1 导语区块链的主要工作就是出块，出块的制度、方式叫做共识；\块里的内容是不可篡改的信息记录，块连接成链就是区块链。出块又叫挖矿，有各种挖矿的方式，比如POW、DPOS，本文主要分析DPOS共识源码。以太坊存在多种共识：PoW （etash）在主网使用PoA（clique） 在测试网使用FakePow 在单元测试使用DPOS 新增共识替代POW既然是源码分析，主要读者群体应该是看代码的人，读者须要结合代码看此类文章。明白此类文章的作用是：提供一个分析的切入口，将散落的代码按某种内在逻辑串起来，用图文的形式叙述代码的大意，引领读者有一个系统化的认知，同时对自己阅读代码过程中不理解的地方起到一定参考作用。2 DPOS的共识逻辑DPOS的基本逻辑可以概述为：成为候选人-获得他人投票-被选举为验证人-在周期内轮流出块。从这个过程可以看到，成为候选人和投票是用户主动发起的行为，获得投票和被选为验证人是系统行为。DPOS的主要功能就是成为候选人、投票（对方获得投票），以及系统定期自动执行的选举。2.1 最初的验证人验证人就是出块人，在创世的时候，系统还没运行，用户自然不能投票，本系统采用的方法是，在创世配置文件中定义好最初的一批出块验证人（Validator），由这一批验证人在第一个出块周期内轮流出块，默认是21个验证人。{ “config”: { “chainId”: 8888, “eip155Block”: 0, “eip158Block”: 0, “byzantiumBlock”:0, “dpos”:{ “validators”:[ “0x8807fa0db2c60675a8f833dd010469e408428b83”, “0xdf5f5a7abc5d0821c50deb4368528d8691f18737”, “0xe0d64bfb1a30d66ae0f06ce36d5f4edf6835cd7c” …… ] } }, “nonce”: “0x0000000000000042”, “difficulty”: “0x020000”, “mixHash”: “0x0000000000000000000000000000000000000000000000000000000000000000”, “coinbase”: “0x0000000000000000000000000000000000000000”, “timestamp”: “0x00”, “parentHash”: “0x0000000000000000000000000000000000000000000000000000000000000000”, “extraData”: “0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa”, “gasLimit”: “0x500000”, “alloc”: {}}2.2 成为候选人系统运行之后，任何人随时可以投票，同时也可以获得他人投票。因为只有候选人才允许获得投票，所以任何人被投票之前都要先成为候选人（candidate）。\从外部用户角度看，成为候选人只需要自己发一笔交易即可：eth.sendTransaction({ from: ‘0x646ba1fa42eb940aac67103a71e9a908ef484ec3’, to: ‘0x646ba1fa42eb940aac67103a71e9a908ef484ec3’, value: 0, type: 1})在系统内部，成为候选人和投票均被定义为交易，其实DPOS定义的所有交易有四种类型，是针对这两种行为的正向和反向操作。type TxType uint8const ( Binary TxType = iota LoginCandidate //成为候选人 LogoutCandidate //取消候选人 Delegate //投票 UnDelegate //取消投票)type txdata struct { Type TxType json:"type" …… }成为候选人代码非常简单，就是更新(插入)一下candidateTrie，这棵树的键和值都是候选人的地址，它保存着所有当前时间的候选人。func (d *DposContext) BecomeCandidate(candidateAddr common.Address) error { candidate := candidateAddr.Bytes() return d.candidateTrie.TryUpdate(candidate, candidate)}具体执行交易的时候，它取的地址是from，这意味着只能将自己设为候选人。case types.LoginCandidate: dposContext.BecomeCandidate(msg.From())除了这里提到的candidateTrie，DPOS总共有五棵树：type DposContext struct { epochTrie *trie.Trie //记录出块周期内的验证人列表 ("validator",[]validator) delegateTrie *trie.Trie //(append(candidate, delegator...), delegator) voteTrie *trie.Trie //(delegator, candidate) candidateTrie *trie.Trie //(candidate, candidate) mintCntTrie *trie.Trie //记录验证人在周期内的出块数目(append(epoch, validator.Bytes()...),count) 这里的epoch=header.Time/86400 db ethdb.Database}delegator是投票人2.3 投票从外部用户角度看，投票也是一笔交易：eth.sendTransaction({ from: '0x646ba1fa42eb940aac67103a71e9a908ef484ec3', to: '0x5b76fff970bf8a351c1c9ebfb5e5a9493e956ddd', value: 0, type: 3})系统内部的投票代码，主要更新delegateTrie和voteTrie：func (d *DposContext) Delegate(delegatorAddr, candidateAddr common.Address) error { delegator, candidate := delegatorAddr.Bytes(), candidateAddr.Bytes() // 获得投票的候选人一定要在candidateTrie中 candidateInTrie, err := d.candidateTrie.TryGet(candidate) if err != nil { return err } if candidateInTrie == nil { return errors.New("invalid candidate to delegate") } // delete old candidate if exists oldCandidate, err := d.voteTrie.TryGet(delegator) if err != nil { if _, ok := err.(*trie.MissingNodeError); !ok { return err } } if oldCandidate != nil { d.delegateTrie.Delete(append(oldCandidate, delegator...)) } if err = d.delegateTrie.TryUpdate(append(candidate, delegator...), delegator); err != nil { return err } return d.voteTrie.TryUpdate(delegator, candidate)}2.4 选举投票虽然随时可以进行，但是验证人的选出，则是周期性的触发。\选举周期默认设定为24小时，每过24小时，对验证人进行一次重新选举。\每次区块被打包的时候（Finalize）都会调用选举函数，选举函数判断是否到了重新选举的时刻，它根据当前块和上一块的时间，计算两块是否属于同一个选举周期，如果是同一个周期，不触发重选，如果不是同一个周期，则说明当前块是新周期的第一块，触发重选。\\选举函数：func (ec *EpochContext) tryElect(genesis, parent *types.Header) error { genesisEpoch := genesis.Time.Int64() / epochInterval //0 prevEpoch := parent.Time.Int64() / epochInterval //ec.TimeStamp从Finalize传过来的当前块的header.Time currentEpoch := ec.TimeStamp / epochInterval prevEpochIsGenesis := prevEpoch == genesisEpoch if prevEpochIsGenesis && prevEpoch < currentEpoch { prevEpoch = currentEpoch - 1 } prevEpochBytes := make([]byte, 8) binary.BigEndian.PutUint64(prevEpochBytes, uint64(prevEpoch)) iter := trie.NewIterator(ec.DposContext.MintCntTrie().PrefixIterator(prevEpochBytes)) //currentEpoch只有在比prevEpoch至少大于1的时候执行下面代码。 //大于1意味着当前块的时间,距离上一块所处的周期起始时间,已经超过epochInterval即24小时了。 //大于2过了48小时…… for i := prevEpoch; i < currentEpoch; i++ { // 如果前一个周期不是创世周期，触发踢出验证人规则 if !prevEpochIsGenesis && iter.Next() { if err := ec.kickoutValidator(prevEpoch); err != nil { return err } } //计票，按票数从高到低得出safeSize个验证人 // 候选人的票数cnt=所有投他的delegator的账户余额之和 votes, err := ec.countVotes() if err != nil { return err } candidates := sortableAddresses{} for candidate, cnt := range votes { candidates = append(candidates, &sortableAddress{candidate, cnt}) } if len(candidates) < safeSize { return errors.New("too few candidates") } sort.Sort(candidates) if len(candidates) > maxValidatorSize { candidates = candidates[:maxValidatorSize] } // shuffle candidates //用父块的hash和当前周期编号做验证人列表随机乱序的种子 //打乱验证人列表顺序，由seed确保每个节点计算出来的验证人顺序都是一致的。 seed := int64(binary.LittleEndian.Uint32(crypto.Keccak512(parent.Hash().Bytes()))) + i r := rand.New(rand.NewSource(seed)) for i := len(candidates) - 1; i > 0; i-- { j := int(r.Int31n(int32(i + 1))) candidates[i], candidates[j] = candidates[j], candidates[i] } sortedValidators := make([]common.Address, 0) for _, candidate := range candidates { sortedValidators = append(sortedValidators, candidate.address) } epochTrie, _ := types.NewEpochTrie(common.Hash{}, ec.DposContext.DB()) ec.DposContext.SetEpoch(epochTrie) ec.DposContext.SetValidators(sortedValidators) log.Info("Come to new epoch", "prevEpoch", i, "nextEpoch", i+1) } return nil}当epochContext最终调用了dposContext的SetValidators()后，新的一批验证人就产生了，这批新的验证人将开始轮流出块。