Inside Bitcoin

1// Copyright (c) 2023-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#include <test/util/random.h>
6
7#include <random.h>
8#include <uint256.h>
9#include <util/check.h>
10#include <util/log.h>
11
12#include <cstdlib>
13#include <iostream>
14
15std::atomic<bool> g_seeded_g_prng_zero{false};
16
17extern void MakeRandDeterministicDANGEROUS(const uint256& seed) noexcept;
18
19void SeedRandomStateForTest(SeedRand seedtype)
20{
21    constexpr auto RANDOM_CTX_SEED{"RANDOM_CTX_SEED"};
22
23    // Do this once, on the first call, regardless of seedtype, because once
24    // MakeRandDeterministicDANGEROUS is called, the output of GetRandHash is
25    // no longer truly random. It should be enough to get the seed once for the
26    // process.
27    static const auto g_ctx_seed = []() -> std::optional<uint256> {
28        if (EnableFuzzDeterminism()) return {};
29        // If RANDOM_CTX_SEED is set, use that as seed.
30        if (const char* num{std::getenv(RANDOM_CTX_SEED)}) {
31            if (auto num_parsed{uint256::FromUserHex(num)}) {
32                return *num_parsed;
33            } else {
34                std::cerr << RANDOM_CTX_SEED << " must consist of up to " << uint256::size() * 2 << " hex digits (\"0x\" prefix allowed), it was set to: '" << num << "'.\n";
35                std::abort();
36            }
37        }
38        // Otherwise use a (truly) random value.
39        return GetRandHash();
40    }();
41
42    g_seeded_g_prng_zero = seedtype == SeedRand::ZEROS;
43    if (EnableFuzzDeterminism()) {
44        Assert(g_seeded_g_prng_zero); // Only SeedRandomStateForTest(SeedRand::ZEROS) is allowed in fuzz tests
45        Assert(!g_used_g_prng);       // The global PRNG must not have been used before SeedRandomStateForTest(SeedRand::ZEROS)
46    }
47    const uint256& seed{seedtype == SeedRand::FIXED_SEED ? g_ctx_seed.value() : uint256::ZERO};
48    LogInfo("Setting random seed for current tests to %s=%s\n", RANDOM_CTX_SEED, seed.GetHex());
49    MakeRandDeterministicDANGEROUS(seed);
50}
51