path: root/src/db.cpp

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2012 The Bitcoin developers
// Distributed under the MIT/X11 software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include "db.h"
#include "util.h"
#include "main.h"
#include <boost/version.hpp>
#include <boost/filesystem.hpp>
#include <boost/filesystem/fstream.hpp>

#ifndef WIN32
#include "sys/stat.h"
#endif

using namespace std;
using namespace boost;


unsigned int nWalletDBUpdated;



//
// CDB
//

CCriticalSection cs_db;
static bool fDbEnvInit = false;
bool fDetachDB = false;
DbEnv dbenv(0);
map<string, int> mapFileUseCount;
static map<string, Db*> mapDb;

static void EnvShutdown()
{
    if (!fDbEnvInit)
        return;

    fDbEnvInit = false;
    try
    {
        dbenv.close(0);
    }
    catch (const DbException& e)
    {
        printf("EnvShutdown exception: %s (%d)\n", e.what(), e.get_errno());
    }
    DbEnv(0).remove(GetDataDir().string().c_str(), 0);
}

class CDBInit
{
public:
    CDBInit()
    {
    }
    ~CDBInit()
    {
        EnvShutdown();
    }
}
instance_of_cdbinit;


CDB::CDB(const char *pszFile, const char* pszMode) : pdb(NULL)
{
    int ret;
    if (pszFile == NULL)
        return;

    fReadOnly = (!strchr(pszMode, '+') && !strchr(pszMode, 'w'));
    bool fCreate = strchr(pszMode, 'c');
    unsigned int nFlags = DB_THREAD;
    if (fCreate)
        nFlags |= DB_CREATE;

    {
        LOCK(cs_db);
        if (!fDbEnvInit)
        {
            if (fShutdown)
                return;
            filesystem::path pathDataDir = GetDataDir();
            filesystem::path pathLogDir = pathDataDir / "database";
            filesystem::create_directory(pathLogDir);
            filesystem::path pathErrorFile = pathDataDir / "db.log";
            printf("dbenv.open LogDir=%s ErrorFile=%s\n", pathLogDir.string().c_str(), pathErrorFile.string().c_str());

            int nDbCache = GetArg("-dbcache", 25);
            dbenv.set_lg_dir(pathLogDir.string().c_str());
            dbenv.set_cachesize(nDbCache / 1024, (nDbCache % 1024)*1048576, 1);
            dbenv.set_lg_bsize(1048576);
            dbenv.set_lg_max(10485760);
            dbenv.set_lk_max_locks(10000);
            dbenv.set_lk_max_objects(10000);
            dbenv.set_errfile(fopen(pathErrorFile.string().c_str(), "a")); /// debug
            dbenv.set_flags(DB_AUTO_COMMIT, 1);
            dbenv.log_set_config(DB_LOG_AUTO_REMOVE, 1);
            ret = dbenv.open(pathDataDir.string().c_str(),
                             DB_CREATE     |
                             DB_INIT_LOCK  |
                             DB_INIT_LOG   |
                             DB_INIT_MPOOL |
                             DB_INIT_TXN   |
                             DB_THREAD     |
                             DB_RECOVER,
                             S_IRUSR | S_IWUSR);
            if (ret > 0)
                throw runtime_error(strprintf("CDB() : error %d opening database environment", ret));
            fDbEnvInit = true;
        }

        strFile = pszFile;
        ++mapFileUseCount[strFile];
        pdb = mapDb[strFile];
        if (pdb == NULL)
        {
            pdb = new Db(&dbenv, 0);

            ret = pdb->open(NULL,      // Txn pointer
                            pszFile,   // Filename
                            "main",    // Logical db name
                            DB_BTREE,  // Database type
                            nFlags,    // Flags
                            0);

            if (ret > 0)
            {
                delete pdb;
                pdb = NULL;
                {
                     LOCK(cs_db);
                    --mapFileUseCount[strFile];
                }
                strFile = "";
                throw runtime_error(strprintf("CDB() : can't open database file %s, error %d", pszFile, ret));
            }

            if (fCreate && !Exists(string("version")))
            {
                bool fTmp = fReadOnly;
                fReadOnly = false;
                WriteVersion(CLIENT_VERSION);
                fReadOnly = fTmp;
            }

            mapDb[strFile] = pdb;
        }
    }
}

void CDB::Close()
{
    if (!pdb)
        return;
    if (!vTxn.empty())
        vTxn.front()->abort();
    vTxn.clear();
    pdb = NULL;