2.5 DPOS相关类图EpochContext是选举周期（默认24小时）相关实体类，所以主要功能是仅在周期时刻发生的事情，包括选举、计票、踢出验证人。它是更大范围上的存在，不直接操作DPOS的五棵树，而是通过它聚合的DposContext对五棵树进行增删改查。DposContext和Trie是强组合关系，DPOS的交易行为（成为候选人、取消为候选人、投票、取消投票、设置验证人）就是它的主要功能。Dpos is a engine，实现Engine接口。func (self *worker) mintBlock(now int64) { engine, ok := self.engine.(*dpos.Dpos) ……}3 DPOS引擎实现DPOS是共识引擎的具体实现，Engine接口定义了九个方法。3.1 Authorfunc (d *Dpos) Author(header *types.Header) (common.Address, error) { return header.Validator, nil}这个接口的意思是返回出块人。在POW共识中，返回的是header.Coinbase。\DPOS中Header增加了一个Validator，是有意将Coinbase和Validator的概念分开。Validator默认等于Coinbase，也可以设为不一样的地址。3.2 VerifyHeader验证header里的一些字段是否符合dpos共识规则。\符合以下判断都是错的：header.Time.Cmp(big.NewInt(time.Now().Unix())) > 0len(header.Extra) < extraVanity+extraSeal //32+65header.MixDigest != (common.Hash{})header.Difficulty.Uint64() != 1header.UncleHash != types.CalcUncleHash(nil)parent == nil || parent.Number.Uint64() != number-1 || parent.Hash() != header.ParentHash//与父块出块时间间隔小于了10（blockInterval）秒parent.Time.Uint64()+uint64(blockInterval) > header.Time.Uint64()3.3 VerifyHeaders批量验证header3.4 VerifyUnclesdpos里不应有uncles。func (d *Dpos) VerifyUncles(chain consensus.ChainReader, block *types.Block) error { if len(block.Uncles()) > 0 { return errors.New("uncles not allowed") } return nil}3.5 Prepare为Header准备部分字段：\Nonce为空；\Extra预留为32+65个0字节，Extra字段包括32字节的extraVanity前缀和65字节的extraSeal后缀，都为预留字节,extraSeal在区块Seal的时候写入验证人的签名。\Difficulty置为1；\Validator设置为signer；signer是在启动挖矿的时候设置的，其实就是本节点的验证人（Ethereum.validator）。func (d *Dpos) Prepare(chain consensus.ChainReader, header *types.Header) error { header.Nonce = types.BlockNonce{} number := header.Number.Uint64() //如果header.Extra不足32字节，则用0填充满32字节。 if len(header.Extra) < extraVanity { header.Extra = append(header.Extra, bytes.Repeat([]byte{0x00}, extraVanity-len(header.Extra))...) } header.Extra = header.Extra[:extraVanity] //header.Extra再填65字节 header.Extra = append(header.Extra, make([]byte, extraSeal)...) parent := chain.GetHeader(header.ParentHash, number-1) if parent == nil { return consensus.ErrUnknownAncestor } header.Difficulty = d.CalcDifficulty(chain, header.Time.Uint64(), parent) //header.Validator赋值为Dpos的signer。 header.Validator = d.signer return nil}关于难度在DPOS里，不需要求难度值，给定一个即可。func (d *Dpos) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int { return big.NewInt(1)}而在POW中，难度是根据父块和最新块的时间差动态调整的，小于10增加难度，大于等于20减小难度。block_diff = parent_diff + 难度调整 + 难度炸弹难度调整 = parent_diff // 2048 * MAX(1 - (block_timestamp - parent_timestamp) // 10, -99)难度炸弹 = INT(2^((block_number // 100000) - 2))关于singer调用API，人为设置本节点的验证人func (api *PrivateMinerAPI) SetValidator(validator common.Address) bool { api.e.SetValidator(validator) //e *Ethereum return true}func (self *Ethereum) SetValidator(validator common.Address) { self.lock.Lock() //lock sync.RWMutex self.validator = validator self.lock.Unlock()}节点启动挖矿时调用了dpos.Authorize将验证人赋值给了dpos.signerfunc (s *Ethereum) StartMining(local bool) error { validator, err := s.Validator() …… if dpos, ok := s.engine.(*dpos.Dpos); ok { wallet, err := s.accountManager.Find(accounts.Account{Address: validator}) if wallet == nil || err != nil { log.Error("Coinbase account unavailable locally", "err", err) return fmt.Errorf("signer missing: %v", err) } dpos.Authorize(validator, wallet.SignHash) } ……}func (s *Ethereum) Validator() (validator common.Address, err error) { s.lock.RLock() //lock sync.RWMutex validator = s.validator s.lock.RUnlock() ……}func (d *Dpos) Authorize(signer common.Address, signFn SignerFn) { d.mu.Lock() d.signer = signer d.signFn = signFn d.mu.Unlock()}3.6 Finalize<span id="finalize"></span>生成一个新的区块，不过不是最终的区块。该函数功能请看注释。func (d *Dpos) Finalize(……){ //把奖励打入Coinbase，拜占庭版本以后奖励3个eth，之前奖励5个 AccumulateRewards(chain.Config(), state, header, uncles) //调用选举，函数内部判断是否到了新一轮选举周期 err := epochContext.tryElect(genesis, parent) //每出一个块，将该块验证人的出块数+1，即更新DposContext.mintCntTrie。 updateMintCnt(parent.Time.Int64(), header.Time.Int64(), header.Validator, dposContext) //给区块设置header,transactions,Bloom,uncles； //给header设置TxHash,ReceiptHash,UncleHash； return types.NewBlock(header, txs, uncles, receipts), nil}3.7 Seal<span id="seal"></span>dpos的Seal主要是给新区块进行签名，即把签名写入header.Extra，返回最终状态的区块。\d.signFn是个函数类型的声明，首先源码定义了一个钱包接口SignHash用于给一段hash进行签名，然后将这个接口作为形参调用dpos.Authorize，这样d.signFn就被赋予了这个函数，而具体实现是keystoreWallet.SignHash，所以d.signFn的执行就是在执行keystoreWallet.SignHash。func (d *Dpos) Seal(chain consensus.ChainReader, block *types.Block, stop <-chan struct{}) (*types.Block, error) { header := block.Header() number := header.Number.Uint64() // Sealing the genesis block is not supported if number == 0 { return nil, errUnknownBlock } now := time.Now().Unix() delay := NextSlot(now) - now if delay > 0 { select { case <-stop: return nil, nil //等到下一个出块时刻slot，如10秒1块的节奏，10秒内等到第10秒，11秒则要等到第20秒，以此类推。 case <-time.After(time.Duration(delay) * time.Second): } } block.Header().Time.SetInt64(time.Now().Unix()) // time's up, sign the block sighash, err := d.signFn(accounts.Account{Address: d.signer}, sigHash(header).Bytes()) if err != nil { return nil, err } //将签名赋值给header.Extra的后缀。这里数组索引不会为负，因为在Prepare的时候，Extra就保留了32（前缀）+65（后缀）个字节。 