first commit: echo server

include/event/Epoll.hpp

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+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   Epoll.hpp                                          :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: acossari <acossari@student.codam.nl>       +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2026/08/26 11:34:23 by acossari          #+#    #+#             */
+/*   Updated: 2026/08/26 11:34:25 by acossari         ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+#pragma once
+
+#include <sys/epoll.h>
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <exception>
+#include <span>
+#include <string>
+
+#include "net/FileDescriptor.hpp"
+
+namespace webserv {
+
+class Epoll final {
+  public:
+    class Error : public std::exception {
+      public:
+        explicit Error(std::string message);
+        const char* what() const noexcept override;
+
+      private:
+        std::string msg_;
+    };
+
+    // wait() returns at most this many ready events per call. Smaller batches
+    // require more calls, while larger batches delay the next loop iteration.
+    // The value is a middle ground. Excess events remain for later calls.
+    static constexpr std::size_t EVENT_BATCH_CAPACITY = 256;
+
+    Epoll();
+
+    void add(int fd, std::uint32_t events, std::uint64_t token);
+    void modify(int fd, std::uint32_t events, std::uint64_t token);
+    void remove(int fd) noexcept;
+
+    std::span<const epoll_event> wait(int timeoutMillis);
+
+  private:
+    FileDescriptor fd_;
+    std::array<epoll_event, EVENT_BATCH_CAPACITY> events_{};
+};
+
+}  // namespace webserv

include/event/EventToken.hpp

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+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   EventToken.hpp                                     :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: acossari <acossari@student.codam.nl>       +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2026/08/25 13:26:42 by acossari          #+#    #+#             */
+/*   Updated: 2026/08/25 19:06:13 by acossari         ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+#pragma once
+
+#include <cstdint>
+
+namespace webserv {
+
+enum class EndpointKind {
+  ClientSocket,
+  CgiStdin,
+  CgiStdout,
+  Listener,
+};
+
+// Identifies which registered endpoint produced an epoll event without storing
+// a pointer. For Listener, index selects a listener; for every other kind it
+// selects a connection slot, while kind identifies its client socket or CGI
+// pipe. epoll_wait() returns a batch in which an old event may remain after its
+// endpoint has been retired and re-registered. generation distinguishes that
+// old registration from the current one even when index and kind are equal.
+//
+// Packed layout in epoll_event.data.u64:
+// bits  0-29 | index      | 30 bits
+// bits 30-31 | kind       |  2 bits
+// bits 32-63 | generation | 32 bits
+struct EventToken {
+    static constexpr std::uint64_t INDEX_BITS = 30;
+    static constexpr std::uint64_t KIND_BITS = 2;
+
+    // List-initialization gives 1 the exact std::uint32_t type before shifting.
+    // std::uint32_t{1} << INDEX_BITS       = 1,073,741,824
+    // (std::uint32_t{1} << INDEX_BITS) - 1 = 1,073,741,823
+    // Binary: 100...000 (30 zeros) - 1 = 011...111 (30 ones).
+    static constexpr std::uint32_t MAX_INDEX =
+        (std::uint32_t{1} << INDEX_BITS) - 1;
+
+    std::uint32_t index;
+    EndpointKind kind;
+    std::uint32_t generation;
+};
+
+std::uint64_t pack(EventToken token);
+EventToken unpack(std::uint64_t token);
+
+}  // namespace webserv