    // Flush database activity from memory pool to disk log
    unsigned int nMinutes = 0;
    if (fReadOnly)
        nMinutes = 1;
    if (strFile == "blkindex.dat")
        nMinutes = 2;
    if (strFile == "blkindex.dat" && IsInitialBlockDownload())
        nMinutes = 5;

    dbenv.txn_checkpoint(nMinutes ? GetArg("-dblogsize", 100)*1024 : 0, nMinutes, 0);

    {
        LOCK(cs_db);
        --mapFileUseCount[strFile];
    }
}

void CloseDb(const string& strFile)
{
    {
        LOCK(cs_db);
        if (mapDb[strFile] != NULL)
        {
            // Close the database handle
            Db* pdb = mapDb[strFile];
            pdb->close(0);
            delete pdb;
            mapDb[strFile] = NULL;
        }
    }
}

bool CDB::Rewrite(const string& strFile, const char* pszSkip)
{
    while (!fShutdown)
    {
        {
            LOCK(cs_db);
            if (!mapFileUseCount.count(strFile) || mapFileUseCount[strFile] == 0)
            {
                // Flush log data to the dat file
                CloseDb(strFile);
                dbenv.txn_checkpoint(0, 0, 0);
                dbenv.lsn_reset(strFile.c_str(), 0);
                mapFileUseCount.erase(strFile);

                bool fSuccess = true;
                printf("Rewriting %s...\n", strFile.c_str());
                string strFileRes = strFile + ".rewrite";
                { // surround usage of db with extra {}
                    CDB db(strFile.c_str(), "r");
                    Db* pdbCopy = new Db(&dbenv, 0);
    
                    int ret = pdbCopy->open(NULL,                 // Txn pointer
                                            strFileRes.c_str(),   // Filename
                                            "main",    // Logical db name
                                            DB_BTREE,  // Database type
                                            DB_CREATE,    // Flags
                                            0);
                    if (ret > 0)
                    {
                        printf("Cannot create database file %s\n", strFileRes.c_str());
                        fSuccess = false;
                    }
    
                    Dbc* pcursor = db.GetCursor();
                    if (pcursor)
                        while (fSuccess)
                        {
                            CDataStream ssKey(SER_DISK, CLIENT_VERSION);
                            CDataStream ssValue(SER_DISK, CLIENT_VERSION);
                            int ret = db.ReadAtCursor(pcursor, ssKey, ssValue, DB_NEXT);
                            if (ret == DB_NOTFOUND)
                            {
                                pcursor->close();
                                break;
                            }
                            else if (ret != 0)
                            {
                                pcursor->close();
                                fSuccess = false;
                                break;
                            }
                            if (pszSkip &&
                                strncmp(&ssKey[0], pszSkip, std::min(ssKey.size(), strlen(pszSkip))) == 0)
                                continue;
                            if (strncmp(&ssKey[0], "\x07version", 8) == 0)
                            {
                                // Update version:
                                ssValue.clear();
                                ssValue << CLIENT_VERSION;
                            }
                            Dbt datKey(&ssKey[0], ssKey.size());
                            Dbt datValue(&ssValue[0], ssValue.size());
                            int ret2 = pdbCopy->put(NULL, &datKey, &datValue, DB_NOOVERWRITE);
                            if (ret2 > 0)
                                fSuccess = false;
                        }
                    if (fSuccess)
                    {
                        db.Close();
                        CloseDb(strFile);
                        if (pdbCopy->close(0))
                            fSuccess = false;
                        delete pdbCopy;
                    }
                }
                if (fSuccess)
                {
                    Db dbA(&dbenv, 0);
                    if (dbA.remove(strFile.c_str(), NULL, 0))
                        fSuccess = false;
                    Db dbB(&dbenv, 0);
                    if (dbB.rename(strFileRes.c_str(), NULL, strFile.c_str(), 0))
                        fSuccess = false;
                }
                if (!fSuccess)
                    printf("Rewriting of %s FAILED!\n", strFileRes.c_str());
                return fSuccess;
            }
        }
        Sleep(100);
    }
    return false;
}


