randapi.hpp

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//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012- OpenVPN Inc.
//
//    SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//
 
#pragma once
 
#include <cstdint>
#include <limits>
#include <string>
#include <type_traits>
 
#include <openvpn/common/size.hpp>
#include <openvpn/common/rc.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/random/randistrib.hpp>
 
namespace openvpn {
 
class RandomAPI : public RC<thread_unsafe_refcount>
{
  public:
    using Ptr = RCPtr<RandomAPI>;
 
    virtual std::string name() const = 0;
 
    virtual void rand_bytes(unsigned char *buf, size_t size) = 0;
 
    virtual bool rand_bytes_noexcept(unsigned char *buf, size_t size) = 0;
 
    template <typename T>
    void rand_fill(T &obj)
    {
        rand_bytes(reinterpret_cast<unsigned char *>(&obj), sizeof(T));
    }
 
    template <typename T>
    T rand_get()
    {
        T ret;
        rand_fill(ret);
        return ret;
    }
 
    template <typename T>
    T rand_get_positive()
    {
        T ret = rand_get<T>();
        if constexpr (std::is_signed_v<T>)
        {
            // maps (T:min, -1) to (0, T:max) which is fine for random generation
            ret &= std::numeric_limits<T>::max();
        }
        return ret;
    }
 
    template <typename T>
    T randrange(const T end)
    {
        return rand_get_positive<T>() % end;
    }
 
    template <typename T>
    T randrange(const T start, const T end)
    {
        if (start >= end)
            return start;
        return start + rand_get_positive<T>() % (end - start + 1);
    }
 
    std::uint32_t randrange32(const std::uint32_t end)
    {
        std::uint32_t r;
        rand_fill(r);
        return rand32_distribute(r, end);
    }
 
    std::uint32_t randrange32(const std::uint32_t start, const std::uint32_t end)
    {
        if (start >= end)
            return start;
        return start + randrange32(end - start + 1);
    }
 
    std::uint8_t randbyte()
    {
        std::uint8_t byte;
        rand_fill(byte);
        return byte;
    }
 
    bool randbool()
    {
        return bool(randbyte() & 1);
    }
 
    using result_type = unsigned int;
    static constexpr result_type min()
    {
        return result_type(0);
    }
    static constexpr result_type max()
    {
        return ~result_type(0);
    }
    result_type operator()()
    {
        return rand_get<result_type>();
    }
 
  private:
    friend class StrongRandomAPI;
    friend class WeakRandomAPI;
    RandomAPI() = default;
};
 
class StrongRandomAPI : public RandomAPI
{
  public:
    using Ptr = RCPtr<StrongRandomAPI>;
};
 
class WeakRandomAPI : public RandomAPI
{
  public:
    using Ptr = RCPtr<WeakRandomAPI>;
};
 
} // namespace openvpn