copy(header.Extra[len(header.Extra)-extraSeal:], sighash) return block.WithSeal(header), nil}func (b *Block) WithSeal(header *Header) *Block { cpy := *header return &Block{ header: &cpy, transactions: b.transactions, uncles: b.uncles, // add dposcontext DposContext: b.DposContext, }}3.8 VerifySealSeal接口是区块产生的最后一道工序，也是各种共识算法最核心的实现，VerifySeal就是对这种封装的真伪验证。\\1）从epochTrie里获取到验证人列表，(epochTrie的key就是字面量“validator”，它全局唯一，每轮选举后都会被覆盖更新)再用header的时间计算本区块验证人所在列表的偏移量（作为验证人列表数组索引），获得验证人地址。validator, err := epochContext.lookupValidator(header.Time.Int64())2）用Dpos的签名还原出这个验证人的地址。两者进行对比，看是否一致，再用还原的地址和header.Validator对比看是否一致。if err := d.verifyBlockSigner(validator, header); err != nil { return err }func (d *Dpos) verifyBlockSigner(validator common.Address, header *types.Header) error { signer, err := ecrecover(header, d.signatures) if err != nil { return err } if bytes.Compare(signer.Bytes(), validator.Bytes()) != 0 { return ErrInvalidBlockValidator } if bytes.Compare(signer.Bytes(), header.Validator.Bytes()) != 0 { return ErrMismatchSignerAndValidator } return nil}其中：\header.Validator是在Prepare接口中被赋值的。\d.signatures这个签名是怎么赋值的？不要顾名思义它存的不是签名，它的类型是一种有名的缓存，(key,value)分别是(区块头hash，验证人地址)，它的赋值也是在ecrecover里进行的。ecrecover根据区块头hash从缓存中获取到验证人地址，如果没有就从header.Extra的签名部分还原出验证人地址。3)VerifySeal经过上面两步验证后，最后这个操作待详细分析。return d.updateConfirmedBlockHeader(chain)3.9 APIs用于容纳API。func (d *Dpos) APIs(chain consensus.ChainReader) []rpc.API { return []rpc.API{{ Namespace: "dpos", Version: "1.0", Service: &API{chain: chain, dpos: d}, Public: true, }}}它在eth包里被赋值具体APIapis = append(apis, s.engine.APIs(s.BlockChain())...)func (s *Ethereum) APIs() []rpc.API { apis := ethapi.GetAPIs(s.ApiBackend) // Append any APIs exposed explicitly by the consensus engine apis = append(apis, s.engine.APIs(s.BlockChain())...) // Append all the local APIs and return return append(apis, []rpc.API{ { Namespace: "eth", Version: "1.0", Service: NewPublicEthereumAPI(s), Public: true, }, { Namespace: "eth", Version: "1.0", Service: NewPublicMinerAPI(s), Public: true, }, { Namespace: "eth", Version: "1.0", Service: downloader.NewPublicDownloaderAPI(s.protocolManager.downloader, s.eventMux), Public: true, }, { Namespace: "miner", Version: "1.0", Service: NewPrivateMinerAPI(s), Public: false, }, { Namespace: "eth", Version: "1.0", Service: filters.NewPublicFilterAPI(s.ApiBackend, false), Public: true, }, { Namespace: "admin", Version: "1.0", Service: NewPrivateAdminAPI(s), }, { Namespace: "debug", Version: "1.0", Service: NewPublicDebugAPI(s), Public: true, }, { Namespace: "debug", Version: "1.0", Service: NewPrivateDebugAPI(s.chainConfig, s), }, { Namespace: "net", Version: "1.0", Service: s.netRPCService, Public: true, }, }...)}这些赋值的其实是结构体，通过结构体可以访问到自身的方法，这些结构体大多都是Ethereum，只不过区分了Namespace用于不同场景。type PublicEthereumAPI struct { e *Ethereum}type PublicMinerAPI struct { e *Ethereum}type PublicDownloaderAPI struct { d *Downloader mux *event.TypeMux installSyncSubscription chan chan interface{} uninstallSyncSubscription chan *uninstallSyncSubscriptionRequest}type PrivateMinerAPI struct { e *Ethereum}type PublicDebugAPI struct { eth *Ethereum}看看都有哪些API服务：<img src="https://i.loli.net/2018/11/09...; width=350>4 DPOS引擎如何驱动以太坊挖矿以太坊好比一台机器，生产区块，这台机器的引擎上面已经讲过了，接下来再看看这台机器是如何运作的。从控制台启动节点挖矿开始：>miner.start()这个命令将会调用api的Start方法。4.1 以太坊启动时序图在mintLoop方法里，worker无限循环，阻塞监听stopper通道，每秒调用一次mintBlock。\用户主动停止以太坊节点的时候，stopper通道被关闭，worker就停止了。4.2 mintBlock挖矿函数分析这个函数的作用即用引擎(POW、DPOS)出块。在POW版本中，worker还需要启动agent（分为CpuAgent和何RemoteAgent两种实现），agent进行Seal操作。在DPOS中，去掉了agent这一层，直接在mintBlock里Seal。mintLoop每秒都调用mintBlock，但并非每秒都出块，逻辑在下面分析。func (self *worker) mintLoop() { ticker := time.NewTicker(time.Second).C for { select { case now := <-ticker: self.mintBlock(now.Unix()) case <-self.stopper: close(self.quitCh) self.quitCh = make(chan struct{}, 1) self.stopper = make(chan struct{}, 1) return } }}func (self *worker) mintBlock(now int64) { engine, ok := self.engine.(*dpos.Dpos) if !ok { log.Error("Only the dpos engine was allowed") return } err := engine.CheckValidator(self.chain.CurrentBlock(), now) if err != nil { switch err { case dpos.ErrWaitForPrevBlock, dpos.ErrMintFutureBlock, dpos.ErrInvalidBlockValidator, dpos.ErrInvalidMintBlockTime: log.Debug("Failed to mint the block, while ", "err", err) default: log.Error("Failed to mint the block", "err", err) } return } work, err := self.createNewWork() if err != nil { log.Error("Failed to create the new work", "err", err) return } result, err := self.engine.Seal(self.chain, work.Block, self.quitCh) if err != nil { log.Error("Failed to seal the block", "err", err) return } self.recv <- &Result{work, result}}如时序图和源码所示，mintBlock函数包含3个主要方法：4.2.1 CheckValidator出块前验证该函数判断当前出块人（validator）是否与dpos规则计算得到的validator一样，同时判断是否到了出块时间点。