Client.cpp

// Aleth: Ethereum C++ client, tools and libraries.
// Copyright 2014-2019 Aleth Authors.
// Licensed under the GNU General Public License, Version 3.

#include "Client.h"
#include "Block.h"
#include "EthereumCapability.h"
#include "Executive.h"
#include "SnapshotStorage.h"
#include "TransactionQueue.h"
#include <libdevcore/DBFactory.h>
#include <libdevcore/Log.h>
#include <libp2p/Host.h>
#include <boost/filesystem.hpp>
#include <chrono>
#include <memory>
#include <thread>

using namespace std;
using namespace dev;
using namespace dev::eth;
using namespace p2p;
namespace fs = boost::filesystem;

static_assert(BOOST_VERSION >= 106400, "Wrong boost headers version");

namespace
{
constexpr unsigned c_syncMinBlockCount = 1;
constexpr unsigned c_syncMaxBlockCount = 1000;
constexpr double c_targetDurationS = 1;

std::string filtersToString(h256Hash const& _fs)
{
    std::stringstream str;
    str << "{";
    unsigned i = 0;
    for (h256 const& f : _fs)
    {
        str << (i++ ? ", " : "");
        if (f == PendingChangedFilter)
            str << "pending";
        else if (f == ChainChangedFilter)
            str << "chain";
        else
            str << f;
    }
    str << "}";
    return str.str();
}
}  // namespace

std::ostream& dev::eth::operator<<(std::ostream& _out, ActivityReport const& _r)
{
    _out << "Since " << toString(_r.since) << " (" << std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now() - _r.since).count();
    _out << "): " << _r.ticks << "ticks";
    return _out;
}

Client::Client(ChainParams const& _params, int _networkID, p2p::Host& _host,
    std::shared_ptr<GasPricer> _gpForAdoption, fs::path const& _dbPath,
    fs::path const& _snapshotPath, WithExisting _forceAction, TransactionQueue::Limits const& _l)
  : Worker("eth", 0),
    m_bc(_params, _dbPath, _forceAction,
        [](unsigned d, unsigned t) {
            std::cerr << "REVISING BLOCKCHAIN: Processed " << d << " of " << t << "...\r";
        }),
    m_tq(_l),
    m_gp(_gpForAdoption ? _gpForAdoption : make_shared<TrivialGasPricer>()),
    m_preSeal(chainParams().accountStartNonce),
    m_postSeal(chainParams().accountStartNonce),
    m_working(chainParams().accountStartNonce)
{
    init(_host, _dbPath, _snapshotPath, _forceAction, _networkID);
}

Client::~Client()
{
    m_signalled.notify_all(); // to wake up the thread from Client::doWork()
    stopWorking();
    terminate();
}

void Client::init(p2p::Host& _extNet, fs::path const& _dbPath,
    fs::path const& _snapshotDownloadPath, WithExisting _forceAction, u256 _networkId)
{
    DEV_TIMED_FUNCTION_ABOVE(500);

    // Cannot be opened until after blockchain is open, since BlockChain may upgrade the database.
    // TODO: consider returning the upgrade mechanism here. will delaying the opening of the blockchain database
    // until after the construction.
    m_stateDB = State::openDB(_dbPath, bc().genesisHash(), _forceAction);
    // LAZY. TODO: move genesis state construction/commiting to stateDB openning and have this just take the root from the genesis block.
    m_preSeal = bc().genesisBlock(m_stateDB);
    m_postSeal = m_preSeal;

    m_bq.setChain(bc());

    m_lastGetWork = std::chrono::system_clock::now() - chrono::seconds(30);
    m_tqReady = m_tq.onReady([=]() {
        this->onTransactionQueueReady();
    });  // TODO: should read m_tq->onReady(thisThread, syncTransactionQueue);
    m_tqReplaced = m_tq.onReplaced([=](h256 const&) { m_needStateReset = true; });
    m_bqReady = m_bq.onReady([=]() {
        this->onBlockQueueReady();
    });  // TODO: should read m_bq->onReady(thisThread, syncBlockQueue);
    m_bq.setOnBad([=](Exception& ex) { this->onBadBlock(ex); });
    bc().setOnBad([=](Exception& ex) { this->onBadBlock(ex); });
    bc().setOnBlockImport([=](BlockHeader const& _info) {
        if (auto h = m_host.lock())
            h->onBlockImported(_info);
    });

    if (_forceAction == WithExisting::Rescue)
        bc().rescue(m_stateDB);

    m_gp->update(bc());

