StateTransition
状态转换模型
/*
The State Transitioning Model
状态转换模型
A state transition is a change made when a transaction is applied to the current world state
状态转换 是指用当前的world state来执行交易，并改变当前的world state
The state transitioning model does all all the necessary work to work out a valid new state root.
状态转换做了所有所需的工作来产生一个新的有效的state root
1) Nonce handling Nonce 处理
2) Pre pay gas 预先支付Gas
3) Create a new state object if the recipient is \0*32 如果接收人是空，那么创建一个新的state object
4) Value transfer 转账
== If contract creation ==
4a) Attempt to run transaction data 尝试运行输入的数据
4b) If valid, use result as code for the new state object 如果有效，那么用运行的结果作为新的state object的code
== end ==
5) Run Script section 运行脚本部分
6) Derive new state root 导出新的state root
*/
type StateTransition struct {
gp *GasPool //用来追踪区块内部的Gas的使用情况
msg Message // Message Call
gas uint64
gasPrice *big.Int // gas的价格
initialGas *big.Int // 最开始的gas
value *big.Int // 转账的值
data []byte // 输入数据
state vm.StateDB // StateDB
evm *vm.EVM // 虚拟机
}
// Message represents a message sent to a contract.
type Message interface {
From() common.Address
//FromFrontier() (common.Address, error)
To() *common.Address //
GasPrice() *big.Int // Message 的 GasPrice
Gas() *big.Int //message 的 GasLimit
Value() *big.Int
Nonce() uint64
CheckNonce() bool
Data() []byte
}
构造
// 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(),
initialGas: new(big.Int),
value: msg.Value(),
data: msg.Data(),
state: evm.StateDB,
}
}
执行Message
// ApplyMessage computes the new state by applying the given message
// against the old state within the environment.
// ApplyMessage 通过应用给定的Message 和状态来生成新的状态
// 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.
// ApplyMessage返回由任何EVM执行（如果发生）返回的字节，
// 使用的Gas（包括Gas退款），如果失败则返回错误。 一个错误总是表示一个核心错误，
// 意味着这个消息对于这个特定的状态将总是失败，并且永远不会在一个块中被接受。
func ApplyMessage(evm *vm.EVM, msg Message, gp *GasPool) ([]byte, *big.Int, bool, error) {
st := NewStateTransition(evm, msg, gp)
ret, _, gasUsed, failed, err := st.TransitionDb()
return ret, gasUsed, failed, err
}
TransitionDb
// TransitionDb will transition the state by applying the current message and returning the result
// including the required gas for the operation as well as the used gas. It returns an error if it
// failed. An error indicates a consensus issue.
// TransitionDb
func (st *StateTransition) TransitionDb() (ret []byte, requiredGas, usedGas *big.Int, failed bool, err error) {
if err = st.preCheck(); err != nil {
return
}
msg := st.msg
sender := st.from() // err checked in preCheck
homestead := st.evm.ChainConfig().IsHomestead(st.evm.BlockNumber)
contractCreation := msg.To() == nil // 如果msg.To是nil 那么认为是一个合约创建
// Pay intrinsic gas
// TODO convert to uint64
// 计算最开始的Gas g0
intrinsicGas := IntrinsicGas(st.data, contractCreation, homestead)
if intrinsicGas.BitLen() > 64 {
return nil, nil, nil, false, vm.ErrOutOfGas
}
if err = st.useGas(intrinsicGas.Uint64()); err != nil {
return nil, nil, nil, 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 { //如果是合约创建， 那么调用evm的Create方法
ret, _, st.gas, vmerr = evm.Create(sender, st.data, st.gas, st.value)
} else {
// Increment the nonce for the next transaction
// 如果是方法调用。那么首先设置sender的nonce。
st.state.SetNonce(sender.Address(), st.state.GetNonce(sender.Address())+1)
ret, st.gas, vmerr = evm.Call(sender, st.to().Address(), 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, nil, nil, false, vmerr
}
}
requiredGas = new(big.Int).Set(st.gasUsed()) // 计算被使用的Gas数量
st.refundGas() //计算Gas的退费 会增加到 st.gas上面。 所以矿工拿到的是退税后的
st.state.AddBalance(st.evm.Coinbase, new(big.Int).Mul(st.gasUsed(), st.gasPrice)) // 给矿工增加收入。
