1 files changed, 255 insertions, 0 deletions
diff --git a/core/state_transition.go b/core/state_transition.go
new file mode 100644
index 0000000..f648bce
--- /dev/null
+++ b/core/state_transition.go
@@ -0,0 +1,255 @@
+// 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 (
+	"errors"
+	"math"
+	"math/big"
+
+	"github.com/ava-labs/go-ethereum/common"
+	"github.com/ava-labs/go-ethereum/core/vm"
+	"github.com/ava-labs/go-ethereum/log"
+	"github.com/ava-labs/go-ethereum/params"
+)
+
+var (
+	errInsufficientBalanceForGas = errors.New("insufficient balance to pay for gas")
+)
+
+/*
+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 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        uint64
+	gasPrice   *big.Int
+	initialGas uint64
+	value      *big.Int
+	data       []byte
+	state      vm.StateDB
+	evm        *vm.EVM
+}
+
+// Message represents a message sent to a contract.
+type Message interface {
+	From() common.Address
+	//FromFrontier() (common.Address, error)
+	To() *common.Address
+
+	GasPrice() *big.Int
+	Gas() uint64
+	Value() *big.Int
+
+	Nonce() uint64
+	CheckNonce() bool
+	Data() []byte
+}
+
+// IntrinsicGas computes the 'intrinsic gas' for a message with the given data.
+func IntrinsicGas(data []byte, contractCreation, isEIP155 bool, isEIP2028 bool) (uint64, error) {
+	// Set the starting gas for the raw transaction
+	var gas uint64
+	if contractCreation && isEIP155 {
+		gas = params.TxGasContractCreation
+	} else {
+		gas = params.TxGas
+	}
+	// Bump the required gas by the amount of transactional data
+	if len(data) > 0 {
+		// Zero and non-zero bytes are priced differently
+		var nz uint64
+		for _, byt := range data {
+			if byt != 0 {
+				nz++
+			}
+		}
+		// Make sure we don't exceed uint64 for all data combinations
+		nonZeroGas := params.TxDataNonZeroGasFrontier
+		if isEIP2028 {
+			nonZeroGas = params.TxDataNonZeroGasEIP2028
+		}
+		if (math.MaxUint64-gas)/nonZeroGas < nz {
+			return 0, vm.ErrOutOfGas
+		}
+		gas += nz * nonZeroGas
+
+		z := uint64(len(data)) - nz
+		if (math.MaxUint64-gas)/params.TxDataZeroGas < z {
+			return 0, vm.ErrOutOfGas
+		}
+		gas += z * params.TxDataZeroGas
+	}
+	return gas, nil
+}
+
+// NewStateTransition initialises and returns a new state transition object.
+func NewStateTransition(evm *vm.EVM, msg Message, gp *GasPool) *StateTransition {
+	return &StateTransition{
+		gp:       gp,
+		evm:      evm,
+		msg:      msg,
+		gasPrice: msg.GasPrice(),
+		value:    msg.Value(),
+		data:     msg.Data(),
+		state:    evm.StateDB,
+	}
+}
+
+// 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(evm *vm.EVM, msg Message, gp *GasPool) ([]byte, uint64, bool, error) {
+	return NewStateTransition(evm, msg, gp).TransitionDb()
+}
+
+// to returns the recipient of the message.
+func (st *StateTransition) to() common.Address {
+	if st.msg == nil || st.msg.To() == nil /* contract creation */ {
+		return common.Address{}
+	}
+	return *st.msg.To()
+}
+
+func (st *StateTransition) useGas(amount uint64) error {
+	if st.gas < amount {
+		return vm.ErrOutOfGas
+	}
+	st.gas -= amount
+
+	return nil
+}
+
+func (st *StateTransition) buyGas() error {
+	mgval := new(big.Int).Mul(new(big.Int).SetUint64(st.msg.Gas()), st.gasPrice)
+	if st.state.GetBalance(st.msg.From()).Cmp(mgval) < 0 {
+		return errInsufficientBalanceForGas
+	}
+	if err := st.gp.SubGas(st.msg.Gas()); err != nil {
+		return err
+	}
+	st.gas += st.msg.Gas()
+
+	st.initialGas = st.msg.Gas()
+	st.state.SubBalance(st.msg.From(), mgval)
+	return nil
+}
+
+func (st *StateTransition) preCheck() error {
+	// Make sure this transaction's nonce is correct.
+	if st.msg.CheckNonce() {
+		nonce := st.state.GetNonce(st.msg.From())
+		if nonce < st.msg.Nonce() {
+			return ErrNonceTooHigh
+		} else if nonce > st.msg.Nonce() {
+			return ErrNonceTooLow
+		}
+	}
+	return st.buyGas()
+}
+
+// TransitionDb will transition the state by applying the current message and
+// returning the result including the used gas. It returns an error if failed.
+// An error indicates a consensus issue.
+func (st *StateTransition) TransitionDb() (ret []byte, usedGas uint64, failed bool, err error) {
+	if err = st.preCheck(); err != nil {
+		return
+	}
+	msg := st.msg
+	sender := vm.AccountRef(msg.From())
+	homestead := st.evm.ChainConfig().IsHomestead(st.evm.BlockNumber)
+	istanbul := st.evm.ChainConfig().IsIstanbul(st.evm.BlockNumber)
+	contractCreation := msg.To() == nil
+
+	// Pay intrinsic gas
+	gas, err := IntrinsicGas(st.data, contractCreation, homestead, istanbul)
+	if err != nil {
+		return nil, 0, false, err
+	}
+	if err = st.useGas(gas); err != nil {
+		return nil, 0, false, err
+	}
+
+	var (
+		evm = st.evm
+		// vm errors do not effect consensus and are therefor
+		// not assigned to err, except for insufficient balance
+		// error.
+		vmerr error
+	)
+	if contractCreation {
+		ret, _, st.gas, vmerr = evm.Create(sender, st.data, st.gas, st.value)
+	} else {
+		// Increment the nonce for the next transaction
+		st.state.SetNonce(msg.From(), st.state.GetNonce(sender.Address())+1)
+		ret, st.gas, vmerr = evm.Call(sender, st.to(), st.data, st.gas, st.value)
+	}
+	if vmerr != nil {
+		log.Debug("VM returned with error", "err", vmerr)
+		// The only possible consensus-error would be if there wasn't
+		// sufficient balance to make the transfer happen. The first
+		// balance transfer may never fail.
+		if vmerr == vm.ErrInsufficientBalance {
+			return nil, 0, false, vmerr
+		}
+	}
+	st.refundGas()
+	st.state.AddBalance(st.evm.Coinbase, new(big.Int).Mul(new(big.Int).SetUint64(st.gasUsed()), st.gasPrice))
+
+	return ret, st.gasUsed(), vmerr != nil, err
+}
+
+func (st *StateTransition) refundGas() {
+	// Apply refund counter, capped to half of the used gas.
+	refund := st.gasUsed() / 2
+	if refund > st.state.GetRefund() {
+		refund = st.state.GetRefund()
+	}
+	st.gas += refund
+
+	// Return ETH for remaining gas, exchanged at the original rate.
+	remaining := new(big.Int).Mul(new(big.Int).SetUint64(st.gas), st.gasPrice)
+	st.state.AddBalance(st.msg.From(), remaining)
+
+	// Also return remaining gas to the block gas counter so it is
+	// available for the next transaction.
+	st.gp.AddGas(st.gas)
+}
+
+// gasUsed returns the amount of gas used up by the state transition.
+func (st *StateTransition) gasUsed() uint64 {
+	return st.initialGas - st.gas
+}