kevacoin/src/wallet/walletdb.cpp

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2016 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 "wallet/walletdb.h"

#include "base58.h"
#include "consensus/validation.h"
#include "validation.h" // For CheckTransaction
#include "protocol.h"
#include "serialize.h"
#include "sync.h"
#include "util.h"
#include "utiltime.h"
#include "wallet/wallet.h"

#include <atomic>

#include <boost/version.hpp>
#include <boost/filesystem.hpp>
#include <boost/foreach.hpp>
#include <boost/thread.hpp>

using namespace std;

static uint64_t nAccountingEntryNumber = 0;

static std::atomic<unsigned int> nWalletDBUpdateCounter;

//
// CWalletDB
//

bool CWalletDB::WriteName(const string& strAddress, const string& strName)
{
    nWalletDBUpdateCounter++;
    return Write(make_pair(string("name"), strAddress), strName);
}

bool CWalletDB::EraseName(const string& strAddress)
{
    // This should only be used for sending addresses, never for receiving addresses,
    // receiving addresses must always have an address book entry if they're not change return.
    nWalletDBUpdateCounter++;
    return Erase(make_pair(string("name"), strAddress));
}

bool CWalletDB::WritePurpose(const string& strAddress, const string& strPurpose)
{
    nWalletDBUpdateCounter++;
    return Write(make_pair(string("purpose"), strAddress), strPurpose);
}

bool CWalletDB::ErasePurpose(const string& strPurpose)
{
    nWalletDBUpdateCounter++;
    return Erase(make_pair(string("purpose"), strPurpose));
}

bool CWalletDB::WriteTx(const CWalletTx& wtx)
{
    nWalletDBUpdateCounter++;
    return Write(std::make_pair(std::string("tx"), wtx.GetHash()), wtx);
}

bool CWalletDB::EraseTx(uint256 hash)
{
    nWalletDBUpdateCounter++;
    return Erase(std::make_pair(std::string("tx"), hash));
}

bool CWalletDB::WriteKey(const CPubKey& vchPubKey, const CPrivKey& vchPrivKey, const CKeyMetadata& keyMeta)
{
    nWalletDBUpdateCounter++;

    if (!Write(std::make_pair(std::string("keymeta"), vchPubKey),
               keyMeta, false))
        return false;

    // hash pubkey/privkey to accelerate wallet load
    std::vector<unsigned char> vchKey;
    vchKey.reserve(vchPubKey.size() + vchPrivKey.size());
    vchKey.insert(vchKey.end(), vchPubKey.begin(), vchPubKey.end());
    vchKey.insert(vchKey.end(), vchPrivKey.begin(), vchPrivKey.end());

    return Write(std::make_pair(std::string("key"), vchPubKey), std::make_pair(vchPrivKey, Hash(vchKey.begin(), vchKey.end())), false);
}

bool CWalletDB::WriteCryptedKey(const CPubKey& vchPubKey,
                                const std::vector<unsigned char>& vchCryptedSecret,
                                const CKeyMetadata &keyMeta)
{
    const bool fEraseUnencryptedKey = true;
    nWalletDBUpdateCounter++;

    if (!Write(std::make_pair(std::string("keymeta"), vchPubKey),
            keyMeta))
        return false;

    if (!Write(std::make_pair(std::string("ckey"), vchPubKey), vchCryptedSecret, false))
        return false;
    if (fEraseUnencryptedKey)
    {
        Erase(std::make_pair(std::string("key"), vchPubKey));
        Erase(std::make_pair(std::string("wkey"), vchPubKey));
    }
    return true;
}

bool CWalletDB::WriteMasterKey(unsigned int nID, const CMasterKey& kMasterKey)
{
    nWalletDBUpdateCounter++;
    return Write(std::make_pair(std::string("mkey"), nID), kMasterKey, true);
}

bool CWalletDB::WriteCScript(const uint160& hash, const CScript& redeemScript)
{
    nWalletDBUpdateCounter++;
    return Write(std::make_pair(std::string("cscript"), hash), *(const CScriptBase*)(&redeemScript), false);
}