    // create Ethereum capability only if we're not downloading the snapshot
    if (_snapshotDownloadPath.empty())
    {
        auto ethCapability = make_shared<EthereumCapability>(
            _extNet.capabilityHost(), bc(), m_stateDB, m_tq, m_bq, _networkId);
        _extNet.registerCapability(ethCapability);
        m_host = ethCapability;
    }

    // create Warp capability if we either download snapshot or can give out snapshot
    auto const importedSnapshot = importedSnapshotPath(_dbPath, bc().genesisHash());
    bool const importedSnapshotExists = fs::exists(importedSnapshot);
    if (!_snapshotDownloadPath.empty() || importedSnapshotExists)
    {
        std::shared_ptr<SnapshotStorageFace> snapshotStorage(
            importedSnapshotExists ? createSnapshotStorage(importedSnapshot) : nullptr);
        auto warpCapability = make_shared<WarpCapability>(
            _extNet.capabilityHost(), bc(), _networkId, _snapshotDownloadPath, snapshotStorage);
        _extNet.registerCapability(warpCapability);
        m_warpHost = warpCapability;
    }

    doWork(false);
}

ImportResult Client::queueBlock(bytes const& _block, bool _isSafe)
{
    if (m_bq.status().verified + m_bq.status().verifying + m_bq.status().unverified > 10000)
        this_thread::sleep_for(std::chrono::milliseconds(500));
    return m_bq.import(&_block, _isSafe);
}

tuple<ImportRoute, bool, unsigned> Client::syncQueue(unsigned _max)
{
    stopWorking();
    return bc().sync(m_bq, m_stateDB, _max);
}

void Client::onBadBlock(Exception& _ex) const
{
    // BAD BLOCK!!!
    bytes const* block = boost::get_error_info<errinfo_block>(_ex);
    if (!block)
    {
        cwarn << "ODD: onBadBlock called but exception (" << _ex.what() << ") has no block in it.";
        cwarn << boost::diagnostic_information(_ex);
        return;
    }

    badBlock(*block, _ex.what());
}

void Client::callQueuedFunctions()
{
    while (true)
    {
        function<void()> f;
        DEV_WRITE_GUARDED(x_functionQueue)
            if (!m_functionQueue.empty())
            {
                f = m_functionQueue.front();
                m_functionQueue.pop();
            }
        if (f)
            f();
        else
            break;
    }
}

u256 Client::networkId() const
{
    if (auto h = m_host.lock())
        return h->networkId();
    return 0;
}

void Client::setNetworkId(u256 const& _n)
{
    if (auto h = m_host.lock())
        h->setNetworkId(_n);
}

bool Client::isSyncing() const
{
    if (auto h = m_host.lock())
        return h->isSyncing();
    return false;
}

bool Client::isMajorSyncing() const
{
    if (auto h = m_host.lock())
    {
        SyncState state = h->status().state;
        return state != SyncState::Idle || h->bq().items().first > 10;
    }
    return false;
}

void Client::startedWorking()
{
    // Synchronise the state according to the head of the block chain.
    // TODO: currently it contains keys for *all* blocks. Make it remove old ones.
    LOG(m_loggerDetail) << "startedWorking()";

