比特币源码分析(十一) - 加载钱包(load wallet)

接下来主要是分析Bitcoin Core初始化中的加载钱包过程，对应的源码是src/init.cpp的AppInitMain()方法的Step 8: load wallet这部分，详见：https://github.com/bitcoin/bitcoin/blob/v0.16.1/src/init.cpp

    // ********************************************************* Step 8: load wallet
#ifdef ENABLE_WALLET
    if (!OpenWallets())
        return false;
#else
    LogPrintf("No wallet support compiled in!\n");
#endif

关键的就是OpenWallets()方法：

bool OpenWallets()
{
    if (gArgs.GetBoolArg("-disablewallet", DEFAULT_DISABLE_WALLET)) {
        LogPrintf("Wallet disabled!\n");
        return true;
    }

    for (const std::string& walletFile : gArgs.GetArgs("-wallet")) {
        CWallet * const pwallet = CWallet::CreateWalletFromFile(walletFile);
        if (!pwallet) {
            return false;
        }
        vpwallets.push_back(pwallet);
    }

    return true;
}

根据"-wallet"参数设置的钱包文件路径读取相应文件从而创建钱包，而"-wallet"参数由WalletParameterInteraction()方法设定：

bool WalletParameterInteraction()
{
    if (gArgs.GetBoolArg("-disablewallet", DEFAULT_DISABLE_WALLET)) {
        for (const std::string& wallet : gArgs.GetArgs("-wallet")) {
            LogPrintf("%s: parameter interaction: -disablewallet -> ignoring -wallet=%s\n", __func__, wallet);
        }

        return true;
    }

    gArgs.SoftSetArg("-wallet", DEFAULT_WALLET_DAT);

......

可以看到"-wallet"参数默认设置为DEFAULT_WALLET_DAT，而DEFAULT_WALLET_DAT定义在src/wallet/wallet.cpp中：

const char * DEFAULT_WALLET_DAT = "wallet.dat";

也就是说默认是从wallet.dat中加载钱包文件从而创建钱包。
WalletParameterInteraction()方法由之前讲过的AppInitParameterInteraction()方法调用。

接下来主要是分析关键的CreateWalletFromFile()方法，定义在src/wallet/wallet.cpp中：

CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
{
    // needed to restore wallet transaction meta data after -zapwallettxes
    std::vector vWtx;

1、清除钱包的交易数据

接下去看源码：

    if (gArgs.GetBoolArg("-zapwallettxes", false)) {
        uiInterface.InitMessage(_("Zapping all transactions from wallet..."));

        std::unique_ptr dbw(new CWalletDBWrapper(&bitdb, walletFile));
        std::unique_ptr tempWallet = MakeUnique(std::move(dbw));
        DBErrors nZapWalletRet = tempWallet->ZapWalletTx(vWtx);
        if (nZapWalletRet != DB_LOAD_OK) {
            InitError(strprintf(_("Error loading %s: Wallet corrupted"), walletFile));
            return nullptr;
        }
    }

如果用户设置了"-zapwallettxes"选项，则清除钱包的所有的交易数据，为什么清除交易数据，这是因为可能存在交易费过低或者没有交易费的交易，通过这个选项可以清除掉这种交易。
这里是调用CWallet类的ZapWalletTx()方法清除交易的，进一步跟进去，可以发现是调用CWalletDB类的ZapWalletTx()方法清除交易的：

DBErrors CWalletDB::ZapWalletTx(std::vector& vWtx)
{
    // build list of wallet TXs
    std::vector vTxHash;
    DBErrors err = FindWalletTx(vTxHash, vWtx);
    if (err != DB_LOAD_OK)
        return err;

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

    return DB_LOAD_OK;
}

通过CWalletDB::FindWalletTx()方法找到所有交易对应的hash放在集合vTxHash中，然后遍历该集合，调用CWalletDB::EraseTx()方法清除交易。

