Socket epoll non bloc mulitple sockets ...

#include <cstring>
#include <iostream>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>
#include <string>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <errno.h>

//#define IP "127.0.0.1"
#define IP "192.168.10.11"
#define PORT 3310
#define BUFFER_SIZE 1024
#define MAX_EVENTS 1

using namespace std;

int setNonBlocking(int fd) {
    int flags = fcntl(fd, F_GETFL, 0);
    if (flags == -1) return -1;
    return fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}

int main() {
    int clientSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (clientSocket == -1) {
        cerr << "Failed to create socket" << endl;
        return 1;
    }

    sockaddr_in serverAddress;
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(PORT);
    serverAddress.sin_addr.s_addr = inet_addr(IP);

    if (connect(clientSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) == -1) {
        if (errno != EINPROGRESS) {
            cerr << "Connection failed to " << IP << ":" << PORT << endl;
            close(clientSocket);
            return 1;
        }
    }

    if (setNonBlocking(clientSocket) == -1) {
        cerr << "Failed to set socket to non-blocking" << endl;
        close(clientSocket);
        return 1;
    }

    int epollfd = epoll_create1(0);
    if (epollfd == -1) {
        cerr << "Failed to create epoll file descriptor" << endl;
        close(clientSocket);
        return 1;
    }

    struct epoll_event ev, events[MAX_EVENTS];
    ev.events = EPOLLOUT | EPOLLIN;
    ev.data.fd = clientSocket;
    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, clientSocket, &ev) == -1) {
        cerr << "Failed to add file descriptor to epoll" << endl;
        close(epollfd);
        close(clientSocket);
        return 1;
    }

    const char* message = "PING\n";
    bool messageSent = false;
    char buffer[BUFFER_SIZE] = {0};
    int bytesReceived = 0;

    while (true) {
        int nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
        if (nfds == -1) {
            cerr << "epoll_wait failed" << endl;
            break;
        }

        for (int n = 0; n < nfds; ++n) {
            if (events[n].events & EPOLLOUT) {
                if (!messageSent) {
                    int bytesSent = send(clientSocket, message, strlen(message), 0);
                    if (bytesSent == -1) {
                        cerr << "Failed to send message" << endl;
                        goto cleanup;
                    }
                    cout << "Message sent: " << message;
                    messageSent = true;
                    ev.events = EPOLLIN;
                    epoll_ctl(epollfd, EPOLL_CTL_MOD, clientSocket, &ev);
                }
            } else if (events[n].events & EPOLLIN) {
                bytesReceived = recv(clientSocket, buffer, BUFFER_SIZE - 1, 0);
                if (bytesReceived == -1) {
                    if (errno != EAGAIN && errno != EWOULDBLOCK) {
                        cerr << "Failed to receive response" << endl;
                        goto cleanup;
                    }
                } else if (bytesReceived == 0) {
                    cout << "Server closed the connection" << endl;
                    goto cleanup;
                } else {
                    cout << "Response received: " << buffer << " , Bytes Rx: " << bytesReceived << endl;
                    goto cleanup;
                }
            }
        }
    }

cleanup:
    close(epollfd);
    close(clientSocket);
    return 0;
}