func (self *worker) mintBlock(now int64) { …… //检查出块验证人validator是否正确 //CurrentBlock()是截止当前时间，最后加入到链的块 //CurrentBlock()是BlockChain.insert的时候赋的值 err := engine.CheckValidator(self.chain.CurrentBlock(), now) ……}func (d *Dpos) CheckValidator(lastBlock *types.Block, now int64) error { //检查是否到达出块间隔最后1秒（slot），出块间隔设置为10秒 if err := d.checkDeadline(lastBlock, now); err != nil { return err } dposContext, err := types.NewDposContextFromProto(d.db, lastBlock.Header().DposContext) if err != nil { return err } epochContext := &EpochContext{DposContext: dposContext} //根据dpos规则计算：先从epochTrie里获得本轮选举周期的验证人列表 //然后根据当前时间计算偏移量，获得应该由谁挖掘当前块的验证人 validator, err := epochContext.lookupValidator(now) if err != nil { return err } //判断dpos规则计算得到的validator和d.signer即节点设置的validator是否一致 if (validator == common.Address{}) || bytes.Compare(validator.Bytes(), d.signer.Bytes()) != 0 { return ErrInvalidBlockValidator } return nil}func (d *Dpos) checkDeadline(lastBlock *types.Block, now int64) error { prevSlot := PrevSlot(now) nextSlot := NextSlot(now) //假如当前时间是1542117655，则prevSlot = 1542117650，nextSlot = 1542117660 if lastBlock.Time().Int64() >= nextSlot { return ErrMintFutureBlock } // nextSlot-now <= 1是要求出块时间需要接近出块间隔最后1秒 if lastBlock.Time().Int64() == prevSlot || nextSlot-now <= 1 { return nil } //时间不到，就返回等待错误 return ErrWaitForPrevBlock}CheckValidator()判断不通过则跳出mintBlock，继续下一秒mintBlock循环。\判断通过进入createNewWork()。4.2.2 createNewWork生成新块并定型这个函数涉及具体执行交易、生成收据和日志、向监听者发送相关事件、调用dpos引擎Finalize打包、将未Seal的新块加入未确认块集等事项。4.2.2.1 挖矿时序图func (self *worker) createNewWork() (*Work, error) { self.mu.Lock() defer self.mu.Unlock() self.uncleMu.Lock() defer self.uncleMu.Unlock() self.currentMu.Lock() defer self.currentMu.Unlock() tstart := time.Now() parent := self.chain.CurrentBlock() tstamp := tstart.Unix() if parent.Time().Cmp(new(big.Int).SetInt64(tstamp)) >= 0 { tstamp = parent.Time().Int64() + 1 } // this will ensure we're not going off too far in the future if now := time.Now().Unix(); tstamp > now+1 { wait := time.Duration(tstamp-now) * time.Second log.Info("Mining too far in the future", "wait", common.PrettyDuration(wait)) time.Sleep(wait) } num := parent.Number() header := &types.Header{ ParentHash: parent.Hash(), Number: num.Add(num, common.Big1), GasLimit: core.CalcGasLimit(parent), GasUsed: new(big.Int), Extra: self.extra, Time: big.NewInt(tstamp), } // Only set the coinbase if we are mining (avoid spurious block rewards) if atomic.LoadInt32(&self.mining) == 1 { header.Coinbase = self.coinbase } if err := self.engine.Prepare(self.chain, header); err != nil { return nil, fmt.Errorf("got error when preparing header, err: %s", err) } // If we are care about TheDAO hard-fork check whether to override the extra-data or not if daoBlock := self.config.DAOForkBlock; daoBlock != nil { // Check whether the block is among the fork extra-override range limit := new(big.Int).Add(daoBlock, params.DAOForkExtraRange) if header.Number.Cmp(daoBlock) >= 0 && header.Number.Cmp(limit) < 0 { // Depending whether we support or oppose the fork, override differently if self.config.DAOForkSupport { header.Extra = common.CopyBytes(params.DAOForkBlockExtra) } else if bytes.Equal(header.Extra, params.DAOForkBlockExtra) { header.Extra = []byte{} // If miner opposes, don't let it use the reserved extra-data } } } // Could potentially happen if starting to mine in an odd state. err := self.makeCurrent(parent, header) if err != nil { return nil, fmt.Errorf("got error when create mining context, err: %s", err) } // Create the current work task and check any fork transitions needed work := self.current if self.config.DAOForkSupport && self.config.DAOForkBlock != nil && self.config.DAOForkBlock.Cmp(header.Number) == 0 { misc.ApplyDAOHardFork(work.state) } pending, err := self.eth.TxPool().Pending() if err != nil { return nil, fmt.Errorf("got error when fetch pending transactions, err: %s", err) } txs := types.NewTransactionsByPriceAndNonce(self.current.signer, pending) work.commitTransactions(self.mux, txs, self.chain, self.coinbase) // compute uncles for the new block. var ( uncles []*types.Header badUncles []common.Hash ) for hash, uncle := range self.possibleUncles { if len(uncles) == 2 { break } if err := self.commitUncle(work, uncle.Header()); err != nil { log.Trace("Bad uncle found and will be removed", "hash", hash) log.Trace(fmt.Sprint(uncle)) badUncles = append(badUncles, hash) } else { log.Debug("Committing new uncle to block", "hash", hash) uncles = append(uncles, uncle.Header()) } } for _, hash := range badUncles { delete(self.possibleUncles, hash) } // Create the new block to seal with the consensus engine if work.Block, err = self.engine.Finalize(self.chain, header, work.state, work.txs, uncles, work.receipts, work.dposContext); err != nil { return nil, fmt.Errorf("got error when finalize block for sealing, err: %s", err) } work.Block.DposContext = work.dposContext // update the count for the miner of new block // We only care about logging if we're actually mining. if atomic.LoadInt32(&self.mining) == 1 { log.Info("Commit new mining work", "number", work.Block.Number(), "txs", work.tcount, "uncles", len(uncles), "elapsed", common.PrettyDuration(time.Since(tstart))) self.unconfirmed.Shift(work.Block.NumberU64() - 1) } return work, nil}4.2.2.2 准备区块头先调用dpos引擎的Prepare填充区块头字段。 …… num := parent.Number() header := &types.Header{ ParentHash: parent.Hash(), Number: num.Add(num, common.Big1), GasLimit: core.CalcGasLimit(parent), GasUsed: new(big.Int), Extra: self.extra, Time: big.NewInt(tstamp), } // 确保出块时间不要偏离太大（过早或过晚） if atomic.LoadInt32(&self.mining) == 1 { header.Coinbase = self.coinbase } self.engine.Prepare(self.chain, header) ……此时，即将产生的区块Header的GasUsed和Extra都为空，Extra通过前面引擎分析的时候，我们知道会在Prepare里用0字节填充32+65的前后缀，除了Extra，Prepare还将填充其他的Header字段（详见3.5 Prepare分析），当Prepare执行完成，大部分字段都设置好了，还有少部分待填。4.2.2.3 准备挖矿环境接下来把父块和本块的header传给makeCurrent方法执行。 