编写一个动作服务器和客户端（C++）

目标： 在C++中实现一个动作服务器和客户端。

教程级别： 中级

时间： 15分钟

内容

背景
先决条件
任务
总结
相关内容

背景 

动作是ROS中的一种异步通信形式。*动作客户端*向*动作服务器*发送目标请求。*动作服务器*向*动作客户端*发送目标反馈和结果。

先决条件 

你需要使用``action_tutorials_interfaces``包和前面教程中定义的``Fibonacci.action``接口。参见创建一个动作。

任务 

1 创建 action_tutorials_cpp 包 

正如我们在创建软件包教程中所看到的，我们需要创建一个新的包来保存我们的C++代码和支持代码。

1.1 创建 action_tutorials_cpp 包

进入你在上一个教程中创建的操作工作空间（记得要加载工作空间），并为C++操作服务器创建一个新包：

cd ~/ros2_ws/src
ros2 pkg create --dependencies action_tutorials_interfaces rclcpp rclcpp_action rclcpp_components -- action_tutorials_cpp

cd ~/ros2_ws/src
ros2 pkg create --dependencies action_tutorials_interfaces rclcpp rclcpp_action rclcpp_components -- action_tutorials_cpp

cd \dev\ros2_ws\src
ros2 pkg create --dependencies action_tutorials_interfaces rclcpp rclcpp_action rclcpp_components -- action_tutorials_cpp

1.2 添加可见性控制

为了使该包在Windows上编译和工作，我们需要添加一些"可见性控制"。更多详细信息，请参阅 Windows Tips and Tricks文档中的Windows符号可见性。

打开 action_tutorials_cpp/include/action_tutorials_cpp/visibility_control.h，并添加以下代码：

#ifndef ACTION_TUTORIALS_CPP__VISIBILITY_CONTROL_H_
#define ACTION_TUTORIALS_CPP__VISIBILITY_CONTROL_H_

#ifdef __cplusplus
extern "C"
{
#endif

// This logic was borrowed (then namespaced) from the examples on the gcc wiki:
//     https://gcc.gnu.org/wiki/Visibility

#if defined _WIN32 || defined __CYGWIN__
  #ifdef __GNUC__
    #define ACTION_TUTORIALS_CPP_EXPORT __attribute__ ((dllexport))
    #define ACTION_TUTORIALS_CPP_IMPORT __attribute__ ((dllimport))
  #else
    #define ACTION_TUTORIALS_CPP_EXPORT __declspec(dllexport)
    #define ACTION_TUTORIALS_CPP_IMPORT __declspec(dllimport)
  #endif
  #ifdef ACTION_TUTORIALS_CPP_BUILDING_DLL
    #define ACTION_TUTORIALS_CPP_PUBLIC ACTION_TUTORIALS_CPP_EXPORT
  #else
    #define ACTION_TUTORIALS_CPP_PUBLIC ACTION_TUTORIALS_CPP_IMPORT
  #endif
  #define ACTION_TUTORIALS_CPP_PUBLIC_TYPE ACTION_TUTORIALS_CPP_PUBLIC
  #define ACTION_TUTORIALS_CPP_LOCAL
#else
  #define ACTION_TUTORIALS_CPP_EXPORT __attribute__ ((visibility("default")))
  #define ACTION_TUTORIALS_CPP_IMPORT
  #if __GNUC__ >= 4
    #define ACTION_TUTORIALS_CPP_PUBLIC __attribute__ ((visibility("default")))
    #define ACTION_TUTORIALS_CPP_LOCAL  __attribute__ ((visibility("hidden")))
  #else
    #define ACTION_TUTORIALS_CPP_PUBLIC
    #define ACTION_TUTORIALS_CPP_LOCAL
  #endif
  #define ACTION_TUTORIALS_CPP_PUBLIC_TYPE
#endif