void DBFlush(bool fShutdown)
{
    int64 nStart = GetTimeMillis();
    // Flush log data to the actual data file
    //  on all files that are not in use
    printf("DBFlush(%s)%s\n", fShutdown ? "true" : "false", fDbEnvInit ? "" : " db not started");
    if (!fDbEnvInit)
        return;
    {
        LOCK(cs_db);
        map<string, int>::iterator mi = mapFileUseCount.begin();
        while (mi != mapFileUseCount.end())
        {
            string strFile = (*mi).first;
            int nRefCount = (*mi).second;
            printf("%s refcount=%d\n", strFile.c_str(), nRefCount);
            if (nRefCount == 0)
            {
                // Move log data to the dat file
                CloseDb(strFile);
                printf("%s checkpoint\n", strFile.c_str());
                dbenv.txn_checkpoint(0, 0, 0);
                if (strFile != "blkindex.dat" || fDetachDB) {
                    printf("%s detach\n", strFile.c_str());
                    dbenv.lsn_reset(strFile.c_str(), 0);
                }
                printf("%s closed\n", strFile.c_str());
                mapFileUseCount.erase(mi++);
            }
            else
                mi++;
        }
        printf("DBFlush(%s)%s ended %15"PRI64d"ms\n", fShutdown ? "true" : "false", fDbEnvInit ? "" : " db not started", GetTimeMillis() - nStart);
        if (fShutdown)
        {
            char** listp;
            if (mapFileUseCount.empty())
            {
                dbenv.log_archive(&listp, DB_ARCH_REMOVE);
                EnvShutdown();
            }
        }
    }
}






//
// CTxDB
//

bool CTxDB::ReadTxIndex(uint256 hash, CTxIndex& txindex)
{
    assert(!fClient);
    txindex.SetNull();
    return Read(make_pair(string("tx"), hash), txindex);
}

bool CTxDB::UpdateTxIndex(uint256 hash, const CTxIndex& txindex)
{
    assert(!fClient);
    return Write(make_pair(string("tx"), hash), txindex);
}

bool CTxDB::AddTxIndex(const CTransaction& tx, const CDiskTxPos& pos, int nHeight)
{
    assert(!fClient);

    // Add to tx index
    uint256 hash = tx.GetHash();
    CTxIndex txindex(pos, tx.vout.size());
    return Write(make_pair(string("tx"), hash), txindex);
}

bool CTxDB::EraseTxIndex(const CTransaction& tx)
{
    assert(!fClient);
    uint256 hash = tx.GetHash();

    return Erase(make_pair(string("tx"), hash));
}

bool CTxDB::ContainsTx(uint256 hash)
{
    assert(!fClient);
    return Exists(make_pair(string("tx"), hash));
}

bool CTxDB::ReadOwnerTxes(uint160 hash160, int nMinHeight, vector<CTransaction>& vtx)
{
    assert(!fClient);
    vtx.clear();

    // Get cursor
    Dbc* pcursor = GetCursor();
    if (!pcursor)
        return false;

    unsigned int fFlags = DB_SET_RANGE;
    loop
    {
        // Read next record
        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
        if (fFlags == DB_SET_RANGE)
            ssKey << string("owner") << hash160 << CDiskTxPos(0, 0, 0);
        CDataStream ssValue(SER_DISK, CLIENT_VERSION);
        int ret = ReadAtCursor(pcursor, ssKey, ssValue, fFlags);
        fFlags = DB_NEXT;
        if (ret == DB_NOTFOUND)
            break;
        else if (ret != 0)
        {
            pcursor->close();
            return false;
        }

