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
}
 

執行前的檢查
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())
    // 當前本地的nonce 需要和 msg的Nonce一樣 不然就是狀態不同步了。
    if nonce < msg.Nonce() {
        return ErrNonceTooHigh
    } else if nonce > msg.Nonce() {
        return ErrNonceTooLow
    }
}
return st.buyGas()
 

}
buyGas， 實現Gas的預扣費， 首先就扣除你的GasLimit GasPrice的錢。 然後根據計算完的狀態在退還一部分。
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 { // 從區塊的gaspool裏面減去， 因為區塊是由GasLimit限制整個區塊的Gas使用的。
    return err
}
st.gas += mgas.Uint64()

st.initialGas.Set(mgas)
state.SubBalance(sender.Address(), mgval)
// 從賬號裏面減去 GasLimit * GasPrice
return nil
 

}

退稅，退稅是為了獎勵大家運行一些能夠減輕區塊鏈負擔的指令， 比如清空賬戶的storage. 或者是運行suicide命令來清空賬號。

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)
// 首先把用戶還剩下的Gas還回去。
st.state.AddBalance(sender.Address(), remaining)

// Apply refund counter, capped to half of the used gas.
// 然後退稅的總金額不會超過用戶Gas總使用的1/2。
uhalf := remaining.Div(st.gasUsed(), common.Big2)
refund := math.BigMin(uhalf, st.state.GetRefund())
st.gas += refund.Uint64()
// 把退稅的金額加到用戶賬戶上。
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.
// 同時也把退稅的錢還給gaspool給下個交易騰點Gas空間。
st.gp.AddGas(new(big.Int).SetUint64(st.gas))

}

StateProcessor

StateTransition是用來處理一個一個的交易的。那麽StateProcessor就是用來處理區塊級別的交易的。

結構和構造

// 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，這個方法會被blockchain調用。

// 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 根據以太坊規則運行交易信息來對statedb進行狀態改變，以及獎勵挖礦者或者是其他的叔父節點。
// 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返回執行過程中累計的收據和日誌，並返回過程中使用的Gas。 如果由於Gas不足而導致任何交易執行失敗，將返回錯誤。
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 事件的硬分叉處理
    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)
    // 返回收據 日誌 總的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嘗試將事務應用於給定的狀態數據庫，並使用其環境的輸入參數。
//它返回事務的收據，使用的Gas和錯誤，如果交易失敗，表明塊是無效的。

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) {
    // 把交易轉換成Message
    // 這裏如何驗證消息確實是Sender發送的。 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
    // 每一個交易都創建了新的虛擬機環境。
    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
    // 求得中間狀態
    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.
    // 創建一個收據, 用來存儲中間狀態的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.
    // 如果是創建合約的交易.那麽我們把創建地址存儲到收據裏面.
    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})
    // 拿到所有的日誌並創建日誌的布隆過濾器.
    return receipt, gas, err
}

區塊鏈教程以太坊源碼分析core-state-process源碼分析（二）