#ifdef __cplusplus
}
#endif

#endif  // ACTION_TUTORIALS_CPP__VISIBILITY_CONTROL_H_

2 编写一个操作服务器 

让我们专注于编写一个使用我们在创建一个动作教程中创建的操作来计算斐波那契数列的操作服务器。

2.1 编写动作服务器代码

打开 action_tutorials_cpp/src/fibonacci_action_server.cpp 文件，并将以下代码放入其中：

#include <functional>
#include <memory>
#include <thread>

#include "action_tutorials_interfaces/action/fibonacci.hpp"
#include "rclcpp/rclcpp.hpp"
#include "rclcpp_action/rclcpp_action.hpp"
#include "rclcpp_components/register_node_macro.hpp"

#include "action_tutorials_cpp/visibility_control.h"

namespace action_tutorials_cpp
{
class FibonacciActionServer : public rclcpp::Node
{
public:
  using Fibonacci = action_tutorials_interfaces::action::Fibonacci;
  using GoalHandleFibonacci = rclcpp_action::ServerGoalHandle<Fibonacci>;

  ACTION_TUTORIALS_CPP_PUBLIC
  explicit FibonacciActionServer(const rclcpp::NodeOptions & options = rclcpp::NodeOptions())
  : Node("fibonacci_action_server", options)
  {
    using namespace std::placeholders;

    this->action_server_ = rclcpp_action::create_server<Fibonacci>(
      this,
      "fibonacci",
      std::bind(&FibonacciActionServer::handle_goal, this, _1, _2),
      std::bind(&FibonacciActionServer::handle_cancel, this, _1),
      std::bind(&FibonacciActionServer::handle_accepted, this, _1));
  }

private:
  rclcpp_action::Server<Fibonacci>::SharedPtr action_server_;

  rclcpp_action::GoalResponse handle_goal(
    const rclcpp_action::GoalUUID & uuid,
    std::shared_ptr<const Fibonacci::Goal> goal)
  {
    RCLCPP_INFO(this->get_logger(), "Received goal request with order %d", goal->order);
    (void)uuid;
    return rclcpp_action::GoalResponse::ACCEPT_AND_EXECUTE;
  }

  rclcpp_action::CancelResponse handle_cancel(
    const std::shared_ptr<GoalHandleFibonacci> goal_handle)
  {
    RCLCPP_INFO(this->get_logger(), "Received request to cancel goal");
    (void)goal_handle;
    return rclcpp_action::CancelResponse::ACCEPT;
  }

  void handle_accepted(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
  {
    using namespace std::placeholders;
    // this needs to return quickly to avoid blocking the executor, so spin up a new thread
    std::thread{std::bind(&FibonacciActionServer::execute, this, _1), goal_handle}.detach();
  }

  void execute(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
  {
    RCLCPP_INFO(this->get_logger(), "Executing goal");
    rclcpp::Rate loop_rate(1);
    const auto goal = goal_handle->get_goal();
    auto feedback = std::make_shared<Fibonacci::Feedback>();
    auto & sequence = feedback->partial_sequence;
    sequence.push_back(0);
    sequence.push_back(1);
    auto result = std::make_shared<Fibonacci::Result>();

    for (int i = 1; (i < goal->order) && rclcpp::ok(); ++i) {
      // Check if there is a cancel request
      if (goal_handle->is_canceling()) {
        result->sequence = sequence;
        goal_handle->canceled(result);
        RCLCPP_INFO(this->get_logger(), "Goal canceled");
        return;
      }
      // Update sequence
      sequence.push_back(sequence[i] + sequence[i - 1]);
      // Publish feedback
      goal_handle->publish_feedback(feedback);
      RCLCPP_INFO(this->get_logger(), "Publish feedback");

      loop_rate.sleep();
    }

    // Check if goal is done
    if (rclcpp::ok()) {
      result->sequence = sequence;
      goal_handle->succeed(result);
      RCLCPP_INFO(this->get_logger(), "Goal succeeded");
    }
  }
};  // class FibonacciActionServer

}  // namespace action_tutorials_cpp

RCLCPP_COMPONENTS_REGISTER_NODE(action_tutorials_cpp::FibonacciActionServer)

