path: root/core/state_transition.go

package core

import (
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/state"
    "github.com/ethereum/go-ethereum/core/vm"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/ethereum/go-ethereum/params"
)

/*
 * The State transitioning model
 *
 * A state transition is a change made when a transaction is applied to the current world state
 * The state transitioning model does all all the necessary work to work out a valid new state root.
 * 1) Nonce handling
 * 2) Pre pay / buy gas of the coinbase (miner)
 * 3) Create a new state object if the recipient is \0*32
 * 4) Value transfer
 * == If contract creation ==
 * 4a) Attempt to run transaction data
 * 4b) If valid, use result as code for the new state object
 * == end ==
 * 5) Run Script section
 * 6) Derive new state root
 */
type StateTransition struct {
    coinbase      common.Address
    msg           Message
    gas, gasPrice *big.Int
    initialGas    *big.Int
    value         *big.Int
    data          []byte
    state         *state.StateDB

    cb, rec, sen *state.StateObject

    env vm.Environment
}

// Message represents a message sent to a contract.
type Message interface {
    From() (common.Address, error)
    To() *common.Address

    GasPrice() *big.Int
    Gas() *big.Int
    Value() *big.Int

    Nonce() uint64
    Data() []byte
}

func MessageCreatesContract(msg Message) bool {
    return msg.To() == nil
}

// IntrinsicGas computes the 'intrisic gas' for a message
// with the given data.
func IntrinsicGas(data []byte) *big.Int {
    igas := new(big.Int).Set(params.TxGas)
    if len(data) > 0 {
        var nz int64
        for _, byt := range data {
            if byt != 0 {
                nz++
            }
        }
        m := big.NewInt(nz)
        m.Mul(m, params.TxDataNonZeroGas)
        igas.Add(igas, m)
        m.SetInt64(int64(len(data)) - nz)
        m.Mul(m, params.TxDataZeroGas)
        igas.Add(igas, m)
    }
    return igas
}

func ApplyMessage(env vm.Environment, msg Message, coinbase *state.StateObject) ([]byte, *big.Int, error) {
    return NewStateTransition(env, msg, coinbase).transitionState()
}

func NewStateTransition(env vm.Environment, msg Message, coinbase *state.StateObject) *StateTransition {
    return &StateTransition{
        coinbase:   coinbase.Address(),
        env:        env,
        msg:        msg,
        gas:        new(big.Int),
        gasPrice:   msg.GasPrice(),
        initialGas: new(big.Int),
        value:      msg.Value(),
        data:       msg.Data(),
        state:      env.State(),
        cb:         coinbase,
    }
}

func (self *StateTransition) Coinbase() *state.StateObject {
    return self.state.GetOrNewStateObject(self.coinbase)
}
func (self *StateTransition) From() (*state.StateObject, error) {
    f, err := self.msg.From()
    if err != nil {
        return nil, err
    }
    return self.state.GetOrNewStateObject(f), nil
}
func (self *StateTransition) To() *state.StateObject {
    if self.msg == nil {
        return nil
    }
    to := self.msg.To()
    if to == nil {
        return nil // contract creation
    }
    return self.state.GetOrNewStateObject(*to)
}

func (self *StateTransition) UseGas(amount *big.Int) error {
    if self.gas.Cmp(amount) < 0 {
        return vm.OutOfGasError
    }
    self.gas.Sub(self.gas, amount)

    return nil
}

func (self *StateTransition) AddGas(amount *big.Int) {
    self.gas.Add(self.gas, amount)
}

func (self *StateTransition) BuyGas() error {
    mgas := self.msg.Gas()
    mgval := new(big.Int).Mul(mgas, self.gasPrice)

    sender, err := self.From()
    if err != nil {
        return err
    }
    if sender.Balance().Cmp(mgval) < 0 {
        return fmt.Errorf("insufficient ETH for gas (%x). Req %v, has %v", sender.Address().Bytes()[:4], mgval, sender.Balance())
    }
    if err = self.Coinbase().SubGas(mgas, self.gasPrice); err != nil {
        return err
    }
    self.AddGas(mgas)
    self.initialGas.Set(mgas)
    sender.SubBalance(mgval)
    return nil
}

func (self *StateTransition) preCheck() (err error) {
    msg := self.msg
    sender, err := self.From()
    if err != nil {
        return err
    }

    // Make sure this transaction's nonce is correct
    if sender.Nonce() != msg.Nonce() {
        return NonceError(msg.Nonce(), sender.Nonce())
    }

    // Pre-pay gas / Buy gas of the coinbase account
    if err = self.BuyGas(); err != nil {
        if state.IsGasLimitErr(err) {
            return err
        }
        return InvalidTxError(err)
    }

    return nil
}

func (self *StateTransition) transitionState() (ret []byte, usedGas *big.Int, err error) {
    if err = self.preCheck(); err != nil {
        return
    }

    msg := self.msg
    sender, _ := self.From() // err checked in preCheck

    // Pay intrinsic gas
    if err = self.UseGas(IntrinsicGas(self.data)); err != nil {
        return nil, nil, InvalidTxError(err)
    }

    vmenv := self.env
    var ref vm.ContextRef
    if MessageCreatesContract(msg) {
        ret, err, ref = vmenv.Create(sender, self.data, self.gas, self.gasPrice, self.value)
        if err == nil {
            dataGas := big.NewInt(int64(len(ret)))
            dataGas.Mul(dataGas, params.CreateDataGas)
            if err := self.UseGas(dataGas); err == nil {
                ref.SetCode(ret)
            } else {
                ret = nil // does not affect consensus but useful for StateTests validations
                glog.V(logger.Core).Infoln("Insufficient gas for creating code. Require", dataGas, "and have", self.gas)
            }
        }
        glog.V(logger.Core).Infoln("VM create err:", err)
    } else {
        // Increment the nonce for the next transaction
        self.state.SetNonce(sender.Address(), sender.Nonce()+1)
        ret, err = vmenv.Call(sender, self.To().Address(), self.data, self.gas, self.gasPrice, self.value)
        glog.V(logger.Core).Infoln("VM call err:", err)
    }

    if err != nil && IsValueTransferErr(err) {
        return nil, nil, InvalidTxError(err)
    }

    // We aren't interested in errors here. Errors returned by the VM are non-consensus errors and therefor shouldn't bubble up
    if err != nil {
        err = nil
    }

    if vm.Debug {
        vm.StdErrFormat(vmenv.StructLogs())
    }

    self.refundGas()
    self.state.AddBalance(self.coinbase, new(big.Int).Mul(self.gasUsed(), self.gasPrice))

    return ret, self.gasUsed(), err
}

func (self *StateTransition) refundGas() {
    coinbase := self.Coinbase()
    sender, _ := self.From() // err already checked
    // Return remaining gas
    remaining := new(big.Int).Mul(self.gas, self.gasPrice)
    sender.AddBalance(remaining)

    uhalf := remaining.Div(self.gasUsed(), common.Big2)
    refund := common.BigMin(uhalf, self.state.Refunds())
    self.gas.Add(self.gas, refund)
    self.state.AddBalance(sender.Address(), refund.Mul(refund, self.gasPrice))

    coinbase.AddGas(self.gas, self.gasPrice)
}

func (self *StateTransition) gasUsed() *big.Int {
    return new(big.Int).Sub(self.initialGas, self.gas)
}