    DEV_WRITE_GUARDED(x_preSeal)
        m_preSeal.sync(bc());
    DEV_READ_GUARDED(x_preSeal)
    {
        DEV_WRITE_GUARDED(x_working)
            m_working = m_preSeal;
        DEV_WRITE_GUARDED(x_postSeal)
            m_postSeal = m_preSeal;
    }
}

void Client::doneWorking()
{
    // Synchronise the state according to the head of the block chain.
    // TODO: currently it contains keys for *all* blocks. Make it remove old ones.
    DEV_WRITE_GUARDED(x_preSeal)
        m_preSeal.sync(bc());
    DEV_READ_GUARDED(x_preSeal)
    {
        DEV_WRITE_GUARDED(x_working)
            m_working = m_preSeal;
        DEV_WRITE_GUARDED(x_postSeal)
            m_postSeal = m_preSeal;
    }
}

void Client::reopenChain(WithExisting _we)
{
    reopenChain(bc().chainParams(), _we);
}

void Client::reopenChain(ChainParams const& _p, WithExisting _we)
{
    m_signalled.notify_all(); // to wake up the thread from Client::doWork()
    bool wasSealing = wouldSeal();
    if (wasSealing)
        stopSealing();
    stopWorking();

    m_tq.clear();
    m_bq.clear();
    sealEngine()->cancelGeneration();

    {
        WriteGuard l(x_postSeal);
        WriteGuard l2(x_preSeal);
        WriteGuard l3(x_working);

        m_preSeal = Block(chainParams().accountStartNonce);
        m_postSeal = Block(chainParams().accountStartNonce);
        m_working = Block(chainParams().accountStartNonce);

        m_stateDB = OverlayDB();
        bc().reopen(_p, _we);
        m_stateDB = State::openDB(db::databasePath(), bc().genesisHash(), _we);

        m_preSeal = bc().genesisBlock(m_stateDB);
        m_preSeal.setAuthor(_p.author);
        m_postSeal = m_preSeal;
        m_working = Block(chainParams().accountStartNonce);
    }

    if (auto h = m_host.lock())
        h->reset();

    startedWorking();
    doWork();

    startWorking();
    if (wasSealing)
        startSealing();
}

void Client::executeInMainThread(function<void ()> const& _function)
{
    DEV_WRITE_GUARDED(x_functionQueue)
        m_functionQueue.push(_function);
    m_signalled.notify_all();
}

void Client::clearPending()
{
    DEV_WRITE_GUARDED(x_postSeal)
    {
        if (!m_postSeal.pending().size())
            return;
        m_tq.clear();
        DEV_READ_GUARDED(x_preSeal)
            m_postSeal = m_preSeal;
    }

    startSealing();
    h256Hash changeds;
    noteChanged(changeds);
}

void Client::appendFromNewPending(TransactionReceipt const& _receipt, h256Hash& io_changed, h256 _sha3)
{
    Guard l(x_filtersWatches);
    io_changed.insert(PendingChangedFilter);
    m_specialFilters.at(PendingChangedFilter).push_back(_sha3);
    for (pair<h256 const, InstalledFilter>& i: m_filters)
    {
        // acceptable number.
        auto m = i.second.filter.matches(_receipt);
        if (m.size())
        {
            // filter catches them
            for (LogEntry const& l: m)
                i.second.changes.push_back(LocalisedLogEntry(l));
            io_changed.insert(i.first);
        }
    }
}

void Client::appendFromBlock(h256 const& _block, BlockPolarity _polarity, h256Hash& io_changed)
{
    // TODO: more precise check on whether the txs match.
    auto receipts = bc().receipts(_block).receipts;

    Guard l(x_filtersWatches);
    io_changed.insert(ChainChangedFilter);
    m_specialFilters.at(ChainChangedFilter).push_back(_block);
    for (pair<h256 const, InstalledFilter>& i: m_filters)
    {
        // acceptable number & looks like block may contain a matching log entry.
        for (size_t j = 0; j < receipts.size(); j++)
        {
            auto tr = receipts[j];
            auto m = i.second.filter.matches(tr);
            if (m.size())
            {
                auto transactionHash = transaction(_block, j).sha3();
                // filter catches them
                for (LogEntry const& l: m)
                    i.second.changes.push_back(LocalisedLogEntry(l, _block, (BlockNumber)bc().number(_block), transactionHash, j, 0, _polarity));
                io_changed.insert(i.first);
            }
        }
    }
}

void Client::syncBlockQueue()
{
//  cdebug << "syncBlockQueue()";

