请解释Message switching

Message switching 是一种计算机网络通信方式，它将数据分割成小的消息并通过网络传输。每个消息都包含了目标地址和数据，消息在网络中通过节点传递，直到到达目标地址。这种通信方式可以提高网络的效率和可靠性。

相关问题

请给出一个moveit控制器的代码示例

以下是一个基于MoveIt Simple Controller Manager的ROS控制器示例：

#include <ros/ros.h>
#include <moveit_simple_controller_manager/simple_controller_manager.h>
#include <moveit/move_group_interface/move_group_interface.h>
#include <moveit/robot_model_loader/robot_model_loader.h>
#include <moveit/robot_model/robot_model.h>
#include <moveit/robot_state/robot_state.h>
#include <moveit/trajectory_processing/iterative_time_parameterization.h>

class MyRobotController : public moveit_simple_controller_manager::SimpleControllerManager
{
public:
    MyRobotController() : moveit_simple_controller_manager::SimpleControllerManager()
    {
        // Initialize MoveIt
        move_group_.reset(new moveit::planning_interface::MoveGroupInterface("arm"));

        // Load the robot model and get the robot state
        robot_model_loader_.reset(new robot_model_loader::RobotModelLoader("robot_description"));
        robot_model_ = robot_model_loader_->getModel();
        robot_state_.reset(new robot_state::RobotState(robot_model_));

        // Set the joint model group
        joint_model_group_ = robot_model_->getJointModelGroup("arm");

        // Set the trajectory processing
        trajectory_processing_.reset(new trajectory_processing::IterativeParabolicTimeParameterization());

        // Set the desired joint state
        desired_joint_state_.resize(joint_model_group_->getVariableCount());
        desired_joint_state_.setZero();
    }

    virtual bool initialize(const std::string& robot_description, const std::string& controller_name)
    {
        // Initialize the controller with the robot description and the controller name
        if (!SimpleControllerManager::initialize(robot_description, controller_name))
        {
            ROS_ERROR("Failed to initialize the controller");
            return false;
        }

        // Set the callback function for the controller
        controller_->setTrajectoryExecutionCallback(boost::bind(&MyRobotController::trajectoryExecutionCallback, this, _1));

        // Print a message to indicate successful initialization
        ROS_INFO("Controller initialized successfully");
        return true;
    }

    virtual bool canSwitch(const std::vector<std::string>& start_controllers, const std::vector<std::string>& stop_controllers) const
    {
        // This controller does not support switching
        return false;
    }

    virtual bool switchControllers(const std::vector<std::string>& start_controllers, const std::vector<std::string>& stop_controllers)
    {
        // This controller does not support switching
        return false;
    }

    virtual bool isActive()
    {
        // Return true if the controller is active
        return controller_->isActive();
    }

    virtual void stopping()
    {
        // Stop the controller
        controller_->stop();
    }

    void trajectoryExecutionCallback(const moveit_msgs::RobotTrajectory& trajectory)
    {
        // Get the start state of the robot
        robot_state_->setToDefaultValues();
        const robot_state::JointModelGroup* start_joint_model_group = robot_state_->getJointModelGroup("arm");

        // Get the start and end time of the trajectory
        double start_time = ros::Time::now().toSec();
        double end_time = start_time + trajectory.joint_trajectory.points.back().time_from_start.toSec();

        // Execute the trajectory
        move_group_->execute(trajectory);

        // Wait until the end of the trajectory
        while (ros::Time::now().toSec() < end_time)
        {
            ros::Duration(0.01).sleep();
        }

        // Get the current joint state of the robot
        robot_state_->getCurrentState(*move_group_->getCurrentState());
        const robot_state::JointModelGroup* current_joint_model_group = robot_state_->getJointModelGroup("arm");

        // Get the current joint values
        robot_state_->copyJointGroupPositions(current_joint_model_group, desired_joint_state_);

        // Set the current joint values as the desired joint state
        controller_->setDesiredJointState(desired_joint_state_);

        // Print a message to indicate successful trajectory execution
        ROS_INFO("Trajectory executed successfully");
    }

private:
    ros::NodeHandle nh_;
    moveit::planning_interface::MoveGroupInterfacePtr move_group_;
    robot_model_loader::RobotModelLoaderPtr robot_model_loader_;
    robot_model::RobotModelPtr robot_model_;
    robot_state::RobotStatePtr robot_state_;
    const robot_model::JointModelGroup* joint_model_group_;
    std::unique_ptr<trajectory_processing::IterativeParabolicTimeParameterization> trajectory_processing_;
    Eigen::VectorXd desired_joint_state_;
};

int main(int argc, char** argv)
{
    // Initialize ROS
    ros::init(argc, argv, "my_robot_controller");

    // Create the controller
    MyRobotController controller;

    // Initialize the controller
    if (!controller.initialize("robot_description", "my_robot_controller"))
    {
        return -1;
    }

