rippled/src/xrpld/app/misc/NegativeUNLVote.cpp

#include <xrpld/app/misc/NegativeUNLVote.h>

#include <xrpld/app/consensus/RCLValidations.h>

#include <xrpl/basics/Log.h>
#include <xrpl/basics/UnorderedContainers.h>
#include <xrpl/basics/base_uint.h>
#include <xrpl/beast/utility/Journal.h>
#include <xrpl/beast/utility/instrumentation.h>
#include <xrpl/ledger/Ledger.h>
#include <xrpl/protocol/Indexes.h>
#include <xrpl/protocol/Protocol.h>
#include <xrpl/protocol/PublicKey.h>
#include <xrpl/protocol/SField.h>
#include <xrpl/protocol/STTx.h>
#include <xrpl/protocol/Serializer.h>
#include <xrpl/protocol/TxFormats.h>
#include <xrpl/protocol/UintTypes.h>
#include <xrpl/shamap/SHAMapItem.h>
#include <xrpl/shamap/SHAMapTreeNode.h>

#include <cmath>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <mutex>
#include <optional>
#include <vector>

namespace xrpl {

NegativeUNLVote::NegativeUNLVote(NodeID const& myId, beast::Journal j) : myId_(myId), j_(j)
{
}

void
NegativeUNLVote::doVoting(
    std::shared_ptr<Ledger const> const& prevLedger,
    hash_set<PublicKey> const& unlKeys,
    RCLValidations& validations,
    std::shared_ptr<SHAMap> const& initialSet)
{
    // Voting steps:
    // -- build a reliability score table of validators
    // -- process the table and find all candidates to disable or to re-enable
    // -- pick one to disable and one to re-enable if any
    // -- if found candidates, add ttUNL_MODIFY Tx

    // Build NodeID set for internal use.
    // Build NodeID to PublicKey map for lookup before creating ttUNL_MODIFY Tx.
    hash_set<NodeID> unlNodeIDs;
    hash_map<NodeID, PublicKey> nidToKeyMap;
    for (auto const& k : unlKeys)
    {
        auto nid = calcNodeID(k);
        nidToKeyMap.emplace(nid, k);
        unlNodeIDs.emplace(nid);
    }

    // Build a reliability score table of validators
    if (std::optional<hash_map<NodeID, std::uint32_t>> scoreTable =
            buildScoreTable(prevLedger, unlNodeIDs, validations))
    {
        // build next negUnl
        auto negUnlKeys = prevLedger->negativeUNL();
        auto negUnlToDisable = prevLedger->validatorToDisable();
        auto negUnlToReEnable = prevLedger->validatorToReEnable();
        if (negUnlToDisable)
            negUnlKeys.insert(*negUnlToDisable);
        if (negUnlToReEnable)
            negUnlKeys.erase(*negUnlToReEnable);

        hash_set<NodeID> negUnlNodeIDs;
        for (auto const& k : negUnlKeys)
        {
            auto nid = calcNodeID(k);
            negUnlNodeIDs.emplace(nid);
            if (!nidToKeyMap.contains(nid))
            {
                nidToKeyMap.emplace(nid, k);
            }
        }

        auto const seq = prevLedger->header().seq + 1;
        purgeNewValidators(seq);

        // Process the table and find all candidates to disable or to re-enable
        auto const candidates = findAllCandidates(unlNodeIDs, negUnlNodeIDs, *scoreTable);

        // Pick one to disable and one to re-enable if any, add ttUNL_MODIFY Tx
        if (!candidates.toDisableCandidates.empty())
        {
            auto n = choose(prevLedger->header().hash, candidates.toDisableCandidates);
            XRPL_ASSERT(
                nidToKeyMap.contains(n), "xrpl::NegativeUNLVote::doVoting : found node to disable");
            addTx(seq, nidToKeyMap.at(n), NegativeUNLModify::ToDisable, initialSet);
        }

        if (!candidates.toReEnableCandidates.empty())
        {
            auto n = choose(prevLedger->header().hash, candidates.toReEnableCandidates);
            XRPL_ASSERT(
                nidToKeyMap.contains(n), "xrpl::NegativeUNLVote::doVoting : found node to enable");
            addTx(seq, nidToKeyMap.at(n), NegativeUNLModify::ToReEnable, initialSet);
        }
    }
}

void
NegativeUNLVote::addTx(
    LedgerIndex seq,
    PublicKey const& vp,
    NegativeUNLModify modify,
    std::shared_ptr<SHAMap> const& initialSet)
{
    STTx const negUnlTx(ttUNL_MODIFY, [&](auto& obj) {
        obj.setFieldU8(sfUNLModifyDisabling, modify == NegativeUNLModify::ToDisable ? 1 : 0);
        obj.setFieldU32(sfLedgerSequence, seq);
        obj.setFieldVL(sfUNLModifyValidator, vp.slice());
    });

