path: root/core/state_transition.go

package core

import (
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/ethutil"
    "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
    msg                Message
    gas, gasPrice      *big.Int
    initialGas         *big.Int
    value              *big.Int
    data               []byte
    state              *state.StateDB
    block              *types.Block

    cb, rec, sen *state.StateObject

    Env vm.Environment
}

type Message interface {
    Hash() []byte

    From() []byte
    To() []byte

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

    Nonce() uint64
    Data() []byte
}

func AddressFromMessage(msg Message) []byte {
    // Generate a new address
    return crypto.Sha3(ethutil.NewValue([]interface{}{msg.From(), msg.Nonce()}).Encode())[12:]
}

func MessageCreatesContract(msg Message) bool {
    return len(msg.To()) == 0
}

func MessageGasValue(msg Message) *big.Int {
    return new(big.Int).Mul(msg.Gas(), msg.GasPrice())
}

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

func (self *StateTransition) VmEnv() vm.Environment {
    if self.Env == nil {
        self.Env = NewEnv(self.state, self.msg, self.block)
    }

    return self.Env
}

func (self *StateTransition) Coinbase() *state.StateObject {
    return self.state.GetOrNewStateObject(self.coinbase)
}
func (self *StateTransition) From() *state.StateObject {
    return self.state.GetOrNewStateObject(self.msg.From())
}
func (self *StateTransition) To() *state.StateObject {
    if self.msg != nil && MessageCreatesContract(self.msg) {
        return nil
    }
    return self.state.GetOrNewStateObject(self.msg.To())
}

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.From()
    if sender.Balance().Cmp(MessageGasValue(self.msg)) < 0 {
        return fmt.Errorf("Insufficient funds to pre-pay gas. Req %v, has %v", MessageGasValue(self.msg), sender.Balance())
    }

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

    self.AddGas(self.msg.Gas())
    self.initialGas.Set(self.msg.Gas())
    sender.SubAmount(MessageGasValue(self.msg))

    return nil
}

func (self *StateTransition) preCheck() (err error) {
    var (
        msg    = self.msg
        sender = self.From()
    )

    // 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 {
        return err
    }

    return nil
}

func (self *StateTransition) TransitionState() (ret []byte, err error) {
    statelogger.Debugf("(~) %x\n", self.msg.Hash())

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

    var (
        msg    = self.msg
        sender = self.From()
    )

    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
    }

    vmenv := self.VmEnv()
    var ref vm.ClosureRef
    if MessageCreatesContract(msg) {
        self.rec = MakeContract(msg, self.state)

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

    return
}

// Converts an transaction in to a state object
func MakeContract(msg Message, state *state.StateDB) *state.StateObject {
    addr := AddressFromMessage(msg)

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

    return contract
}

func (self *StateTransition) RefundGas() {
    coinbaseSub := new(big.Int).Set(self.gas)
    uhalf := new(big.Int).Div(self.GasUsed(), ethutil.Big2)
    for addr, refs := range self.state.Refunds() {
        for _, ref := range refs {
            coinbaseSub.Add(self.gas, ref)
            refund := ethutil.BigMin(uhalf, ref)
            self.state.AddBalance([]byte(addr), refund.Mul(refund, self.msg.GasPrice()))
        }
    }

    coinbase, sender := self.Coinbase(), self.From()
    coinbase.RefundGas(coinbaseSub, self.msg.GasPrice())

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

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