path: root/eth/backend.go

// Copyright 2014 The go-ethereum Authors
// This file is part of go-ethereum.
//
// go-ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// go-ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with go-ethereum.  If not, see <http://www.gnu.org/licenses/>.

package eth

import (
    "crypto/ecdsa"
    "encoding/json"
    "fmt"
    "io/ioutil"
    "math/big"
    "os"
    "path/filepath"
    "strings"
    "time"

    "github.com/ethereum/ethash"
    "github.com/ethereum/go-ethereum/accounts"
    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/compiler"
    "github.com/ethereum/go-ethereum/core"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/core/vm"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/eth/downloader"
    "github.com/ethereum/go-ethereum/ethdb"
    "github.com/ethereum/go-ethereum/event"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/ethereum/go-ethereum/metrics"
    "github.com/ethereum/go-ethereum/miner"
    "github.com/ethereum/go-ethereum/p2p"
    "github.com/ethereum/go-ethereum/p2p/discover"
    "github.com/ethereum/go-ethereum/p2p/nat"
    "github.com/ethereum/go-ethereum/whisper"
)

const (
    epochLength    = 30000
    ethashRevision = 23

    autoDAGcheckInterval = 10 * time.Hour
    autoDAGepochHeight   = epochLength / 2
)

var (
    jsonlogger = logger.NewJsonLogger()

    defaultBootNodes = []*discover.Node{
        // ETH/DEV Go Bootnodes
        discover.MustParseNode("enode://a979fb575495b8d6db44f750317d0f4622bf4c2aa3365d6af7c284339968eef29b69ad0dce72a4d8db5ebb4968de0e3bec910127f134779fbcb0cb6d3331163c@52.16.188.185:30303"),
        discover.MustParseNode("enode://de471bccee3d042261d52e9bff31458daecc406142b401d4cd848f677479f73104b9fdeb090af9583d3391b7f10cb2ba9e26865dd5fca4fcdc0fb1e3b723c786@54.94.239.50:30303"),
        // ETH/DEV cpp-ethereum (poc-9.ethdev.com)
        discover.MustParseNode("enode://487611428e6c99a11a9795a6abe7b529e81315ca6aad66e2a2fc76e3adf263faba0d35466c2f8f68d561dbefa8878d4df5f1f2ddb1fbeab7f42ffb8cd328bd4a@5.1.83.226:30303"),
    }

    staticNodes  = "static-nodes.json"  // Path within <datadir> to search for the static node list
    trustedNodes = "trusted-nodes.json" // Path within <datadir> to search for the trusted node list
)

type Config struct {
    Name         string
    NetworkId    int
    GenesisNonce int

    BlockChainVersion  int
    SkipBcVersionCheck bool // e.g. blockchain export

    DataDir   string
    LogFile   string
    Verbosity int
    LogJSON   string
    VmDebug   bool
    NatSpec   bool
    AutoDAG   bool
    PowTest   bool

    MaxPeers        int
    MaxPendingPeers int
    Discovery       bool
    Port            string

    // Space-separated list of discovery node URLs
    BootNodes string

    // This key is used to identify the node on the network.
    // If nil, an ephemeral key is used.
    NodeKey *ecdsa.PrivateKey

    NAT  nat.Interface
    Shh  bool
    Dial bool

    Etherbase      common.Address
    GasPrice       *big.Int
    MinerThreads   int
    AccountManager *accounts.Manager
    SolcPath       string

    GpoMinGasPrice          *big.Int
    GpoMaxGasPrice          *big.Int
    GpoFullBlockRatio       int
    GpobaseStepDown         int
    GpobaseStepUp           int
    GpobaseCorrectionFactor int

