---
# System prepended metadata

title: ROS 2 Intermediate
tags: [Intermediate, ROS2, tutorials]

---

# ROS 2 Intermediate
###### tags: `ROS2` `Intermediate` `tutorials`
## rosdep
**rosdep** 是 ROS 用來管理 **dependencies** 的實用程序，可以與 ROS packages 和 external libraries 一起使用。 **rosdep** 是一個 command-line utility，用於識別和檢查 **dependencies** 以創建或安裝 package 。
在以下情況下可以或被調用：

* **Building a workspace** 需要適當的 **dependencies** ，我們利用他來 build packages。

* **Install packages** (e.g. `sudo apt install ros-foxy-demo-nodes-cpp`)我們利用他來檢查執行所需的 **dependencies**。
 
它能夠處理單個 package 或包目錄（e.g. workspace）。
### 使用rosdep
如果這是第一次使用，則必須通過以下方式對其進行初始化：
```
sudo rosdep init
rosdep update
rosdep install --from-paths src -y --ignore-src
```
## Creating an action
創建一個工作區名為`action_tutorials_interfaces`：
```
mkdir -p action_ws/src
cd action_ws/src
ros2 pkg create action_tutorials_interfaces
```
### Defining an action
```
cd action_tutorials_interfaces
mkdir action
```
然後到`action`目錄中，創建一個名為的文件`Fibonacci.action`，其內容如下：
```a
int32 order
---
int32[] sequence
---
int32[] partial_sequence
```
**order** 是我們要計算的斐波那契數列 ，他的 result 會傳到 **sequence** 的 ，而他的 feedback 是 **partial_sequence** 。
###  Building an action
使用斐波那契 action 之前，我們必須先把定義傳遞給 rosidl code 。
在`action_tutorials_interfaces`資料夾中找到`CMakeLists.txt`，並在 `ament_package()` 前放入以下程式:
```c
find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "action/Fibonacci.action"
)
```
修改完成的` CMakeLists.txt` 應該長這樣:

```c
cmake_minimum_required(VERSION 3.8)
project(action_tutorials_interfaces)

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)
# uncomment the following section in order to fill in
# further dependencies manually.
# find_package(<dependency> REQUIRED)

if(BUILD_TESTING)
  find_package(ament_lint_auto REQUIRED)
  # the following line skips the linter which checks for copyrights
  # comment the line when a copyright and license is added to all source files
  set(ament_cmake_copyright_FOUND TRUE)
  # the following line skips cpplint (only works in a git repo)
  # comment the line when this package is in a git repo and when
  # a copyright and license is added to all source files
  set(ament_cmake_cpplint_FOUND TRUE)
  ament_lint_auto_find_test_dependencies()
endif()

find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "action/Fibonacci.action"
)

ament_package()
```
Add the required dependencies to our `package.xml`:
```xml
<buildtool_depend>rosidl_default_generators</buildtool_depend>

<depend>action_msgs</depend>

<member_of_group>rosidl_interface_packages</member_of_group>
```
整體像這樣
```xml
<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
  <name>action_tutorials_interfaces</name>
  <version>0.0.0</version>
    <description>Examples of action using interfaces</description>
    <maintainer email="you@email.com">Enor</maintainer>
    <license>Apache License 2.0</license>
  
  <buildtool_depend>rosidl_default_generators</buildtool_depend>
  
  <depend>action_msgs</depend>

  <member_of_group>rosidl_interface_packages</member_of_group>

  <buildtool_depend>ament_cmake</buildtool_depend>

  <test_depend>ament_lint_auto</test_depend>
  <test_depend>ament_lint_common</test_depend>

  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>
```

Build the package containing the **Fibonacci** **action** definition:
```
# Change to the root of the workspace
cd ~/action_ws
# Build
colcon build
```
![](https://i.imgur.com/i9cLTSu.png)

```
. install/setup.bash
ros2 interface show action_tutorials_interfaces/action/Fibonacci
```
![](https://i.imgur.com/L01RwF2.png)

