Ethereum DPOS源码分析

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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 uint8
const (
    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

image

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 Author

func (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())) > 0
len(header.Extra) < extraVanity+extraSeal //32+65
header.MixDigest != (common.Hash{})
header.Difficulty.Uint64() != 1
header.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header

3.4 VerifyUncles

dpos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.signer

func (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 VerifySeal

Seal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API

apis = 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

image

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

image

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 = pending

txs := 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.Hash `json:"topics" gencodec:"required"`
    // supplied by the contract, usually ABI-encoded
    Data []byte `json:"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 uint64 `json:"blockNumber"`
    // hash of the transaction
    TxHash common.Hash `json:"transactionHash" gencodec:"required"`
    // index of the transaction in the block
    TxIndex uint `json:"transactionIndex" gencodec:"required"`
    // hash of the block in which the transaction was included
    BlockHash common.Hash `json:"blockHash"`
    // index of the log in the receipt
    Index uint `json:"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 bool `json:"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 NewMinedBlockEvent

3)PostChainEvents

4)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……

本文来自:Segmentfault

感谢作者:ChainHeader

查看原文:Ethereum DPOS源码分析

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