err := self.makeCurrent(parent, header) if err != nil { return nil, fmt.Errorf("got error when create mining context, err: %s", err) } // Create the current work task and check any fork transitions needed work := self.current if self.config.DAOForkSupport && self.config.DAOForkBlock != nil && self.config.DAOForkBlock.Cmp(header.Number) == 0 { misc.ApplyDAOHardFork(work.state) }makeCurrent先新建stateDB和dposContext，然后组装一个Work结构体。func (self *worker) makeCurrent(parent *types.Block, header *types.Header) error { state, err := self.chain.StateAt(parent.Root()) if err != nil { return err } dposContext, err := types.NewDposContextFromProto(self.chainDb, parent.Header().DposContext) if err != nil { return err } work := &Work{ config: self.config, signer: types.NewEIP155Signer(self.config.ChainId), state: state, dposContext: dposContext, ancestors: set.New(), family: set.New(), uncles: set.New(), header: header, createdAt: time.Now(), } // when 08 is processed ancestors contain 07 (quick block) for _, ancestor := range self.chain.GetBlocksFromHash(parent.Hash(), 7) { for _, uncle := range ancestor.Uncles() { work.family.Add(uncle.Hash()) } work.family.Add(ancestor.Hash()) work.ancestors.Add(ancestor.Hash()) } // Keep track of transactions which return errors so they can be removed work.tcount = 0 self.current = work return nil}Work结构体中，ancestors存储的是6个祖先块，family存储的是6个祖先块和它们各自的叔块，组装后的Work结构体赋值给*worker.current。4.2.2.3 从交易池获取pending交易集然后从交易池里获取所有pending状态的交易，这些交易按账户分组，每个账户里的交易按nonce排序后返回交易集，这里暂且叫S1：pending, err := self.eth.TxPool().Pending() //S1 = pendingtxs := types.NewTransactionsByPriceAndNonce(self.current.signer, pending)4.2.2.4 交易集结构化处理再然后通过NewTransactionsByPriceAndNonce函数对交易集进行结构化，它把S1集合里每个账户的第一笔交易分离出来作为heads集合，返回如下结构：return &TransactionsByPriceAndNonce{ txs: txs, //S1集合中每个账户除去第一个交易后的交易集 heads: heads, //这个集合由每个账户的第一个交易组成 signer: signer, }4.2.2.5 交易执行过程分析调用commitTransactions方法，执行新区块包含的所有交易。这个方法是对处理后的交易集txs的具体执行，所谓执行交易，笼统地说就是把转账、合约或dpos交易类型的数据写入对应的内存Trie，再从Trie刷到本地DB中去。func (env *Work) commitTransactions(mux *event.TypeMux, txs *types.TransactionsByPriceAndNonce, bc *core.BlockChain, coinbase common.Address) { gp := new(core.GasPool).AddGas(env.header.GasLimit) var coalescedLogs []*types.Log for { // Retrieve the next transaction and abort if all done tx := txs.Peek() if tx == nil { break } // Error may be ignored here. The error has already been checked // during transaction acceptance is the transaction pool. // // We use the eip155 signer regardless of the current hf. from, _ := types.Sender(env.signer, tx) // Check whether the tx is replay protected. If we're not in the EIP155 hf // phase, start ignoring the sender until we do. if tx.Protected() && !env.config.IsEIP155(env.header.Number) { log.Trace("Ignoring reply protected transaction", "hash", tx.Hash(), "eip155", env.config.EIP155Block) txs.Pop() continue } // Start executing the transaction env.state.Prepare(tx.Hash(), common.Hash{}, env.tcount) err, logs := env.commitTransaction(tx, bc, coinbase, gp) switch err { case core.ErrGasLimitReached: // Pop the current out-of-gas transaction without shifting in the next from the account log.Trace("Gas limit exceeded for current block", "sender", from) txs.Pop() case core.ErrNonceTooLow: // New head notification data race between the transaction pool and miner, shift log.Trace("Skipping transaction with low nonce", "sender", from, "nonce", tx.Nonce()) txs.Shift() case core.ErrNonceTooHigh: // Reorg notification data race between the transaction pool and miner, skip account = log.Trace("Skipping account with hight nonce", "sender", from, "nonce", tx.Nonce()) txs.Pop() case nil: // Everything ok, collect the logs and shift in the next transaction from the same account coalescedLogs = append(coalescedLogs, logs...) env.tcount++ txs.Shift() default: // Strange error, discard the transaction and get the next in line (note, the // nonce-too-high clause will prevent us from executing in vain). log.Debug("Transaction failed, account skipped", "hash", tx.Hash(), "err", err) txs.Shift() } } if len(coalescedLogs) > 0 || env.tcount > 0 { // make a copy, the state caches the logs and these logs get "upgraded" from pending to mined // logs by filling in the block hash when the block was mined by the local miner. This can // cause a race condition if a log was "upgraded" before the PendingLogsEvent is processed. cpy := make([]*types.Log, len(coalescedLogs)) for i, l := range coalescedLogs { cpy[i] = new(types.Log) *cpy[i] = *l } go func(logs []*types.Log, tcount int) { if len(logs) > 0 { mux.Post(core.PendingLogsEvent{Logs: logs}) } if tcount > 0 { mux.Post(core.PendingStateEvent{}) } }(cpy, env.tcount) }}该方法对结构化处理后的txs遍历执行,分为几步：Work.state.Prepare()\这是给StateDB设置交易hash、区块hash（此时为空）、交易索引。\StateDB是用来操作整个账户树也即world state trie的，每执行一笔交易就更改一次world state trie。\交易索引是指在对txs.heads进行遍历的时候的自增数，这个索引在本区块内唯一，因为它是本区块包含的所有pending交易涉及的账户及各账户下所有交易的总递增。commitTransactions函数对txs的遍历方式是：从遍历txs.heads开始，获取第一个账户的第一笔交易，然后获取同一账户的第二笔交易以此类推，如果该账户没有交易了，继续txs.heads的下一个账户。\也就是按账户优先级先遍历其下的所有交易，其次遍历所有账户（堆级别操作），txs结构化就是为这种循环方式准备的。func (self *StateDB) Prepare(thash, bhash common.Hash, ti int) { self.thash = thash self.bhash = bhash self.txIndex = ti}Work.commitTransaction()\执行单笔交易，先对stateDB这个大结构做一个版本号快照，也要对dpos的五棵树上下文即dposContext做一个备份，然后调用core.ApplyTransaction()方法，如果出错就退回快照和备份，执行成功后把交易加入Work.txs，（这个txs是为Finalize的时候传参用的，因为在遍历执行交易的时候会把原txs结构破坏，做个备份）交易收据加入Work.receipts，最后返回收据日志。