    // NewDB is used to create databases.
    // If nil, the default is to create leveldb databases on disk.
    NewDB func(path string) (common.Database, error)
}

func (cfg *Config) parseBootNodes() []*discover.Node {
    if cfg.BootNodes == "" {
        return defaultBootNodes
    }
    var ns []*discover.Node
    for _, url := range strings.Split(cfg.BootNodes, " ") {
        if url == "" {
            continue
        }
        n, err := discover.ParseNode(url)
        if err != nil {
            glog.V(logger.Error).Infof("Bootstrap URL %s: %v\n", url, err)
            continue
        }
        ns = append(ns, n)
    }
    return ns
}

// parseNodes parses a list of discovery node URLs loaded from a .json file.
func (cfg *Config) parseNodes(file string) []*discover.Node {
    // Short circuit if no node config is present
    path := filepath.Join(cfg.DataDir, file)
    if _, err := os.Stat(path); err != nil {
        return nil
    }
    // Load the nodes from the config file
    blob, err := ioutil.ReadFile(path)
    if err != nil {
        glog.V(logger.Error).Infof("Failed to access nodes: %v", err)
        return nil
    }
    nodelist := []string{}
    if err := json.Unmarshal(blob, &nodelist); err != nil {
        glog.V(logger.Error).Infof("Failed to load nodes: %v", err)
        return nil
    }
    // Interpret the list as a discovery node array
    var nodes []*discover.Node
    for _, url := range nodelist {
        if url == "" {
            continue
        }
        node, err := discover.ParseNode(url)
        if err != nil {
            glog.V(logger.Error).Infof("Node URL %s: %v\n", url, err)
            continue
        }
        nodes = append(nodes, node)
    }
    return nodes
}

func (cfg *Config) nodeKey() (*ecdsa.PrivateKey, error) {
    // use explicit key from command line args if set
    if cfg.NodeKey != nil {
        return cfg.NodeKey, nil
    }
    // use persistent key if present
    keyfile := filepath.Join(cfg.DataDir, "nodekey")
    key, err := crypto.LoadECDSA(keyfile)
    if err == nil {
        return key, nil
    }
    // no persistent key, generate and store a new one
    if key, err = crypto.GenerateKey(); err != nil {
        return nil, fmt.Errorf("could not generate server key: %v", err)
    }
    if err := crypto.SaveECDSA(keyfile, key); err != nil {
        glog.V(logger.Error).Infoln("could not persist nodekey: ", err)
    }
    return key, nil
}

type Ethereum struct {
    // Channel for shutting down the ethereum
    shutdownChan chan bool

    // DB interfaces
    blockDb common.Database // Block chain database
    stateDb common.Database // State changes database
    extraDb common.Database // Extra database (txs, etc)

    // Closed when databases are flushed and closed
    databasesClosed chan bool

    //*** SERVICES ***
    // State manager for processing new blocks and managing the over all states
    blockProcessor  *core.BlockProcessor
    txPool          *core.TxPool
    chainManager    *core.ChainManager
    accountManager  *accounts.Manager
    whisper         *whisper.Whisper
    pow             *ethash.Ethash
    protocolManager *ProtocolManager
    SolcPath        string
    solc            *compiler.Solidity

    GpoMinGasPrice          *big.Int
    GpoMaxGasPrice          *big.Int
    GpoFullBlockRatio       int
    GpobaseStepDown         int
    GpobaseStepUp           int
    GpobaseCorrectionFactor int

    net      *p2p.Server
    eventMux *event.TypeMux
    miner    *miner.Miner

    // logger logger.LogSystem

    Mining        bool
    MinerThreads  int
    NatSpec       bool
    DataDir       string
    AutoDAG       bool
    PowTest       bool
    autodagquit   chan bool
    etherbase     common.Address
    clientVersion string
    netVersionId  int
    shhVersionId  int
}

func New(config *Config) (*Ethereum, error) {
    // Bootstrap database
    logger.New(config.DataDir, config.LogFile, config.Verbosity)
    if len(config.LogJSON) > 0 {
        logger.NewJSONsystem(config.DataDir, config.LogJSON)
    }

