/rclcpp/node_impl.hpp

@@ -36,6 +36,7 @@
 #include "rcl_interfaces/msg/intra_process_message.hpp"
 
 #include "rclcpp/contexts/default_context.hpp"
+#include "rclcpp/create_client.hpp"
 #include "rclcpp/create_publisher.hpp"
 #include "rclcpp/create_service.hpp"
 #include "rclcpp/create_subscription.hpp"
@@ -211,21 +212,13 @@ Node::create_client(
   const rmw_qos_profile_t & qos_profile,
   rclcpp::callback_group::CallbackGroup::SharedPtr group)
 {
-  rcl_client_options_t options = rcl_client_get_default_options();
-  options.qos = qos_profile;
-
-  using rclcpp::Client;
-  using rclcpp::ClientBase;
-
-  auto cli = Client<ServiceT>::make_shared(
-    node_base_.get(),
+  return rclcpp::create_client<ServiceT>(
+    node_base_,
     node_graph_,
+    node_services_,
     extend_name_with_sub_namespace(service_name, this->get_sub_namespace()),
-    options);
-
-  auto cli_base_ptr = std::dynamic_pointer_cast<ClientBase>(cli);
-  node_services_->add_client(cli_base_ptr, group);
-  return cli;
+    qos_profile,
+    group);
 }
 
 template<typename ServiceT, typename CallbackT>

rclcpp/test/test_client.cpp

@@ -81,6 +81,29 @@ TEST_F(TestClient, construction_and_destruction) {
   }
 }
 
+TEST_F(TestClient, construction_with_free_function) {
+  {
+    auto client = rclcpp::create_client<rcl_interfaces::srv::ListParameters>(
+      node->get_node_base_interface(),
+      node->get_node_graph_interface(),
+      node->get_node_services_interface(),
+      "service",
+      rmw_qos_profile_services_default,
+      nullptr);
+  }
+  {
+    ASSERT_THROW({
+      auto client = rclcpp::create_client<rcl_interfaces::srv::ListParameters>(
+        node->get_node_base_interface(),
+        node->get_node_graph_interface(),
+        node->get_node_services_interface(),
+        "invalid_?service",
+        rmw_qos_profile_services_default,
+        nullptr);
+    }, rclcpp::exceptions::InvalidServiceNameError);
+  }
+}
+
 /*
    Testing client construction and destruction for subnodes.
  */