func (env *Work) commitTransaction(tx *types.Transaction, bc *core.BlockChain, coinbase common.Address, gp *core.GasPool) (error, []*types.Log) { snap := env.state.Snapshot() dposSnap := env.dposContext.Snapshot() receipt, _, err := core.ApplyTransaction(env.config, env.dposContext, bc, &coinbase, gp, env.state, env.header, tx, env.header.GasUsed, vm.Config{}) if err != nil { env.state.RevertToSnapshot(snap) env.dposContext.RevertToSnapShot(dposSnap) return err, nil } env.txs = append(env.txs, tx) env.receipts = append(env.receipts, receipt) return nil, receipt.Logs}看一下ApplyTransaction()是如何具体执行交易的：func ApplyTransaction(config *params.ChainConfig, dposContext *types.DposContext, 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) { msg, err := tx.AsMessage(types.MakeSigner(config, header.Number)) if err != nil { return nil, nil, err } if msg.To() == nil && msg.Type() != types.Binary { return nil, nil, types.ErrInvalidType } // Create a new context to be used in the EVM environment 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 } if msg.Type() != types.Binary { if err = applyDposMessage(dposContext, msg); err != nil { return nil, nil, err } } // Update the state with pending changes 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. 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. 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}) return receipt, gas, err}NewEVMContext是构建一个EVM执行环境，这个环境如下：return vm.Context{ //是否能够转账函数，会判断发起交易账户余额是否大于转账数量 CanTransfer: CanTransfer, //转账函数，给转账地址减去转账额，同时给接收地址加上转账额 Transfer: Transfer, //区块头hash GetHash: GetHashFn(header, chain), Origin: msg.From(), Coinbase: beneficiary, BlockNumber: new(big.Int).Set(header.Number), Time: new(big.Int).Set(header.Time), Difficulty: new(big.Int).Set(header.Difficulty), GasLimit: new(big.Int).Set(header.GasLimit), GasPrice: new(big.Int).Set(msg.GasPrice()),}==beneficiary是Coinbase，这里是指如果没有指定coinbase就从header里获取validator的地址作为coinbase。==\NewEVM是创建一个携带了EVM环境和编译器的虚拟机。然后调用ApplyMessage()，这个函数最主要的是对当前交易进行状态转换TransitionDb()。TransitionDb详解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 // Pay intrinsic gas // TODO convert to uint64 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 { ret, _, st.gas, vmerr = evm.Create(sender, st.data, st.gas, st.value) } else { // Increment the nonce for the next transaction 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()) st.refundGas() st.state.AddBalance(st.evm.Coinbase, new(big.Int).Mul(st.gasUsed(), st.gasPrice)) return ret, requiredGas, st.gasUsed(), vmerr != nil, err}其中preCheck检查当前交易nonce和发送账户当前nonce是否一致，同时检查发送账户余额是否大于GasLimit，足够的话就先将余额减去gaslimit（过度状态转换），不足就返回一个常见的错误：“insufficient balance to pay for gas”。IntrinsicGas()是计算交易所需固定费用：如果是创建合约交易，固定费用为53000gas，转账交易固定费用是21000gas，如果交易携带数据，这个数据对于创建合约是合约代码数据，对于转账交易是转账的附加说明数据，这些数据按字节存储收费，非0字节每位68gas，0字节每位4gas，总计起来就是执行交易所需的gas费。useGas()判断提供的gas是否满足上面计算出的内部所需费用，足够的话从提供的gas里扣除内部所需费用（状态转换）。因为ApplyTransaction传的参数msg已经将dpos类型且to为空的交易排除出去了。所以当这里msg.To() == nil的时候，只剩下msg.Type == 0这一种原始交易的可能了。msg.To为空说明该交易不是转账、不是合约调用，只能是创建合约交易，根据msg.To是否为空，分两种情况，Create创建合约和Call调用合约，这两种情况都覆盖了转账行为。1）if contractCreation{…}，即to==nil，说明是创建合约交易，调用evm.Create()。// Create creates a new contract using code as deployment code.func (evm *EVM) Create(caller ContractRef, code []byte, gas uint64, value *big.Int) (ret []byte, contractAddr common.Address, leftOverGas uint64, err error) { // Depth check execution. Fail if we're trying to execute above the // limit. if evm.depth > int(params.CallCreateDepth) { return nil, common.Address{}, gas, ErrDepth } if !evm.CanTransfer(evm.StateDB, caller.Address(), value) { return nil, common.Address{}, gas, ErrInsufficientBalance } // Ensure there's no existing contract already at the designated address nonce := evm.StateDB.GetNonce(caller.Address()) evm.StateDB.SetNonce(caller.Address(), nonce+1) contractAddr = crypto.CreateAddress(caller.Address(), nonce) contractHash := evm.StateDB.GetCodeHash(contractAddr) if evm.StateDB.GetNonce(contractAddr) != 0 || (contractHash != (common.Hash{}) && contractHash != emptyCodeHash) { return nil, common.Address{}, 0, ErrContractAddressCollision } // Create a new account on the state snapshot := evm.StateDB.Snapshot() evm.StateDB.CreateAccount(contractAddr) if evm.ChainConfig().IsEIP158(evm.BlockNumber) { evm.StateDB.SetNonce(contractAddr, 1) } evm.Transfer(evm.StateDB, caller.Address(), contractAddr, value) // initialise a new contract and set the code that is to be used by the // E The contract is a scoped evmironment for this execution context // only. contract := NewContract(caller, AccountRef(contractAddr), value, gas) contract.SetCallCode(&contractAddr, crypto.Keccak256Hash(code), code) if evm.vmConfig.NoRecursion && evm.depth > 0 { return nil, contractAddr, gas, nil } ret, err = run(evm, snapshot, contract, nil) // check whether the max code size has been exceeded maxCodeSizeExceeded := evm.ChainConfig().IsEIP158(evm.BlockNumber) && len(ret) > params.MaxCodeSize // if the contract creation ran successfully and no errors were returned // calculate the gas required to store the code. If the code could not // be stored due to not enough gas set an error and let it be handled // by the error checking condition below. if err == nil && !maxCodeSizeExceeded { createDataGas := uint64(len(ret)) * params.CreateDataGas if contract.UseGas(createDataGas) { evm.StateDB.SetCode(contractAddr, ret) } else { err = ErrCodeStoreOutOfGas } } // When an error was returned by the EVM or when setting the creation code // above we revert to the snapshot and consume any gas remaining. Additionally // when we're in homestead this also counts for code storage gas errors. if maxCodeSizeExceeded || (err != nil && (evm.ChainConfig().IsHomestead(evm.BlockNumber) || err != ErrCodeStoreOutOfGas)) { evm.StateDB.RevertToSnapshot(snapshot) if err != errExecutionReverted { contract.UseGas(contract.Gas) } } // Assign err if contract code size exceeds the max while the err is still empty. if maxCodeSizeExceeded && err == nil { err = errMaxCodeSizeExceeded } return ret, contractAddr, contract.Gas, err}注意这里传入的gas是已经扣除了固定费用的剩余gas。