    Serializer s;
    negUnlTx.add(s);
    if (!initialSet->addGiveItem(
            SHAMapNodeType::TnTransactionNm,
            makeShamapitem(negUnlTx.getTransactionID(), s.slice())))
    {
        JLOG(j_.warn()) << "N-UNL: ledger seq=" << seq << ", add ttUNL_MODIFY tx failed";
    }
    else
    {
        JLOG(j_.debug()) << "N-UNL: ledger seq=" << seq
                         << ", add a ttUNL_MODIFY Tx with txID: " << negUnlTx.getTransactionID()
                         << ", the validator to "
                         << (modify == NegativeUNLModify::ToDisable ? "disable: " : "re-enable: ")
                         << vp;
    }
}

NodeID
NegativeUNLVote::choose(uint256 const& randomPadData, std::vector<NodeID> const& candidates)
{
    XRPL_ASSERT(!candidates.empty(), "xrpl::NegativeUNLVote::choose : non-empty input");
    static_assert(NodeID::kBytes <= uint256::kBytes);
    NodeID const randomPad = NodeID::fromVoid(randomPadData.data());
    NodeID txNodeID = candidates[0];
    for (int j = 1; j < candidates.size(); ++j)
    {
        if ((candidates[j] ^ randomPad) < (txNodeID ^ randomPad))
        {
            txNodeID = candidates[j];
        }
    }
    return txNodeID;
}

std::optional<hash_map<NodeID, std::uint32_t>>
NegativeUNLVote::buildScoreTable(
    std::shared_ptr<Ledger const> const& prevLedger,
    hash_set<NodeID> const& unl,
    RCLValidations& validations)
{
    // Find agreed validation messages received for
    // the last FLAG_LEDGER_INTERVAL (i.e. 256) ledgers,
    // for every validator, and fill the score table.

    // Ask the validation container to keep enough validation message history
    // for next time.
    auto const seq = prevLedger->header().seq + 1;
    validations.setSeqToKeep(seq - 1, seq + kFlagLedgerInterval);

    // Find FLAG_LEDGER_INTERVAL (i.e. 256) previous ledger hashes
    auto const hashIndex = prevLedger->read(keylet::skip());
    if (!hashIndex || !hashIndex->isFieldPresent(sfHashes))
    {
        JLOG(j_.debug()) << "N-UNL: ledger " << seq << " no history.";
        return {};
    }
    auto const ledgerAncestors = hashIndex->getFieldV256(sfHashes).value();
    auto const numAncestors = ledgerAncestors.size();
    if (numAncestors < kFlagLedgerInterval)
    {
        JLOG(j_.debug()) << "N-UNL: ledger " << seq << " not enough history. Can trace back only "
                         << numAncestors << " ledgers.";
        return {};
    }

    // have enough ledger ancestors, build the score table
    hash_map<NodeID, std::uint32_t> scoreTable;
    for (auto const& k : unl)
    {
        scoreTable[k] = 0;
    }

    // Query the validation container for every ledger hash and fill
    // the score table.
    for (int i = 0; i < kFlagLedgerInterval; ++i)
    {
        for (auto const& v :
             validations.getTrustedForLedger(ledgerAncestors[numAncestors - 1 - i], seq - 2 - i))
        {
            if (scoreTable.contains(v->getNodeID()))
                ++scoreTable[v->getNodeID()];
        }
    }

    // Return false if the validation message history or local node's
    // participation in the history is not good.
    auto const myValidationCount = [&]() -> std::uint32_t {
        if (auto const it = scoreTable.find(myId_); it != scoreTable.end())
            return it->second;
        return 0;
    }();
    if (myValidationCount < kNegativeUnlMinLocalValsToVote)
    {
        JLOG(j_.debug()) << "N-UNL: ledger " << seq << ". Local node only issued "
                         << myValidationCount << " validations in last " << kFlagLedgerInterval
                         << " ledgers."
                         << " The reliability measurement could be wrong.";
        return {};
    }
    if (myValidationCount > kNegativeUnlMinLocalValsToVote &&
        myValidationCount <= kFlagLedgerInterval)
    {
        return scoreTable;
    }