bool CWalletDB::WriteWatchOnly(const CScript &dest, const CKeyMetadata& keyMeta)
{
    nWalletDBUpdateCounter++;
    if (!Write(std::make_pair(std::string("watchmeta"), *(const CScriptBase*)(&dest)), keyMeta))
        return false;
    return Write(std::make_pair(std::string("watchs"), *(const CScriptBase*)(&dest)), '1');
}

bool CWalletDB::EraseWatchOnly(const CScript &dest)
{
    nWalletDBUpdateCounter++;
    if (!Erase(std::make_pair(std::string("watchmeta"), *(const CScriptBase*)(&dest))))
        return false;
    return Erase(std::make_pair(std::string("watchs"), *(const CScriptBase*)(&dest)));
}

bool CWalletDB::WriteBestBlock(const CBlockLocator& locator)
{
    nWalletDBUpdateCounter++;
    Write(std::string("bestblock"), CBlockLocator()); // Write empty block locator so versions that require a merkle branch automatically rescan
    return Write(std::string("bestblock_nomerkle"), locator);
}

bool CWalletDB::ReadBestBlock(CBlockLocator& locator)
{
    if (Read(std::string("bestblock"), locator) && !locator.vHave.empty()) return true;
    return Read(std::string("bestblock_nomerkle"), locator);
}

bool CWalletDB::WriteOrderPosNext(int64_t nOrderPosNext)
{
    nWalletDBUpdateCounter++;
    return Write(std::string("orderposnext"), nOrderPosNext);
}

bool CWalletDB::WriteDefaultKey(const CPubKey& vchPubKey)
{
    nWalletDBUpdateCounter++;
    return Write(std::string("defaultkey"), vchPubKey);
}

bool CWalletDB::ReadPool(int64_t nPool, CKeyPool& keypool)
{
    return Read(std::make_pair(std::string("pool"), nPool), keypool);
}

bool CWalletDB::WritePool(int64_t nPool, const CKeyPool& keypool)
{
    nWalletDBUpdateCounter++;
    return Write(std::make_pair(std::string("pool"), nPool), keypool);
}

bool CWalletDB::ErasePool(int64_t nPool)
{
    nWalletDBUpdateCounter++;
    return Erase(std::make_pair(std::string("pool"), nPool));
}

bool CWalletDB::WriteMinVersion(int nVersion)
{
    return Write(std::string("minversion"), nVersion);
}

bool CWalletDB::ReadAccount(const string& strAccount, CAccount& account)
{
    account.SetNull();
    return Read(make_pair(string("acc"), strAccount), account);
}

bool CWalletDB::WriteAccount(const string& strAccount, const CAccount& account)
{
    return Write(make_pair(string("acc"), strAccount), account);
}

bool CWalletDB::WriteAccountingEntry(const uint64_t nAccEntryNum, const CAccountingEntry& acentry)
{
    return Write(std::make_pair(std::string("acentry"), std::make_pair(acentry.strAccount, nAccEntryNum)), acentry);
}

bool CWalletDB::WriteAccountingEntry_Backend(const CAccountingEntry& acentry)
{
    return WriteAccountingEntry(++nAccountingEntryNumber, acentry);
}

CAmount CWalletDB::GetAccountCreditDebit(const string& strAccount)
{
    list<CAccountingEntry> entries;
    ListAccountCreditDebit(strAccount, entries);

    CAmount nCreditDebit = 0;
    BOOST_FOREACH (const CAccountingEntry& entry, entries)
        nCreditDebit += entry.nCreditDebit;

    return nCreditDebit;
}

void CWalletDB::ListAccountCreditDebit(const string& strAccount, list<CAccountingEntry>& entries)
{
    bool fAllAccounts = (strAccount == "*");

