服务端流程步骤

socket函数创建监听套接字lfd

bind函数将监听套接字绑定ip和端口

listen函数设置服务器为被动监听状态，同时创建一条未完成连接队列（没走完tcp三次握手流程的连接），和一条已完成连接队列（已完成tcp三次握手的连接）

accept函数循环的从已完成连接队列中提取连接，并返回一个新的套接字cfd跟客户端进行通信

fork函数创建一个子进程，让子进程与客户端进行通信

子进程：read函数循环的从r缓冲区读取客户端发送的数据，write函数将要发送的数据写入w缓冲区

close函数关闭套接字

客户端流程步骤

socket函数创建套接字

connect函数连接服务器

write函数将要发送的数据写入w缓冲区，read函数从r缓冲区读取服务器发送给客户端的数据

close函数关闭套接字

客户端跟服务器通信流程图

服务端代码

#include #include #include #include #include #include #include #include #include #include #define BUF_SIZE 256void do_sigchld(int signo, siginfo_t *siginfo, void *p){    int status;    pid_t pid;    while((pid = waitpid(0, &status, WNOHANG)) > 0) //0:回收跟调用进程同组的子进程的资源，WNOHANG:不阻塞    {        if (WIFEXITED(status))            printf("pid = %d, parent pid = %d, child pid = %d, exit status %d\n", pid, getpid(), siginfo->si_pid, WEXITSTATUS(status));        else if (WEXITSTATUS(status))            printf("pid = %d, parent pid = %d, child pid = %d, exit by signal %d\n ", pid, getpid(), siginfo->si_pid, WIFSIGNALED(status));    }}void sys_err(const char *str, int err){    perror(str);    exit(err);}int main(int argc, char *argv[]){    if (argc < 2)    {        printf("%s port\n", argv[0]);        exit(1);    }    //创建流式套接字    int lfd = socket(AF_INET, SOCK_STREAM, 0);    if (lfd < 0)        sys_err("socket", 1);    //绑定ip端口        struct sockaddr_in server_addr;    server_addr.sin_family = AF_INET;    server_addr.sin_port = htons((unsigned short)atoi(argv[1]));    server_addr.sin_addr.s_addr = 0; //0表示将本机所有ip都绑定上    int ret = bind(lfd, (struct sockaddr *)&server_addr, sizeof(server_addr));    if (ret < 0)        sys_err("bind", 1);        //监听    ret = listen(lfd, 128);    if (ret < 0)        sys_err("listen", 1);        //阻塞SIGCHLD信号    sigset_t set;    sigemptyset(&set);    sigaddset(&set, SIGCHLD);    sigprocmask(SIG_BLOCK, &set, NULL);    int block = 1;    //循环提取    int cfd;    pid_t pid;    struct sockaddr_in client_addr;     socklen_t len = sizeof(client_addr);    char buf[BUF_SIZE];    ssize_t size;    char ip[INET_ADDRSTRLEN] = "";    while(1)    {        cfd = accept(lfd, (struct sockaddr *)&client_addr, &len);        if (cfd  0)        {            //in parent            close(cfd); //关闭不用了的跟客户端通讯的套接字            if (1 == block)            {                //先捕捉                struct sigaction sa;                sa.sa_sigaction = do_sigchld;                sigemptyset(&sa.sa_mask);                sa.sa_flags = SA_SIGINFO;                sigaction(SIGCHLD, &sa, NULL);                //后解除阻塞                sigprocmask(SIG_UNBLOCK, &set, NULL);                block = 0;            }        }        else            sys_err("fork", 1);    }        //关闭套接字    if (pid == 0)        close(cfd);    else if (pid > 0)        close(lfd);    return 0;}

客户端代码

#include #include #include #include #include #include int main(int argc, char *argv[]){    if (argc < 3)    {        printf("%s sever_ip server_port\n", argv[0]);        exit(1);    }    //创建流式套接字    int fd = socket(AF_INET, SOCK_STREAM, 0);    if (fd < 0)    {        perror("socket");        exit(1);    }    //连接服务器    struct sockaddr_in addr;    addr.sin_family = AF_INET;    addr.sin_port = htons((unsigned short)atoi(argv[2]));    addr.sin_addr.s_addr = inet_addr(argv[1]);    int ret = connect(fd, (struct sockaddr *)&addr, sizeof(addr));    printf("connect ret = %d\n", ret);    if (ret < 0)    {        perror("connect");        exit(1);    }    //读写数据    char buf_w[128] = "";    char buf_r[128] = "";    ssize_t size_r = 0;    while(1)    {        fgets(buf_w, sizeof(buf_w), stdin);        buf_w[strlen(buf_w) - 1] = 0;        write(fd, buf_w, strlen(buf_w));        size_r = read(fd, buf_r, sizeof(buf_r));        if (size_r == 0) //服务器断开            break;        else            printf("%s\n", buf_r);        memset(buf_w, 0, sizeof(buf_w));        memset(buf_r, 0, sizeof(buf_r));    }    //关闭套接字    close(fd);    return 0;}