#include <stdio.h> #include <stdlib.h> #include <string.h> #include <netdb.h> #include <netinet/in.h> #include <sys/types.h> #include <sys/socket.h> #include <arpa/inet.h> #include <fcntl.h> #include <sys/epoll.h> #include <sys/errno.h> #define PORT 4444 #define BACKLOG 5 #define MAX_FD 256 void setnonblocking(int); int main(int argc, char *argv[]) {     int sock_fd, new_fd, new_fd2, epfd, nfds;     struct sockaddr_in server_addr, client_addr;     int sin_size;     int nbytes;     int on = 1;     char buffer[1024];     struct epoll_event ev, events[20];     epfd = epoll_create(MAX_FD);     if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {         perror("socket");         exit(1);     }     setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));     setnonblocking(sock_fd);     ev.data.fd  = sock_fd;     ev.events   = EPOLLIN | EPOLLET;     epoll_ctl(epfd, EPOLL_CTL_ADD, sock_fd, &ev);     memset(&server_addr, 0, sizeof(struct sockaddr_in));     server_addr.sin_family      = AF_INET;     server_addr.sin_addr.s_addr = htonl(INADDR_ANY);     server_addr.sin_port        = htons(PORT);     if (bind(sock_fd, (struct sockaddr *)(&server_addr), sizeof(struct sockaddr)) == -1) {         perror("bind");         exit(1);     }     if (listen(sock_fd, BACKLOG) == -1) {         perror("listen");         exit(1);     }     printf("Server start... \n");     sin_size = sizeof(struct sockaddr_in);     int i;     while (1) {         nfds = epoll_wait(epfd, events, 20, 500);         for (i = 0; i < nfds; i++) {             if (events[i].data.fd == sock_fd) {                 if ((new_fd = accept(sock_fd, (struct sockaddr *)(&client_addr), &sin_size)) == -1) {                     perror("accept");                     exit(1);                 }                 printf("Server get connection from %s\n", inet_ntoa(client_addr.sin_addr));                 setnonblocking(new_fd);                 ev.data.fd = new_fd;                 ev.events = EPOLLIN | EPOLLET;                 epoll_ctl(epfd, EPOLL_CTL_ADD, new_fd, &ev);             } else if (events[i].events & EPOLLIN) {                 if ((new_fd2 = events[i].data.fd) < 0) continue;                 if ((nbytes = read(new_fd2, buffer, 1024)) == -1) {                     perror("read");                     exit(1);                 } else if (nbytes == 0) {                     close(new_fd2);                     events[i].data.fd = -1;                 }                 printf("Server read from %s\n", inet_ntoa(client_addr.sin_addr));                 ev.data.fd = new_fd2;                 ev.events = EPOLLOUT | EPOLLET;                 epoll_ctl(epfd, EPOLL_CTL_MOD, new_fd2, &ev);             } else if (events[i].events & EPOLLOUT) {                 new_fd2 = events[i].data.fd;                 write(new_fd2, "Server Received", 16);                 ev.data.fd = new_fd2;                 ev.events = EPOLLIN | EPOLLET;                 epoll_ctl(epfd, EPOLL_CTL_MOD, new_fd2, &ev);             }         }     }     return 0; } void setnonblocking(int fd) {     int opts;     if ((opts = fcntl(fd, F_GETFL)) < 0) {         perror("fcntl(fd, F_GETFL");         exit(1);     }     opts = opts | O_NONBLOCK;     if (fcntl(fd, F_SETFL, opts) < 0) {         perror("fcntl(fd, F_SETFL, opts");         exit(1);     } }

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <netdb.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #define PORT 4444 int main(int argc, char *argv[]) {     int sock_fd;     struct sockaddr_in server_addr;     struct hostent *host;     char buffer[1024];     if (argc < 2) {         perror("Need hostname");         exit(1);     }     if ((host = gethostbyname(argv[1])) == NULL) {         perror("gethostbyname");         exit(1);     }     if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {         perror("socket");         exit(1);     }     memset(&server_addr, 0, sizeof(struct sockaddr_in));     server_addr.sin_family  = AF_INET;     server_addr.sin_port    = htons(PORT);     server_addr.sin_addr    = *((struct in_addr *)host->h_addr);     if (connect(sock_fd, (struct sockaddr *)(&server_addr), sizeof(struct sockaddr)) == -1) {         perror("connect");         exit(1);     }     while (1) {         printf("Please input something:\n");         fgets(buffer, 1024, stdin);         write(sock_fd, buffer, strlen(buffer));         read(sock_fd, buffer, 1024);         printf("From server: %s\n", buffer);     }     close(sock_fd);     return 0; }