前几行包含了我们编译所需的所有头文件。

接下来，我们创建一个派生自 rclcpp::Node 的类：

class FibonacciActionServer : public rclcpp::Node

FibonacciActionServer 类的构造函数将节点名称初始化为 fibonacci_action_server：

  explicit FibonacciActionServer(const rclcpp::NodeOptions & options = rclcpp::NodeOptions())
  : Node("fibonacci_action_server", options)

构造函数还实例化了一个新的动作服务器：

    this->action_server_ = rclcpp_action::create_server<Fibonacci>(
      this,
      "fibonacci",
      std::bind(&FibonacciActionServer::handle_goal, this, _1, _2),
      std::bind(&FibonacciActionServer::handle_cancel, this, _1),
      std::bind(&FibonacciActionServer::handle_accepted, this, _1));

一个动作服务器需要6个要素：

模板化的动作类型名称：Fibonacci。
要添加动作的ROS 2节点：this。
动作名称：'fibonacci'。
处理目标的回调函数：handle_goal。
处理取消的回调函数：handle_cancel。
处理目标接受的回调函数：handle_accept。

接下来是对各种回调函数的实现。请注意，所有回调函数都需要快速返回，否则我们可能会导致执行程序饥饿。

我们首先处理处理新目标的回调函数：

  rclcpp_action::GoalResponse handle_goal(
    const rclcpp_action::GoalUUID & uuid,
    std::shared_ptr<const Fibonacci::Goal> goal)
  {
    RCLCPP_INFO(this->get_logger(), "Received goal request with order %d", goal->order);
    (void)uuid;
    return rclcpp_action::GoalResponse::ACCEPT_AND_EXECUTE;
  }

这个实现只是接受所有目标。

接下来是处理取消的回调函数：

  rclcpp_action::CancelResponse handle_cancel(
    const std::shared_ptr<GoalHandleFibonacci> goal_handle)
  {
    RCLCPP_INFO(this->get_logger(), "Received request to cancel goal");
    (void)goal_handle;
    return rclcpp_action::CancelResponse::ACCEPT;
  }

这个实现只是告诉客户端它接受了取消请求。

最后一个回调函数接受一个新的目标并开始处理它：

  void handle_accepted(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
  {
    using namespace std::placeholders;
    // this needs to return quickly to avoid blocking the executor, so spin up a new thread
    std::thread{std::bind(&FibonacciActionServer::execute, this, _1), goal_handle}.detach();
  }

由于执行是一个长时间运行的操作，我们创建一个线程来执行实际的工作，并快速从``handle_accepted``返回。

所有进一步的处理和更新都在新线程的``execute``方法中进行：

  void execute(const std::shared_ptr<GoalHandleFibonacci> goal_handle)
  {
    RCLCPP_INFO(this->get_logger(), "Executing goal");
    rclcpp::Rate loop_rate(1);
    const auto goal = goal_handle->get_goal();
    auto feedback = std::make_shared<Fibonacci::Feedback>();
    auto & sequence = feedback->partial_sequence;
    sequence.push_back(0);
    sequence.push_back(1);
    auto result = std::make_shared<Fibonacci::Result>();

    for (int i = 1; (i < goal->order) && rclcpp::ok(); ++i) {
      // Check if there is a cancel request
      if (goal_handle->is_canceling()) {
        result->sequence = sequence;
        goal_handle->canceled(result);
        RCLCPP_INFO(this->get_logger(), "Goal canceled");
        return;
      }
      // Update sequence
      sequence.push_back(sequence[i] + sequence[i - 1]);
      // Publish feedback
      goal_handle->publish_feedback(feedback);
      RCLCPP_INFO(this->get_logger(), "Publish feedback");

      loop_rate.sleep();
    }

    // Check if goal is done
    if (rclcpp::ok()) {
      result->sequence = sequence;
      goal_handle->succeed(result);
      RCLCPP_INFO(this->get_logger(), "Goal succeeded");
    }
  }