evm是基于栈的简单虚拟机，最多支持1024栈深度，超过就报错。然后在这里调用evmContext的CanTransfer()判断发起交易地址余额是否大于转账数量，是的话就将发起交易的账户的nonce+1。生成合约账户地址：合约账户的地址生成规则是，由发起交易的地址和该nonce计算生成，生成地址后，此时仅有地址，根据地址获取该合约账户的nonce应该为0、codeHash应该为空hash，不符合这些判断说明地址冲突，报错退出。紧接着创建一个新账户evm.StateDB.CreateAccount(contractAddr)，这个函数创建的是一个普通账户（即EOA和Contract账户的未分化形式）。\新账户的地址就是上面计算生成的地址，Nonce设为0，Balance设为0，但是如果之前已存在同样地址的账户那么Balance就设为之前账户的余额,CodeHash设为空hash注意不是空。EIP158之后的新账号nonce设为1。evm.Transfer():如果创建账户的时候有资助代币（eth），则将代币从发起地址转移到新账户地址。然后NewContract()构建一个合约上下文环境contract。SetCallCode()，给contract环境对象设置入参Code、CodeHash。run()：EVM编译、执行合约的创建，执行EVM栈操作。\run执行返回合约body字节码（code storage），如果长度超过24576也存储不了，然后计算存储这个合约字节码的gas费用=长度*200。最后给stateObject对象设置code，给账户(Account)设置codeHash，这样那个新账户就成了一个合约账户。2）else{…}如果不是创建合约交易（即to!=nil），调用evm.Call()。这个Call是执行合约交易，包括转账类型的交易、调用合约交易。func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, leftOverGas uint64, err error) { if evm.vmConfig.NoRecursion && evm.depth > 0 { return nil, gas, nil } // Fail if we're trying to execute above the call depth limit if evm.depth > int(params.CallCreateDepth) { return nil, gas, ErrDepth } // Fail if we're trying to transfer more than the available balance if !evm.Context.CanTransfer(evm.StateDB, caller.Address(), value) { return nil, gas, ErrInsufficientBalance } var ( to = AccountRef(addr) snapshot = evm.StateDB.Snapshot() ) if !evm.StateDB.Exist(addr) { precompiles := PrecompiledContractsHomestead if evm.ChainConfig().IsByzantium(evm.BlockNumber) { precompiles = PrecompiledContractsByzantium } if precompiles[addr] == nil && evm.ChainConfig().IsEIP158(evm.BlockNumber) && value.Sign() == 0 { return nil, gas, nil } evm.StateDB.CreateAccount(addr) } evm.Transfer(evm.StateDB, caller.Address(), to.Address(), value) // initialise a new contract and set the code that is to be used by the // E The contract is a scoped environment for this execution context // only. contract := NewContract(caller, to, value, gas) contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr)) ret, err = run(evm, snapshot, contract, input) // When an error was returned by the EVM or when setting the creation code // above we revert to the snapshot and consume any gas remaining. Additionally // when we're in homestead this also counts for code storage gas errors. if err != nil { evm.StateDB.RevertToSnapshot(snapshot) if err != errExecutionReverted { contract.UseGas(contract.Gas) } } return ret, contract.Gas, err}Call函数先来三个判断：evm编译器被禁用或者evm执行栈深超过1024或者转账数额超过余额就报错。注意以下几个Call步骤和Create的区别：evm.StateDB.Exist(addr)是从stateObjects这个所有stateObject的map集合中查找是否存to地址，如果不存在，则调用evm.StateDB.CreateAccount(addr)创建一个新账户，这和Create里调的是同一个函数，即CreateAccount创建的是一个普通账户。evm.Transfer():将代币从发起地址转移到to地址（包括纯转账类型的交易、给合约地址转入代币等）NewContract()构建一个合约上下文环境contract。SetCallCode()：这个函数和Create里的SetCallCode()传的入参不一样，它是从to地址获取code，然后才给to账户设置code、codehash等，这隐含了两种可能性，如果获取到了code那么这个账户自然是合约账户，如果没有获取到，那这个账户就是外部拥有账户（EOA）run()：EVM编译、执行EVM栈操作。这个Call除了转账、调用合约，还包括执dpos交易，当交易是dpos类型的交易的时候，它其实是个空合约，之所以要执行dpos这类空合约是要计算其gas。TransitionDB()在交易执行完后，将剩余gas返退回给发起者账户地址，同时把挖矿节点设置的Coinbase的余额增加上消耗的gas。</td></tr></table>除了Call()，evm还提供了另外3个合约调用方法：\CallCode()，已经弃用，由DelegateCall()替代\DelegateCall()\StaticCall()暂时未用type CallContext interface { // Call another contract Call(env *EVM, me ContractRef, addr common.Address, data []byte, gas, value *big.Int) ([]byte, error) // Take another's contract code and execute within our own context CallCode(env *EVM, me ContractRef, addr common.Address, data []byte, gas, value *big.Int) ([]byte, error) // Same as CallCode except sender and value is propagated from parent to child scope DelegateCall(env *EVM, me ContractRef, addr common.Address, data []byte, gas *big.Int) ([]byte, error) // Create a new contract Create(env *EVM, me ContractRef, data []byte, gas, value *big.Int) ([]byte, common.Address, error)}我们上面讨论的是交易，根据黄皮书的定义交易就两种：创建合约、消息调用。区分二者的标志就是to是否为空。由外部用户触发的才能叫交易，所以用户发起创建合约、用户发起合约调用都叫交易，对应的就是我们上面分析的Create和Call两种情况。转账这种交易执行的是Call()而不是Create()，因为to不为空。用户调用合约A，这叫交易，执行的是Call()，紧接着A里边又调用了合约B，那么这不叫交易叫内部调用，执行的就不是Call()，而是DelegateCall()了，Call和DelegateCall的区别是：Call总是直接改变to的的storage，而DelegateCall改变的是caller（即A）的storage，而不是to的storage。那个NewContract上下文构造函数就是做msg.caller、to等指向工作的。\至于DelegateCall为什么替代CallCode，是修改了一点即msg.sender在DelegateCall里永远指向用户，而CallCode里的sender则指向的是caller。ApplyMessage()结束后，判断一下是否属于DPOS交易，是的话就执行applyDposMessage中对应的交易，即dpos的四种交易：成为候选人、退出候选人、投票、取消投票，具体执行就是更改对应的Trie。\然后调用statedb.Finalise删除掉空账户，再更新状态树，得到最新的world state root hash(intermediate root)。