    Dbc* pcursor = GetCursor();
    if (!pcursor)
        throw runtime_error(std::string(__func__) + ": cannot create DB cursor");
    bool setRange = true;
    while (true)
    {
        // Read next record
        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
        if (setRange)
            ssKey << std::make_pair(std::string("acentry"), std::make_pair((fAllAccounts ? string("") : strAccount), uint64_t(0)));
        CDataStream ssValue(SER_DISK, CLIENT_VERSION);
        int ret = ReadAtCursor(pcursor, ssKey, ssValue, setRange);
        setRange = false;
        if (ret == DB_NOTFOUND)
            break;
        else if (ret != 0)
        {
            pcursor->close();
            throw runtime_error(std::string(__func__) + ": error scanning DB");
        }

        // Unserialize
        string strType;
        ssKey >> strType;
        if (strType != "acentry")
            break;
        CAccountingEntry acentry;
        ssKey >> acentry.strAccount;
        if (!fAllAccounts && acentry.strAccount != strAccount)
            break;

        ssValue >> acentry;
        ssKey >> acentry.nEntryNo;
        entries.push_back(acentry);
    }

    pcursor->close();
}

class CWalletScanState {
public:
    unsigned int nKeys;
    unsigned int nCKeys;
    unsigned int nWatchKeys;
    unsigned int nKeyMeta;
    bool fIsEncrypted;
    bool fAnyUnordered;
    int nFileVersion;
    vector<uint256> vWalletUpgrade;

    CWalletScanState() {
        nKeys = nCKeys = nWatchKeys = nKeyMeta = 0;
        fIsEncrypted = false;
        fAnyUnordered = false;
        nFileVersion = 0;
    }
};

bool
ReadKeyValue(CWallet* pwallet, CDataStream& ssKey, CDataStream& ssValue,
             CWalletScanState &wss, string& strType, string& strErr)
{
    try {
        // Unserialize
        // Taking advantage of the fact that pair serialization
        // is just the two items serialized one after the other
        ssKey >> strType;
        if (strType == "name")
        {
            string strAddress;
            ssKey >> strAddress;
            ssValue >> pwallet->mapAddressBook[CBitcoinAddress(strAddress).Get()].name;
        }
        else if (strType == "purpose")
        {
            string strAddress;
            ssKey >> strAddress;
            ssValue >> pwallet->mapAddressBook[CBitcoinAddress(strAddress).Get()].purpose;
        }
        else if (strType == "tx")
        {
            uint256 hash;
            ssKey >> hash;
            CWalletTx wtx;
            ssValue >> wtx;
            CValidationState state;
            if (!(CheckTransaction(wtx, state) && (wtx.GetHash() == hash) && state.IsValid()))
                return false;

            // Undo serialize changes in 31600
            if (31404 <= wtx.fTimeReceivedIsTxTime && wtx.fTimeReceivedIsTxTime <= 31703)
            {
                if (!ssValue.empty())
                {
                    char fTmp;
                    char fUnused;
                    ssValue >> fTmp >> fUnused >> wtx.strFromAccount;
                    strErr = strprintf("LoadWallet() upgrading tx ver=%d %d '%s' %s",
                                       wtx.fTimeReceivedIsTxTime, fTmp, wtx.strFromAccount, hash.ToString());
                    wtx.fTimeReceivedIsTxTime = fTmp;
                }
                else
                {
                    strErr = strprintf("LoadWallet() repairing tx ver=%d %s", wtx.fTimeReceivedIsTxTime, hash.ToString());
                    wtx.fTimeReceivedIsTxTime = 0;
                }
                wss.vWalletUpgrade.push_back(hash);
            }

            if (wtx.nOrderPos == -1)
                wss.fAnyUnordered = true;

            pwallet->LoadToWallet(wtx);
        }
        else if (strType == "acentry")
        {
            string strAccount;
            ssKey >> strAccount;
            uint64_t nNumber;
            ssKey >> nNumber;
            if (nNumber > nAccountingEntryNumber)
                nAccountingEntryNumber = nNumber;

