dns_cache.hpp

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/*
 * BastionGuard™
 * Copyright (C) 2025–2026 Calogero Scarnà
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * BastionGuard™ is a trademark of Calogero Scarnà.
 * The BastionGuard™ name and branding are not licensed under the GPL.
 */
 
#pragma once
#include <string>
#include <vector>
#include <unordered_map>
#include <mutex>
#include <chrono>
 
class DNSCache {
public:
    static DNSCache &instance();
 
    bool lookup(const std::string &host, std::vector<std::string> &out);
    std::string lookup_one(const std::string &host);
 
    void store(const std::string &host, const std::vector<std::string> &addrs, int ttl_seconds = -1);
    void set_default_ttl(int seconds);
    void clear();
 
    size_t size() const;
 
private:
    struct DNSResult {
        std::vector<std::string> addrs;
        std::chrono::steady_clock::time_point expires;
    };
 
    DNSCache() = default;
    DNSCache(const DNSCache&) = delete;
    DNSCache& operator=(const DNSCache&) = delete;
 
    mutable std::mutex mu_;
    std::unordered_map<std::string, DNSResult> map_;
    int default_ttl_ = 60;
};