        // Unserialize
        string strType;
        uint160 hashItem;
        CDiskTxPos pos;
        ssKey >> strType >> hashItem >> pos;
        int nItemHeight;
        ssValue >> nItemHeight;

        // Read transaction
        if (strType != "owner" || hashItem != hash160)
            break;
        if (nItemHeight >= nMinHeight)
        {
            vtx.resize(vtx.size()+1);
            if (!vtx.back().ReadFromDisk(pos))
            {
                pcursor->close();
                return false;
            }
        }
    }

    pcursor->close();
    return true;
}

bool CTxDB::ReadDiskTx(uint256 hash, CTransaction& tx, CTxIndex& txindex)
{
    assert(!fClient);
    tx.SetNull();
    if (!ReadTxIndex(hash, txindex))
        return false;
    return (tx.ReadFromDisk(txindex.pos));
}

bool CTxDB::ReadDiskTx(uint256 hash, CTransaction& tx)
{
    CTxIndex txindex;
    return ReadDiskTx(hash, tx, txindex);
}

bool CTxDB::ReadDiskTx(COutPoint outpoint, CTransaction& tx, CTxIndex& txindex)
{
    return ReadDiskTx(outpoint.hash, tx, txindex);
}

bool CTxDB::ReadDiskTx(COutPoint outpoint, CTransaction& tx)
{
    CTxIndex txindex;
    return ReadDiskTx(outpoint.hash, tx, txindex);
}

bool CTxDB::WriteBlockIndex(const CDiskBlockIndex& blockindex)
{
    return Write(make_pair(string("blockindex"), blockindex.GetBlockHash()), blockindex);
}

bool CTxDB::ReadHashBestChain(uint256& hashBestChain)
{
    return Read(string("hashBestChain"), hashBestChain);
}

bool CTxDB::WriteHashBestChain(uint256 hashBestChain)
{
    return Write(string("hashBestChain"), hashBestChain);
}

bool CTxDB::ReadBestInvalidWork(CBigNum& bnBestInvalidWork)
{
    return Read(string("bnBestInvalidWork"), bnBestInvalidWork);
}

bool CTxDB::WriteBestInvalidWork(CBigNum bnBestInvalidWork)
{
    return Write(string("bnBestInvalidWork"), bnBestInvalidWork);
}

CBlockIndex static * InsertBlockIndex(uint256 hash)
{
    if (hash == 0)
        return NULL;

    // Return existing
    map<uint256, CBlockIndex*>::iterator mi = mapBlockIndex.find(hash);
    if (mi != mapBlockIndex.end())
        return (*mi).second;

    // Create new
    CBlockIndex* pindexNew = new CBlockIndex();
    if (!pindexNew)
        throw runtime_error("LoadBlockIndex() : new CBlockIndex failed");
    mi = mapBlockIndex.insert(make_pair(hash, pindexNew)).first;
    pindexNew->phashBlock = &((*mi).first);

    return pindexNew;
}

bool CTxDB::LoadBlockIndex()
{
    // Get database cursor
    Dbc* pcursor = GetCursor();
    if (!pcursor)
        return false;

    // Load mapBlockIndex
    unsigned int fFlags = DB_SET_RANGE;
    loop
    {
        // Read next record
        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
        if (fFlags == DB_SET_RANGE)
            ssKey << make_pair(string("blockindex"), uint256(0));
        CDataStream ssValue(SER_DISK, CLIENT_VERSION);
        int ret = ReadAtCursor(pcursor, ssKey, ssValue, fFlags);
        fFlags = DB_NEXT;
        if (ret == DB_NOTFOUND)
            break;
        else if (ret != 0)
            return false;