            if (!wss.fAnyUnordered)
            {
                CAccountingEntry acentry;
                ssValue >> acentry;
                if (acentry.nOrderPos == -1)
                    wss.fAnyUnordered = true;
            }
        }
        else if (strType == "watchs")
        {
            wss.nWatchKeys++;
            CScript script;
            ssKey >> *(CScriptBase*)(&script);
            char fYes;
            ssValue >> fYes;
            if (fYes == '1')
                pwallet->LoadWatchOnly(script);
        }
        else if (strType == "key" || strType == "wkey")
        {
            CPubKey vchPubKey;
            ssKey >> vchPubKey;
            if (!vchPubKey.IsValid())
            {
                strErr = "Error reading wallet database: CPubKey corrupt";
                return false;
            }
            CKey key;
            CPrivKey pkey;
            uint256 hash;

            if (strType == "key")
            {
                wss.nKeys++;
                ssValue >> pkey;
            } else {
                CWalletKey wkey;
                ssValue >> wkey;
                pkey = wkey.vchPrivKey;
            }

            // Old wallets store keys as "key" [pubkey] => [privkey]
            // ... which was slow for wallets with lots of keys, because the public key is re-derived from the private key
            // using EC operations as a checksum.
            // Newer wallets store keys as "key"[pubkey] => [privkey][hash(pubkey,privkey)], which is much faster while
            // remaining backwards-compatible.
            try
            {
                ssValue >> hash;
            }
            catch (...) {}

            bool fSkipCheck = false;

            if (!hash.IsNull())
            {
                // hash pubkey/privkey to accelerate wallet load
                std::vector<unsigned char> vchKey;
                vchKey.reserve(vchPubKey.size() + pkey.size());
                vchKey.insert(vchKey.end(), vchPubKey.begin(), vchPubKey.end());
                vchKey.insert(vchKey.end(), pkey.begin(), pkey.end());

                if (Hash(vchKey.begin(), vchKey.end()) != hash)
                {
                    strErr = "Error reading wallet database: CPubKey/CPrivKey corrupt";
                    return false;
                }

                fSkipCheck = true;
            }

            if (!key.Load(pkey, vchPubKey, fSkipCheck))
            {
                strErr = "Error reading wallet database: CPrivKey corrupt";
                return false;
            }
            if (!pwallet->LoadKey(key, vchPubKey))
            {
                strErr = "Error reading wallet database: LoadKey failed";
                return false;
            }
        }
        else if (strType == "mkey")
        {
            unsigned int nID;
            ssKey >> nID;
            CMasterKey kMasterKey;
            ssValue >> kMasterKey;
            if(pwallet->mapMasterKeys.count(nID) != 0)
            {
                strErr = strprintf("Error reading wallet database: duplicate CMasterKey id %u", nID);
                return false;
            }
            pwallet->mapMasterKeys[nID] = kMasterKey;
            if (pwallet->nMasterKeyMaxID < nID)
                pwallet->nMasterKeyMaxID = nID;
        }
        else if (strType == "ckey")
        {
            CPubKey vchPubKey;
            ssKey >> vchPubKey;
            if (!vchPubKey.IsValid())
            {
                strErr = "Error reading wallet database: CPubKey corrupt";
                return false;
            }
            vector<unsigned char> vchPrivKey;
            ssValue >> vchPrivKey;
            wss.nCKeys++;

            if (!pwallet->LoadCryptedKey(vchPubKey, vchPrivKey))
            {
                strErr = "Error reading wallet database: LoadCryptedKey failed";
                return false;
            }
            wss.fIsEncrypted = true;
        }
        else if (strType == "keymeta" || strType == "watchmeta")
        {
            CTxDestination keyID;
            if (strType == "keymeta")
            {
              CPubKey vchPubKey;
              ssKey >> vchPubKey;
              keyID = vchPubKey.GetID();
            }
            else if (strType == "watchmeta")
            {
              CScript script;
              ssKey >> *(CScriptBase*)(&script);
              keyID = CScriptID(script);
            }