## Writing an action server and client (C++)
建立一個新的 package:

```
cd ~/action_ws/src
ros2 pkg create --dependencies action_tutorials_interfaces rclcpp rclcpp_action rclcpp_components -- action_tutorials_cpp
```
 開啟`action_tutorials_cpp/include/action_tutorials_cpp/visibility_control.h`並編輯:

```h
#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_
```
開啟 `action_tutorials_cpp/src/fibonacci_action_server.cpp`並編輯:

```cpp
#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
{
    //創建一個rclcpp::Node
class FibonacciActionServer : public rclcpp::Node
{
public:
  using Fibonacci = action_tutorials_interfaces::action::Fibonacci;
  using GoalHandleFibonacci = rclcpp_action::ServerGoalHandle<Fibonacci>;

  ACTION_TUTORIALS_CPP_PUBLIC
  //初始化節點名稱
  explicit FibonacciActionServer(const rclcpp::NodeOptions & options = rclcpp::NodeOptions())
  : Node("fibonacci_action_server", options)
  {
    using namespace std::placeholders;
    
//實體化 action server
/*
 一個 action server 需要 6 個東西：

操作類型名稱：Fibonacci。
將操作添加到的 ROS 2 節點：this.
動作名稱：'fibonacci'.
處理目標的回傳函數：handle_goal
處理取消的回傳函數：handle_cancel.
用於處理目標的回傳接受函數：handle_accept。
 */

    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_;
//處理新目標的回傳(從這開始)
  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;
    //他實現有ACCEPT_AND_EXECUTE的目標
    return rclcpp_action::GoalResponse::ACCEPT_AND_EXECUTE;
  }
//處理取消的回傳
  rclcpp_action::CancelResponse handle_cancel(
    const std::shared_ptr<GoalHandleFibonacci> goal_handle)
  {
  //然後會告訴客戶端他接受取消
    RCLCPP_INFO(this->get_logger(), "Received request to cancel goal");
    (void)goal_handle;
    return rclcpp_action::CancelResponse::ACCEPT;
  }
//最後接收到回傳，並接受一個新目標並回傳
//由於該執行是一段長時間運型的操作，因此獨立 handle_accepted 出來讓他能快速給予回饋
  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();
  }
//所有的處理與更新都在 execute 中完成
  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();
    }
    //這邊每秒會處理一個斐波那契數列的序號，為每一步發布一個feedback。當它完成處理時，它將標記goal_handle為succeed，然後退出。
    // 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)
```
### compile the package:

```
cd ~/action_ws
colcon build
```
![](https://i.imgur.com/znuzcJ3.png)


### Writing the action client code
打開`action_tutorials_cpp/src/fibonacci_action_client.cpp`，將code放入：
```cpp
#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(std::shared_future<GoalHandleFibonacci::SharedPtr> future)
  {
    auto goal_handle = future.get();
    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)
```
打開action_tutorials_cpp/CMakeLists.txt
添加以下內容在 find_package 後：

```c
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)
```
完成後的 CMakeLists.txt 應該長這樣:

```c
cmake_minimum_required(VERSION 3.8)
project(action_tutorials_cpp)

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)
find_package(action_tutorials_interfaces REQUIRED)
find_package(rclcpp REQUIRED)
find_package(rclcpp_action REQUIRED)
find_package(rclcpp_components REQUIRED)

if(BUILD_TESTING)

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)
    
  find_package(ament_lint_auto REQUIRED)
  
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)
  
  # the following line skips the linter which checks for copyrights
  # comment the line when a copyright and license is added to all source files
  set(ament_cmake_copyright_FOUND TRUE)
  # the following line skips cpplint (only works in a git repo)
  # comment the line when this package is in a git repo and when
  # a copyright and license is added to all source files
  set(ament_cmake_cpplint_FOUND TRUE)
  ament_lint_auto_find_test_dependencies()
endif()

ament_package()
```
```
colcon build
```
![](https://i.imgur.com/WTRIqE5.png)
### Running the action server
```
ros2 run action_tutorials_cpp fibonacci_action_server
```
![](https://i.imgur.com/EElfkSY.png)

### Running the action client
```
ros2 run action_tutorials_cpp fibonacci_action_client
```

![](https://i.imgur.com/RFVJqgZ.png)