    ImportRoute ir;
    h256s badBlockHashes;
    unsigned count;
    Timer t;

    // The verified blocks list needs to be a shared_ptr since we propagate them on the network
    // thread and import them into our local chain on the client thread.
    std::shared_ptr<VerifiedBlocks> verifiedBlocks = std::make_shared<VerifiedBlocks>();
    m_bq.drain(*verifiedBlocks, m_syncAmount);

    // Propagate new blocks to peers before importing them into the chain.
    auto h = m_host.lock();
    assert(h);  // capability is owned by Host and should be available for the duration of the
                // Client's lifetime
    h->propagateNewBlocks(verifiedBlocks);

    std::tie(ir, badBlockHashes, count) = bc().sync(*verifiedBlocks, m_stateDB);
    m_syncBlockQueue = m_bq.doneDrain(badBlockHashes);

    double elapsed = t.elapsed();

    if (count)
    {
        LOG(m_logger) << count << " blocks imported in " << unsigned(elapsed * 1000) << " ms ("
                      << (count / elapsed) << " blocks/s) in #" << bc().number();
    }

    if (elapsed > c_targetDurationS * 1.1 && count > c_syncMinBlockCount)
        m_syncAmount = max(c_syncMinBlockCount, count * 9 / 10);
    else if (count == m_syncAmount && elapsed < c_targetDurationS * 0.9 && m_syncAmount < c_syncMaxBlockCount)
        m_syncAmount = min(c_syncMaxBlockCount, m_syncAmount * 11 / 10 + 1);
    if (ir.liveBlocks.empty())
        return;
    onChainChanged(ir);
}

void Client::syncTransactionQueue()
{
    resyncStateFromChain();

    Timer timer;

    h256Hash changeds;
    TransactionReceipts newPendingReceipts;

    DEV_WRITE_GUARDED(x_working)
    {
        if (m_working.isSealed())
        {
            ctrace << "Skipping txq sync for a sealed block.";
            return;
        }

        tie(newPendingReceipts, m_syncTransactionQueue) = m_working.sync(bc(), m_tq, *m_gp);
    }

    if (newPendingReceipts.empty())
    {
        auto s = m_tq.status();
        ctrace << "No transactions to process. " << m_working.pending().size() << " pending, " << s.current << " queued, " << s.future << " future, " << s.unverified << " unverified";
        return;
    }

    DEV_READ_GUARDED(x_working)
        DEV_WRITE_GUARDED(x_postSeal)
            m_postSeal = m_working;

    DEV_READ_GUARDED(x_postSeal)
        for (size_t i = 0; i < newPendingReceipts.size(); i++)
            appendFromNewPending(newPendingReceipts[i], changeds, m_postSeal.pending()[i].sha3());

    // Tell farm about new transaction (i.e. restart mining).
    onPostStateChanged();

    // Tell watches about the new transactions.
    noteChanged(changeds);

    // Tell network about the new transactions.
    if (auto h = m_host.lock())
        h->noteNewTransactions();

    ctrace << "Processed " << newPendingReceipts.size() << " transactions in" << (timer.elapsed() * 1000) << "(" << (bool)m_syncTransactionQueue << ")";
}

void Client::onDeadBlocks(h256s const& _blocks, h256Hash& io_changed)
{
    // insert transactions that we are declaring the dead part of the chain
    for (auto const& h: _blocks)
    {
        LOG(m_loggerDetail) << "Dead block: " << h;
        for (auto const& t: bc().transactions(h))
        {
            LOG(m_loggerDetail) << "Resubmitting dead-block transaction "
                                << Transaction(t, CheckTransaction::None);
            ctrace << "Resubmitting dead-block transaction " << Transaction(t, CheckTransaction::None);
            m_tq.import(t, IfDropped::Retry);
        }
    }

