【Linux】网络编程套接字

秒速五厘米 2024-03-23 20:46 52阅读 0赞

#### 文章目录 ####

*  网络编程套接字
 *   *  1. 认识TCP协议
     *  2. 认识UDP协议
     *  3. 网络字节序
     *  4. socket编程接口
     *   *  4.1 sockaddr 结构
     *  5. 简单的UDP网络程序
     *  6. 简单的TCP网络程序
     *   *  6.1 TCP socket的封装
         *  6.2 TCP协议通讯流程
     *  7. 守护进程

## 网络编程套接字 ##

### 1. 认识TCP协议 ###

*  传输层协议
 *  有连接
 *  可靠传输
 *  面向字节流

### 2. 认识UDP协议 ###

*  传输层协议
 *  无连接
 *  不可靠传输
 *  面向数据包

### 3. 网络字节序 ###

不管这台主机是大端还是小端，就需要先将数据转换为大端字节序

![b31xq9ivwl-1691562183517.png][]

`h表示本地,n 表示 network， l表示32为长整数， s表示16位短整数`

### 4. socket编程接口 ###

// 创建 socket 文件描述符 (TCP/UDP, 客户端 + 服务器)
    int socket(int domain, int type, int protocol);
    // 绑定端口号 (TCP/UDP, 服务器) 
    int bind(int socket, const struct sockaddr *address,
     socklen_t address_len);
    // 开始监听socket (TCP, 服务器)
    int listen(int socket, int backlog);
    // 接收请求 (TCP, 服务器)
    int accept(int socket, struct sockaddr* address,
     socklen_t* address_len);
    // 建立连接 (TCP, 客户端)
    int connect(int sockfd, const struct sockaddr *addr,
     socklen_t addrlen);

#### 4.1 sockaddr 结构 ####

![d86s9hjfue-1691562350564.png][]

### 5. 简单的UDP网络程序 ###

void InitServer()
    {
        
        _sock = socket(AF_INET, SOCK_DGRAM, 0);
        if (_sock < 0)
        {
        
            std::cout << "create sock error" << strerror(errno) << std::endl;
            exit(SOCKET_ERR);
        }
        std::cout << "create sock success" << std::endl;
        struct sockaddr_in local;
        sizeof (local, 0, sizeof(local));
        local.sin_family = AF_INET;
        local.sin_port = htons(_port);
        local.sin_addr.s_addr = inet_addr(_ip.c_str());
        if (bind(_sock, (struct sockaddr*)&local, sizeof(local)) < 0)
        {
        
            std::cout << "bind socket error" << strerror(errno) << std::endl;
            exit(BIND_ERR);
        }
        std::cout << "bind socket success" << std::endl;
    }

下面是实现的简单群聊服务器：

1.  环形队列
    
        #pragma once
        
        #include <iostream>
        #include <vector>
        #include <pthread.h>
        #include <semaphore.h>
        
        static const int N = 50;
        
        template <class T>
        class RingQueue
        {
              
        private:
            void P(sem_t &s)
            {
              
                sem_wait(&s);
            }
            void V(sem_t &s)
            {
              
                sem_post(&s);
            }
            void Lock(pthread_mtuex_t &m)
            {
              
                pthread_mutex_lock(&m);
            }
            void Unlock(pthread_mutex_t &m)
            {
              
                pthread_mutex_unlock(&m);
            }
        
        public:
            RingQueue(int num = N) : _ring(num), _cap(num)
            {
              
                sem_init(&_data_sem, 0, 0);
                sem_init(&_space_sem, 0, num);
                _c_step = _p_step = 0;
                pthread_mutex_init(&_c_mutex, nullptr);
                pthread_mutex_init(&_p_mutex, nullptr);
            }
            void push(const T &in)
            {
              
                P(_space_sem);
                Lock(_p_mutex);
                _ring[_p_step++] = in;
                _p_step %= _cap;
                Unlock(_p_mutex);
                V(_data_sem);
            }
        
            void pop(T *out)
            {
              
                P(_data_sem);
                Lock(_c_mutex);
                *out = _ring[_c_step++];
                _c_step %= _cap;
                Unlock(_c_mutex);
                V(_space_sem);
            }
        
            ~RingQueue()
            {
              
                sem_destroy(&_data_sem);
                sem_destroy(&_space_sem);
                pthread_mutex_destroy(&_p_mutex);
                pthread_mutex_destroy(&_c_mutex);
            }
        
        private:
            std::vector<T> _ring;
            int _cap; // 环形队列的大小
            sem_t _data_sem; // 消费者关心
            sem_t _space_sem;  // 生产者关心
            int _c_step; // 消费位置
            int _p_step; // 生产位置
            pthread_mutex_t _c_mutex;
            pthread_mutex_t _p_mutex;
        };
2.  线程包装
    