2、创建钱包

    uiInterface.InitMessage(_("Loading wallet..."));

    int64_t nStart = GetTimeMillis();
    bool fFirstRun = true;
    std::unique_ptr dbw(new CWalletDBWrapper(&bitdb, walletFile));
    CWallet *walletInstance = new CWallet(std::move(dbw));
    DBErrors nLoadWalletRet = walletInstance->LoadWallet(fFirstRun);

创建了CWallet对象，然后调用LoadWallet()方法从wallet.dat文件中加载数据。

3、升级钱包

    if (gArgs.GetBoolArg("-upgradewallet", fFirstRun))
    {
        int nMaxVersion = gArgs.GetArg("-upgradewallet", 0);
        if (nMaxVersion == 0) // the -upgradewallet without argument case
        {
            LogPrintf("Performing wallet upgrade to %i\n", FEATURE_LATEST);
            nMaxVersion = CLIENT_VERSION;
            walletInstance->SetMinVersion(FEATURE_LATEST); // permanently upgrade the wallet immediately
        }
        else
            LogPrintf("Allowing wallet upgrade up to %i\n", nMaxVersion);
        if (nMaxVersion < walletInstance->GetVersion())
        {
            InitError(_("Cannot downgrade wallet"));
            return nullptr;
        }
        walletInstance->SetMaxVersion(nMaxVersion);
    }

如果设置了"-upgradewallet"选项，则根据参数进行钱包升级。

4、生成主私钥和子私钥

    if (fFirstRun)
    {
        // ensure this wallet.dat can only be opened by clients supporting HD with chain split and expects no default key
        if (!gArgs.GetBoolArg("-usehd", true)) {
            InitError(strprintf(_("Error creating %s: You can't create non-HD wallets with this version."), walletFile));
            return nullptr;
        }
        walletInstance->SetMinVersion(FEATURE_NO_DEFAULT_KEY);

        // generate a new master key  生成主私钥
        CPubKey masterPubKey = walletInstance->GenerateNewHDMasterKey();
        if (!walletInstance->SetHDMasterKey(masterPubKey))
            throw std::runtime_error(std::string(__func__) + ": Storing master key failed");

        // Top up the keypool 生成子私钥，填充满密钥池
        if (!walletInstance->TopUpKeyPool()) {
            InitError(_("Unable to generate initial keys") += "\n");
            return nullptr;
        }

        walletInstance->SetBestChain(chainActive.GetLocator());
    }

《精通比特币》里讲过钱包就是私钥的集合，分层确定性钱包(即HD Wallets)需要先生成一个主私钥，再根据这个主私钥生成很多子私钥。
4.1 生成主私钥
看下CPubKey CWallet::GenerateNewHDMasterKey()源码

CPubKey CWallet::GenerateNewHDMasterKey()
{
	//创建私钥
    CKey key;
    key.MakeNewKey(true);

    int64_t nCreationTime = GetTime();
    CKeyMetadata metadata(nCreationTime);

	//根据secp256k1椭圆曲线算法由私钥生成公钥
    // calculate the pubkey
    CPubKey pubkey = key.GetPubKey();
    assert(key.VerifyPubKey(pubkey));

	//标记为主密钥
    // set the hd keypath to "m" -> Master, refers the masterkeyid to itself
    metadata.hdKeypath     = "m";
    metadata.hdMasterKeyID = pubkey.GetID();

    {
        LOCK(cs_wallet);

        // mem store the metadata
        mapKeyMetadata[pubkey.GetID()] = metadata;

		//将公钥私钥对写入到钱包的数据库文件中
        // write the key&metadata to the database
        if (!AddKeyPubKey(key, pubkey))
            throw std::runtime_error(std::string(__func__) + ": AddKeyPubKey failed");
    }

    return pubkey;
}

上述关键代码已经做了注释，下面做进一步分析
4.1.1创建私钥
调用 CKey::MakeNewKey()方法使用加密PRNG生成一个私钥。

4.1.2由私钥生成公钥
调用CPubKey CKey::GetPubKey() 方法根据secp256k1椭圆曲线算法由私钥生成公钥:

CPubKey CKey::GetPubKey() const {
    assert(fValid);
    secp256k1_pubkey pubkey;
    size_t clen = CPubKey::PUBLIC_KEY_SIZE;
    CPubKey result;
    int ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pubkey, begin());
    assert(ret);
    secp256k1_ec_pubkey_serialize(secp256k1_context_sign, (unsigned char*)result.begin(), &clen, &pubkey, fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
    assert(result.size() == clen);
    assert(result.IsValid());
    return result;
}

4.1.3标记为主密钥
调用pubkey.GetID()计算一个CKeyID ，CKeyID 其实是私钥CKey的引用，用来唯一标识一个私钥，只不过是采用私钥对应的公钥的Hash160哈希值来表示的。
看下源码：

    //! Get the KeyID of this public key (hash of its serialization)
    CKeyID GetID() const
    {
        return CKeyID(Hash160(vch, vch + size()));
    }

4.1.4将公钥私钥对写入到钱包的数据库文件中
调用CWallet::AddKeyPubKey()方法将公钥私钥对写入到钱包的数据库文件中：

bool CWallet::AddKeyPubKey(const CKey& secret, const CPubKey &pubkey)
{
    CWalletDB walletdb(*dbw);
    return CWallet::AddKeyPubKeyWithDB(walletdb, secret, pubkey);
}

4.2生成子私钥
看下bool CWallet::TopUpKeyPool(unsigned int kpSize)源码：

bool CWallet::TopUpKeyPool(unsigned int kpSize)
{
    {
        LOCK(cs_wallet);

        if (IsLocked())
            return false;

        // Top up key pool
        unsigned int nTargetSize;
        if (kpSize > 0)
            nTargetSize = kpSize;
        else
            nTargetSize = std::max(gArgs.GetArg("-keypool", DEFAULT_KEYPOOL_SIZE), (int64_t) 0);

        // count amount of available keys (internal, external)
        // make sure the keypool of external and internal keys fits the user selected target (-keypool)
        int64_t missingExternal = std::max(std::max((int64_t) nTargetSize, (int64_t) 1) - (int64_t)setExternalKeyPool.size(), (int64_t) 0);
        int64_t missingInternal = std::max(std::max((int64_t) nTargetSize, (int64_t) 1) - (int64_t)setInternalKeyPool.size(), (int64_t) 0);

        if (!IsHDEnabled() || !CanSupportFeature(FEATURE_HD_SPLIT))
        {
            // don't create extra internal keys
            missingInternal = 0;
        }
        bool internal = false;
        CWalletDB walletdb(*dbw);
        for (int64_t i = missingInternal + missingExternal; i--;)
        {
            if (i < missingInternal) {
                internal = true;
            }

            assert(m_max_keypool_index < std::numeric_limits::max()); // How in the hell did you use so many keys?
            int64_t index = ++m_max_keypool_index;
			
			//调用GenerateNewKey()方法生成公钥私钥对
            CPubKey pubkey(GenerateNewKey(walletdb, internal));
            if (!walletdb.WritePool(index, CKeyPool(pubkey, internal))) {
                throw std::runtime_error(std::string(__func__) + ": writing generated key failed");
            }

            if (internal) {
                setInternalKeyPool.insert(index);
            } else {
                setExternalKeyPool.insert(index);
            }
            m_pool_key_to_index[pubkey.GetID()] = index;
        }
        if (missingInternal + missingExternal > 0) {
            LogPrintf("keypool added %d keys (%d internal), size=%u (%u internal)\n", missingInternal + missingExternal, missingInternal, setInternalKeyPool.size() + setExternalKeyPool.size(), setInternalKeyPool.size());
        }
    }
    return true;
}