        // Unserialize
        string strType;
        ssKey >> strType;
        if (strType == "blockindex" && !fRequestShutdown)
        {
            CDiskBlockIndex diskindex;
            ssValue >> diskindex;

            // Construct block index object
            CBlockIndex* pindexNew = InsertBlockIndex(diskindex.GetBlockHash());
            pindexNew->pprev          = InsertBlockIndex(diskindex.hashPrev);
            pindexNew->pnext          = InsertBlockIndex(diskindex.hashNext);
            pindexNew->nFile          = diskindex.nFile;
            pindexNew->nBlockPos      = diskindex.nBlockPos;
            pindexNew->nHeight        = diskindex.nHeight;
            pindexNew->nVersion       = diskindex.nVersion;
            pindexNew->hashMerkleRoot = diskindex.hashMerkleRoot;
            pindexNew->nTime          = diskindex.nTime;
            pindexNew->nBits          = diskindex.nBits;
            pindexNew->nNonce         = diskindex.nNonce;

            // Watch for genesis block
            if (pindexGenesisBlock == NULL && diskindex.GetBlockHash() == hashGenesisBlock)
                pindexGenesisBlock = pindexNew;

            if (!pindexNew->CheckIndex())
                return error("LoadBlockIndex() : CheckIndex failed at %d", pindexNew->nHeight);
        }
        else
        {
            break; // if shutdown requested or finished loading block index
        }
    }
    pcursor->close();

    if (fRequestShutdown)
        return true;

    // Calculate bnChainWork
    vector<pair<int, CBlockIndex*> > vSortedByHeight;
    vSortedByHeight.reserve(mapBlockIndex.size());
    BOOST_FOREACH(const PAIRTYPE(uint256, CBlockIndex*)& item, mapBlockIndex)
    {
        CBlockIndex* pindex = item.second;
        vSortedByHeight.push_back(make_pair(pindex->nHeight, pindex));
    }
    sort(vSortedByHeight.begin(), vSortedByHeight.end());
    BOOST_FOREACH(const PAIRTYPE(int, CBlockIndex*)& item, vSortedByHeight)
    {
        CBlockIndex* pindex = item.second;
        pindex->bnChainWork = (pindex->pprev ? pindex->pprev->bnChainWork : 0) + pindex->GetBlockWork();
    }

    // Load hashBestChain pointer to end of best chain
    if (!ReadHashBestChain(hashBestChain))
    {
        if (pindexGenesisBlock == NULL)
            return true;
        return error("CTxDB::LoadBlockIndex() : hashBestChain not loaded");
    }
    if (!mapBlockIndex.count(hashBestChain))
        return error("CTxDB::LoadBlockIndex() : hashBestChain not found in the block index");
    pindexBest = mapBlockIndex[hashBestChain];
    nBestHeight = pindexBest->nHeight;
    bnBestChainWork = pindexBest->bnChainWork;
    printf("LoadBlockIndex(): hashBestChain=%s  height=%d\n", hashBestChain.ToString().substr(0,20).c_str(), nBestHeight);

    // Load bnBestInvalidWork, OK if it doesn't exist
    ReadBestInvalidWork(bnBestInvalidWork);