        #pragma once
        
        #include <iostream>
        #include <string>
        #include <cstdlib>
        #include <pthread.h>
        #include <functional>
        
        
        class Thread
        {
              
        public:
            typedef enum
            {
              
                NEW = 0, 
                RUNNING, 
                EXITED
            } ThreadStatus;
        
            using func_t = std::function<void ()>;
        
        public:
            Thread(int num, func_t func) : _tid(0), _status(NEW), _func(func)
            {
              
                char name[128];
                snprintf(name, sizeof(name), "thread-%d", num);
                _name = name;   
            }
            int status() 
            {
              
                return _status;
            }
            std::string threadname()
            {
              
                return _name;
            }
            pthread_t pthreadid()
            {
              
                if (_status == RUNNING)
                {
              
                    return _tid;
                }
                else
                {
              
                    return 0;
                }
            }
            void operator()() // 仿函数
            {
              
                if (_func != nullptr) _func();
            }
            static void *runHelper(void *args)
            {
              
                Thread* ts = (Thread*)args;
                (*ts)();
                return nullptr;
            }
            void run()
            {
              
                int n = pthread_create(&_tid, nullptr, runHelper, this);
                if (n != 0) exit(1);
                _status = RUNNING;
            }
            void join()
            {
              
                int n = pthread_join(_tid, nullptr);
                if (n != 0)
                {
              
                    std::cout << "man thread join thread" << _name << " error" << std::endl;
                    return;
                }
                _status = EXITED;
            }
            ~Thread()
            {
              }
        
        private:
            pthread_t _tid;
            std::string _name;
            func_t _func;
            ThreadStatus _status;
        };
3.  锁包装
    
        #pragma once
        
        #include <iostream>
        #include <pthread.h>
        
        class Mutex // 自己不维护锁，外部传入
        {
              
        private:
            pthread_mutex_t *_pmutex;
        public:
            Mutex(pthread_mutex_t *mutex) : _pmutex(mutex)
            {
              }
            void lock()
            {
              
                pthread_mutex_lock(_pmutex);
            }
            void unlock()
            {
              
                pthread_mutex_unlock(_pmutex);
            }
            ~Mutex()
            {
              }
        };
        
        class lockGuard
        {
              
        private:
            Mutex _mutex;
        public:
            lockGuard(pthread_mutex_t *mutex) : _mutex(mutex)
            {
              
                _mutex.lock();
            }
            ~lockGuard()
            {
              
                _mutex.unlock();
            }
        };
4.  服务器
    
        #pragma once
        
        #include <iostream>
        #include <cerrno>
        #include <cstring>
        #include <cstdlib>
        #include <functional>
        #include <strings.h>
        #include <sys/types.h>
        #include <sys/socket.h>
        #include <netinet/in.h>
        #include <arpa/inet.h>
        #include <pthread.h>
        #include <unordered_map>
        #include "err.hpp"
        #include "RingQueue.hpp"
        #include "lockGuard.hpp"
        #include "Thread.hpp"
        
        const static uint16_t port = 8888;
        using func_t = std::function<std::string(std::string)>;
        
        class UdpServer
        {
              
        private:
            uint16_t _port;
            int _sock;
            std::unordered_map<std::string, struct sockaddr_in> _onlineuser;
            pthread_mutex_t _lock;
            RingQueue<std::string> _rq;
            Thread *c;
            Thread *p;
        
        public:
            UdpServer(uint16_t port = port) : _port(port)
            {
              
                std::cout << "server addr " << _port << std::endl;
                pthread_mutex_init(&_lock, nullptr);
                p = new Thread(1, std::bind(&UdpServer::Recv, this));
                c = new Thread(1, std::bind(&UdpServer::Broadcast, this));
            }
            void start()
            {
              