            CKeyMetadata keyMeta;
            ssValue >> keyMeta;
            wss.nKeyMeta++;

            pwallet->LoadKeyMetadata(keyID, keyMeta);
        }
        else if (strType == "defaultkey")
        {
            ssValue >> pwallet->vchDefaultKey;
        }
        else if (strType == "pool")
        {
            int64_t nIndex;
            ssKey >> nIndex;
            CKeyPool keypool;
            ssValue >> keypool;

            pwallet->LoadKeyPool(nIndex, keypool);
        }
        else if (strType == "version")
        {
            ssValue >> wss.nFileVersion;
            if (wss.nFileVersion == 10300)
                wss.nFileVersion = 300;
        }
        else if (strType == "cscript")
        {
            uint160 hash;
            ssKey >> hash;
            CScript script;
            ssValue >> *(CScriptBase*)(&script);
            if (!pwallet->LoadCScript(script))
            {
                strErr = "Error reading wallet database: LoadCScript failed";
                return false;
            }
        }
        else if (strType == "orderposnext")
        {
            ssValue >> pwallet->nOrderPosNext;
        }
        else if (strType == "destdata")
        {
            std::string strAddress, strKey, strValue;
            ssKey >> strAddress;
            ssKey >> strKey;
            ssValue >> strValue;
            if (!pwallet->LoadDestData(CBitcoinAddress(strAddress).Get(), strKey, strValue))
            {
                strErr = "Error reading wallet database: LoadDestData failed";
                return false;
            }
        }
        else if (strType == "hdchain")
        {
            CHDChain chain;
            ssValue >> chain;
            if (!pwallet->SetHDChain(chain, true))
            {
                strErr = "Error reading wallet database: SetHDChain failed";
                return false;
            }
        }
    } catch (...)
    {
        return false;
    }
    return true;
}

static bool IsKeyType(string strType)
{
    return (strType== "key" || strType == "wkey" ||
            strType == "mkey" || strType == "ckey");
}

DBErrors CWalletDB::LoadWallet(CWallet* pwallet)
{
    pwallet->vchDefaultKey = CPubKey();
    CWalletScanState wss;
    bool fNoncriticalErrors = false;
    DBErrors result = DB_LOAD_OK;

    LOCK(pwallet->cs_wallet);
    try {
        int nMinVersion = 0;
        if (Read((string)"minversion", nMinVersion))
        {
            if (nMinVersion > CLIENT_VERSION)
                return DB_TOO_NEW;
            pwallet->LoadMinVersion(nMinVersion);
        }

        // Get cursor
        Dbc* pcursor = GetCursor();
        if (!pcursor)
        {
            LogPrintf("Error getting wallet database cursor\n");
            return DB_CORRUPT;
        }

        while (true)
        {
            // Read next record
            CDataStream ssKey(SER_DISK, CLIENT_VERSION);
            CDataStream ssValue(SER_DISK, CLIENT_VERSION);
            int ret = ReadAtCursor(pcursor, ssKey, ssValue);
            if (ret == DB_NOTFOUND)
                break;
            else if (ret != 0)
            {
                LogPrintf("Error reading next record from wallet database\n");
                return DB_CORRUPT;
            }

            // Try to be tolerant of single corrupt records:
            string strType, strErr;
            if (!ReadKeyValue(pwallet, ssKey, ssValue, wss, strType, strErr))
            {
                // losing keys is considered a catastrophic error, anything else
                // we assume the user can live with:
                if (IsKeyType(strType))
                    result = DB_CORRUPT;
                else
                {
                    // Leave other errors alone, if we try to fix them we might make things worse.
                    fNoncriticalErrors = true; // ... but do warn the user there is something wrong.
                    if (strType == "tx")
                        // Rescan if there is a bad transaction record:
                        SoftSetBoolArg("-rescan", true);
                }
            }
            if (!strErr.empty())
                LogPrintf("%s\n", strErr);
        }
        pcursor->close();
    }
    catch (const boost::thread_interrupted&) {
        throw;
    }
    catch (...) {
        result = DB_CORRUPT;
    }

    if (fNoncriticalErrors && result == DB_LOAD_OK)
        result = DB_NONCRITICAL_ERROR;

