socket编程 ------ 建立 TCP 服务器和客户端流程（阻塞方式）

服务器端：

服务器端先创建一个socket，然后把这个socket绑定到端口上，接着让它向tcp/ip协议栈请求一个监听服务并创建一个accept队列来接受客户端请求。

void creat_tcpServer()
{
    int32    listenfd;
    
    /*    Create socket for incoming connections    */
    do{
        //AF_INET（又称 PF_INET）是 IPv4 网络协议的套接字类型
        //SOCK_STREAM 指TCP通信
　　　　　//0：系统根据地址格式和套接字类型，自动选择一个合适的协议，因为这里是TCP，也可填IPPROTO_TCP

        listenfd = socket(AF_INET, SOCK_STREAM, 0);
        if(listenfd    ==    -1)    
        {
            vTaskDelay(1000/portTICK_RATE_MS);
        }
    }while(listenfd    ==    -1);
    
    
    
    struct    sockaddr_in    server_addr;
    int32    ret;
    /*    Construct local address structure    */
    memset(&server_addr, 0, sizeof(server_addr));/*    Zero out structure */
    server_addr.sin_family    = AF_INET;    /*    Internet address family    */
    server_addr.sin_addr.s_addr    = INADDR_ANY;
    server_addr.sin_len    = sizeof(server_addr);
    server_addr.sin_port = htons(9999);    /* Local port */
    //绑定socket：将创建的socket绑定到本地的IP地址和端口，此socket是半相关的，只是负责
    //侦听客户端的连接请求，并不能用于和客户端通信
    do{
        ret    = bind(listenfd, (struct sockaddr *)&server_addr, sizeof(server_addr));
        if    (ret !=    0)    
        {
            vTaskDelay(1000/portTICK_RATE_MS);
        }
    }while(ret != 0);

    
    
    //listen侦听: 第一个参数是套接字，第二个参数为accept队列大小，当服务器接收到第三次握手后
    //将连接放到这个队列中，直到被accept处理才清除。当accept队列满了之后，即使client继续向server发
    //送ACK的包，也会不被响应，此时ListenOverflows+1，同时server通
    //过/proc/sys/net/ipv4/tcp_abort_on_overflow(linux kernel 2.2之后)来
    //决定如何返回，0表示直接丢弃该ACK，1表示发送RST通知client；相
    //应的，client则会分别返回read timeout 或者 connection reset by peer。
    do{
    /*    Listen    to    the    local    connection    */
        ret    = listen(listenfd, 1);
        if(ret != 0)
        {
            vTaskDelay(1000/portTICK_RATE_MS);
        }
    }while(ret    !=    0);

    
    
    int32 client_socket;
    int32 len = sizeof(struct sockaddr_in);
    int32 recbytes;
    struct    sockaddr_in    remote_addr;
    
    for(;;)
    {
        /*block    here waiting remote connect request*/
        if((client_socket = accept(listenfd, (struct sockaddr *)&remote_addr,    (socklen_t *)&len))    < 0)    
        {
            continue;
        }

        char *recv_buf = (char *)zalloc(129);

        while ((recbytes = read(client_socket , recv_buf, 128)) > 0)    
        {
            //数据保存在recv_buf
        }
        free(recv_buf);

        if(recbytes <= 0)
        {
            close(client_socket);
        }
    }
}

 客户端：

    for(;;)
    {
        
        sta_socket = socket(PF_INET, SOCK_STREAM, 0);
        if (-1 == sta_socket)
        {
            close(sta_socket);
            vTaskDelay(1000/portTICK_RATE_MS);
            printf("ESP8266 TCP client task > socket fail!
");
            continue;
        }
        printf("ESP8266 TCP client task > socket ok!
");
        
　　　　  //开启keepalive
　　　　  keepalive = 1;
        if(setsockopt(sta_socket, SOL_SOCKET, SO_KEEPALIVE, (void *)&keepalive, sizeof(keepalive)) < 0)
        {
            printf("set keepalive fail");
        }
        
        bzero(&remote_ip, sizeof(struct sockaddr_in));
        remote_ip.sin_family = AF_INET;
        remote_ip.sin_addr.s_addr = inet_addr(server_ip);
        remote_ip.sin_port = htons(server_port);
        if(0 != (connect_status = connect(sta_socket, (struct sockaddr *)(&remote_ip), sizeof(struct sockaddr))))    
        {
            close(sta_socket);
            vTaskDelay(1000/portTICK_RATE_MS);
            printf("ESP8266 TCP client task > connect fail!
");
            continue;
        }
        printf("ESP8266 TCP client task > connect ok!
");
        
　　　　  //如该连接在60秒没有任何数据往来，则进行探测
        keepidle = 60
        setsockopt(sta_socket, IPPROTO_TCP, TCP_KEEPIDLE, (void*)&keepidle , sizeof(keepidle));
　　　　　//探测时发包的时间间隔为5秒
　　　　  keepinterval = 5;
        setsockopt(sta_socket, IPPROTO_TCP, TCP_KEEPINTVL, (void *)&keepinterval , sizeof(keepinterval));
　　　　  //探测尝试的次数，如果第1次探测包就收到响应，则后2次的不再发
        keepcount = 3;
        setsockopt(sta_socket, IPPROTO_TCP, TCP_KEEPCNT, (void *)&keepcount , sizeof(keepcount));　　　　
        setsockopt(sta_socket, IPPROTO_TCP, TCP_NODELAY, (void *)&flag , sizeof(flag));
        while ((recbytes = read(sta_socket , recv_buf, 32)) > 0)    
        {
            handle_server_data(recv_buf, recbytes);
        }
        if(recbytes <= 0)    
        {
            close(sta_socket);
            printf("ESP8266 TCP client task > server closed!
");
        }
        
        
    }