                _sock = socket(AF_INET, SOCK_DGRAM, 0); // 创建套接字
                if (_sock < 0)
                {
              
                    std::cout << "create _sock error" << std::endl;
                    exit(SOCKET_ERR);
                }
                std::cout << "create _sock success" << std::endl;
                struct sockaddr_in local;
                memset(&local, 0, sizeof(local));
                local.sin_port = htons(_port);
                local.sin_family = AF_INET;
                local.sin_addr.s_addr = INADDR_ANY;
                if (bind(_sock, (struct sockaddr *)&local, sizeof(local)) < 0) // 绑定套接字
                {
              
                    std::cout << "bind socket error" << std::endl;
                    exit(BIND_ERR);
                }
                std::cout << "bind socket success" << std::endl;
                p->run();
                c->run();
            }
            void addUser(const std::string &name, const struct sockaddr_in &peer)
            {
              
                lockGuard guard(&_lock);
                auto it = _onlineuser.find(name);
                if (it != _onlineuser.end())
                {
              
                    return;
                }
                _onlineuser.insert(std::pair<const std::string, const struct sockaddr_in>(name, peer));
            }
            void Recv()
            {
              
                char buf[2056];
                while (true)
                {
              
                    struct sockaddr_in peer;
                    socklen_t len = sizeof(peer);
                    int n = recvfrom(_sock, buf, sizeof(buf) - 1, 0, (struct sockaddr *)&peer, &len);
                    if (n > 0)
                    {
              
                        buf[n] = '\0';
                    }
                    else
                        continue;
                    std::cout << "recv done" << std::endl;
                    std::string clientip = inet_ntoa(peer.sin_addr);
                    uint16_t clientport = ntohs(peer.sin_port);
                    std::cout << clientip << "-" << clientport << "#" << buf << std::endl;
        
                    std::string name = clientip;
                    name += "-";
                    name += std::to_string(clientport);
                    addUser(name, peer);
                    _rq.push(buf);
                }
            }
            void Broadcast()
            {
              
                while (true)
                {
              
                    std::string sendstring;
                    _rq.pop(&sendstring);
                    std::vector<struct sockaddr_in> v;
                    {
              
                        lockGuard guard(&_lock);
                        for (auto user : _onlineuser)
                        {
              
                            v.push_back(user.second);
                        }
                    }
                    for (auto user : v)
                    {
              
                        sendto(_sock, sendstring.c_str(), sendstring.size(), 0, (struct sockaddr*)&(user), sizeof(user));
                        std::cout << "send done" << sendstring << std::endl;
                    }
                }
            }
            ~UdpServer()
            {
              
                pthread_mutex_destroy(&_lock);
                c->join();
                p->join();
                delete p, c;
            }
        };
    
    **地址转换函数**
    
    `inet_ntoa` 是把返回结果放到了静态区，这个时候不需要手动释放。如果多次调用，会覆盖掉上一次的值
    
    ### 6. 简单的TCP网络程序 ###
    
    TCP由于是全双工的，所以初始化工作一共有五步
    
    1.  socket
    2.  bind
    3.  listen
    4.  accept
    5.  connect
    
    `listen` 声明socket fd处于监听状态，并且允许多个客户端来连接等待状态
    
    `accept` 三次握手完成后，调用服务器连接，
    
    ![id4zt0ehel-1691576412570.png][]

`connect` 客户端需要调用这个函数连接服务器

TCP 简单服务器：

#pragma once
    
    #include <iostream>
    #include <cstdlib>
    #include <cstring>
    #include <functional>
    #include <sys/types.h> /* See NOTES */
    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <arpa/inet.h>
    #include <unistd.h>
    #include <sys/types.h>
    #include <sys/wait.h>
    #include <signal.h>
    #include <pthread.h>
    #include "err.hpp"
    
    static const int defaultport = 8888;
    static const int backlog = 32;
    using func_t = std::function<std::string(const std::string &)>;
    
    class TcpServer;
    
    class ThreadData
    {
        
    public:
        int _sock;
        std::string _clientip;
        uint16_t _port;
        TcpServer *_current;
    public: 
        ThreadData(int fd, const std::string &ip, const uint16_t &port, TcpServer *ts)
        : _sock(fd), _clientip(ip), _port(port), _current(ts)
        {
        }
    };
    
    class TcpServer
    {
        
    public:
        TcpServer(func_t func, uint16_t port = defaultport) : _port(port), _func(func)
        {
        
        }
        void initServer()
        {
        
            _listensock = socket(AF_INET, SOCK_STREAM, 0);
            if (_listensock < 0)
            {
        
                std::cout << "create socket error" << std::endl;
                exit(SOCKET_ERR);
            }
            struct sockaddr_in local;
            memset(&local, 0, sizeof(local));
            local.sin_family = AF_INET;
            local.sin_addr.s_addr = htonl(INADDR_ANY);
            local.sin_port = htons(_port);
            if (bind(_listensock, (struct sockaddr*)&local, sizeof(local)) < 0)
            {
        
                std::cout << "create bind error" << std::endl;
                exit(BIND_ERR);
            }
            if (listen(_listensock, backlog) < 0)
            {
        
                std::cout << "create listen error" << std::endl;
                exit(LISTEN_ERR);
            }
        }
        static void* threadRuntinue(void* args)
        {
        
            pthread_detach(pthread_self());
            ThreadData *td = static_cast<ThreadData*>(args);
            td->_current->server(td->_sock, td->_clientip, td->_port);
            delete td;
            return nullptr;
        }
        void start()
        {
        
