path: root/core/state_transition.go

package core

import (
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/state"
    "github.com/ethereum/go-ethereum/vm"
)

/*
 * 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, receiver []byte
    tx                 *types.Transaction
    gas, gasPrice      *big.Int
    value              *big.Int
    data               []byte
    state              *state.StateDB
    block              *types.Block

    cb, rec, sen *state.StateObject
}

func NewStateTransition(coinbase *state.StateObject, tx *types.Transaction, state *state.StateDB, block *types.Block) *StateTransition {
    return &StateTransition{coinbase.Address(), tx.Recipient, tx, new(big.Int), new(big.Int).Set(tx.GasPrice), tx.Value, tx.Data, state, block, coinbase, nil, nil}
}

func (self *StateTransition) Coinbase() *state.StateObject {
    if self.cb != nil {
        return self.cb
    }

    self.cb = self.state.GetOrNewStateObject(self.coinbase)
    return self.cb
}
func (self *StateTransition) Sender() *state.StateObject {
    if self.sen != nil {
        return self.sen
    }

    self.sen = self.state.GetOrNewStateObject(self.tx.Sender())

    return self.sen
}
func (self *StateTransition) Receiver() *state.StateObject {
    if self.tx != nil && self.tx.CreatesContract() {
        return nil
    }

    if self.rec != nil {
        return self.rec
    }

    self.rec = self.state.GetOrNewStateObject(self.tx.Recipient)
    return self.rec
}

func (self *StateTransition) UseGas(amount *big.Int) error {
    if self.gas.Cmp(amount) < 0 {
        return 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 {
    var err error

    sender := self.Sender()
    if sender.Balance().Cmp(self.tx.GasValue()) < 0 {
        return fmt.Errorf("Insufficient funds to pre-pay gas. Req %v, has %v", self.tx.GasValue(), sender.Balance())
    }

    coinbase := self.Coinbase()
    err = coinbase.BuyGas(self.tx.Gas, self.tx.GasPrice)
    if err != nil {
        return err
    }

    self.AddGas(self.tx.Gas)
    sender.SubAmount(self.tx.GasValue())

    return nil
}

func (self *StateTransition) RefundGas() {
    coinbase, sender := self.Coinbase(), self.Sender()
    coinbase.RefundGas(self.gas, self.tx.GasPrice)

    // Return remaining gas
    remaining := new(big.Int).Mul(self.gas, self.tx.GasPrice)
    sender.AddAmount(remaining)
}

func (self *StateTransition) preCheck() (err error) {
    var (
        tx     = self.tx
        sender = self.Sender()
    )

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

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

    return nil
}

func (self *StateTransition) TransitionState() (err error) {
    statelogger.Debugf("(~) %x\n", self.tx.Hash())

    // XXX Transactions after this point are considered valid.
    if err = self.preCheck(); err != nil {
        return
    }

    var (
        tx     = self.tx
        sender = self.Sender()
    )

    defer self.RefundGas()

    // Increment the nonce for the next transaction
    sender.Nonce += 1

    // Transaction gas
    if err = self.UseGas(vm.GasTx); err != nil {
        return
    }

    // Pay data gas
    var dgas int64
    for _, byt := range self.data {
        if byt != 0 {
            dgas += vm.GasData.Int64()
        } else {
            dgas += 1 // This is 1/5. If GasData changes this fails
        }
    }
    if err = self.UseGas(big.NewInt(dgas)); err != nil {
        return
    }

    var ret []byte
    vmenv := NewEnv(self.state, self.tx, self.block)
    var ref vm.ClosureRef
    if tx.CreatesContract() {
        self.rec = MakeContract(tx, self.state)

        ret, err, ref = vmenv.Create(sender, self.rec.Address(), self.tx.Data, self.gas, self.gasPrice, self.value)
        ref.SetCode(ret)
    } else {
        ret, err = vmenv.Call(self.Sender(), self.Receiver().Address(), self.tx.Data, self.gas, self.gasPrice, self.value)
    }
    if err != nil {
        statelogger.Debugln(err)
    }

    return
}

// Converts an transaction in to a state object
func MakeContract(tx *types.Transaction, state *state.StateDB) *state.StateObject {
    addr := tx.CreationAddress(state)

    contract := state.GetOrNewStateObject(addr)
    contract.InitCode = tx.Data

    return contract
}