    // Let the database take 3/4 of the max open files (TODO figure out a way to get the actual limit of the open files)
    const dbCount = 3
    ethdb.OpenFileLimit = 128 / (dbCount + 1)

    newdb := config.NewDB
    if newdb == nil {
        newdb = func(path string) (common.Database, error) { return ethdb.NewLDBDatabase(path) }
    }
    blockDb, err := newdb(filepath.Join(config.DataDir, "blockchain"))
    if err != nil {
        return nil, fmt.Errorf("blockchain db err: %v", err)
    }
    if db, ok := blockDb.(*ethdb.LDBDatabase); ok {
        db.GetTimer = metrics.NewTimer("eth/db/block/user/gets")
        db.PutTimer = metrics.NewTimer("eth/db/block/user/puts")
        db.MissMeter = metrics.NewMeter("eth/db/block/user/misses")
        db.ReadMeter = metrics.NewMeter("eth/db/block/user/reads")
        db.WriteMeter = metrics.NewMeter("eth/db/block/user/writes")
        db.CompTimeMeter = metrics.NewMeter("eth/db/block/compact/time")
        db.CompReadMeter = metrics.NewMeter("eth/db/block/compact/input")
        db.CompWriteMeter = metrics.NewMeter("eth/db/block/compact/output")
    }
    stateDb, err := newdb(filepath.Join(config.DataDir, "state"))
    if err != nil {
        return nil, fmt.Errorf("state db err: %v", err)
    }
    if db, ok := stateDb.(*ethdb.LDBDatabase); ok {
        db.GetTimer = metrics.NewTimer("eth/db/state/user/gets")
        db.PutTimer = metrics.NewTimer("eth/db/state/user/puts")
        db.MissMeter = metrics.NewMeter("eth/db/state/user/misses")
        db.ReadMeter = metrics.NewMeter("eth/db/state/user/reads")
        db.WriteMeter = metrics.NewMeter("eth/db/state/user/writes")
        db.CompTimeMeter = metrics.NewMeter("eth/db/state/compact/time")
        db.CompReadMeter = metrics.NewMeter("eth/db/state/compact/input")
        db.CompWriteMeter = metrics.NewMeter("eth/db/state/compact/output")
    }
    extraDb, err := newdb(filepath.Join(config.DataDir, "extra"))
    if err != nil {
        return nil, fmt.Errorf("extra db err: %v", err)
    }
    if db, ok := extraDb.(*ethdb.LDBDatabase); ok {
        db.GetTimer = metrics.NewTimer("eth/db/extra/user/gets")
        db.PutTimer = metrics.NewTimer("eth/db/extra/user/puts")
        db.MissMeter = metrics.NewMeter("eth/db/extra/user/misses")
        db.ReadMeter = metrics.NewMeter("eth/db/extra/user/reads")
        db.WriteMeter = metrics.NewMeter("eth/db/extra/user/writes")
        db.CompTimeMeter = metrics.NewMeter("eth/db/extra/compact/time")
        db.CompReadMeter = metrics.NewMeter("eth/db/extra/compact/input")
        db.CompWriteMeter = metrics.NewMeter("eth/db/extra/compact/output")
    }
    nodeDb := filepath.Join(config.DataDir, "nodes")

    // Perform database sanity checks
    /*
        // The databases were previously tied to protocol versions. Currently we
        // are moving away from this decision as approaching Frontier. The below
        // check was left in for now but should eventually be just dropped.

        d, _ := blockDb.Get([]byte("ProtocolVersion"))
        protov := int(common.NewValue(d).Uint())
        if protov != config.ProtocolVersion && protov != 0 {
            path := filepath.Join(config.DataDir, "blockchain")
            return nil, fmt.Errorf("Database version mismatch. Protocol(%d / %d). `rm -rf %s`", protov, config.ProtocolVersion, path)
        }
        saveProtocolVersion(blockDb, config.ProtocolVersion)
    */
    glog.V(logger.Info).Infof("Protocol Versions: %v, Network Id: %v", ProtocolVersions, config.NetworkId)