该工作线程每秒处理斐波那契数列的一个序列数，对每一步都发布一个反馈更新。当它完成处理时，将``goal_handle``标记为成功并退出。

现在我们有一个完全功能的动作服务器。让我们构建并运行它。

2.2 编译动作服务器

在前一节中，我们已经放置了动作服务器的代码。为了使其编译和运行，我们还需要进行一些额外的操作。

首先，我们需要设置CMakeLists.txt以便编译动作服务器。打开``action_tutorials_cpp/CMakeLists.txt``文件，在``find_package``调用之后添加以下内容：

add_library(action_server SHARED
  src/fibonacci_action_server.cpp)
target_include_directories(action_server PRIVATE
  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
  $<INSTALL_INTERFACE:include>)
target_compile_definitions(action_server
  PRIVATE "ACTION_TUTORIALS_CPP_BUILDING_DLL")
ament_target_dependencies(action_server
  "action_tutorials_interfaces"
  "rclcpp"
  "rclcpp_action"
  "rclcpp_components")
rclcpp_components_register_node(action_server PLUGIN "action_tutorials_cpp::FibonacciActionServer" EXECUTABLE fibonacci_action_server)
install(TARGETS
  action_server
  ARCHIVE DESTINATION lib
  LIBRARY DESTINATION lib
  RUNTIME DESTINATION bin)

现在我们可以编译该软件包。进入``ros2_ws``的顶级目录，运行以下命令：

colcon build

这将编译整个工作空间，包括``action_tutorials_cpp``软件包中的``fibonacci_action_server``。

2.3 运行动作服务器

现在我们已经构建了动作服务器，可以运行它了。源激活我们刚刚构建的工作空间（ros2_ws），并尝试运行动作服务器：

ros2 run action_tutorials_cpp fibonacci_action_server

3 编写动作客户端 

3.1 编写动作客户端代码

打开 action_tutorials_cpp/src/fibonacci_action_client.cpp，并将以下代码放入其中：

#include <functional>
#include <future>
#include <memory>
#include <string>
#include <sstream>

#include "action_tutorials_interfaces/action/fibonacci.hpp"

#include "rclcpp/rclcpp.hpp"
#include "rclcpp_action/rclcpp_action.hpp"
#include "rclcpp_components/register_node_macro.hpp"

namespace action_tutorials_cpp
{
class FibonacciActionClient : public rclcpp::Node
{
public:
  using Fibonacci = action_tutorials_interfaces::action::Fibonacci;
  using GoalHandleFibonacci = rclcpp_action::ClientGoalHandle<Fibonacci>;

  explicit FibonacciActionClient(const rclcpp::NodeOptions & options)
  : Node("fibonacci_action_client", options)
  {
    this->client_ptr_ = rclcpp_action::create_client<Fibonacci>(
      this,
      "fibonacci");

    this->timer_ = this->create_wall_timer(
      std::chrono::milliseconds(500),
      std::bind(&FibonacciActionClient::send_goal, this));
  }

  void send_goal()
  {
    using namespace std::placeholders;

    this->timer_->cancel();

    if (!this->client_ptr_->wait_for_action_server()) {
      RCLCPP_ERROR(this->get_logger(), "Action server not available after waiting");
      rclcpp::shutdown();
    }

    auto goal_msg = Fibonacci::Goal();
    goal_msg.order = 10;

