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
}
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