pmtud_controller.h

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// BSD 3-Clause License
// Copyright (c) 2024, 🍀☀🌕🌥 🌊
// See the LICENSE file in the project root for full license information.
 
#pragma once
 
#include <chrono>
#include <cstddef>
#include <optional>
 
namespace kcenon::network::protocols::quic
{
 
enum class pmtud_state
{
    disabled,        
    base,            
    searching,       
    search_complete, 
    error,           
};
 
[[nodiscard]] auto pmtud_state_to_string(pmtud_state state) noexcept -> const char*;
 
struct pmtud_config
{
    size_t min_mtu = 1200;
 
    size_t max_probe_mtu = 1500;
 
    size_t probe_step = 32;
 
    std::chrono::seconds probe_timeout{3};
 
    size_t max_probes = 3;
 
    std::chrono::milliseconds probe_interval{1000};
 
    std::chrono::seconds confirmation_interval{600}; // 10 minutes
};
 
class pmtud_controller
{
public:
    pmtud_controller();
 
    explicit pmtud_controller(pmtud_config config);
 
    // ========================================================================
    // MTU Access
    // ========================================================================
 
    [[nodiscard]] auto current_mtu() const noexcept -> size_t
    {
        return current_mtu_;
    }
 
    [[nodiscard]] auto min_mtu() const noexcept -> size_t
    {
        return config_.min_mtu;
    }
 
    [[nodiscard]] auto max_mtu() const noexcept -> size_t
    {
        return config_.max_probe_mtu;
    }
 
    // ========================================================================
    // State Access
    // ========================================================================
 
    [[nodiscard]] auto state() const noexcept -> pmtud_state
    {
        return state_;
    }
 
    [[nodiscard]] auto is_enabled() const noexcept -> bool
    {
        return state_ != pmtud_state::disabled;
    }
 
    [[nodiscard]] auto is_search_complete() const noexcept -> bool
    {
        return state_ == pmtud_state::search_complete;
    }
 
    // ========================================================================
    // Control
    // ========================================================================
 
    void enable();
 
    void disable();
 
    void reset();
 
    // ========================================================================
    // Probing
    // ========================================================================
 
    [[nodiscard]] auto should_probe(
        std::chrono::steady_clock::time_point now) const noexcept -> bool;
 
    [[nodiscard]] auto probe_size() const noexcept -> std::optional<size_t>;
 
    void on_probe_sent(size_t size, std::chrono::steady_clock::time_point sent_time);
 
    void on_probe_acked(size_t size);
 
    void on_probe_lost(size_t size);
 
    // ========================================================================
    // ICMP Handling
    // ========================================================================
 
    void on_packet_too_big(size_t reported_mtu);
 
    // ========================================================================
    // Timers
    // ========================================================================
 
    [[nodiscard]] auto next_timeout() const noexcept
        -> std::optional<std::chrono::steady_clock::time_point>;
 
    void on_timeout(std::chrono::steady_clock::time_point now);
 
private:
    // ========================================================================
    // Private Methods
    // ========================================================================
 
    void start_search();
 
    [[nodiscard]] auto calculate_next_probe_size() const noexcept -> size_t;
 
    void complete_search();
 
    void handle_black_hole();
 
    // ========================================================================
    // Private Members
    // ========================================================================
 
    pmtud_config config_;
 
    pmtud_state state_{pmtud_state::disabled};
 
    size_t current_mtu_;
 
    size_t search_low_;
 
    size_t search_high_;
 
    size_t probing_mtu_{0};
 
    size_t probe_count_{0};
 
    size_t consecutive_failures_{0};
 
    std::chrono::steady_clock::time_point last_probe_time_;
 
    std::chrono::steady_clock::time_point search_complete_time_;
 
    bool probe_in_flight_{false};
 
    static constexpr size_t kBlackHoleThreshold = 6;
};
 
} // namespace kcenon::network::protocols::quic