    if !config.SkipBcVersionCheck {
        b, _ := blockDb.Get([]byte("BlockchainVersion"))
        bcVersion := int(common.NewValue(b).Uint())
        if bcVersion != config.BlockChainVersion && bcVersion != 0 {
            return nil, fmt.Errorf("Blockchain DB version mismatch (%d / %d). Run geth upgradedb.\n", bcVersion, config.BlockChainVersion)
        }
        saveBlockchainVersion(blockDb, config.BlockChainVersion)
    }
    glog.V(logger.Info).Infof("Blockchain DB Version: %d", config.BlockChainVersion)

    eth := &Ethereum{
        shutdownChan:            make(chan bool),
        databasesClosed:         make(chan bool),
        blockDb:                 blockDb,
        stateDb:                 stateDb,
        extraDb:                 extraDb,
        eventMux:                &event.TypeMux{},
        accountManager:          config.AccountManager,
        DataDir:                 config.DataDir,
        etherbase:               config.Etherbase,
        clientVersion:           config.Name, // TODO should separate from Name
        netVersionId:            config.NetworkId,
        NatSpec:                 config.NatSpec,
        MinerThreads:            config.MinerThreads,
        SolcPath:                config.SolcPath,
        AutoDAG:                 config.AutoDAG,
        PowTest:                 config.PowTest,
        GpoMinGasPrice:          config.GpoMinGasPrice,
        GpoMaxGasPrice:          config.GpoMaxGasPrice,
        GpoFullBlockRatio:       config.GpoFullBlockRatio,
        GpobaseStepDown:         config.GpobaseStepDown,
        GpobaseStepUp:           config.GpobaseStepUp,
        GpobaseCorrectionFactor: config.GpobaseCorrectionFactor,
    }

    if config.PowTest {
        glog.V(logger.Info).Infof("ethash used in test mode")
        eth.pow, err = ethash.NewForTesting()
        if err != nil {
            return nil, err
        }
    } else {
        eth.pow = ethash.New()
    }
    genesis := core.GenesisBlock(uint64(config.GenesisNonce), stateDb)
    eth.chainManager, err = core.NewChainManager(genesis, blockDb, stateDb, extraDb, eth.pow, eth.EventMux())
    if err != nil {
        return nil, err
    }
    eth.txPool = core.NewTxPool(eth.EventMux(), eth.chainManager.State, eth.chainManager.GasLimit)

    eth.blockProcessor = core.NewBlockProcessor(stateDb, extraDb, eth.pow, eth.chainManager, eth.EventMux())
    eth.chainManager.SetProcessor(eth.blockProcessor)
    eth.protocolManager = NewProtocolManager(config.NetworkId, eth.eventMux, eth.txPool, eth.pow, eth.chainManager)

    eth.miner = miner.New(eth, eth.EventMux(), eth.pow)
    eth.miner.SetGasPrice(config.GasPrice)
    if config.Shh {
        eth.whisper = whisper.New()
        eth.shhVersionId = int(eth.whisper.Version())
    }

    netprv, err := config.nodeKey()
    if err != nil {
        return nil, err
    }
    protocols := append([]p2p.Protocol{}, eth.protocolManager.SubProtocols...)
    if config.Shh {
        protocols = append(protocols, eth.whisper.Protocol())
    }
    eth.net = &p2p.Server{
        PrivateKey:      netprv,
        Name:            config.Name,
        MaxPeers:        config.MaxPeers,
        MaxPendingPeers: config.MaxPendingPeers,
        Discovery:       config.Discovery,
        Protocols:       protocols,
        NAT:             config.NAT,
        NoDial:          !config.Dial,
        BootstrapNodes:  config.parseBootNodes(),
        StaticNodes:     config.parseNodes(staticNodes),
        TrustedNodes:    config.parseNodes(trustedNodes),
        NodeDatabase:    nodeDb,
    }
    if len(config.Port) > 0 {
        eth.net.ListenAddr = ":" + config.Port
    }

