以太坊原始碼分析(22)core-genesis創世區塊原始碼分析

尹成發表於2018-05-14
原始碼
genesis 是創世區塊的意思. 一個區塊鏈就是從同一個創世區塊開始,通過規則形成的.不同的網路有不同的創世區塊, 主網路和測試網路的創世區塊是不同的.

這個模組根據傳入的genesis的初始值和database，來設定genesis的狀態，如果不存在創世區塊，那麼在database裡面建立它。

資料結構
    
    // Genesis specifies the header fields, state of a genesis block. It also defines hard
    // fork switch-over blocks through the chain configuration.
    // Genesis指定header的欄位，起始塊的狀態。 它還通過配置來定義硬叉切換塊。
    type Genesis struct {
        Config *params.ChainConfig `json:"config"`
        Nonce uint64 `json:"nonce"`
        Timestamp uint64 `json:"timestamp"`
        ExtraData []byte `json:"extraData"`
        GasLimit uint64 `json:"gasLimit" gencodec:"required"`
        Difficulty *big.Int `json:"difficulty" gencodec:"required"`
        Mixhash common.Hash `json:"mixHash"`
        Coinbase common.Address `json:"coinbase"`
        Alloc GenesisAlloc `json:"alloc" gencodec:"required"`
    
        // These fields are used for consensus tests. Please don't use them
        // in actual genesis blocks.
        Number uint64 `json:"number"`
        GasUsed uint64 `json:"gasUsed"`
        ParentHash common.Hash `json:"parentHash"`
    }
    
    // GenesisAlloc specifies the initial state that is part of the genesis block.
    // GenesisAlloc 指定了最開始的區塊的初始狀態.
    type GenesisAlloc map[common.Address]GenesisAccount


SetupGenesisBlock,
    
    // SetupGenesisBlock writes or updates the genesis block in db.
    //
    // The block that will be used is:
    //
    // genesis == nil genesis != nil
    // +------------------------------------------
    // db has no genesis | main-net default | genesis
    // db has genesis | from DB | genesis (if compatible)
    //
    // The stored chain configuration will be updated if it is compatible (i.e. does not
    // specify a fork block below the local head block). In case of a conflict, the
    // error is a *params.ConfigCompatError and the new, unwritten config is returned.
    // 如果儲存的區塊鏈配置不相容那麼會被更新(). 為了避免發生衝突,會返回一個錯誤,並且新的配置和原來的配置會返回.
    // The returned chain configuration is never nil.

    // genesis 如果是 testnet dev 或者是 rinkeby 模式， 那麼不為nil。如果是mainnet或者是私有連結。那麼為空
    func SetupGenesisBlock(db ethdb.Database, genesis *Genesis) (*params.ChainConfig, common.Hash, error) {
        if genesis != nil && genesis.Config == nil {
            return params.AllProtocolChanges, common.Hash{}, errGenesisNoConfig
        }
    
        // Just commit the new block if there is no stored genesis block.
        stored := GetCanonicalHash(db, 0) //獲取genesis對應的區塊
        if (stored == common.Hash{}) { //如果沒有區塊 最開始啟動geth會進入這裡。
            if genesis == nil {
                //如果genesis是nil 而且stored也是nil 那麼使用主網路
                // 如果是test dev rinkeby 那麼genesis不為空 會設定為各自的genesis
                log.Info("Writing default main-net genesis block")
                genesis = DefaultGenesisBlock()
            } else { // 否則使用配置的區塊
                log.Info("Writing custom genesis block")
            }
            // 寫入資料庫
            block, err := genesis.Commit(db)
            return genesis.Config, block.Hash(), err
        }
    
        // Check whether the genesis block is already written.
        if genesis != nil { //如果genesis存在而且區塊也存在 那麼對比這兩個區塊是否相同
            block, _ := genesis.ToBlock()
            hash := block.Hash()
            if hash != stored {
                return genesis.Config, block.Hash(), &GenesisMismatchError{stored, hash}
            }
        }
    