    // cannot happen because validations.getTrustedForLedger does not
    // return multiple validations of the same ledger from a validator.
    JLOG(j_.error()) << "N-UNL: ledger " << seq << ". Local node issued " << myValidationCount
                     << " validations in last " << kFlagLedgerInterval << " ledgers. Too many!";
    return {};
}

NegativeUNLVote::Candidates
NegativeUNLVote::findAllCandidates(
    hash_set<NodeID> const& unl,
    hash_set<NodeID> const& negUnl,
    hash_map<NodeID, std::uint32_t> const& scoreTable)
{
    // Compute if need to find more validators to disable
    auto const canAdd = [&]() -> bool {
        auto const maxNegativeListed =
            static_cast<std::size_t>(std::ceil(unl.size() * kNegativeUnlMaxListed));
        std::size_t negativeListed = 0;
        for (auto const& n : unl)
        {
            if (negUnl.contains(n))
                ++negativeListed;
        }
        bool const result = negativeListed < maxNegativeListed;
        JLOG(j_.trace()) << "N-UNL: nodeId " << myId_ << " lowWaterMark "
                         << kNegativeUnlLowWaterMark << " highWaterMark "
                         << kNegativeUnlHighWaterMark << " canAdd " << result << " negativeListed "
                         << negativeListed << " maxNegativeListed " << maxNegativeListed;
        return result;
    }();

    Candidates candidates;
    for (auto const& [nodeId, score] : scoreTable)
    {
        JLOG(j_.trace()) << "N-UNL: node " << nodeId << " score " << score;

        // Find toDisable Candidates: check if
        //  (1) canAdd,
        //  (2) has less than negativeUNLLowWaterMark validations,
        //  (3) is not in negUnl, and
        //  (4) is not a new validator.
        if (canAdd && score < kNegativeUnlLowWaterMark && !negUnl.contains(nodeId) &&
            !newValidators_.contains(nodeId))
        {
            JLOG(j_.trace()) << "N-UNL: toDisable candidate " << nodeId;
            candidates.toDisableCandidates.push_back(nodeId);
        }

        // Find toReEnable Candidates: check if
        //  (1) has more than negativeUNLHighWaterMark validations,
        //  (2) is in negUnl
        if (score > kNegativeUnlHighWaterMark && negUnl.contains(nodeId))
        {
            JLOG(j_.trace()) << "N-UNL: toReEnable candidate " << nodeId;
            candidates.toReEnableCandidates.push_back(nodeId);
        }
    }

    // If a negative UNL validator is removed from nodes' UNLs, it is no longer
    // a validator. It should be removed from the negative UNL too.
    // Note that even if it is still offline and in minority nodes' UNLs, it
    // will not be re-added to the negative UNL. Because the UNLModify Tx will
    // not be included in the agreed TxSet of a ledger.
    //
    // Find this kind of toReEnable Candidate if did not find any toReEnable
    // candidate yet: check if
    //  (1) is in negUnl
    //  (2) is not in unl.
    if (candidates.toReEnableCandidates.empty())
    {
        for (auto const& n : negUnl)
        {
            if (!unl.contains(n))
            {
                candidates.toReEnableCandidates.push_back(n);
            }
        }
    }
    return candidates;
}

void
NegativeUNLVote::newValidators(LedgerIndex seq, hash_set<NodeID> const& nowTrusted)
{
    std::scoped_lock const lock(mutex_);
    for (auto const& n : nowTrusted)
    {
        if (!newValidators_.contains(n))
        {
            JLOG(j_.trace()) << "N-UNL: add a new validator " << n << " at ledger seq=" << seq;
            newValidators_[n] = seq;
        }
    }
}

void
NegativeUNLVote::purgeNewValidators(LedgerIndex seq)
{
    std::scoped_lock const lock(mutex_);
    auto i = newValidators_.begin();
    while (i != newValidators_.end())
    {
        if (seq - i->second > kNewValidatorDisableSkip)
        {
            i = newValidators_.erase(i);
        }
        else
        {
            ++i;
        }
    }
}

}  // namespace xrpl