    // Verify blocks in the best chain
    int nCheckLevel = GetArg("-checklevel", 1);
    int nCheckDepth = GetArg( "-checkblocks", 2500);
    if (nCheckDepth == 0)
        nCheckDepth = 1000000000; // suffices until the year 19000
    if (nCheckDepth > nBestHeight)
        nCheckDepth = nBestHeight;
    printf("Verifying last %i blocks at level %i\n", nCheckDepth, nCheckLevel);
    CBlockIndex* pindexFork = NULL;
    map<pair<unsigned int, unsigned int>, CBlockIndex*> mapBlockPos;
    for (CBlockIndex* pindex = pindexBest; pindex && pindex->pprev; pindex = pindex->pprev)
    {
        if (fRequestShutdown || pindex->nHeight < nBestHeight-nCheckDepth)
            break;
        CBlock block;
        if (!block.ReadFromDisk(pindex))
            return error("LoadBlockIndex() : block.ReadFromDisk failed");
        // check level 1: verify block validity
        if (nCheckLevel>0 && !block.CheckBlock())
        {
            printf("LoadBlockIndex() : *** found bad block at %d, hash=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString().c_str());
            pindexFork = pindex->pprev;
        }
        // check level 2: verify transaction index validity
        if (nCheckLevel>1)
        {
            pair<unsigned int, unsigned int> pos = make_pair(pindex->nFile, pindex->nBlockPos);
            mapBlockPos[pos] = pindex;
            BOOST_FOREACH(const CTransaction &tx, block.vtx)
            {
                uint256 hashTx = tx.GetHash();
                CTxIndex txindex;
                if (ReadTxIndex(hashTx, txindex))
                {
                    // check level 3: checker transaction hashes
                    if (nCheckLevel>2 || pindex->nFile != txindex.pos.nFile || pindex->nBlockPos != txindex.pos.nBlockPos)
                    {
                        // either an error or a duplicate transaction
                        CTransaction txFound;
                        if (!txFound.ReadFromDisk(txindex.pos))
                        {
                            printf("LoadBlockIndex() : *** cannot read mislocated transaction %s\n", hashTx.ToString().c_str());
                            pindexFork = pindex->pprev;
                        }
                        else
                            if (txFound.GetHash() != hashTx) // not a duplicate tx
                            {
                                printf("LoadBlockIndex(): *** invalid tx position for %s\n", hashTx.ToString().c_str());
                                pindexFork = pindex->pprev;
                            }
                    }
                    // check level 4: check whether spent txouts were spent within the main chain
                    unsigned int nOutput = 0;
                    if (nCheckLevel>3)
                    {
                        BOOST_FOREACH(const CDiskTxPos &txpos, txindex.vSpent)
                        {
                            if (!txpos.IsNull())
                            {
                                pair<unsigned int, unsigned int> posFind = make_pair(txpos.nFile, txpos.nBlockPos);
                                if (!mapBlockPos.count(posFind))
                                {
                                    printf("LoadBlockIndex(): *** found bad spend at %d, hashBlock=%s, hashTx=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString().c_str(), hashTx.ToString().c_str());
                                    pindexFork = pindex->pprev;
                                }
                                // check level 6: check whether spent txouts were spent by a valid transaction that consume them
                                if (nCheckLevel>5)
                                {
                                    CTransaction txSpend;
                                    if (!txSpend.ReadFromDisk(txpos))
                                    {
                                        printf("LoadBlockIndex(): *** cannot read spending transaction of %s:%i from disk\n", hashTx.ToString().c_str(), nOutput);
                                        pindexFork = pindex->pprev;
                                    }
                                    else if (!txSpend.CheckTransaction())
                                    {
                                        printf("LoadBlockIndex(): *** spending transaction of %s:%i is invalid\n", hashTx.ToString().c_str(), nOutput);
                                        pindexFork = pindex->pprev;
                                    }
                                    else
                                    {
                                        bool fFound = false;
                                        BOOST_FOREACH(const CTxIn &txin, txSpend.vin)
                                            if (txin.prevout.hash == hashTx && txin.prevout.n == nOutput)
                                                fFound = true;
                                        if (!fFound)
                                        {
                                            printf("LoadBlockIndex(): *** spending transaction of %s:%i does not spend it\n", hashTx.ToString().c_str(), nOutput);
                                            pindexFork = pindex->pprev;
                                        }
                                    }
                                }
                            }
                            nOutput++;
                        }
                    }
                }
                // check level 5: check whether all prevouts are marked spent
                if (nCheckLevel>4)
                {
                     BOOST_FOREACH(const CTxIn &txin, tx.vin)
                     {
                          CTxIndex txindex;
                          if (ReadTxIndex(txin.prevout.hash, txindex))
                              if (txindex.vSpent.size()-1 < txin.prevout.n || txindex.vSpent[txin.prevout.n].IsNull())
                              {
                                  printf("LoadBlockIndex(): *** found unspent prevout %s:%i in %s\n", txin.prevout.hash.ToString().c_str(), txin.prevout.n, hashTx.ToString().c_str());
                                  pindexFork = pindex->pprev;
                              }
                     }
                }
            }
        }
    }
    if (pindexFork && !fRequestShutdown)
    {
        // Reorg back to the fork
        printf("LoadBlockIndex() : *** moving best chain pointer back to block %d\n", pindexFork->nHeight);
        CBlock block;
        if (!block.ReadFromDisk(pindexFork))
            return error("LoadBlockIndex() : block.ReadFromDisk failed");
        CTxDB txdb;
        block.SetBestChain(txdb, pindexFork);
    }