\然后生成一个收据，收据里包括：交易的hash\执行成败状态\消耗的费用\若是创建合约交易就把合约地址也写到收据的ContractAddress字段里\日志\Bloom关于日志，栈操作的时候会记录下日志，日志信息如下：type Log struct { // Consensus fields: // address of the contract that generated the event Address common.Address json:“address” gencodec:“required” // list of topics provided by the contract. Topics []common.Hashjson:“topics” gencodec:“required” // supplied by the contract, usually ABI-encoded Data []bytejson:“data” gencodec:“required” // Derived fields. These fields are filled in by the node // but not secured by consensus. // block in which the transaction was included BlockNumber uint64json:“blockNumber” // hash of the transaction TxHash common.Hashjson:“transactionHash” gencodec:“required” // index of the transaction in the block TxIndex uintjson:“transactionIndex” gencodec:“required” // hash of the block in which the transaction was included BlockHash common.Hashjson:“blockHash” // index of the log in the receipt Index uintjson:“logIndex” gencodec:“required” // The Removed field is true if this log was reverted due to a chain reorganisation. // You must pay attention to this field if you receive logs through a filter query. Removed booljson:“removed”`}ApplyTransaction()最终返回收据。至此，单笔交易执行过程commitTransaction()结束。如此循环执行，直到所有交易执行完成。\在循环执行交易的过程中，我们把所有交易收据的日志写入了一个集合，等交易全部执行完成，异步将这个日志集合向所有已注册的事件接收者发送：mux.Post(core.PendingLogsEvent{Logs: logs})mux.Post(core.PendingStateEvent{})func (mux *TypeMux) Post(ev interface{}) error { event := &TypeMuxEvent{ Time: time.Now(), Data: ev, } rtyp := reflect.TypeOf(ev) mux.mutex.RLock() if mux.stopped { mux.mutex.RUnlock() return ErrMuxClosed } subs := mux.subm[rtyp] mux.mutex.RUnlock() for _, sub := range subs { sub.deliver(event) } return nil}投递相应的事件到TypeMuxSubscription的postC通道中。func (s *TypeMuxSubscription) deliver(event *TypeMuxEvent) { // Short circuit delivery if stale event if s.created.After(event.Time) { return } // Otherwise deliver the event s.postMu.RLock() defer s.postMu.RUnlock() select { case s.postC <- event: case <-s.closing: }}关于事件的订阅、发送单列章节讲。commitTransactions()结束，现在回到了createNewWork中，代码继续遍历叔块和损坏的叔块，这段代码其实在DPOS中已经不需要了，因为DPOS中没有叔块，chainSideCh事件被删除，possibleUncles没有被赋值的机会了。4.2.2.6 Finalize定型新块把header、账户状态、交易、收据等信息传给dpos引擎去定型。参见3.6节。4.2.2.7 检查之前的块是否上链注意：是检查本节点之前挖的块是否上链，而不是当前挖出的块。当前块离上链为时尚早。每个以太坊节点会维护一个未确认块集，集合内有个环状容器，这个容器容纳仅由自身挖出的块，在最乐观的情况下（即连续由本节点挖出块的情况下），最大容纳5个块。当第6个连续的块由本节点挖出的时候就会触发unconfirmedBlocks.Shift()的执行（这里“执行”的上下文含义是满足函数内部的判断条件，而不仅仅指函数被调用，下同）。但大多数情况下，一个节点不会连续出块，那么可能在本节点第二次挖出块的时候，当前区块链高度就已经超过之前挖出的那个块6个高度了，也会触发unconfirmedBlocks.Shift()执行。换句话说就是通常情况下检查自己出的前一个块有没有加入到链上。Shift的作用，是检查未确认块集，这个未确认集并不是说真的就全是一直未被加入到链上的块，而是当该节点满足上面两段描述的“执行”条件时，都会检查一下之前挖出的块有没有被确认（加入区块链），如果当前区块链高度，高于未确认集环状容器内那些块6个高度之后，那些块还没有被加入到链上，就从未确认块集合中删除那些块。这个函数的意思着重表达：在至少6个高度的==时间==之后，才会去检查是否加入到链上，至于上没上链它也不能改变什么，就是给本节点一个之前的块被怎么处理了的通知。为什么是这样的时点呢？可能是要留出6个高度的时间等所有节点都确认吧，后文再说。func (set *unconfirmedBlocks) Shift(height uint64) { set.lock.Lock() defer set.lock.Unlock() for set.blocks != nil { // Retrieve the next unconfirmed block and abort if too fresh next := set.blocks.Value.(*unconfirmedBlock) if next.index+uint64(set.depth) > height { break } // Block seems to exceed depth allowance, check for canonical status header := set.chain.GetHeaderByNumber(next.index) switch { case header == nil: log.Warn(“Failed to retrieve header of mined block”, “number”, next.index, “hash”, next.hash) case header.Hash() == next.hash: log.Info("???? block reached canonical chain", “number”, next.index, “hash”, next.hash) default: log.Info("⑂ block became a side fork", “number”, next.index, “hash”, next.hash) } // Drop the block out of the ring if set.blocks.Value == set.blocks.Next().Value { set.blocks = nil } else { //下面的代码处于循环中，实现对for set.blocks的迭代赋值 set.blocks = set.blocks.Move(-1) //指向最后一个环元素 set.blocks.Unlink(1) //删除原第一个 set.blocks = set.blocks.Move(1) //指向原第二个 } }}4.2.3 Seal封装新块为最终状态这里就是调用dpos引擎的Seal规则了，即给区块签名，参见3.7节。func (self *worker) mintBlock(now int64) { …… result, err := self.engine.Seal(self.chain, work.Block, self.quitCh) ……}这个result和work对象都被发送到self.recv通道中去了。func (self *worker) mintBlock(now int64) { …… self.recv <- &Result{work, result} ……}4.3 新块入库、广播work.wait()在geth运行的时候就监听了work.recv通道，它做了如下几件事：func (self *worker) wait() { for { for result := range self.recv { atomic.AddInt32(&self.atWork, -1) if result == nil || result.Block == nil { continue } block := result.Block work := result.Work // Update the block hash in all logs since it is now available and not when the // receipt/log of individual transactions were created. for _, r := range work.receipts { for _, l := range r.Logs { l.BlockHash = block.Hash() } } for _, log := range work.state.Logs() { log.BlockHash = block.Hash() } stat, err := self.chain.WriteBlockAndState(block, work.receipts, work.state) if err != nil { log.Error(“Failed writing block to chain”, “err”, err) continue } // check if canon block and write transactions if stat == core.CanonStatTy { // implicit by posting ChainHeadEvent } // Broadcast the block and announce chain insertion event self.mux.Post(core.NewMinedBlockEvent{Block: block}) var ( events []interface{} logs = work.state.Logs() ) events = append(events, core.ChainEvent{Block: block, Hash: block.Hash(), Logs: logs}) if stat == core.CanonStatTy { events = append(events, core.ChainHeadEvent{Block: block}) } self.chain.PostChainEvents(events, logs) // Insert the block into the set of pending ones to wait for confirmations self.unconfirmed.Insert(block.NumberU64(), block.Hash()) log.Info(“Successfully sealed new block”, “number”, block.Number(), “hash”, block.Hash()) } }}1）写入本节点数据库（WriteBlockAndState）当通道里接收到新区块后，wait就调用chain.WriteBlockAndState()里的WriteBlock()把区块写入数据库，区块的body部分和header部分独立存储在db中，body的key是“b”+blockNumber+blockHash，值是交易集、叔块集的rlp。header的key是“h”+blockNumber。2）Post NewMinedBlockEvent3）PostChainEvents4）将区块插入unconfirmedBlocks集合4.3.1 事件订阅发送机制Subscribe函数实现1个订阅者订阅多个事件。4.4 新块上链后续再贴上来……
...