C language network programming standard steps of improved version

server.c

#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 %sn", 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 %sn", 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);
    }
}

client.c

#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: %sn", buffer);
    }
    close(sock_fd);

    return 0;
}