echo_mpserv.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30
void error_handling(char *message);
void read_childproc(int sig);

int main(int argc, char *argv[])
{
    int serv_sock, clnt_sock;
    struct sockaddr_in serv_adr, clnt_adr;

    pid_t pid;
    struct sigaction act;
    socklen_t adr_sz;
    int str_len, state;
    char buf[BUF_SIZE];
    if (argc != 2)
    {
        printf("Usgae : %s <port>\n", argv[0]);
        exit(1);
    }
    act.sa_handler = read_childproc; //防止僵尸进程
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    state = sigaction(SIGCHLD, &act, 0);         //注册信号处理器,把成功的返回值给 state
    serv_sock = socket(PF_INET, SOCK_STREAM, 0); //创建服务端套接字
    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_adr.sin_port = htons(atoi(argv[1]));

    if (bind(serv_sock, (struct sockaddr *)&serv_adr, sizeof(serv_adr)) == -1) //分配IP地址和端口号
        error_handling("bind() error");
    if (listen(serv_sock, 5) == -1) //进入等待连接请求状态
        error_handling("listen() error");

    while (1)
    {
        adr_sz = sizeof(clnt_adr);
        clnt_sock = accept(serv_sock, (struct sockaddr *)&clnt_adr, &adr_sz);
        if (clnt_sock == -1)
            continue;
        else
            puts("new client connected...");
        pid = fork(); //此时，父子进程分别带有一个套接字
        if (pid == -1)
        {
            close(clnt_sock);
            continue;
        }
        if (pid == 0) //子进程运行区域,此部分向客户端提供回声服务
        {
            close(serv_sock); //关闭服务器套接字，因为从父进程传递到了子进程
            while ((str_len = read(clnt_sock, buf, BUFSIZ)) != 0)
                write(clnt_sock, buf, str_len);

            close(clnt_sock);
            puts("client disconnected...");
            return 0;
        }
        else
            close(clnt_sock); //通过 accept 函数创建的套接字文件描述符已经复制给子进程，因为服务器端要销毁自己拥有的
    }
    close(serv_sock);

    return 0;
}

void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}
void read_childproc(int sig)
{
    pid_t pid;
    int status;
    pid = waitpid(-1, &status, WNOHANG);
    printf("removed proc id: %d \n", pid);
}