// requiredGas和gasUsed的区别一个是没有退税的， 一个是退税了的。
// 看上面的调用 ApplyMessage直接丢弃了requiredGas, 说明返回的是退税了的。
return ret, requiredGas, st.gasUsed(), vmerr != nil, err
}
关于g0的计算，在黄皮书上由详细的介绍
和黄皮书有一定出入的部分在于if contractCreation && homestead {igas.SetUint64(params.TxGasContractCreation) 这是因为 Gtxcreate+Gtransaction = TxGasContractCreation
func IntrinsicGas(data []byte, contractCreation, homestead bool) *big.Int {
igas := new(big.Int)
if contractCreation && homestead {
igas.SetUint64(params.TxGasContractCreation)
} else {
igas.SetUint64(params.TxGas)
}
if len(data) > 0 {
var nz int64
for _, byt := range data {
if byt != 0 {
nz++
}
}
m := big.NewInt(nz)
m.Mul(m, new(big.Int).SetUint64(params.TxDataNonZeroGas))
igas.Add(igas, m)
m.SetInt64(int64(len(data)) - nz)
m.Mul(m, new(big.Int).SetUint64(params.TxDataZeroGas))
igas.Add(igas, m)
}
return igas
}
执行前的检查
func (st *StateTransition) preCheck() error {
msg := st.msg
sender := st.from()
// Make sure this transaction's nonce is correct
if msg.CheckNonce() {
nonce := st.state.GetNonce(sender.Address())
// 当前本地的nonce 需要和 msg的Nonce一样 不然就是状态不同步了。
if nonce < msg.Nonce() {
return ErrNonceTooHigh
} else if nonce > msg.Nonce() {
return ErrNonceTooLow
}
}
return st.buyGas()
}
buyGas， 实现Gas的预扣费， 首先就扣除你的GasLimit * GasPrice的钱。 然后根据计算完的状态在退还一部分。
func (st *StateTransition) buyGas() error {
mgas := st.msg.Gas()
if mgas.BitLen() > 64 {
return vm.ErrOutOfGas
}
mgval := new(big.Int).Mul(mgas, st.gasPrice)
var (
state = st.state
sender = st.from()
)
if state.GetBalance(sender.Address()).Cmp(mgval) < 0 {
return errInsufficientBalanceForGas
}
if err := st.gp.SubGas(mgas); err != nil { // 从区块的gaspool里面减去， 因为区块是由GasLimit限制整个区块的Gas使用的。
return err
}
st.gas += mgas.Uint64()
st.initialGas.Set(mgas)
state.SubBalance(sender.Address(), mgval)
// 从账号里面减去 GasLimit * GasPrice
return nil
}
退税，退税是为了奖励大家运行一些能够减轻区块链负担的指令， 比如清空账户的storage. 或者是运行suicide命令来清空账号。
func (st *StateTransition) refundGas() {
// Return eth for remaining gas to the sender account,
// exchanged at the original rate.
sender := st.from() // err already checked
remaining := new(big.Int).Mul(new(big.Int).SetUint64(st.gas), st.gasPrice)
// 首先把用户还剩下的Gas还回去。
st.state.AddBalance(sender.Address(), remaining)
// Apply refund counter, capped to half of the used gas.
// 然后退税的总金额不会超过用户Gas总使用的1/2。
uhalf := remaining.Div(st.gasUsed(), common.Big2)
refund := math.BigMin(uhalf, st.state.GetRefund())
st.gas += refund.Uint64()
// 把退税的金额加到用户账户上。
st.state.AddBalance(sender.Address(), refund.Mul(refund, st.gasPrice))
// Also return remaining gas to the block gas counter so it is
// available for the next transaction.
// 同时也把退税的钱还给gaspool给下个交易腾点Gas空间。
st.gp.AddGas(new(big.Int).SetUint64(st.gas))
}
StateProcessor
StateTransition是用来处理一个一个的交易的。那么StateProcessor就是用来处理区块级别的交易的。
结构和构造
// StateProcessor is a basic Processor, which takes care of transitioning
// state from one point to another.
//
// StateProcessor implements Processor.
type StateProcessor struct {
config *params.ChainConfig // Chain configuration options
bc *BlockChain // Canonical block chain
engine consensus.Engine // Consensus engine used for block rewards
}
// NewStateProcessor initialises a new StateProcessor.
func NewStateProcessor(config *params.ChainConfig, bc *BlockChain, engine consensus.Engine) *StateProcessor {
return &StateProcessor{
config: config,
bc: bc,
engine: engine,
}
}
Process，这个方法会被blockchain调用。
// Process processes the state changes according to the Ethereum rules by running
// the transaction messages using the statedb and applying any rewards to both
// the processor (coinbase) and any included uncles.
