兄弟连区块链技术培训以太坊源码分析(11)eth目前的共识算法pow的整理
### eth目前的共识算法pow的整理
> 涉及的代码子包主要有consensus,miner,core,geth
```
/consensus 共识算法
 
1. Prepare方法
2. CalcDifficulty方法：计算工作量
3. AccumulateRewards方法：计算每个块的出块奖励
4. VerifySeal方法：校验pow的工作量难度是否符合要求，返回nil则通过
5. verifyHeader方法：校验区块头是否符合共识规则
```

/miner 挖矿
commitNewWork():提交新的块，新的交易,从交易池中获取未打包的交易，然后提交交易,进行打包
__核心代码__:
```
// Create the current work task and check any fork transitions needed
    work := self.current
    fig.DAOForkSupport && fig.DAOForkBlock != nil && fig.DAOFor
kBlock.Cmp(header.Number) == 0 {
        misc.ApplyDAOHardFork(work.state)
    }
    pending, err := h.TxPool().Pending()
    if err != nil {
        log.Error("Failed to fetch pending transactions", "err", err)
        return
    }
    txs := types.NewTransactionsByPriceAndNonce(self.current.signer, pending)
    workmitTransactions(self.mux, txs, self.chain, inbase)
```

```
    NewProtocolManager --> verifyHeader --> VerifySeal
```
__整条链的运行,打包交易,出块的流程__
```
/cmd//main
    makeFullNode-->RegisterEthService-->eth.New-->NewProtocolManager --> verifyHeader --> VerifySeal
```
> eth的共识算法pow调用栈详解
># 核心的逻辑需要从//NewProtocolManager方法下开始,关键代码:
```
manager.downloader = downloader.New(mode, chaindb, manager.eventMux, blockchain, nil, vePeer)
    validator := func(header *types.Header) error {
        return engine.VerifyHeader(blockchain, header, true)
    }
    heighter := func() uint64 {
        return blockchain.CurrentBlock().NumberU64()
    }
    inserter := func(blocks types.Blocks) (int, error) {
        // If fast sync is running, deny importing weird blocks
        if atomic.LoadUint32(&manager.fastSync) == 1 {
            log.Warn("Discarded bad propagated block", "number", blocks[0].Number(), "hash", blocks[0].Hash())
            return 0, nil
        }
        atomic.StoreUint32(&manager.acceptTxs, 1) // Mark initial sync done on any fetcher import
        return manager.blockchain.InsertChain(blocks)
    }
    manager.fetcher = fetcher.New(blockchain.GetBlockByHash, validator, manager.BroadcastBlock, heighter, inserter, vePeer)
    return manager, nil
```
># 该方法中生成了一个校验区块头部的对象`validator`
># 让我们继续跟进`engine.VerifyHeader(blockchain, header, true)`方法:
```
// VerifyHeader checks whether a header conforms to the consensus rules of the
// stock Ethereum ethash engine.
func (ethash *Ethash) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
    // If we're running a full engine faking, accept any input as valid
    if ethash.fakeFull {
        return nil
    }
    // Short circuit if the header is known, or it's parent not
    number := header.Number.Uint64()
    if chain.GetHeader(header.Hash(), number) != nil {
        return nil
    }
    parent := chain.GetHeader(header.ParentHash, number-1)
    if parent == nil {
        return consensus.ErrUnknownAncestor
    }
    // Sanity checks passed, do a proper verification
    return ethash.verifyHeader(chain, header, parent, false, seal)
}
```
hue trunc函数># 首先看第一个if,它的逻辑判断是如果为true,那么就关闭所有的共识规则校验,紧跟着两个if判断是只要该block的header的hash和number或者上一个header的hash和number存在链上,那么它header的共识规则校验就通过,如果都不通过,那么该区块校验失败跑出错误.如果走到最后一个return,那么就需要做一些其他额外验证
```
// verifyHeader checks whether a header conforms to the consensus rules of the
// stock Ethereum ethash engine.
// See YP section 4.3.4. "Block Header Validity"
func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *types.Header, uncle bool, seal bool) error {
    // Ensure that the header's extra-data section is of a reasonable size
    if uint64(len(header.Extra)) > params.MaximumExtraDataSize {
        return fmt.Errorf("extra-data too long: %d > %d", len(header.Extra), params.MaximumExtraDataSize)
    }
    // Verify the header's timestamp
    if uncle {
        if header.Time.Cmp(math.MaxBig256) > 0 {
            return errLargeBlockTime
        }
    } else {
        if header.Time.Cmp(big.NewInt(time.Now().Unix())) > 0 {
            return consensus.ErrFutureBlock
        }
    }
    if header.Time.Cmp(parent.Time) <= 0 {
        return errZeroBlockTime

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