    for (auto const& h: _blocks)
        appendFromBlock(h, BlockPolarity::Dead, io_changed);
}

void Client::onNewBlocks(h256s const& _blocks, h256Hash& io_changed)
{
    // remove transactions from m_tq nicely rather than relying on out of date nonce later on.
    for (auto const& h: _blocks)
        LOG(m_loggerDetail) << "Live block: " << h;

    if (auto h = m_host.lock())
        h->noteNewBlocks();

    for (auto const& h: _blocks)
        appendFromBlock(h, BlockPolarity::Live, io_changed);
}

void Client::resyncStateFromChain()
{
    DEV_READ_GUARDED(x_working)
        if (bc().currentHash() == m_working.info().parentHash())
            return;

    restartMining();
}

void Client::restartMining()
{
    bool preChanged = false;
    Block newPreMine(chainParams().accountStartNonce);
    DEV_READ_GUARDED(x_preSeal)
        newPreMine = m_preSeal;

    // TODO: use m_postSeal to avoid re-evaluating our own blocks.
    preChanged = newPreMine.sync(bc());

    DEV_READ_GUARDED(x_preSeal) DEV_READ_GUARDED(x_postSeal)
            if (!preChanged && m_preSeal.author() == m_postSeal.author())
    {
        onTransactionQueueReady();
        return;
    }

    DEV_WRITE_GUARDED(x_preSeal)
        m_preSeal = newPreMine;
    DEV_WRITE_GUARDED(x_working)
        m_working = newPreMine;
    DEV_READ_GUARDED(x_postSeal)
        if (!m_postSeal.isSealed() || m_postSeal.info().hash() != newPreMine.info().parentHash())
            for (auto const& t : m_postSeal.pending())
            {
                LOG(m_loggerDetail) << "Resubmitting post-seal transaction " << t;
                //                      ctrace << "Resubmitting post-seal transaction " << t;
                auto ir = m_tq.import(t, IfDropped::Retry);
                if (ir != ImportResult::Success)
                    onTransactionQueueReady();
            }
    DEV_READ_GUARDED(x_working) DEV_WRITE_GUARDED(x_postSeal)
        m_postSeal = m_working;

    onPostStateChanged();

    // Quick hack for now - the TQ at this point already has the prior pending transactions in it;
    // we should resync with it manually until we are stricter about what constitutes "knowing".
    onTransactionQueueReady();
}

void Client::resetState()
{
    Block newPreMine(chainParams().accountStartNonce);
    DEV_READ_GUARDED(x_preSeal)
        newPreMine = m_preSeal;

    DEV_WRITE_GUARDED(x_working)
        m_working = newPreMine;
    DEV_READ_GUARDED(x_working) DEV_WRITE_GUARDED(x_postSeal)
        m_postSeal = m_working;

    onPostStateChanged();
    onTransactionQueueReady();
}

void Client::onChainChanged(ImportRoute const& _ir)
{
//  ctrace << "onChainChanged()";
    h256Hash changeds;
    onDeadBlocks(_ir.deadBlocks, changeds);
    vector<h256> goodTransactions;
    goodTransactions.reserve(_ir.goodTransactions.size());
    for (auto const& t: _ir.goodTransactions)
    {
        LOG(m_loggerDetail) << "Safely dropping transaction " << t.sha3();
        m_tq.dropGood(t);
        goodTransactions.push_back(t.sha3());
    }
    auto h = m_host.lock();
    if (h)
        h->removeSentTransactions(goodTransactions);
    onNewBlocks(_ir.liveBlocks, changeds);
    if (!isMajorSyncing())
        resyncStateFromChain();
    noteChanged(changeds);
    m_onChainChanged(_ir.deadBlocks, _ir.liveBlocks);
}

bool Client::remoteActive() const
{
    return chrono::system_clock::now() - m_lastGetWork < chrono::seconds(30);
}

void Client::onPostStateChanged()
{
    LOG(m_loggerDetail) << "Post state changed.";
    m_signalled.notify_all();
    m_remoteWorking = false;
}

void Client::startSealing()
{
    if (m_wouldSeal == true)
        return;
    LOG(m_logger) << "Mining Beneficiary: " << author();
    if (author())
    {
        m_wouldSeal = true;
        m_signalled.notify_all();
    }
    else
        LOG(m_logger) << "You need to set an author in order to seal!";
}

void Client::rejigSealing()
{
    if ((wouldSeal() || remoteActive()) && !isMajorSyncing())
    {
        if (sealEngine()->shouldSeal(this))
        {
            m_wouldButShouldnot = false;