    RCLCPP_INFO(this->get_logger(), "Sending goal");

    auto send_goal_options = rclcpp_action::Client<Fibonacci>::SendGoalOptions();
    send_goal_options.goal_response_callback =
      std::bind(&FibonacciActionClient::goal_response_callback, this, _1);
    send_goal_options.feedback_callback =
      std::bind(&FibonacciActionClient::feedback_callback, this, _1, _2);
    send_goal_options.result_callback =
      std::bind(&FibonacciActionClient::result_callback, this, _1);
    this->client_ptr_->async_send_goal(goal_msg, send_goal_options);
  }

private:
  rclcpp_action::Client<Fibonacci>::SharedPtr client_ptr_;
  rclcpp::TimerBase::SharedPtr timer_;

  void goal_response_callback(const GoalHandleFibonacci::SharedPtr & goal_handle)
  {
    if (!goal_handle) {
      RCLCPP_ERROR(this->get_logger(), "Goal was rejected by server");
    } else {
      RCLCPP_INFO(this->get_logger(), "Goal accepted by server, waiting for result");
    }
  }

  void feedback_callback(
    GoalHandleFibonacci::SharedPtr,
    const std::shared_ptr<const Fibonacci::Feedback> feedback)
  {
    std::stringstream ss;
    ss << "Next number in sequence received: ";
    for (auto number : feedback->partial_sequence) {
      ss << number << " ";
    }
    RCLCPP_INFO(this->get_logger(), ss.str().c_str());
  }

  void result_callback(const GoalHandleFibonacci::WrappedResult & result)
  {
    switch (result.code) {
      case rclcpp_action::ResultCode::SUCCEEDED:
        break;
      case rclcpp_action::ResultCode::ABORTED:
        RCLCPP_ERROR(this->get_logger(), "Goal was aborted");
        return;
      case rclcpp_action::ResultCode::CANCELED:
        RCLCPP_ERROR(this->get_logger(), "Goal was canceled");
        return;
      default:
        RCLCPP_ERROR(this->get_logger(), "Unknown result code");
        return;
    }
    std::stringstream ss;
    ss << "Result received: ";
    for (auto number : result.result->sequence) {
      ss << number << " ";
    }
    RCLCPP_INFO(this->get_logger(), ss.str().c_str());
    rclcpp::shutdown();
  }
};  // class FibonacciActionClient

}  // namespace action_tutorials_cpp

RCLCPP_COMPONENTS_REGISTER_NODE(action_tutorials_cpp::FibonacciActionClient)

前几行包含了我们编译所需的所有头文件。

接下来，我们创建一个派生自 rclcpp::Node 的类：

class FibonacciActionClient : public rclcpp::Node

FibonacciActionClient 类的构造函数将节点名称初始化为 fibonacci_action_client：

  explicit FibonacciActionClient(const rclcpp::NodeOptions & options)
  : Node("fibonacci_action_client", options)

构造函数还实例化了一个新的动作客户端：

    this->client_ptr_ = rclcpp_action::create_client<Fibonacci>(
      this,
      "fibonacci");

动作客户端需要三样东西：

模板化的动作类型名称：Fibonacci。
一个用于添加动作客户端的ROS 2节点：this。
动作名称：'fibonacci'。

我们还实例化了一个ROS定时器，它将触发对``send_goal``的唯一调用：

    this->timer_ = this->create_wall_timer(
      std::chrono::milliseconds(500),
      std::bind(&FibonacciActionClient::send_goal, this));

当定时器到期时，它将调用``send_goal``：

  void send_goal()
  {
    using namespace std::placeholders;

    this->timer_->cancel();

    if (!this->client_ptr_->wait_for_action_server()) {
      RCLCPP_ERROR(this->get_logger(), "Action server not available after waiting");
      rclcpp::shutdown();
    }

    auto goal_msg = Fibonacci::Goal();
    goal_msg.order = 10;

    RCLCPP_INFO(this->get_logger(), "Sending goal");

    auto send_goal_options = rclcpp_action::Client<Fibonacci>::SendGoalOptions();
    send_goal_options.goal_response_callback =
      std::bind(&FibonacciActionClient::goal_response_callback, this, _1);
    send_goal_options.feedback_callback =
      std::bind(&FibonacciActionClient::feedback_callback, this, _1, _2);
    send_goal_options.result_callback =
      std::bind(&FibonacciActionClient::result_callback, this, _1);
    this->client_ptr_->async_send_goal(goal_msg, send_goal_options);
  }