    vm.Debug = config.VmDebug

    return eth, nil
}

type NodeInfo struct {
    Name       string
    NodeUrl    string
    NodeID     string
    IP         string
    DiscPort   int // UDP listening port for discovery protocol
    TCPPort    int // TCP listening port for RLPx
    Td         string
    ListenAddr string
}

func (s *Ethereum) NodeInfo() *NodeInfo {
    node := s.net.Self()

    return &NodeInfo{
        Name:       s.Name(),
        NodeUrl:    node.String(),
        NodeID:     node.ID.String(),
        IP:         node.IP.String(),
        DiscPort:   int(node.UDP),
        TCPPort:    int(node.TCP),
        ListenAddr: s.net.ListenAddr,
        Td:         s.ChainManager().Td().String(),
    }
}

type PeerInfo struct {
    ID            string
    Name          string
    Caps          string
    RemoteAddress string
    LocalAddress  string
}

func newPeerInfo(peer *p2p.Peer) *PeerInfo {
    var caps []string
    for _, cap := range peer.Caps() {
        caps = append(caps, cap.String())
    }
    return &PeerInfo{
        ID:            peer.ID().String(),
        Name:          peer.Name(),
        Caps:          strings.Join(caps, ", "),
        RemoteAddress: peer.RemoteAddr().String(),
        LocalAddress:  peer.LocalAddr().String(),
    }
}

// PeersInfo returns an array of PeerInfo objects describing connected peers
func (s *Ethereum) PeersInfo() (peersinfo []*PeerInfo) {
    for _, peer := range s.net.Peers() {
        if peer != nil {
            peersinfo = append(peersinfo, newPeerInfo(peer))
        }
    }
    return
}

func (s *Ethereum) ResetWithGenesisBlock(gb *types.Block) {
    s.chainManager.ResetWithGenesisBlock(gb)
}

func (s *Ethereum) StartMining(threads int) error {
    eb, err := s.Etherbase()
    if err != nil {
        err = fmt.Errorf("Cannot start mining without etherbase address: %v", err)
        glog.V(logger.Error).Infoln(err)
        return err
    }

    go s.miner.Start(eb, threads)
    return nil
}

func (s *Ethereum) Etherbase() (eb common.Address, err error) {
    eb = s.etherbase
    if (eb == common.Address{}) {
        err = fmt.Errorf("etherbase address must be explicitly specified")
    }
    return
}

// set in js console via admin interface or wrapper from cli flags
func (self *Ethereum) SetEtherbase(etherbase common.Address) {
    self.etherbase = etherbase
    self.miner.SetEtherbase(etherbase)
}

func (s *Ethereum) StopMining()         { s.miner.Stop() }
func (s *Ethereum) IsMining() bool      { return s.miner.Mining() }
func (s *Ethereum) Miner() *miner.Miner { return s.miner }

// func (s *Ethereum) Logger() logger.LogSystem             { return s.logger }
func (s *Ethereum) Name() string                         { return s.net.Name }
func (s *Ethereum) AccountManager() *accounts.Manager    { return s.accountManager }
func (s *Ethereum) ChainManager() *core.ChainManager     { return s.chainManager }
func (s *Ethereum) BlockProcessor() *core.BlockProcessor { return s.blockProcessor }
func (s *Ethereum) TxPool() *core.TxPool                 { return s.txPool }
func (s *Ethereum) Whisper() *whisper.Whisper            { return s.whisper }
func (s *Ethereum) EventMux() *event.TypeMux             { return s.eventMux }
func (s *Ethereum) BlockDb() common.Database             { return s.blockDb }
func (s *Ethereum) StateDb() common.Database             { return s.stateDb }
func (s *Ethereum) ExtraDb() common.Database             { return s.extraDb }
func (s *Ethereum) IsListening() bool                    { return true } // Always listening
func (s *Ethereum) PeerCount() int                       { return s.net.PeerCount() }
func (s *Ethereum) Peers() []*p2p.Peer                   { return s.net.Peers() }
func (s *Ethereum) MaxPeers() int                        { return s.net.MaxPeers }
func (s *Ethereum) ClientVersion() string                { return s.clientVersion }
func (s *Ethereum) EthVersion() int                      { return int(s.protocolManager.SubProtocols[0].Version) }
func (s *Ethereum) NetVersion() int                      { return s.netVersionId }
func (s *Ethereum) ShhVersion() int                      { return s.shhVersionId }
func (s *Ethereum) Downloader() *downloader.Downloader   { return s.protocolManager.downloader }