            LOG(m_loggerDetail) << "Rejigging seal engine...";
            DEV_WRITE_GUARDED(x_working)
            {
                if (m_working.isSealed())
                {
                    LOG(m_logger) << "Tried to seal sealed block...";
                    return;
                }
                // TODO is that needed? we have "Generating seal on" below
                LOG(m_loggerDetail) << "Starting to seal block #" << m_working.info().number();
                m_working.commitToSeal(bc(), m_extraData);
            }
            DEV_READ_GUARDED(x_working)
            {
                DEV_WRITE_GUARDED(x_postSeal)
                    m_postSeal = m_working;
                m_sealingInfo = m_working.info();
            }

            if (wouldSeal())
            {
                sealEngine()->onSealGenerated([=](bytes const& _header) {
                    LOG(m_logger) << "Block sealed #" << BlockHeader(_header, HeaderData).number();
                    if (this->submitSealed(_header))
                        m_onBlockSealed(_header);
                    else
                        LOG(m_logger) << "Submitting block failed...";
                });
                ctrace << "Generating seal on " << m_sealingInfo.hash(WithoutSeal) << " #" << m_sealingInfo.number();
                sealEngine()->generateSeal(m_sealingInfo);
            }
        }
        else
            m_wouldButShouldnot = true;
    }
    if (!m_wouldSeal)
        sealEngine()->cancelGeneration();
}

void Client::noteChanged(h256Hash const& _filters)
{
    Guard l(x_filtersWatches);
    if (_filters.size())
        LOG(m_loggerWatch) << "noteChanged: " << filtersToString(_filters);
    // accrue all changes left in each filter into the watches.
    for (auto& w: m_watches)
        if (_filters.count(w.second.id))
        {
            if (m_filters.count(w.second.id))
            {
                LOG(m_loggerWatch) << "!!! " << w.first << " " << w.second.id.abridged();
                w.second.changes += m_filters.at(w.second.id).changes;
            }
            else if (m_specialFilters.count(w.second.id))
                for (h256 const& hash: m_specialFilters.at(w.second.id))
                {
                    LOG(m_loggerWatch)
                        << "!!! " << w.first << " "
                        << (w.second.id == PendingChangedFilter ?
                                   "pending" :
                                   w.second.id == ChainChangedFilter ? "chain" : "???");
                    w.second.changes.push_back(LocalisedLogEntry(SpecialLogEntry, hash));
                }
        }
    // clear the filters now.
    for (auto& i: m_filters)
        i.second.changes.clear();
    for (auto& i: m_specialFilters)
        i.second.clear();
}

void Client::doWork(bool _doWait)
{
    bool t = true;
    if (m_syncBlockQueue.compare_exchange_strong(t, false))
        syncBlockQueue();

    if (m_needStateReset)
    {
        resetState();
        m_needStateReset = false;
    }

    t = true;
    bool isSealed = false;
    DEV_READ_GUARDED(x_working)
        isSealed = m_working.isSealed();
    if (!isSealed && !isMajorSyncing() && !m_remoteWorking && m_syncTransactionQueue.compare_exchange_strong(t, false))
        syncTransactionQueue();

    tick();

    rejigSealing();

    callQueuedFunctions();