    return true;
}





//
// CAddrDB
//


CAddrDB::CAddrDB()
{
    pathAddr = GetDataDir() / "peers.dat";
}

bool CAddrDB::Write(const CAddrMan& addr)
{
    // Generate random temporary filename
    unsigned short randv = 0;
    RAND_bytes((unsigned char *)&randv, sizeof(randv));
    std::string tmpfn = strprintf("peers.dat.%04x", randv);

    // serialize addresses, checksum data up to that point, then append csum
    CDataStream ssPeers(SER_DISK, CLIENT_VERSION);
    ssPeers << FLATDATA(pchMessageStart);
    ssPeers << addr;
    uint256 hash = Hash(ssPeers.begin(), ssPeers.end());
    ssPeers << hash;

    // open temp output file, and associate with CAutoFile
    boost::filesystem::path pathTmp = GetDataDir() / tmpfn;
    FILE *file = fopen(pathTmp.string().c_str(), "wb");
    CAutoFile fileout = CAutoFile(file, SER_DISK, CLIENT_VERSION);
    if (!fileout)
        return error("CAddrman::Write() : open failed");

    // Write and commit header, data
    try {
        fileout << ssPeers;
    }
    catch (std::exception &e) {
        return error("CAddrman::Write() : I/O error");
    }
    FileCommit(fileout);
    fileout.fclose();

    // replace existing peers.dat, if any, with new peers.dat.XXXX
    if (!RenameOver(pathTmp, pathAddr))
        return error("CAddrman::Write() : Rename-into-place failed");

    return true;
}

bool CAddrDB::Read(CAddrMan& addr)
{
    // open input file, and associate with CAutoFile
    FILE *file = fopen(pathAddr.string().c_str(), "rb");
    CAutoFile filein = CAutoFile(file, SER_DISK, CLIENT_VERSION);
    if (!filein)
        return error("CAddrman::Read() : open failed");

    // use file size to size memory buffer
    int fileSize = GetFilesize(filein);
    int dataSize = fileSize - sizeof(uint256);
    vector<unsigned char> vchData;
    vchData.resize(dataSize);
    uint256 hashIn;

    // read data and checksum from file
    try {
        filein.read((char *)&vchData[0], dataSize);
        filein >> hashIn;
    }
    catch (std::exception &e) {
        return error("CAddrman::Read() 2 : I/O error or stream data corrupted");
    }
    filein.fclose();

    CDataStream ssPeers(vchData, SER_DISK, CLIENT_VERSION);

    // verify stored checksum matches input data
    uint256 hashTmp = Hash(ssPeers.begin(), ssPeers.end());
    if (hashIn != hashTmp)
        return error("CAddrman::Read() : checksum mismatch; data corrupted");

    // de-serialize address data
    unsigned char pchMsgTmp[4];
    try {
        ssPeers >> FLATDATA(pchMsgTmp);
        ssPeers >> addr;
    }
    catch (std::exception &e) {
        return error("CAddrman::Read() : I/O error or stream data corrupted");
    }

    // finally, verify the network matches ours
    if (memcmp(pchMsgTmp, pchMessageStart, sizeof(pchMsgTmp)))
        return error("CAddrman::Read() : invalid network magic number");

    return true;
}