Repository: bitcoin/bitcoin
File: src/test/headers_sync_chainwork_tests.cpp (C++)

Code before:
// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <chain.h>
#include <chainparams.h>
#include <consensus/params.h>
#include <headerssync.h>
#include <pow.h>
#include <test/util/setup_common.h>
#include <validation.h>
#include <vector>

#include <boost/test/unit_test.hpp>

struct HeadersGeneratorSetup : public RegTestingSetup {
    /** Search for a nonce to meet (regtest) proof of work */
    void FindProofOfWork(CBlockHeader& starting_header);
    /**
     * Generate headers in a chain that build off a given starting hash, using
     * the given nVersion, advancing time by 1 second from the starting
     * prev_time, and with a fixed merkle root hash.
     */
    void GenerateHeaders(std::vector<CBlockHeader>& headers, size_t count,
            const uint256& starting_hash, const int nVersion, int prev_time,
            const uint256& merkle_root, const uint32_t nBits);
};

void HeadersGeneratorSetup::FindProofOfWork(CBlockHeader& starting_header)
{
    while (!CheckProofOfWork(starting_header.GetHash(), starting_header.nBits, Params().GetConsensus())) {
        ++(starting_header.nNonce);
    }
}

void HeadersGeneratorSetup::GenerateHeaders(std::vector<CBlockHeader>& headers,
        size_t count, const uint256& starting_hash, const int nVersion, int prev_time,
        const uint256& merkle_root, const uint32_t nBits)
{
    uint256 prev_hash = starting_hash;

    while (headers.size() < count) {
        headers.emplace_back();
        CBlockHeader& next_header = headers.back();;
        next_header.nVersion = nVersion;
        next_header.hashPrevBlock = prev_hash;
        next_header.hashMerkleRoot = merkle_root;
        next_header.nTime = prev_time+1;
        next_header.nBits = nBits;

        FindProofOfWork(next_header);
        prev_hash = next_header.GetHash();
        prev_time = next_header.nTime;
    }
    return;
}

BOOST_FIXTURE_TEST_SUITE(headers_sync_chainwork_tests, HeadersGeneratorSetup)

// In this test, we construct two sets of headers from genesis, one with
// sufficient proof of work and one without.
// 1. We deliver the first set of headers and verify that the headers sync state
//    updates to the REDOWNLOAD phase successfully.
// 2. Then we deliver the second set of headers and verify that they fail
//    processing (presumably due to commitments not matching).
// 3. Finally, we verify that repeating with the first set of headers in both
//    phases is successful.
BOOST_AUTO_TEST_CASE(headers_sync_state)
{
    std::vector<CBlockHeader> first_chain;
    std::vector<CBlockHeader> second_chain;

    std::unique_ptr<HeadersSyncState> hss;

    const int target_blocks = 15000;
    arith_uint256 chain_work = target_blocks*2;

    // Generate headers for two different chains (using differing merkle roots
    // to ensure the headers are different).
    GenerateHeaders(first_chain, target_blocks-1, Params().GenesisBlock().GetHash(),
            Params().GenesisBlock().nVersion, Params().GenesisBlock().nTime,
            ArithToUint256(0), Params().GenesisBlock().nBits);

    GenerateHeaders(second_chain, target_blocks-2, Params().GenesisBlock().GetHash(),
            Params().GenesisBlock().nVersion, Params().GenesisBlock().nTime,
            ArithToUint256(1), Params().GenesisBlock().nBits);

    const CBlockIndex* chain_start = WITH_LOCK(::cs_main, return m_node.chainman->m_blockman.LookupBlockIndex(Params().GenesisBlock().GetHash()));
    std::vector<CBlockHeader> headers_batch;

    // Feed the first chain to HeadersSyncState, by delivering 1 header
    // initially and then the rest.
    headers_batch.insert(headers_batch.end(), std::next(first_chain.begin()), first_chain.end());

    hss.reset(new HeadersSyncState(0, Params().GetConsensus(), chain_start, chain_work));
    (void)hss->ProcessNextHeaders({first_chain.front()}, true);
    // Pretend the first header is still "full", so we don't abort.
    auto result = hss->ProcessNextHeaders(headers_batch, true);

    // This chain should look valid, and we should have met the proof-of-work
    // requirement.
    BOOST_CHECK(result.success);
    BOOST_CHECK(result.request_more);
    BOOST_CHECK(hss->GetState() == HeadersSyncState::State::REDOWNLOAD);

    // Try to sneakily feed back the second chain.
    result = hss->ProcessNextHeaders(second_chain, true);
    BOOST_CHECK(!result.success); // foiled!
    BOOST_CHECK(hss->GetState() == HeadersSyncState::State::FINAL);

