path: root/ethchain/state_transition.go

package ethchain

import (
    "fmt"
    "github.com/ethereum/eth-go/ethutil"
    "math/big"
)

/*
 * 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 []byte
    tx       *Transaction
    gas      *big.Int
    state    *State
    block    *Block

    cb, rec, sen *StateObject
}

func NewStateTransition(coinbase []byte, tx *Transaction, state *State, block *Block) *StateTransition {
    return &StateTransition{coinbase, tx, new(big.Int), state, block, nil, nil, nil}
}

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

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

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

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

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

func (self *StateTransition) MakeStateObject(state *State, tx *Transaction) *StateObject {
    contract := MakeContract(tx, state)
    if contract != nil {
        state.states[string(tx.CreationAddress())] = contract.state

        return contract
    }

    return nil
}

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.Amount.Cmp(self.tx.GasValue()) < 0 {
        return fmt.Errorf("Insufficient funds to pre-pay gas. Req %v, has %v", self.tx.GasValue(), self.tx.Value)
    }

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

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

    return nil
}

func (self *StateTransition) TransitionState() (err error) {
    //snapshot := st.state.Snapshot()

    defer func() {
        if r := recover(); r != nil {
            ethutil.Config.Log.Infoln(r)
            err = fmt.Errorf("state transition err %v", r)
        }
    }()

    var (
        tx       = self.tx
        sender   = self.Sender()
        receiver *StateObject
    )

    // 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
    }

    // XXX Transactions after this point are considered valid.

    defer func() {
        self.state.UpdateStateObject(sender)
        self.state.UpdateStateObject(receiver)
    }()

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

    // Get the receiver (TODO fix this, if coinbase is the receiver we need to save/retrieve)
    receiver = self.Receiver()

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

    // Pay data gas
    dataPrice := big.NewInt(int64(len(tx.Data)))
    dataPrice.Mul(dataPrice, GasData)
    if err = self.UseGas(dataPrice); err != nil {
        return err
    }

    // If the receiver is nil it's a contract (\0*32).
    if receiver == nil {
        // Create a new state object for the contract
        receiver = self.MakeStateObject(self.state, tx)
        if receiver == nil {
            return fmt.Errorf("ERR. Unable to create contract with transaction %v", tx)
        }
    }

    // Transfer value from sender to receiver
    if err = self.transferValue(sender, receiver); err != nil {
        return err
    }

    // Process the init code and create 'valid' contract
    if tx.CreatesContract() {
        // Evaluate the initialization script
        // and use the return value as the
        // script section for the state object.
        //script, gas, err = sm.Eval(state, contract.Init(), contract, tx, block)
        code, err := self.Eval(receiver.Init(), receiver)
        if err != nil {
            return fmt.Errorf("Error during init script run %v", err)
        }

        receiver.script = code
    } else {
        if len(receiver.Script()) > 0 {
            _, err := self.Eval(receiver.Script(), receiver)
            if err != nil {
                return fmt.Errorf("Error during code execution %v", err)
            }
        }
    }

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

    return nil
}

func (self *StateTransition) transferValue(sender, receiver *StateObject) error {
    if sender.Amount.Cmp(self.tx.Value) < 0 {
        return fmt.Errorf("Insufficient funds to transfer value. Req %v, has %v", self.tx.Value, sender.Amount)
    }

    if self.tx.Value.Cmp(ethutil.Big0) > 0 {
        // Subtract the amount from the senders account
        sender.SubAmount(self.tx.Value)
        // Add the amount to receivers account which should conclude this transaction
        receiver.AddAmount(self.tx.Value)

        ethutil.Config.Log.Debugf("%x => %x (%v) %x\n", sender.Address()[:4], receiver.Address()[:4], self.tx.Value, self.tx.Hash())
    }

    return nil
}

func (self *StateTransition) Eval(script []byte, context *StateObject) (ret []byte, err error) {
    var (
        tx        = self.tx
        block     = self.block
        initiator = self.Sender()
        state     = self.state
    )

    closure := NewClosure(initiator, context, script, state, self.gas, tx.GasPrice)
    vm := NewVm(state, nil, RuntimeVars{
        Origin:      initiator.Address(),
        BlockNumber: block.BlockInfo().Number,
        PrevHash:    block.PrevHash,
        Coinbase:    block.Coinbase,
        Time:        block.Time,
        Diff:        block.Difficulty,
        Value:       tx.Value,
    })
    ret, _, err = closure.Call(vm, tx.Data, nil)

    return
}