#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>

#define MAXLINE 80
#define SERV_PORT 8000
#define OPEN_MAX 1024

//自定义的出错的处理函数 
void perr_exit(char *str) 
{
	perror(str);
	exit(-1);
}

int main(int argc, char *argv[]) {
	int i, j, maxi, listenfd, connfd, sockfd;
	int nready, efd, res;
	ssize_t n;
	char buf[MAXLINE], str[INET_ADDRSTRLEN];
	socklen_t clilen;
	int client[OPEN_MAX];
	struct sockaddr_in cliaddr, servaddr;
	struct epoll_event tep, ep[OPEN_MAX];
	
	//创建监听套接字
	listenfd = socket(AF_INET, SOCK_STREAM, 0);
	
	bzero(&servaddr, sizeof(servaddr));
	
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(SERV_PORT);
	
	//绑定监听套接字和 ip/端口号
	bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
	listen(listenfd, 20);
	
	/* 用-1初始化client[] */
	for (i = 0; i < OPEN_MAX; i++)
		client[i] = -1;
	
	/* client[]的下标 */
	maxi = -1;
	
	//创建一颗红黑树（用来存储所有客户端信息） efd->树根
	efd = epoll_create(OPEN_MAX);
	
	//红黑树创建失败
	if (efd == -1)
		perr_exit("epoll_create");
	
	//把监听套接字加入红黑树
	tep.events = EPOLLIN;
	tep.data.fd = listenfd;
	res = epoll_ctl(efd, EPOLL_CTL_ADD, listenfd, &tep);
	
	//listenfd加入红黑树失败
	if (res == -1)
		perr_exit("epoll_ctl");
	
	for ( ; ; ) 
	{
		/* 阻塞监听红黑树 */
		nready = epoll_wait(efd, ep, OPEN_MAX, -1); 
		
		//监听出错
		if (nready == -1)
			perr_exit("epoll_wait");
		
		//遍历红黑树上需要操作的节点
		for (i = 0; i < nready; i++) 
		{
			//表示红黑树上的文件描述符不可以读则跳过
			if (!(ep[i].events & EPOLLIN))
				continue;
			
			//红黑树上节点的值 == listenfd，说明有新的客户端连接
			if (ep[i].data.fd == listenfd) 
			{
				clilen = sizeof(cliaddr);
				//获取客户端套接字、ip/端口号信息
				connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
				
				//打印新连接得客户端 ip/端口号
				printf("received from %s at PORT %d\n", 
				        inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)), ntohs(cliaddr.sin_port));
				
				printf("客户端新连接");
				
				//新连接得客户端套接字 加入client数组
				for (j = 0; j < OPEN_MAX; j++)
					if (client[j] < 0) 
					{
						client[j] = connfd; /* save descriptor */
						break;
					}
					
				//连接得客户端过多报错	
				if (j == OPEN_MAX)
					perr_exit("too many clients");
				
				//更新maxi的值（maxi代表最后一个连接得的客户端的套接字）
				if (j > maxi)
					maxi = j; /* max index in client[] array */
				
				//新连接的客户端套接字加入红黑数，继续监听。
				tep.events = EPOLLIN;
				tep.data.fd = connfd;
				res = epoll_ctl(efd, EPOLL_CTL_ADD, connfd, &tep);
				
				//新客户端加入失败
				if (res == -1)
					perr_exit("epoll_ctl");
				
			} 
			//红黑树上节点的值 != listenfd，说明有有客户端想要读/写数据
			else 
			{
				//客户端套接字
				sockfd = ep[i].data.fd;
				
				//读取缓存区数据到buf
				n = read(sockfd, buf, MAXLINE);
				
				//设置客户端终止条件（当发送数据为空时）
				if (n == 0) 
				{
					for (j = 0; j <= maxi; j++) 
					{
						if (client[j] == sockfd) 
						{
							client[j] = -1;
							break;
						}
					}
					res = epoll_ctl(efd, EPOLL_CTL_DEL, sockfd, NULL);
					if (res == -1)
						perr_exit("epoll_ctl");
					close(sockfd);
					printf("client[%d] closed connection\n", j);
				} 
				//给客户端发送答应数据（小写——>大写）
				else 
				{
					for (j = 0; j < n; j++)
						buf[j] = toupper(buf[j]);
					write(sockfd, buf, n);
				}
			}
		}
	}
	close(listenfd);
	close(efd);
	return 0;
}

epoll_client.c

/* client.c */
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>

#define MAXLINE 80
#define SERV_PORT 8000
int main(int argc, char *argv[]) 
{
	struct sockaddr_in servaddr;
	char buf[MAXLINE];
	int sockfd, n;
	sockfd = socket(AF_INET, SOCK_STREAM, 0);
	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);
	servaddr.sin_port = htons(SERV_PORT);
	
	//连接服务端
	connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
	
	//从终端输入数据
	while (fgets(buf, MAXLINE, stdin) != NULL) 
	{
		//发送数据
		write(sockfd, buf, strlen(buf));
		
		//接收服务端的答应数据
		n = read(sockfd, buf, MAXLINE);
		if (n == 0)
			printf("the other side has been closed.\n");
		else
			write(STDOUT_FILENO, buf, n);
	}
	close(sockfd);
	return 0;
}