    // Any wallet corruption at all: skip any rewriting or
    // upgrading, we don't want to make it worse.
    if (result != DB_LOAD_OK)
        return result;

    LogPrintf("nFileVersion = %d\n", wss.nFileVersion);

    LogPrintf("Keys: %u plaintext, %u encrypted, %u w/ metadata, %u total\n",
           wss.nKeys, wss.nCKeys, wss.nKeyMeta, wss.nKeys + wss.nCKeys);

    // nTimeFirstKey is only reliable if all keys have metadata
    if ((wss.nKeys + wss.nCKeys + wss.nWatchKeys) != wss.nKeyMeta)
        pwallet->UpdateTimeFirstKey(1);

    BOOST_FOREACH(uint256 hash, wss.vWalletUpgrade)
        WriteTx(pwallet->mapWallet[hash]);

    // Rewrite encrypted wallets of versions 0.4.0 and 0.5.0rc:
    if (wss.fIsEncrypted && (wss.nFileVersion == 40000 || wss.nFileVersion == 50000))
        return DB_NEED_REWRITE;

    if (wss.nFileVersion < CLIENT_VERSION) // Update
        WriteVersion(CLIENT_VERSION);

    if (wss.fAnyUnordered)
        result = pwallet->ReorderTransactions();

    pwallet->laccentries.clear();
    ListAccountCreditDebit("*", pwallet->laccentries);
    BOOST_FOREACH(CAccountingEntry& entry, pwallet->laccentries) {
        pwallet->wtxOrdered.insert(make_pair(entry.nOrderPos, CWallet::TxPair((CWalletTx*)0, &entry)));
    }

    return result;
}

DBErrors CWalletDB::FindWalletTx(CWallet* pwallet, vector<uint256>& vTxHash, vector<CWalletTx>& vWtx)
{
    pwallet->vchDefaultKey = CPubKey();
    bool fNoncriticalErrors = false;
    DBErrors result = DB_LOAD_OK;

    try {
        LOCK(pwallet->cs_wallet);
        int nMinVersion = 0;
        if (Read((string)"minversion", nMinVersion))
        {
            if (nMinVersion > CLIENT_VERSION)
                return DB_TOO_NEW;
            pwallet->LoadMinVersion(nMinVersion);
        }

        // Get cursor
        Dbc* pcursor = GetCursor();
        if (!pcursor)
        {
            LogPrintf("Error getting wallet database cursor\n");
            return DB_CORRUPT;
        }

        while (true)
        {
            // Read next record
            CDataStream ssKey(SER_DISK, CLIENT_VERSION);
            CDataStream ssValue(SER_DISK, CLIENT_VERSION);
            int ret = ReadAtCursor(pcursor, ssKey, ssValue);
            if (ret == DB_NOTFOUND)
                break;
            else if (ret != 0)
            {
                LogPrintf("Error reading next record from wallet database\n");
                return DB_CORRUPT;
            }

            string strType;
            ssKey >> strType;
            if (strType == "tx") {
                uint256 hash;
                ssKey >> hash;

                CWalletTx wtx;
                ssValue >> wtx;

                vTxHash.push_back(hash);
                vWtx.push_back(wtx);
            }
        }
        pcursor->close();
    }
    catch (const boost::thread_interrupted&) {
        throw;
    }
    catch (...) {
        result = DB_CORRUPT;
    }

    if (fNoncriticalErrors && result == DB_LOAD_OK)
        result = DB_NONCRITICAL_ERROR;

    return result;
}

DBErrors CWalletDB::ZapSelectTx(CWallet* pwallet, vector<uint256>& vTxHashIn, vector<uint256>& vTxHashOut)
{
    // build list of wallet TXs and hashes
    vector<uint256> vTxHash;
    vector<CWalletTx> vWtx;
    DBErrors err = FindWalletTx(pwallet, vTxHash, vWtx);
    if (err != DB_LOAD_OK) {
        return err;
    }

    std::sort(vTxHash.begin(), vTxHash.end());
    std::sort(vTxHashIn.begin(), vTxHashIn.end());

