cpp_server/sockets/epoll.hpp

#pragma once

#include <sys/epoll.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <array>
#include <functional>

class EpollSocket {
public:
	using ConnectionHandler = std::function<void(int client_fd)>;
	using DataHandler = std::function<void(int client_fd)>;
	using DisconnectHandler = std::function<void(int client_fd)>;

	explicit EpollSocket(uint16_t port = 8080) : port_(port) {}

	~EpollSocket() {
		if (server_fd_ != -1) close(server_fd_);
		if (epoll_fd_ != -1) close(epoll_fd_);
	}

	bool start() {
		if (!create_server_socket()) return false;
		if (!create_epoll()) return false;
		if (!add_server_to_epoll()) return false;
		return true;
	}

	void run() {
		std::array<epoll_event, MAX_EVENTS> events;

		while (running_) {
			int num_events = epoll_wait(epoll_fd_, events.data(), MAX_EVENTS, -1);
			if (num_events == -1) break;

			for (int i = 0; i < num_events; ++i) {
				if (events[i].data.fd == server_fd_) {
					accept_connections();
				} else {
					handle_client_event(events[i].data.fd);
				}
			}
		}
	}

	void stop() { running_ = false; }

	bool add_client(int client_fd) {
		epoll_event event{};
		event.events = EPOLLIN | EPOLLET;
		event.data.fd = client_fd;

		return epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, client_fd, &event) != -1;
	}

	void remove_client(int client_fd) {
		epoll_ctl(epoll_fd_, EPOLL_CTL_DEL, client_fd, nullptr);
		close(client_fd);
	}

	// Event handlers
	void on_connection(ConnectionHandler handler) { on_connection_ = std::move(handler); }
	void on_data(DataHandler handler) { on_data_ = std::move(handler); }
	void on_disconnect(DisconnectHandler handler) { on_disconnect_ = std::move(handler); }

private:
	static constexpr int MAX_EVENTS = 1024;

	uint16_t port_;
	int server_fd_ = -1;
	int epoll_fd_ = -1;
	bool running_ = true;

	ConnectionHandler on_connection_;
	DataHandler on_data_;
	DisconnectHandler on_disconnect_;

	bool create_server_socket() {
		server_fd_ = socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);
		if (server_fd_ == -1) return false;

		int opt = 1;
		if (setsockopt(server_fd_, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) == -1) {
			return false;
		}

		// Enable port reuse for load balancing
		if (setsockopt(server_fd_, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt)) == -1) {
			return false;
		}

		// Disable Nagle's algorithm for lower latency
		if (setsockopt(server_fd_, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt)) == -1) {
			return false;
		}

		sockaddr_in addr{};
		addr.sin_family = AF_INET;
		addr.sin_addr.s_addr = INADDR_ANY;
		addr.sin_port = htons(port_);

		if (bind(server_fd_, reinterpret_cast<sockaddr*>(&addr), sizeof(addr)) == -1) {
			return false;
		}

		return listen(server_fd_, SOMAXCONN) != -1;
	}

	bool create_epoll() {
		epoll_fd_ = epoll_create1(EPOLL_CLOEXEC);
		return epoll_fd_ != -1;
	}

	bool add_server_to_epoll() {
		epoll_event event{};
		event.events = EPOLLIN | EPOLLET;
		event.data.fd = server_fd_;
		return epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, server_fd_, &event) != -1;
	}

	inline void accept_connections() {
		while (true) {
			sockaddr_in client_addr{};
			socklen_t client_len = sizeof(client_addr);

			// Use accept4 to set non-blocking atomically
			int client_fd = accept4(server_fd_,
				reinterpret_cast<sockaddr*>(&client_addr),
				&client_len,
				SOCK_NONBLOCK | SOCK_CLOEXEC);

			if (client_fd == -1) {
				if (errno == EAGAIN || errno == EWOULDBLOCK) break;
				continue;
			}

			// Set TCP_NODELAY for client connections
			int opt = 1;
			setsockopt(client_fd, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt));

			if (add_client(client_fd)) {
				if (on_connection_) on_connection_(client_fd);
			} else {
				close(client_fd);
			}
		}
	}

	inline void handle_client_event(int client_fd) {
		if (on_data_) on_data_(client_fd);
	}
};