// Start the ethereum
func (s *Ethereum) Start() error {
    jsonlogger.LogJson(&logger.LogStarting{
        ClientString:    s.net.Name,
        ProtocolVersion: s.EthVersion(),
    })
    err := s.net.Start()
    if err != nil {
        return err
    }
    // periodically flush databases
    go s.syncDatabases()

    if s.AutoDAG {
        s.StartAutoDAG()
    }

    s.protocolManager.Start()

    if s.whisper != nil {
        s.whisper.Start()
    }

    glog.V(logger.Info).Infoln("Server started")
    return nil
}

// sync databases every minute. If flushing fails we exit immediatly. The system
// may not continue under any circumstances.
func (s *Ethereum) syncDatabases() {
    ticker := time.NewTicker(1 * time.Minute)
done:
    for {
        select {
        case <-ticker.C:
            // don't change the order of database flushes
            if err := s.extraDb.Flush(); err != nil {
                glog.Fatalf("fatal error: flush extraDb: %v (Restart your node. We are aware of this issue)\n", err)
            }
            if err := s.stateDb.Flush(); err != nil {
                glog.Fatalf("fatal error: flush stateDb: %v (Restart your node. We are aware of this issue)\n", err)
            }
            if err := s.blockDb.Flush(); err != nil {
                glog.Fatalf("fatal error: flush blockDb: %v (Restart your node. We are aware of this issue)\n", err)
            }
        case <-s.shutdownChan:
            break done
        }
    }

    s.blockDb.Close()
    s.stateDb.Close()
    s.extraDb.Close()

    close(s.databasesClosed)
}

func (s *Ethereum) StartForTest() {
    jsonlogger.LogJson(&logger.LogStarting{
        ClientString:    s.net.Name,
        ProtocolVersion: s.EthVersion(),
    })
}

// AddPeer connects to the given node and maintains the connection until the
// server is shut down. If the connection fails for any reason, the server will
// attempt to reconnect the peer.
func (self *Ethereum) AddPeer(nodeURL string) error {
    n, err := discover.ParseNode(nodeURL)
    if err != nil {
        return fmt.Errorf("invalid node URL: %v", err)
    }
    self.net.AddPeer(n)
    return nil
}

func (s *Ethereum) Stop() {
    s.net.Stop()
    s.chainManager.Stop()
    s.protocolManager.Stop()
    s.txPool.Stop()
    s.eventMux.Stop()
    if s.whisper != nil {
        s.whisper.Stop()
    }
    s.StopAutoDAG()

    close(s.shutdownChan)
}

// This function will wait for a shutdown and resumes main thread execution
func (s *Ethereum) WaitForShutdown() {
    <-s.databasesClosed
    <-s.shutdownChan
}