5、扫描区块链，将相关交易加入到钱包中

    CBlockIndex *pindexRescan = chainActive.Genesis();
    if (!gArgs.GetBoolArg("-rescan", false))
    {
        CWalletDB walletdb(*walletInstance->dbw);
        CBlockLocator locator;
        if (walletdb.ReadBestBlock(locator))
            pindexRescan = FindForkInGlobalIndex(chainActive, locator);
    }

    walletInstance->m_last_block_processed = chainActive.Tip();
    RegisterValidationInterface(walletInstance);

    if (chainActive.Tip() && chainActive.Tip() != pindexRescan)
    {
        //We can't rescan beyond non-pruned blocks, stop and throw an error
        //this might happen if a user uses an old wallet within a pruned node
        // or if he ran -disablewallet for a longer time, then decided to re-enable
        if (fPruneMode)
        {
            CBlockIndex *block = chainActive.Tip();
            while (block && block->pprev && (block->pprev->nStatus & BLOCK_HAVE_DATA) && block->pprev->nTx > 0 && pindexRescan != block)
                block = block->pprev;

            if (pindexRescan != block) {
                InitError(_("Prune: last wallet synchronisation goes beyond pruned data. You need to -reindex (download the whole blockchain again in case of pruned node)"));
                return nullptr;
            }
        }

        uiInterface.InitMessage(_("Rescanning..."));
        LogPrintf("Rescanning last %i blocks (from block %i)...\n", chainActive.Height() - pindexRescan->nHeight, pindexRescan->nHeight);

        // No need to read and scan block if block was created before
        // our wallet birthday (as adjusted for block time variability)
        while (pindexRescan && walletInstance->nTimeFirstKey && (pindexRescan->GetBlockTime() < (walletInstance->nTimeFirstKey - TIMESTAMP_WINDOW))) {
            pindexRescan = chainActive.Next(pindexRescan);
        }

        nStart = GetTimeMillis();
        {
            WalletRescanReserver reserver(walletInstance);
            if (!reserver.reserve()) {
                InitError(_("Failed to rescan the wallet during initialization"));
                return nullptr;
            }
            //扫描区块链
            walletInstance->ScanForWalletTransactions(pindexRescan, nullptr, reserver, true);
        }
        LogPrintf(" rescan      %15dms\n", GetTimeMillis() - nStart);
        walletInstance->SetBestChain(chainActive.GetLocator());
        walletInstance->dbw->IncrementUpdateCounter();

        // Restore wallet transaction metadata after -zapwallettxes=1
        if (gArgs.GetBoolArg("-zapwallettxes", false) && gArgs.GetArg("-zapwallettxes", "1") != "2")
        {
            CWalletDB walletdb(*walletInstance->dbw);

            for (const CWalletTx& wtxOld : vWtx)
            {
                uint256 hash = wtxOld.GetHash();
                std::map::iterator mi = walletInstance->mapWallet.find(hash);
                if (mi != walletInstance->mapWallet.end())
                {
                    const CWalletTx* copyFrom = &wtxOld;
                    CWalletTx* copyTo = &mi->second;
                    copyTo->mapValue = copyFrom->mapValue;
                    copyTo->vOrderForm = copyFrom->vOrderForm;
                    copyTo->nTimeReceived = copyFrom->nTimeReceived;
                    copyTo->nTimeSmart = copyFrom->nTimeSmart;
                    copyTo->fFromMe = copyFrom->fFromMe;
                    copyTo->strFromAccount = copyFrom->strFromAccount;
                    copyTo->nOrderPos = copyFrom->nOrderPos;
                    walletdb.WriteTx(*copyTo);
                }
            }
        }
    }

如果用户设置了"-rescan"选项，则从创世区块开始，获取需要重新更新钱包交易的位置，然后开始扫描区块，以将相关交易加入到钱包中。分析下对应的ScanForWalletTransactions()方法：

