#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <errno.h>

#define BUF_SIZE 4 //缓冲区设置为 4 字节
#define EPOLL_SIZE 50
void setnonblockingmode(int fd);
void error_handling(char *message);

int main(int argc, char *argv[])
{
    int serv_sock, clnt_sock;
    struct sockaddr_in serv_adr, clnt_adr;
    socklen_t adr_sz;
    int str_len, i;
    char buf[BUF_SIZE];

    struct epoll_event *ep_events;
    struct epoll_event event;
    int epfd, event_cnt;

    if (argc != 2)
    {
        printf("Usage : %s <port> \n", argv[0]);
        exit(1);
    }
    serv_sock = socket(PF_INET, SOCK_STREAM, 0);
    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)
        error_handling("bind() error");
    if (listen(serv_sock, 5) == -1)
        error_handling("listen() error");

    epfd = epoll_create(EPOLL_SIZE); //可以忽略这个参数，填入的参数为操作系统参考
    ep_events = malloc(sizeof(struct epoll_event) * EPOLL_SIZE);

    setnonblockingmode(serv_sock);
    event.events = EPOLLIN; //需要读取数据的情况
    event.data.fd = serv_sock;
    epoll_ctl(epfd, EPOLL_CTL_ADD, serv_sock, &event); //例程epfd 中添加文件描述符 serv_sock，目的是监听 enevt 中的事件

    while (1)
    {
        event_cnt = epoll_wait(epfd, ep_events, EPOLL_SIZE, -1); //获取改变了的文件描述符，返回数量
        if (event_cnt == -1)
        {
            puts("epoll_wait() error");
            break;
        }

        puts("return epoll_wait");
        for (i = 0; i < event_cnt; i++)
        {
            if (ep_events[i].data.fd == serv_sock) //客户端请求连接时
            {
                adr_sz = sizeof(clnt_adr);
                clnt_sock = accept(serv_sock, (struct sockaddr *)&clnt_adr, &adr_sz);
                setnonblockingmode(clnt_sock);    //将 accept 创建的套接字改为非阻塞模式
                event.events = EPOLLIN | EPOLLET; //改成边缘触发
                event.data.fd = clnt_sock;        //把客户端套接字添加进去
                epoll_ctl(epfd, EPOLL_CTL_ADD, clnt_sock, &event);
                printf("connected client : %d \n", clnt_sock);
            }
            else //是客户端套接字时
            {
                while (1)
                {
                    str_len = read(ep_events[i].data.fd, buf, BUF_SIZE);
                    if (str_len == 0)
                    {
                        epoll_ctl(epfd, EPOLL_CTL_DEL, ep_events[i].data.fd, NULL); //从epoll中删除套接字
                        close(ep_events[i].data.fd);
                        printf("closed client : %d \n", ep_events[i].data.fd);
                        break;
                    }
                    else if (str_len < 0)
                    {
                        if (errno == EAGAIN) //read 返回-1 且 errno 值为 EAGAIN ，意味读取了输入缓冲的全部数据
                            break;
                    }
                    else
                    {
                        write(ep_events[i].data.fd, buf, str_len);
                    }
                }
            }
        }
    }
    close(serv_sock);
    close(epfd);

    return 0;
}

void error_handling(char *message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}
void setnonblockingmode(int fd)
{
    int flag = fcntl(fd, F_GETFL, 0);
    fcntl(fd, F_SETFL, flag | O_NONBLOCK);
}