    DEV_READ_GUARDED(x_working)
        isSealed = m_working.isSealed();
    // If the block is sealed, we have to wait for it to tickle through the block queue
    // (which only signals as wanting to be synced if it is ready).
    if (!m_syncBlockQueue && !m_syncTransactionQueue && (_doWait || isSealed) && isWorking())
    {
        std::unique_lock<std::mutex> l(x_signalled);
        m_signalled.wait_for(l, chrono::seconds(1));
    }
}

void Client::tick()
{
    if (chrono::system_clock::now() - m_lastTick > chrono::seconds(1))
    {
        m_report.ticks++;
        checkWatchGarbage();
        m_bq.tick();
        m_lastTick = chrono::system_clock::now();
        if (m_report.ticks == 15)
            LOG(m_loggerDetail) << activityReport();
    }
}

void Client::checkWatchGarbage()
{
    if (chrono::system_clock::now() - m_lastGarbageCollection > chrono::seconds(5))
    {
        // watches garbage collection
        vector<unsigned> toUninstall;
        DEV_GUARDED(x_filtersWatches)
            for (auto key: keysOf(m_watches))
                if (m_watches[key].lastPoll != chrono::system_clock::time_point::max() && chrono::system_clock::now() - m_watches[key].lastPoll > chrono::seconds(20))
                {
                    toUninstall.push_back(key);
                    LOG(m_loggerDetail)
                        << "GC: Uninstall " << key << " ("
                        << chrono::duration_cast<chrono::seconds>(
                               chrono::system_clock::now() - m_watches[key].lastPoll)
                               .count()
                        << " s old)";
                }
        for (auto i: toUninstall)
            uninstallWatch(i);

        // blockchain GC
        bc().garbageCollect();

        m_lastGarbageCollection = chrono::system_clock::now();
    }
}

void Client::prepareForTransaction()
{
    startWorking();
}

Block Client::block(h256 const& _blockHash) const
{
    try
    {
        Block ret{bc(), m_stateDB};
        ret.populateFromChain(bc(), _blockHash);
        return ret;
    }
    catch (Exception& ex)
    {
        ex << errinfo_block(bc().block(_blockHash));
        onBadBlock(ex);
        return Block{bc()};
    }
}

void Client::flushTransactions()
{
    doWork(false);
}

Transactions Client::pending() const
{
    return m_tq.topTransactions(m_tq.status().current);
}

SyncStatus Client::syncStatus() const
{
    auto h = m_host.lock();
    if (!h)
        return SyncStatus();
    SyncStatus status = h->status();
    status.majorSyncing = isMajorSyncing();
    return status;
}

TransactionSkeleton Client::populateTransactionWithDefaults(TransactionSkeleton const& _t) const
{
    TransactionSkeleton ret(_t);

    // Default gas value meets the intrinsic gas requirements of both
    // send value and create contract transactions and is the same default
    // value used by geth and testrpc.
    const u256 defaultTransactionGas = 90000;
    if (ret.nonce == Invalid256)
        ret.nonce = max<u256>(postSeal().transactionsFrom(ret.from), m_tq.maxNonce(ret.from));
    if (ret.gasPrice == Invalid256)
        ret.gasPrice = gasBidPrice();
    if (ret.gas == Invalid256)
        ret.gas = defaultTransactionGas;

    return ret;
}

bool Client::submitSealed(bytes const& _header)
{
    bytes newBlock;
    {
        UpgradableGuard l(x_working);
        {
            UpgradeGuard l2(l);
            if (!m_working.sealBlock(_header))
                return false;
        }
        DEV_WRITE_GUARDED(x_postSeal)
            m_postSeal = m_working;
        newBlock = m_working.blockData();
    }