    // erase each matching wallet TX
    bool delerror = false;
    vector<uint256>::iterator it = vTxHashIn.begin();
    BOOST_FOREACH (uint256 hash, vTxHash) {
        while (it < vTxHashIn.end() && (*it) < hash) {
            it++;
        }
        if (it == vTxHashIn.end()) {
            break;
        }
        else if ((*it) == hash) {
            pwallet->mapWallet.erase(hash);
            if(!EraseTx(hash)) {
                LogPrint("db", "Transaction was found for deletion but returned database error: %s\n", hash.GetHex());
                delerror = true;
            }
            vTxHashOut.push_back(hash);
        }
    }

    if (delerror) {
        return DB_CORRUPT;
    }
    return DB_LOAD_OK;
}

DBErrors CWalletDB::ZapWalletTx(CWallet* pwallet, vector<CWalletTx>& vWtx)
{
    // build list of wallet TXs
    vector<uint256> vTxHash;
    DBErrors err = FindWalletTx(pwallet, vTxHash, vWtx);
    if (err != DB_LOAD_OK)
        return err;

    // erase each wallet TX
    BOOST_FOREACH (uint256& hash, vTxHash) {
        if (!EraseTx(hash))
            return DB_CORRUPT;
    }

    return DB_LOAD_OK;
}

void ThreadFlushWalletDB()
{
    // Make this thread recognisable as the wallet flushing thread
    RenameThread("bitcoin-wallet");

    static bool fOneThread;
    if (fOneThread)
        return;
    fOneThread = true;
    if (!GetBoolArg("-flushwallet", DEFAULT_FLUSHWALLET))
        return;

    unsigned int nLastSeen = CWalletDB::GetUpdateCounter();
    unsigned int nLastFlushed = CWalletDB::GetUpdateCounter();
    int64_t nLastWalletUpdate = GetTime();
    while (true)
    {
        MilliSleep(500);

        if (nLastSeen != CWalletDB::GetUpdateCounter())
        {
            nLastSeen = CWalletDB::GetUpdateCounter();
            nLastWalletUpdate = GetTime();
        }

        if (nLastFlushed != CWalletDB::GetUpdateCounter() && GetTime() - nLastWalletUpdate >= 2)
        {
            TRY_LOCK(bitdb.cs_db,lockDb);
            if (lockDb)
            {
                // Don't do this if any databases are in use
                int nRefCount = 0;
                map<string, int>::iterator mi = bitdb.mapFileUseCount.begin();
                while (mi != bitdb.mapFileUseCount.end())
                {
                    nRefCount += (*mi).second;
                    mi++;
                }

                if (nRefCount == 0)
                {
                    boost::this_thread::interruption_point();
                    const std::string& strFile = pwalletMain->strWalletFile;
                    map<string, int>::iterator _mi = bitdb.mapFileUseCount.find(strFile);
                    if (_mi != bitdb.mapFileUseCount.end())
                    {
                        LogPrint("db", "Flushing %s\n", strFile);
                        nLastFlushed = CWalletDB::GetUpdateCounter();
                        int64_t nStart = GetTimeMillis();

                        // Flush wallet file so it's self contained
                        bitdb.CloseDb(strFile);
                        bitdb.CheckpointLSN(strFile);

                        bitdb.mapFileUseCount.erase(_mi++);
                        LogPrint("db", "Flushed %s %dms\n", strFile, GetTimeMillis() - nStart);
                    }
                }
            }
        }
    }
}

