go-ethereum源碼分析-consensus - 共識

源碼包路徑：github.com/ethereum/go-ethereum/consensus/

共識演算法引擎介面的定義如下

type Engine interface {   // Author retrieves the Ethereum address of the account that minted the given // block, which may be different from the header's coinbase if a consensus // engine is based on signatures. Author(header *types.Header) (common.Address, error)   // VerifyHeader checks whether a header conforms to the consensus rules of a // given engine. Verifying the seal may be done optionally here, or explicitly // via the VerifySeal method. VerifyHeader(chain ChainReader, header *types.Header, seal bool) error // VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers // concurrently. The method returns a quit channel to abort the operations and // a results channel to retrieve the async verifications (the order is that of // the input slice). VerifyHeaders(chain ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error)   // VerifyUncles verifies that the given block's uncles conform to the consensus // rules of a given engine. VerifyUncles(chain ChainReader, block *types.Block) error // VerifySeal checks whether the crypto seal on a header is valid according to // the consensus rules of the given engine. VerifySeal(chain ChainReader, header *types.Header) error // Prepare initializes the consensus fields of a block header according to the // rules of a particular engine. The changes are executed inline. Prepare(chain ChainReader, header *types.Header) error // Finalize runs any post-transaction state modifications (e.g. block rewards) // and assembles the final block. // Note: The block header and state database might be updated to reflect any // consensus rules that happen at finalization (e.g. block rewards). Finalize(chain ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, uncles []*types.Header, receipts []*types.Receipt) (*types.Block, error)   // Seal generates a new block for the given input block with the local miner's // seal place on top. Seal(chain ChainReader, block *types.Block, stop <-chan struct{}) (*types.Block, error)   // APIs returns the RPC APIs this consensus engine provides. APIs(chain ChainReader) []rpc.API}// PoW is a consensus engine based on proof-of-work.type PoW interface {   Engine   // Hashrate returns the current mining hashrate of a PoW consensus engine. Hashrate() float64}

其中最主要的是 prepare 預先處理當前區塊的頭資訊（比如 挖礦難度）(Homestead)

diff = (parent_diff + (parent_diff / 2048 * max(1 - (block_timestamp - parent_timestamp) / 10, -99)) ) + 2^(periodCount - 2)

parent_diff ：上一個區塊的難度
 block_timestamp ：當前塊的時間戳記 parent_timestamp：上一個塊的時間戳記 periodCount ：區塊num/100000

block_timestamp - parent_timestamp 差值小於10秒 變難

block_timestamp - parent_timestamp 差值10-20秒 不變 block_timestamp - parent_timestamp 差值大於20秒 變容易，並且大的越多，越容易，但是又上限 總體上塊的難度是遞增的 seal 開始做挖礦的事情，“解題”直到成功或者退出 根據挖礦難度計算目標值 選取隨機數nonce+區塊頭(不包含nonce)的hash，再做一次hash，結果小於目標值，則退出，否則迴圈重試 如果外部退出了(比如已經收到這個塊了)，則立馬放棄當前塊的打包 Finalize 做挖礦成功後最後善後的事情 計算礦工的獎勵：區塊獎勵，叔塊獎勵， 但是這裡沒有交易費~~

verifyHeader 校正extra大小 校正區塊時間戳記，跟目前時間比 校正難度值 校正gaslimit上線 校正區塊的總gasuserd小於 gaslimit 校正區塊的gaslimit 是在合理範圍 特殊的校正，比如dao分叉後的幾個塊extra裡面寫了特殊資料，來判斷一下 VerifySeal 校正難度的有效性 nonce是否小於目標值（解題成功）