    // Now try again, this time feeding the first chain twice.
    hss.reset(new HeadersSyncState(0, Params().GetConsensus(), chain_start, chain_work));
    (void)hss->ProcessNextHeaders(first_chain, true);
    BOOST_CHECK(hss->GetState() == HeadersSyncState::State::REDOWNLOAD);

    result = hss->ProcessNextHeaders(first_chain, true);
    BOOST_CHECK(result.success);
    BOOST_CHECK(!result.request_more);
    // All headers should be ready for acceptance:
    BOOST_CHECK(result.pow_validated_headers.size() == first_chain.size());
    // Nothing left for the sync logic to do:
    BOOST_CHECK(hss->GetState() == HeadersSyncState::State::FINAL);

    // Finally, verify that just trying to process the second chain would not
    // succeed (too little work)
    hss.reset(new HeadersSyncState(0, Params().GetConsensus(), chain_start, chain_work));
    BOOST_CHECK(hss->GetState() == HeadersSyncState::State::PRESYNC);
     // Pretend just the first message is "full", so we don't abort.
    (void)hss->ProcessNextHeaders({second_chain.front()}, true);
    BOOST_CHECK(hss->GetState() == HeadersSyncState::State::PRESYNC);

    headers_batch.clear();
    headers_batch.insert(headers_batch.end(), std::next(second_chain.begin(), 1), second_chain.end());
    // Tell the sync logic that the headers message was not full, implying no
    // more headers can be requested. For a low-work-chain, this should causes
    // the sync to end with no headers for acceptance.
    result = hss->ProcessNextHeaders(headers_batch, false);
    BOOST_CHECK(hss->GetState() == HeadersSyncState::State::FINAL);
    BOOST_CHECK(result.pow_validated_headers.empty());
    BOOST_CHECK(!result.request_more);
    // Nevertheless, no validation errors should have been detected with the
    // chain:
    BOOST_CHECK(result.success);
}

BOOST_AUTO_TEST_SUITE_END()


Review comment (suggestion):
this comment is obvious from the code now: `/*exp_locator_hash=*/Params().GenesisBlock().GetHash()` or `/*exp_locator_hash=*/genesis_hash` later in 65a96b507c11b3f34efa996919892fa1a2fcf49c

Code after:
    const auto& second_chain{SecondChain()};

    // Feed the first chain to HeadersSyncState, by delivering 1 header
    // initially and then the rest.
    HeadersSyncState hss{CreateState()};

    // Just feed one header and check state.
    // Pretend the message is still "full", so we don't abort.
    CHECK_RESULT(hss.ProcessNextHeaders({{first_chain.front()}}, /*full_headers_message=*/true),
        hss, /*exp_state=*/State::PRESYNC,
        /*exp_success*/true, /*exp_request_more=*/true,
        /*exp_headers_size=*/0, /*exp_pow_validated_prev=*/std::nullopt,
        /*exp_locator_hash=*/first_chain.front().GetHash());

    // This chain should look valid, and we should have met the proof-of-work
    // requirement during PRESYNC and transitioned to REDOWNLOAD.
    CHECK_RESULT(hss.ProcessNextHeaders(std::span{first_chain}.subspan(1), true),
        hss, /*exp_state=*/State::REDOWNLOAD,
        /*exp_success*/true, /*exp_request_more=*/true,
        /*exp_headers_size=*/0, /*exp_pow_validated_prev=*/std::nullopt,
        /*exp_locator_hash=*/genesis.GetHash());

    // Below is the number of commitment bits that must randomly match between
    // the two chains for this test to spuriously fail. 1 / 2^25 =
    // 1 in 33'554'432 (somewhat less due to HeadersSyncState::m_commit_offset).
    static_assert(TARGET_BLOCKS / COMMITMENT_PERIOD == 25);

    // Try to sneakily feed back the second chain during REDOWNLOAD.
    CHECK_RESULT(hss.ProcessNextHeaders(second_chain, true),
        hss, /*exp_state=*/State::FINAL,
        /*exp_success*/false, // Foiled! We detected mismatching headers.
        /*exp_request_more=*/false,
        /*exp_headers_size=*/0, /*exp_pow_validated_prev=*/std::nullopt,
        /*exp_locator_hash=*/std::nullopt);
}

BOOST_AUTO_TEST_CASE(happy_path)
{
    const auto& first_chain{FirstChain()};

    // Headers message that moves us to the next state doesn't need to be full.
    for (const bool full_headers_message : {false, true}) {
        // This time we feed the first chain twice.
        HeadersSyncState hss{CreateState()};

        // Sufficient work transitions us from PRESYNC to REDOWNLOAD:
        const auto genesis_hash{genesis.GetHash()};
        CHECK_RESULT(hss.ProcessNextHeaders(first_chain, full_headers_message),
            hss, /*exp_state=*/State::REDOWNLOAD,
            /*exp_success*/true, /*exp_request_more=*/true,
            /*exp_headers_size=*/0, /*exp_pow_validated_prev=*/std::nullopt,