An Epoll example -- server and client

/*
 * =====================================================================================
 *
 *       Filename:  tcp_server_epoll.c
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  10/25/2014 10:01:03 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Wei Yang (weiyang), weiyang.kernel@gmail.com
 *        Company:  
 *
 * =====================================================================================
 */

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

#define MAXEVENTS 64

static int socket_fd, epoll_fd;

static void socket_create_bind_local()
{
	struct sockaddr_in server_addr;
	int opt = 1;

        if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
            perror("Socket");
            exit(1);
        }

        if (setsockopt(socket_fd,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(int)) == -1) {
            perror("Setsockopt");
            exit(1);
        }
       
        server_addr.sin_family = AF_INET;        
        server_addr.sin_port = htons(5000);    
        server_addr.sin_addr.s_addr = INADDR_ANY;
        bzero(&(server_addr.sin_zero),8);

        if (bind(socket_fd, (struct sockaddr *)&server_addr, sizeof(struct sockaddr))
                                                                       == -1) {
            perror("Unable to bind");
            exit(1);
        }

}

static int make_socket_non_blocking(int sfd)
{
	int flags;

	flags = fcntl(sfd, F_GETFL, 0);
	if (flags == -1) {
		perror("fcntl");
		return -1;
	}

	flags |= O_NONBLOCK;
	if (fcntl(sfd, F_SETFL, flags) == -1) {
		perror("fcntl");
		return -1;
	}

	return 0;
}

void accept_and_add_new()
{
	struct epoll_event event;
	struct sockaddr in_addr;
	socklen_t in_len = sizeof(in_addr);
	int infd;
	char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];

	while ((infd = accept(socket_fd, &in_addr, &in_len)) != -1) {

		if (getnameinfo(&in_addr, in_len,
				hbuf, sizeof(hbuf),
				sbuf, sizeof(sbuf),
				NI_NUMERICHOST | NI_NUMERICHOST) == 0) {
			printf("Accepted connection on descriptor %d (host=%s, port=%s)\n",
					infd, hbuf, sbuf);
		}
		/* Make the incoming socket non-block
		 * and add it to list of fds to
		 * monitor*/
		if (make_socket_non_blocking(infd) == -1) {
			abort();
		}

		event.data.fd = infd;
		event.events = EPOLLIN | EPOLLET;
		if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, infd, &event) == -1) {
			perror("epoll_ctl");
			abort();
		}
		in_len = sizeof(in_addr);
	}

	if (errno != EAGAIN && errno != EWOULDBLOCK)
		perror("accept");
	/* else
	 *
	 * We hae processed all incomming connectioins
	 *
	 */
}

void process_new_data(int fd)
{
	ssize_t count;
	char buf[512];

	while ((count = read(fd, buf, sizeof(buf) - 1))) {
		if (count == -1) {
			/* EAGAIN, read all data */
			if (errno == EAGAIN)
				return;

			perror("read");
			break;
		}

		/* Write buffer to stdout */
		buf[count] = '\0';
		printf("%s \n", buf);
	}
	
	printf("Close connection on descriptor: %d\n", fd);
	close(fd);
}

int main()
{
	struct epoll_event event, *events;

	socket_create_bind_local();

	if (make_socket_non_blocking(socket_fd) == -1)
		exit(1);
       
        if (listen(socket_fd, 5) == -1) {
            perror("Listen");
            exit(1);
        }
  
	printf("\nTCPServer Waiting for client on port 5000\n");
        fflush(stdout);

	epoll_fd = epoll_create1(0);
	if (epoll_fd == -1) {
		perror("epoll_create1");
		exit(1);
	}

	event.data.fd = socket_fd;
	event.events = EPOLLIN | EPOLLET;
	if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, socket_fd, &event) == -1) {
		perror("epoll_ctl");
		exit(1);
	}

	events = calloc(MAXEVENTS, sizeof(event));

	while(1) {
		int n, i;
		n = epoll_wait(epoll_fd, events, MAXEVENTS, -1);
		for (i = 0; i < n; i++) {
			if (events[i].events & EPOLLERR || events[i].events & EPOLLHUP ||
			    !(events[i].events & EPOLLIN)) {
				/* An error on this fd or socket not ready */
				perror("epoll error");
				close(events[i].data.fd);
			} else if (events[i].data.fd == socket_fd) {
				/* New incoming connection */
				accept_and_add_new();
			} else {
				/* Data incoming on fd */
				process_new_data(events[i].data.fd);
			}
		}
	}

	free(events);
	close(socket_fd);
	return 0;
}
 
 
<pre name="code" class="cpp">/*
 * =====================================================================================
 *
 *       Filename:  tcp_client_epoll.c
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  10/25/2014 10:00:01 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Wei Yang (weiyang), weiyang.kernel@gmail.com
 *        Company:  
 *
 * =====================================================================================
 */
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>


int main()
{
	int sock; 
	char send_data[1024];
	struct hostent *host;
	struct sockaddr_in server_addr; 

	host = gethostbyname("127.0.0.1");

	if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
	    perror("Socket");
	    exit(1);
	}

	server_addr.sin_family = AF_INET;    
	server_addr.sin_port = htons(5000);  
	server_addr.sin_addr = *((struct in_addr *)host->h_addr);
	bzero(&(server_addr.sin_zero),8);

	if (connect(sock, (struct sockaddr *)&server_addr,
		    sizeof(struct sockaddr)) == -1)
	{
	    perror("Connect");
	    exit(1);
	}

	while(1) {
		printf("\nSEND (q or Q to quit) : ");
		gets(send_data);

		if (strcmp(send_data , "q") != 0 && strcmp(send_data , "Q") != 0)
			send(sock,send_data,strlen(send_data), 0);
		else
			break;
	}
	close(sock);
	return 0;
}
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