            _quit = false;
            while (true)
            {
        
                struct sockaddr_in client;
                socklen_t len = sizeof(client);
                int sock = accept(_listensock, (struct sockaddr*)&client, &len);                                                  
                if (sock < 0)
                {
        
                    std::cout << "create accept error" << std::endl;
                    continue;
                }
                std::string clientip = inet_ntoa(client.sin_addr);
                uint16_t clientport = ntohs(client.sin_port);
                std::cout << "accept success" << clientip << " " << clientport << std::endl;
                // server(sock, clientip, clientport); 第一个版本
                // 多线程版本
                pthread_t tid;
                ThreadData *threadDate = new ThreadData(sock, clientip, clientport, this);
                pthread_create(&tid, nullptr, threadRuntinue, threadDate);
            }
        }
        void server(int sock, const std::string ip, uint16_t port)
        {
        
            std::string who = ip + "-" + std::to_string(port);
            char buffer[1024];
            while (true)
            {
        
                size_t s = read(sock, buffer, sizeof(buffer) - 1);
                if (s > 0)
                {
        
                    buffer[s] = 0;
                    std::string res = _func(buffer); // 回调传进来的函数
                    std::cout << who << ">>>" << res << std::endl;
                    write(sock, res.c_str(), res.size());
                }
                else if (s == 0)
                {
        
                    close(sock);
                    std::cout << who << "quit, me too" << std::endl;
                    break;
                }
                else
                {
        
                    close(sock);
                    std::cout << "read error" << std::endl;
                    break;
                }
            }
        }
        ~TcpServer() {
        }
    private:
        uint16_t _port;
        int _listensock;
        bool _quit;
        func_t _func;
    };

TCP 简单的客户端

#include <iostream>
    #include <string>
    #include <cstring>
    #include <sys/types.h> /* See NOTES */
    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <arpa/inet.h>
    #include <unistd.h>
    #include "err.hpp"
    
    int main(int argc, char *argv[])
    {
        
        std::string serverip = argv[1];
        uint16_t serverport = atoi(argv[2]);
        int sock = socket(AF_INET, SOCK_STREAM, 0);
        // 要不要bind? 要
        // 要不要自己bind? 不要，因为client要让OS自动给用户进行bind
        // 要不要listen？不要 要不要accept？不需要
        struct sockaddr_in server;
        memset(&server, 0, sizeof(server));
        server.sin_family = AF_INET;
        server.sin_port = htons(serverport);
        inet_aton(serverip.c_str(), &(server.sin_addr));
        int cnt = 5;
        while (connect(sock, (struct sockaddr*)&server, sizeof(server)) != 0)
        {
        
            sleep(1);
            std::cout << "正在尝试重新连接" << std::endl;
            cnt--;
            if (cnt < 0) break;
        }
        if (cnt <= 0) {
        
            std::cout << "连接失败" << std::endl;
            exit(CONNECT_ERR);
        }
        char buffer[1024];
        while (true)
        {
        
            std::string line;
            std::getline(std::cin, line);
            write(sock, line.c_str(), line.size());
            size_t s = read(sock, buffer, sizeof(buffer) - 1);
            if (s > 0)
            {
        
                buffer[s] = 0;
                std::cout << "server echo" << std::endl;
            }
            else if (s == 0)
            {
        
                std::cout << "server quit" << std::endl;
                break;
            } else {
        
                std::cout << "read error" << std::endl;
                break;
            }
        }
        close(sock);
        return 0;
    }

#### 6.1 TCP socket的封装 ####

#pragma once
    #include <iostream>
    #include <string>
    #include <cstdlib>
    #include <cstring>
    #include <netinet/in.h>
    #include <arpa/inet.h>
    #include <sys/socket.h>
    #include <unistd.h>
    #include "Log.hpp"
    #include "Err.hpp"
    
    static const int gbacklog = 32;
    static const int defaultfd = -1;
    
    class Sock
    {
        
    public:
        Sock() : _sock(defaultfd) {
        }
        void Socket()
        {
        