此函数执行以下操作：

取消定时器的操作（因此只调用一次）。
等待动作服务器启动。
实例化一个新的 Fibonacci::Goal。
设置响应、反馈和结果的回调函数。
将目标发送到服务器。

当服务器接收并接受目标后，它将向客户端发送响应。这个响应由 goal_response_callback 处理：

  void goal_response_callback(const GoalHandleFibonacci::SharedPtr & goal_handle)
  {
    if (!goal_handle) {
      RCLCPP_ERROR(this->get_logger(), "Goal was rejected by server");
    } else {
      RCLCPP_INFO(this->get_logger(), "Goal accepted by server, waiting for result");
    }
  }

假设服务器接受了目标，它将开始处理。任何对客户端的反馈将由 feedback_callback 处理：

  void feedback_callback(
    GoalHandleFibonacci::SharedPtr,
    const std::shared_ptr<const Fibonacci::Feedback> feedback)
  {
    std::stringstream ss;
    ss << "Next number in sequence received: ";
    for (auto number : feedback->partial_sequence) {
      ss << number << " ";
    }
    RCLCPP_INFO(this->get_logger(), ss.str().c_str());
  }

当服务器处理完成后，将向客户端返回结果。结果由 result_callback 处理：

  void result_callback(const GoalHandleFibonacci::WrappedResult & result)
  {
    switch (result.code) {
      case rclcpp_action::ResultCode::SUCCEEDED:
        break;
      case rclcpp_action::ResultCode::ABORTED:
        RCLCPP_ERROR(this->get_logger(), "Goal was aborted");
        return;
      case rclcpp_action::ResultCode::CANCELED:
        RCLCPP_ERROR(this->get_logger(), "Goal was canceled");
        return;
      default:
        RCLCPP_ERROR(this->get_logger(), "Unknown result code");
        return;
    }
    std::stringstream ss;
    ss << "Result received: ";
    for (auto number : result.result->sequence) {
      ss << number << " ";
    }
    RCLCPP_INFO(this->get_logger(), ss.str().c_str());
    rclcpp::shutdown();
  }
};  // class FibonacciActionClient

我们现在拥有一个完全运行的动作客户端。让我们来构建和运行它吧。

3.2 编译动作客户端

在前一节中，我们已经放置了动作客户端的代码。为了使其编译和运行，我们需要进行一些额外的操作。

首先，我们需要设置 CMakeLists.txt，以便编译动作客户端。打开 action_tutorials_cpp/CMakeLists.txt，在 find_package 调用之后添加以下内容：

add_library(action_client SHARED
  src/fibonacci_action_client.cpp)
target_include_directories(action_client PRIVATE
  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
  $<INSTALL_INTERFACE:include>)
target_compile_definitions(action_client
  PRIVATE "ACTION_TUTORIALS_CPP_BUILDING_DLL")
ament_target_dependencies(action_client
  "action_tutorials_interfaces"
  "rclcpp"
  "rclcpp_action"
  "rclcpp_components")
rclcpp_components_register_node(action_client PLUGIN "action_tutorials_cpp::FibonacciActionClient" EXECUTABLE fibonacci_action_client)
install(TARGETS
  action_client
  ARCHIVE DESTINATION lib
  LIBRARY DESTINATION lib
  RUNTIME DESTINATION bin)

现在我们可以编译该软件包。进入``ros2_ws``的顶级目录，运行以下命令：

colcon build

这将编译整个工作空间，包括 action_tutorials_cpp 包中的 fibonacci_action_client。

3.3 运行动作客户端

现在我们已经构建了动作客户端，可以运行它了。首先确保在单独的终端中运行了一个动作服务器。现在，源代码工作空间我们刚刚构建的（ros2_ws），然后尝试运行动作客户端：

ros2 run action_tutorials_cpp fibonacci_action_client

您应该看到有关目标被接受、反馈被打印和最终结果的日志消息。

总结 

在本教程中，您逐行组合了一个C++动作服务器和动作客户端，并配置它们交换目标、反馈和结果。