    // Spin the node
    ros::spin();

    return 0;
}

在上述示例中，MyRobotController是一个自定义的ROS控制器，它继承自MoveIt Simple Controller Manager。在构造函数中，我们初始化了MoveIt，加载了机器人模型，并设置了轨迹处理和期望关节状态。在initialize()函数中，我们初始化了控制器，并设置了回调函数。在trajectoryExecutionCallback()函数中，我们执行了轨迹，并在轨迹执行完成后更新了期望关节状态。最后，在main()函数中，我们创建了并初始化了控制器，并开始运行ROS节点。

websocket

WebSocket是一种在单个TCP连接上进行全双工通信的协议。它提供了一种在Web浏览器和服务器之间进行实时数据传输的方式。下面是一个使用C语言实现WebSocket服务器的例子：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define MAX_BUFFER_SIZE 1024

// WebSocket握手请求的处理函数
void handle_handshake(int client_socket, const char* request) {
    // 解析请求头，获取WebSocket的key
    const char* key_start = strstr(request, "Sec-WebSocket-Key: ") + strlen("Sec-WebSocket-Key: ");
    const char* key_end = strstr(key_start, "\r\n");
    char key[128];
    strncpy(key, key_start, key_end - key_start);
    key[key_end - key_start] = '\0';

    // 构造响应头，进行握手
    char response[256];
    sprintf(response, "HTTP/1.1 101 Switching Protocols\r\n"
                      "Upgrade: websocket\r\n"
                      "Connection: Upgrade\r\n"
                      "Sec-WebSocket-Accept: %s\r\n\r\n", key);
    send(client_socket, response, strlen(response), 0);
}

// WebSocket消息的处理函数
void handle_message(int client_socket, const char* message) {
    // 解析消息头，获取消息长度和掩码
    int payload_length = message[1] & 0x7F;
    int mask_start = 2;
    if (payload_length == 126) {
        payload_length = (message[2] << 8) | message[3];
        mask_start = 4;
    } else if (payload_length == 127) {
        payload_length = (message[2] << 56) | (message[3] << 48) | (message[4] << 40) |
                         (message[5] << 32) | (message[6] << 24) | (message[7] << 16) |
                         (message[8] << 8) | message[9];
        mask_start = 10;
    }

    // 解析掩码，对消息进行解码
    char mask[4] = {message[mask_start], message[mask_start + 1], message[mask_start + 2], message[mask_start + 3]};
    char decoded_message[payload_length + 1];
    for (int i = 0; i < payload_length; i++) {
        decoded_message[i] = message[mask_start + 4 + i] ^ mask[i % 4];
    }
    decoded_message[payload_length] = '\0';

    // 处理解码后的消息
    printf("Received message: %s\n", decoded_message);

    // 构造响应消息，进行回复
    char response[256];
    sprintf(response, "\x81\x05Hello");
    send(client_socket, response, strlen(response), 0);
}

int main() {
    // 创建socket
    int server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket == -1) {
        perror("Failed to create socket");
        exit(EXIT_FAILURE);
    }

    // 绑定地址和端口
    struct sockaddr_in server_address;
    server_address.sin_family = AF_INET;
    server_address.sin_addr.s_addr = INADDR_ANY;
    server_address.sin_port = htons(8080);
    if (bind(server_socket, (struct sockaddr*)&server_address, sizeof(server_address)) == -1) {
        perror("Failed to bind address");
        exit(EXIT_FAILURE);
    }

    // 监听连接
    if (listen(server_socket, 5) == -1) {
        perror("Failed to listen");
        exit(EXIT_FAILURE);
    }

    printf("WebSocket server is running on port 8080...\n");

    while (1) {
        // 接受连接
        struct sockaddr_in client_address;
        socklen_t client_address_length = sizeof(client_address);
        int client_socket = accept(server_socket, (struct sockaddr*)&client_address, &client_address_length);
        if (client_socket == -1) {
            perror("Failed to accept connection");
            continue;
        }

        // 接收请求
        char request[MAX_BUFFER_SIZE];
        ssize_t request_length = recv(client_socket, request, sizeof(request), 0);
        if (request_length == -1) {
            perror("Failed to receive request");
            close(client_socket);
            continue;
        }

        // 处理握手请求
        handle_handshake(client_socket, request);

        // 接收和处理消息
        while (1) {
            char message[MAX_BUFFER_SIZE];
            ssize_t message_length = recv(client_socket, message, sizeof(message), 0);
            if (message_length == -1) {
                perror("Failed to receive message");
                break;
            } else if (message_length == 0) {
                printf("Client disconnected\n");
                break;
            }

            handle_message(client_socket, message);
        }

        // 关闭连接
        close(client_socket);
    }

    // 关闭socket
    close(server_socket);

    return 0;
}

这个例子展示了一个简单的WebSocket服务器的实现，它使用C语言编写，并使用了HTTP解析器、SHA1算法和WebSocket解析器。你可以将这个例子在Visual Studio中修改并在Linux下运行。