            _sock = socket(AF_INET, SOCK_STREAM, 0);
            if (_sock < 0)
            {
        
                logMessage(Fatal, "socket error, code : %d", errno);
                exit(SOCKET_ERR);
            }
        }
        void Bind(const uint16_t &port)
        {
        
            struct sockaddr_in local;
            memset(&local, 0, sizeof(local));
            local.sin_family = AF_INET;
            local.sin_port = htons(port);
            local.sin_addr.s_addr = INADDR_ANY;
            if (bind(_sock, (struct sockaddr *)&local, sizeof(local)) < 0)
            {
        
                logMessage(Fatal, "bind error, code: %d, errstring: %s", errno, strerror(errno));
                exit(BIND_ERR);
            }
        }
        void Listen()
        {
        
            if (listen(_sock, gbacklog) < 0)
            {
        
                logMessage(Fatal, "listen error, code: %d, errstring: %s", errno, strerror(errno));
                exit(LISTEN_ERR);
            }
        }
        int Accept(std::string *clientip, uint16_t *clientport)
        {
        
            struct sockaddr_in temp;
            socklen_t len = sizeof(temp);
            int sock = accept(_sock, (struct sockaddr *)&temp, &len);
            if (sock < 0)
            {
        
                logMessage(Warning, "accept error, code: %d, errstring: %s", errno, strerror(errno));
            }
            else
            {
        
                *clientip = inet_ntoa(temp.sin_addr);
                *clientport = ntohs(temp.sin_port);
            }
            return sock;
        }
        int Connect(const std::string &serverip, const uint16_t &serverport)
        {
        
            struct sockaddr_in server;
            memset(&server, 0, sizeof(server));
            server.sin_family = AF_INET;
            server.sin_port = htons(serverport);
            server.sin_addr.s_addr = inet_addr(serverip.c_str());
            return connect(_sock, (struct sockaddr *)&server, sizeof(server));
        }
        int Fd()
        {
        
            return _sock;
        }
        ~Sock()
        {
        
            if (_sock != defaultfd)
                close(_sock);
        }
    
    private:
        int _sock;
    };

#### 6.2 TCP协议通讯流程 ####

服务器初始化：

*  调用socket，创建文件描述符
 *  调用bind，将当前的文件描述符和ip / port 绑定在一起，如果这个端口被占用了，就会bind失败
 *  调用listen，声明这个文件描述符是服务器的文件描述符，为后面的accept做好准备
 *  调用accept并阻塞，等待客户端连接

建立连接的过程：

*  调用socket，创建文件描述符
 *  调用connect，向服务器发起连接请求
 *  connect会发出SYN并阻塞等待服务器应答
 *  服务器收到客户端的SYN，会应答一个SYN-ACK，表示同意建立连接
 *  客户端收到SYN-ACK后会从connect（）返回，同时应答一个ACK  
    这个建立过程称为**三次握手**

**TCPVSUDP**

*  可靠传输 VS 不可靠传输
 *  有连接 VS 无连接
 *  字节流 VS 数据报

### 7. 守护进程 ###

// 1. setsid();
    // 2. setsid(), 调用进程，不能是组长！我们怎么保证自己不是组长呢？
    // 3. 守护进程a. 忽略异常信号 b. 0,1,2要做特殊处理 c. 进程的工作路径可能要更改 /
    
    #include <cstdlib>
    #include <unistd.h>
    #include <signal.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    
    #include "log.hpp"
    #include "err.hpp"
    
    //守护进程的本质：是孤儿进程的一种！
    void Daemon()
    {
        
        // 1. 忽略信号
        signal(SIGPIPE, SIG_IGN);
        signal(SIGCHLD, SIG_IGN);
        // 2. 让自己不要成为组长
        if (fork() > 0)
            exit(0);
        // 3. 新建会话，自己成为会话的话首进程
        pid_t ret = setsid();
        if ((int)ret == -1)
        {
        
            logMessage(Fatal, "deamon error, code: %d, string: %s", errno, strerror(errno));
            exit(SETSID_ERR);
        }
        // 4. 可选：可以更改守护进程的工作路径
        // chdir("/")
        // 5. 处理后续的对于0,1,2的问题
        int fd = open("/dev/null", O_RDWR);
        if (fd < 0)
        {
        
            logMessage(Fatal, "open error, code: %d, string: %s", errno, strerror(errno));
            exit(OPEN_ERR);
        }
        dup2(fd, 0);
        dup2(fd, 1);
        dup2(fd, 2);
        close(fd);
    }

[b31xq9ivwl-1691562183517.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/4dd95e189a774bb89db021fc861c5927.png
[d86s9hjfue-1691562350564.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/65ffe530269b4b0d977f24d0e4f49dd7.png
[id4zt0ehel-1691576412570.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/7f82a77903894572a8c42fc1f544208d.png