• Jeffrey Wilcke's avatar
    core: transition db now also returns the required gas amount · 1f3596c2
    Jeffrey Wilcke authored
    Exposes some core methods to transition and compute new state
    information and adds an additional return value to the transition db
    method to fetch required gas for that particular message (excluding gas
    refunds from any SSTORE[X] = 0 and SUICIDE.
    
    Fixes #2395
    1f3596c2
state_transition.go 7.93 KB
// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library 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.
//
// The go-ethereum library 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 the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package core

import (
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"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"
)

var (
	Big0 = big.NewInt(0)
)

/*
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 gas
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 {
	gp            *GasPool
	msg           Message
	gas, gasPrice *big.Int
	initialGas    *big.Int
	value         *big.Int
	data          []byte
	state         vm.Database

	env vm.Environment
}

// Message represents a message sent to a contract.
type Message interface {
	From() (common.Address, error)
	FromFrontier() (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 'intrinsic gas' for a message
// with the given data.
func IntrinsicGas(data []byte, contractCreation, homestead bool) *big.Int {
	igas := new(big.Int)
	if contractCreation && homestead {
		igas.Set(params.TxGasContractCreation)
	} else {
		igas.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
}

// NewStateTransition initialises and returns a new state transition object.
func NewStateTransition(env vm.Environment, msg Message, gp *GasPool) *StateTransition {
	return &StateTransition{
		gp:         gp,
		env:        env,
		msg:        msg,
		gas:        new(big.Int),
		gasPrice:   msg.GasPrice(),
		initialGas: new(big.Int),
		value:      msg.Value(),
		data:       msg.Data(),
		state:      env.Db(),
	}
}

// ApplyMessage computes the new state by applying the given message
// against the old state within the environment.
//
// ApplyMessage returns the bytes returned by any EVM execution (if it took place),
// the gas used (which includes gas refunds) and an error if it failed. An error always
// indicates a core error meaning that the message would always fail for that particular
// state and would never be accepted within a block.
func ApplyMessage(env vm.Environment, msg Message, gp *GasPool) ([]byte, *big.Int, error) {
	st := NewStateTransition(env, msg, gp)

	ret, _, gasUsed, err := st.TransitionDb()
	return ret, gasUsed, err
}

func (self *StateTransition) from() (vm.Account, error) {
	var (
		f   common.Address
		err error
	)
	if self.env.RuleSet().IsHomestead(self.env.BlockNumber()) {
		f, err = self.msg.From()
	} else {
		f, err = self.msg.FromFrontier()
	}
	if err != nil {
		return nil, err
	}
	if !self.state.Exist(f) {
		return self.state.CreateAccount(f), nil
	}
	return self.state.GetAccount(f), nil
}

func (self *StateTransition) to() vm.Account {
	if self.msg == nil {
		return nil
	}
	to := self.msg.To()
	if to == nil {
		return nil // contract creation
	}

	if !self.state.Exist(*to) {
		return self.state.CreateAccount(*to)
	}
	return self.state.GetAccount(*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.gp.SubGas(mgas); 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 n := self.state.GetNonce(sender.Address()); n != msg.Nonce() {
		return NonceError(msg.Nonce(), n)
	}

	// Pre-pay gas
	if err = self.buyGas(); err != nil {
		if IsGasLimitErr(err) {
			return err
		}
		return InvalidTxError(err)
	}

	return nil
}

// TransitionDb will move the state by applying the message against the given environment.
func (self *StateTransition) TransitionDb() (ret []byte, requiredGas, usedGas *big.Int, err error) {
	if err = self.preCheck(); err != nil {
		return
	}
	msg := self.msg
	sender, _ := self.from() // err checked in preCheck

	homestead := self.env.RuleSet().IsHomestead(self.env.BlockNumber())
	contractCreation := MessageCreatesContract(msg)
	// Pay intrinsic gas
	if err = self.useGas(IntrinsicGas(self.data, contractCreation, homestead)); err != nil {
		return nil, nil, nil, InvalidTxError(err)
	}

	vmenv := self.env
	//var addr common.Address
	if contractCreation {
		ret, _, err = vmenv.Create(sender, self.data, self.gas, self.gasPrice, self.value)
		if homestead && err == vm.CodeStoreOutOfGasError {
			self.gas = Big0
		}

		if err != nil {
			ret = nil
			glog.V(logger.Core).Infoln("VM create err:", err)
		}
	} else {
		// Increment the nonce for the next transaction
		self.state.SetNonce(sender.Address(), self.state.GetNonce(sender.Address())+1)
		ret, err = vmenv.Call(sender, self.to().Address(), self.data, self.gas, self.gasPrice, self.value)
		if err != nil {
			glog.V(logger.Core).Infoln("VM call err:", err)
		}
	}

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

	requiredGas = new(big.Int).Set(self.gasUsed())

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

	return ret, requiredGas, self.gasUsed(), err
}

func (self *StateTransition) refundGas() {
	// Return eth for remaining gas to the sender account,
	// exchanged at the original rate.
	sender, _ := self.from() // err already checked
	remaining := new(big.Int).Mul(self.gas, self.gasPrice)
	sender.AddBalance(remaining)

	// Apply refund counter, capped to half of the used gas.
	uhalf := remaining.Div(self.gasUsed(), common.Big2)
	refund := common.BigMin(uhalf, self.state.GetRefund())
	self.gas.Add(self.gas, refund)
	self.state.AddBalance(sender.Address(), refund.Mul(refund, self.gasPrice))

	// Also return remaining gas to the block gas counter so it is
	// available for the next transaction.
	self.gp.AddGas(self.gas)
}

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