// StartAutoDAG() spawns a go routine that checks the DAG every autoDAGcheckInterval
// by default that is 10 times per epoch
// in epoch n, if we past autoDAGepochHeight within-epoch blocks,
// it calls ethash.MakeDAG  to pregenerate the DAG for the next epoch n+1
// if it does not exist yet as well as remove the DAG for epoch n-1
// the loop quits if autodagquit channel is closed, it can safely restart and
// stop any number of times.
// For any more sophisticated pattern of DAG generation, use CLI subcommand
// makedag
func (self *Ethereum) StartAutoDAG() {
    if self.autodagquit != nil {
        return // already started
    }
    go func() {
        glog.V(logger.Info).Infof("Automatic pregeneration of ethash DAG ON (ethash dir: %s)", ethash.DefaultDir)
        var nextEpoch uint64
        timer := time.After(0)
        self.autodagquit = make(chan bool)
        for {
            select {
            case <-timer:
                glog.V(logger.Info).Infof("checking DAG (ethash dir: %s)", ethash.DefaultDir)
                currentBlock := self.ChainManager().CurrentBlock().NumberU64()
                thisEpoch := currentBlock / epochLength
                if nextEpoch <= thisEpoch {
                    if currentBlock%epochLength > autoDAGepochHeight {
                        if thisEpoch > 0 {
                            previousDag, previousDagFull := dagFiles(thisEpoch - 1)
                            os.Remove(filepath.Join(ethash.DefaultDir, previousDag))
                            os.Remove(filepath.Join(ethash.DefaultDir, previousDagFull))
                            glog.V(logger.Info).Infof("removed DAG for epoch %d (%s)", thisEpoch-1, previousDag)
                        }
                        nextEpoch = thisEpoch + 1
                        dag, _ := dagFiles(nextEpoch)
                        if _, err := os.Stat(dag); os.IsNotExist(err) {
                            glog.V(logger.Info).Infof("Pregenerating DAG for epoch %d (%s)", nextEpoch, dag)
                            err := ethash.MakeDAG(nextEpoch*epochLength, "") // "" -> ethash.DefaultDir
                            if err != nil {
                                glog.V(logger.Error).Infof("Error generating DAG for epoch %d (%s)", nextEpoch, dag)
                                return
                            }
                        } else {
                            glog.V(logger.Error).Infof("DAG for epoch %d (%s)", nextEpoch, dag)
                        }
                    }
                }
                timer = time.After(autoDAGcheckInterval)
            case <-self.autodagquit:
                return
            }
        }
    }()
}

// dagFiles(epoch) returns the two alternative DAG filenames (not a path)
// 1) <revision>-<hex(seedhash[8])> 2) full-R<revision>-<hex(seedhash[8])>
func dagFiles(epoch uint64) (string, string) {
    seedHash, _ := ethash.GetSeedHash(epoch * epochLength)
    dag := fmt.Sprintf("full-R%d-%x", ethashRevision, seedHash[:8])
    return dag, "full-R" + dag
}

// stopAutoDAG stops automatic DAG pregeneration by quitting the loop
func (self *Ethereum) StopAutoDAG() {
    if self.autodagquit != nil {
        close(self.autodagquit)
        self.autodagquit = nil
    }
    glog.V(logger.Info).Infof("Automatic pregeneration of ethash DAG OFF (ethash dir: %s)", ethash.DefaultDir)
}

/*
    // The databases were previously tied to protocol versions. Currently we
    // are moving away from this decision as approaching Frontier. The below
    // code was left in for now but should eventually be just dropped.

    func saveProtocolVersion(db common.Database, protov int) {
        d, _ := db.Get([]byte("ProtocolVersion"))
        protocolVersion := common.NewValue(d).Uint()

        if protocolVersion == 0 {
            db.Put([]byte("ProtocolVersion"), common.NewValue(protov).Bytes())
        }
    }
*/

func saveBlockchainVersion(db common.Database, bcVersion int) {
    d, _ := db.Get([]byte("BlockchainVersion"))
    blockchainVersion := common.NewValue(d).Uint()

    if blockchainVersion == 0 {
        db.Put([]byte("BlockchainVersion"), common.NewValue(bcVersion).Bytes())
    }
}

func (self *Ethereum) Solc() (*compiler.Solidity, error) {
    var err error
    if self.solc == nil {
        self.solc, err = compiler.New(self.SolcPath)
    }
    return self.solc, err
}

// set in js console via admin interface or wrapper from cli flags
func (self *Ethereum) SetSolc(solcPath string) (*compiler.Solidity, error) {
    self.SolcPath = solcPath
    self.solc = nil
    return self.Solc()
}