    // OPTIMISE: very inefficient to not utilise the existing OverlayDB in m_postSeal that contains all trie changes.
    return m_bq.import(&newBlock, true) == ImportResult::Success;
}

void Client::rewind(unsigned _n)
{
    executeInMainThread([=]() {
        bc().rewind(_n);
        onChainChanged(ImportRoute());
    });

    for (unsigned i = 0; i < 10; ++i)
    {
        u256 n;
        DEV_READ_GUARDED(x_working)
            n = m_working.info().number();
        if (n == _n + 1)
            break;
        this_thread::sleep_for(std::chrono::milliseconds(50));
    }
    auto h = m_host.lock();
    if (h)
        h->reset();
    m_tq.clear();
    m_bq.clear();
}

h256 Client::submitTransaction(TransactionSkeleton const& _t, Secret const& _secret)
{
    TransactionSkeleton ts = populateTransactionWithDefaults(_t);
    ts.from = toAddress(_secret);
    Transaction t(ts, _secret);
    return importTransaction(t);
}

h256 Client::importTransaction(Transaction const& _t)
{
    prepareForTransaction();

    // Use the Executive to perform basic validation of the transaction
    // (e.g. transaction signature, account balance) using the state of
    // the pending block. This can throw but we'll catch the exception at the RPC level.
    try
    {
        Executive e(m_postSeal, bc());
        e.initialize(_t);
    }
    catch (InvalidNonce const& e)
    {
        // Too low nonce is invalid for sure
        bigint const& req = *boost::get_error_info<errinfo_required>(e);
        bigint const& got = *boost::get_error_info<errinfo_got>(e);
        if (req > got)
            throw;

        // Checking against pending block doesn't take into account transactions from the same
        // sender, that are currently in Transaction Queue.
        // If nonce is too high, it could be that previous transactions are in TQ.
        // We'll let TQ deal with nonces, it will order pending transactions by nonce.
    }
    ImportResult res = m_tq.import(_t.rlp());
    switch (res)
    {
        case ImportResult::Success:
            break;
        case ImportResult::ZeroSignature:
            BOOST_THROW_EXCEPTION(ZeroSignatureTransaction());
        case ImportResult::OverbidGasPrice:
            BOOST_THROW_EXCEPTION(GasPriceTooLow());
        case ImportResult::AlreadyKnown:
            BOOST_THROW_EXCEPTION(PendingTransactionAlreadyExists());
        case ImportResult::AlreadyInChain:
            BOOST_THROW_EXCEPTION(TransactionAlreadyInChain());
        default:
            BOOST_THROW_EXCEPTION(UnknownTransactionValidationError());
    }

    return _t.sha3();
}

// TODO: remove try/catch, allow exceptions
ExecutionResult Client::call(Address const& _from, u256 _value, Address _dest, bytes const& _data, u256 _gas, u256 _gasPrice, BlockNumber _blockNumber, FudgeFactor _ff)
{
    ExecutionResult ret;
    try
    {
        Block temp = blockByNumber(_blockNumber);
        u256 nonce = max<u256>(temp.transactionsFrom(_from), m_tq.maxNonce(_from));
        u256 gas = _gas == Invalid256 ? gasLimitRemaining() : _gas;
        u256 gasPrice = _gasPrice == Invalid256 ? gasBidPrice() : _gasPrice;
        Transaction t(_value, gasPrice, gas, _dest, _data, nonce);
        t.forceSender(_from);
        if (_ff == FudgeFactor::Lenient)
            temp.mutableState().addBalance(_from, (u256)(t.gas() * t.gasPrice() + t.value()));
        ret = temp.execute(bc().lastBlockHashes(), t, Permanence::Reverted);
    }
    catch (...)
    {
        cwarn << boost::current_exception_diagnostic_information();
    }
    return ret;
}

std::tuple<h256, h256, h256> Client::getWork()
{
    // lock the work so a later submission isn't invalidated by processing a transaction elsewhere.
    // this will be reset as soon as a new block arrives, allowing more transactions to be
    // processed.
    bool oldShould = shouldServeWork();
    m_lastGetWork = chrono::system_clock::now();
    if (!sealEngine()->shouldSeal(this))
        return std::tuple<h256, h256, h256>();

    // if this request has made us bother to serve work, prep it now.
    if (!oldShould && shouldServeWork())
        onPostStateChanged();
    else
        // otherwise, set this to true so that it gets prepped next time.
        m_remoteWorking = true;

    return sealEngine()->getWork(m_sealingInfo);
}