/**
 * Scan the block chain (starting in pindexStart) for transactions
 * from or to us. If fUpdate is true, found transactions that already
 * exist in the wallet will be updated.
 *
 * Returns null if scan was successful. Otherwise, if a complete rescan was not
 * possible (due to pruning or corruption), returns pointer to the most recent
 * block that could not be scanned.
 *
 * If pindexStop is not a nullptr, the scan will stop at the block-index
 * defined by pindexStop
 *
 * Caller needs to make sure pindexStop (and the optional pindexStart) are on
 * the main chain after to the addition of any new keys you want to detect
 * transactions for.
 */
CBlockIndex* CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, CBlockIndex* pindexStop, const WalletRescanReserver &reserver, bool fUpdate)
{
    int64_t nNow = GetTime();
    const CChainParams& chainParams = Params();

    assert(reserver.isReserved());
    if (pindexStop) {
        assert(pindexStop->nHeight >= pindexStart->nHeight);
    }

    CBlockIndex* pindex = pindexStart;
    CBlockIndex* ret = nullptr;
    {
        fAbortRescan = false;
        ShowProgress(_("Rescanning..."), 0); // show rescan progress in GUI as dialog or on splashscreen, if -rescan on startup
        CBlockIndex* tip = nullptr;
        double dProgressStart;
        double dProgressTip;
        {
            LOCK(cs_main);
            tip = chainActive.Tip();
            dProgressStart = GuessVerificationProgress(chainParams.TxData(), pindex);
            dProgressTip = GuessVerificationProgress(chainParams.TxData(), tip);
        }
        while (pindex && !fAbortRescan)
        {
            if (pindex->nHeight % 100 == 0 && dProgressTip - dProgressStart > 0.0) {
                double gvp = 0;
                {
                    LOCK(cs_main);
                    gvp = GuessVerificationProgress(chainParams.TxData(), pindex);
                }
                ShowProgress(_("Rescanning..."), std::max(1, std::min(99, (int)((gvp - dProgressStart) / (dProgressTip - dProgressStart) * 100))));
            }
            if (GetTime() >= nNow + 60) {
                nNow = GetTime();
                LOCK(cs_main);
                LogPrintf("Still rescanning. At block %d. Progress=%f\n", pindex->nHeight, GuessVerificationProgress(chainParams.TxData(), pindex));
            }

            CBlock block;
            if (ReadBlockFromDisk(block, pindex, Params().GetConsensus())) {
                LOCK2(cs_main, cs_wallet);
                if (pindex && !chainActive.Contains(pindex)) {
                    // Abort scan if current block is no longer active, to prevent
                    // marking transactions as coming from the wrong block.
                    ret = pindex;
                    break;
                }
                for (size_t posInBlock = 0; posInBlock < block.vtx.size(); ++posInBlock) {
                    AddToWalletIfInvolvingMe(block.vtx[posInBlock], pindex, posInBlock, fUpdate);
                }
            } else {
                ret = pindex;
            }
            if (pindex == pindexStop) {
                break;
            }
            {
                LOCK(cs_main);
                pindex = chainActive.Next(pindex);
                if (tip != chainActive.Tip()) {
                    tip = chainActive.Tip();
                    // in case the tip has changed, update progress max
                    dProgressTip = GuessVerificationProgress(chainParams.TxData(), tip);
                }
            }
        }
        if (pindex && fAbortRescan) {
            LogPrintf("Rescan aborted at block %d. Progress=%f\n", pindex->nHeight, GuessVerificationProgress(chainParams.TxData(), pindex));
        }
        ShowProgress(_("Rescanning..."), 100); // hide progress dialog in GUI
    }
    return ret;
}

阅读该方法的源码可以看到，所有的区块数据是存储在磁盘中的，chainActive存储的是区块的位置索引链，通过遍历这个位置索引链，调用ReadBlockFromDisk()方法从磁盘中读取区块信息，然后通过 AddToWalletIfInvolvingMe()方法将区块中的交易数据加入到钱包中。