// Process 根据以太坊规则运行交易信息来对statedb进行状态改变，以及奖励挖矿者或者是其他的叔父节点。
// Process returns the receipts and logs accumulated during the process and
// returns the amount of gas that was used in the process. If any of the
// transactions failed to execute due to insufficient gas it will return an error.
// Process返回执行过程中累计的收据和日志，并返回过程中使用的Gas。 如果由于Gas不足而导致任何交易执行失败，将返回错误。
func (p *StateProcessor) Process(block *types.Block, statedb *state.StateDB, cfg vm.Config) (types.Receipts, []*types.Log, *big.Int, error) {
var (
receipts types.Receipts
totalUsedGas = big.NewInt(0)
header = block.Header()
allLogs []*types.Log
gp = new(GasPool).AddGas(block.GasLimit())
)
// Mutate the the block and state according to any hard-fork specs
// DAO 事件的硬分叉处理
if p.config.DAOForkSupport && p.config.DAOForkBlock != nil && p.config.DAOForkBlock.Cmp(block.Number()) == 0 {
misc.ApplyDAOHardFork(statedb)
}
// Iterate over and process the individual transactions
for i, tx := range block.Transactions() {
statedb.Prepare(tx.Hash(), block.Hash(), i)
receipt, _, err := ApplyTransaction(p.config, p.bc, nil, gp, statedb, header, tx, totalUsedGas, cfg)
if err != nil {
return nil, nil, nil, err
}
receipts = append(receipts, receipt)
allLogs = append(allLogs, receipt.Logs...)
}
// Finalize the block, applying any consensus engine specific extras (e.g. block rewards)
p.engine.Finalize(p.bc, header, statedb, block.Transactions(), block.Uncles(), receipts)
// 返回收据 日志 总的Gas使用量和nil
return receipts, allLogs, totalUsedGas, nil
}
ApplyTransaction
// ApplyTransaction attempts to apply a transaction to the given state database
// and uses the input parameters for its environment. It returns the receipt
// for the transaction, gas used and an error if the transaction failed,
// indicating the block was invalid.
ApplyTransaction尝试将事务应用于给定的状态数据库，并使用其环境的输入参数。
//它返回事务的收据，使用的Gas和错误，如果交易失败，表明块是无效的。
func ApplyTransaction(config *params.ChainConfig, bc *BlockChain, author *common.Address, gp *GasPool, statedb *state.StateDB, header *types.Header, tx *types.Transaction, usedGas *big.Int, cfg vm.Config) (*types.Receipt, *big.Int, error) {
// 把交易转换成Message
// 这里如何验证消息确实是Sender发送的。 TODO
msg, err := tx.AsMessage(types.MakeSigner(config, header.Number))
if err != nil {
return nil, nil, err
}
// Create a new context to be used in the EVM environment
// 每一个交易都创建了新的虚拟机环境。
context := NewEVMContext(msg, header, bc, author)
// Create a new environment which holds all relevant information
// about the transaction and calling mechanisms.
vmenv := vm.NewEVM(context, statedb, config, cfg)
// Apply the transaction to the current state (included in the env)
_, gas, failed, err := ApplyMessage(vmenv, msg, gp)
if err != nil {
return nil, nil, err
}
// Update the state with pending changes
// 求得中间状态
var root []byte
if config.IsByzantium(header.Number) {
statedb.Finalise(true)
} else {
root = statedb.IntermediateRoot(config.IsEIP158(header.Number)).Bytes()
}
usedGas.Add(usedGas, gas)
// Create a new receipt for the transaction, storing the intermediate root and gas used by the tx
// based on the eip phase, we're passing wether the root touch-delete accounts.
// 创建一个收据, 用来存储中间状态的root, 以及交易使用的gas
receipt := types.NewReceipt(root, failed, usedGas)
receipt.TxHash = tx.Hash()
receipt.GasUsed = new(big.Int).Set(gas)
// if the transaction created a contract, store the creation address in the receipt.
// 如果是创建合约的交易.那么我们把创建地址存储到收据里面.
if msg.To() == nil {
receipt.ContractAddress = crypto.CreateAddress(vmenv.Context.Origin, tx.Nonce())
}
// Set the receipt logs and create a bloom for filtering
receipt.Logs = statedb.GetLogs(tx.Hash())
receipt.Bloom = types.CreateBloom(types.Receipts{receipt})
// 拿到所有的日志并创建日志的布隆过滤器.
return receipt, gas, err
}