//
// Try to (very carefully!) recover wallet file if there is a problem.
//
bool CWalletDB::Recover(CDBEnv& dbenv, const std::string& filename, bool fOnlyKeys)
{
    // Recovery procedure:
    // move wallet file to wallet.timestamp.bak
    // Call Salvage with fAggressive=true to
    // get as much data as possible.
    // Rewrite salvaged data to fresh wallet file
    // Set -rescan so any missing transactions will be
    // found.
    int64_t now = GetTime();
    std::string newFilename = strprintf("wallet.%d.bak", now);

    int result = dbenv.dbenv->dbrename(NULL, filename.c_str(), NULL,
                                       newFilename.c_str(), DB_AUTO_COMMIT);
    if (result == 0)
        LogPrintf("Renamed %s to %s\n", filename, newFilename);
    else
    {
        LogPrintf("Failed to rename %s to %s\n", filename, newFilename);
        return false;
    }

    std::vector<CDBEnv::KeyValPair> salvagedData;
    bool fSuccess = dbenv.Salvage(newFilename, true, salvagedData);
    if (salvagedData.empty())
    {
        LogPrintf("Salvage(aggressive) found no records in %s.\n", newFilename);
        return false;
    }
    LogPrintf("Salvage(aggressive) found %u records\n", salvagedData.size());

    std::unique_ptr<Db> pdbCopy(new Db(dbenv.dbenv, 0));
    int ret = pdbCopy->open(NULL,               // Txn pointer
                            filename.c_str(),   // Filename
                            "main",             // Logical db name
                            DB_BTREE,           // Database type
                            DB_CREATE,          // Flags
                            0);
    if (ret > 0)
    {
        LogPrintf("Cannot create database file %s\n", filename);
        return false;
    }
    CWallet dummyWallet;
    CWalletScanState wss;

    DbTxn* ptxn = dbenv.TxnBegin();
    BOOST_FOREACH(CDBEnv::KeyValPair& row, salvagedData)
    {
        if (fOnlyKeys)
        {
            CDataStream ssKey(row.first, SER_DISK, CLIENT_VERSION);
            CDataStream ssValue(row.second, SER_DISK, CLIENT_VERSION);
            string strType, strErr;
            bool fReadOK;
            {
                // Required in LoadKeyMetadata():
                LOCK(dummyWallet.cs_wallet);
                fReadOK = ReadKeyValue(&dummyWallet, ssKey, ssValue,
                                        wss, strType, strErr);
            }
            if (!IsKeyType(strType) && strType != "hdchain")
                continue;
            if (!fReadOK)
            {
                LogPrintf("WARNING: CWalletDB::Recover skipping %s: %s\n", strType, strErr);
                continue;
            }
        }
        Dbt datKey(&row.first[0], row.first.size());
        Dbt datValue(&row.second[0], row.second.size());
        int ret2 = pdbCopy->put(ptxn, &datKey, &datValue, DB_NOOVERWRITE);
        if (ret2 > 0)
            fSuccess = false;
    }
    ptxn->commit(0);
    pdbCopy->close(0);

    return fSuccess;
}

bool CWalletDB::Recover(CDBEnv& dbenv, const std::string& filename)
{
    return CWalletDB::Recover(dbenv, filename, false);
}

bool CWalletDB::WriteDestData(const std::string &address, const std::string &key, const std::string &value)
{
    nWalletDBUpdateCounter++;
    return Write(std::make_pair(std::string("destdata"), std::make_pair(address, key)), value);
}

bool CWalletDB::EraseDestData(const std::string &address, const std::string &key)
{
    nWalletDBUpdateCounter++;
    return Erase(std::make_pair(std::string("destdata"), std::make_pair(address, key)));
}


bool CWalletDB::WriteHDChain(const CHDChain& chain)
{
    nWalletDBUpdateCounter++;
    return Write(std::string("hdchain"), chain);
}

void CWalletDB::IncrementUpdateCounter()
{
    nWalletDBUpdateCounter++;
}

unsigned int CWalletDB::GetUpdateCounter()
{
    return nWalletDBUpdateCounter;
}