兄弟连区块链教程以太坊源码分析core-state-process源码分析（二）

兄弟连区块链教程以太坊源码分析core-state-process源码分析（二）：
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
}

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