        // Get the existing chain configuration.
        // 獲取當前存在的區塊鏈的genesis配置
        newcfg := genesis.configOrDefault(stored)
        // 獲取當前的區塊鏈的配置
        storedcfg, err := GetChainConfig(db, stored)
        if err != nil {
            if err == ErrChainConfigNotFound {
                // This case happens if a genesis write was interrupted.
                log.Warn("Found genesis block without chain config")
                err = WriteChainConfig(db, stored, newcfg)
            }
            return newcfg, stored, err
        }
        // Special case: don't change the existing config of a non-mainnet chain if no new
        // config is supplied. These chains would get AllProtocolChanges (and a compat error)
        // if we just continued here.
        // 特殊情況：如果沒有提供新的配置，請不要更改非主網鏈的現有配置。
        // 如果我們繼續這裡，這些鏈會得到AllProtocolChanges（和compat錯誤）。
        if genesis == nil && stored != params.MainnetGenesisHash {
            return storedcfg, stored, nil // 如果是私有連結會從這裡退出。
        }
    
        // Check config compatibility and write the config. Compatibility errors
        // are returned to the caller unless we're already at block zero.
        // 檢查配置的相容性,除非我們在區塊0,否則返回相容性錯誤.
        height := GetBlockNumber(db, GetHeadHeaderHash(db))
        if height == missingNumber {
            return newcfg, stored, fmt.Errorf("missing block number for head header hash")
        }
        compatErr := storedcfg.CheckCompatible(newcfg, height)
        // 如果區塊已經寫入資料了,那麼就不能更改genesis配置了
        if compatErr != nil && height != 0 && compatErr.RewindTo != 0 {
            return newcfg, stored, compatErr
        }
        // 如果是主網路會從這裡退出。
        return newcfg, stored, WriteChainConfig(db, stored, newcfg)
    }


ToBlock, 這個方法使用genesis的資料，使用基於記憶體的資料庫，然後建立了一個block並返回。
    
    
    // ToBlock creates the block and state of a genesis specification.
    func (g *Genesis) ToBlock() (*types.Block, *state.StateDB) {
        db, _ := ethdb.NewMemDatabase()
        statedb, _ := state.New(common.Hash{}, state.NewDatabase(db))
        for addr, account := range g.Alloc {
            statedb.AddBalance(addr, account.Balance)
            statedb.SetCode(addr, account.Code)
            statedb.SetNonce(addr, account.Nonce)
            for key, value := range account.Storage {
                statedb.SetState(addr, key, value)
            }
        }
        root := statedb.IntermediateRoot(false)
        head := &types.Header{
            Number: new(big.Int).SetUint64(g.Number),
            Nonce: types.EncodeNonce(g.Nonce),
            Time: new(big.Int).SetUint64(g.Timestamp),
            ParentHash: g.ParentHash,
            Extra: g.ExtraData,
            GasLimit: new(big.Int).SetUint64(g.GasLimit),
            GasUsed: new(big.Int).SetUint64(g.GasUsed),
            Difficulty: g.Difficulty,
            MixDigest: g.Mixhash,
            Coinbase: g.Coinbase,
            Root: root,
        }
        if g.GasLimit == 0 {
            head.GasLimit = params.GenesisGasLimit
        }
        if g.Difficulty == nil {
            head.Difficulty = params.GenesisDifficulty
        }
        return types.NewBlock(head, nil, nil, nil), statedb
    }

Commit方法和MustCommit方法, Commit方法把給定的genesis的block和state寫入資料庫， 這個block被認為是規範的區塊鏈頭。
    
    // Commit writes the block and state of a genesis specification to the database.
    // The block is committed as the canonical head block.
    func (g *Genesis) Commit(db ethdb.Database) (*types.Block, error) {
        block, statedb := g.ToBlock()
        if block.Number().Sign() != 0 {
            return nil, fmt.Errorf("can't commit genesis block with number > 0")
        }
        if _, err := statedb.CommitTo(db, false); err != nil {
            return nil, fmt.Errorf("cannot write state: %v", err)
        }
        // 寫入總難度
        if err := WriteTd(db, block.Hash(), block.NumberU64(), g.Difficulty); err != nil {
            return nil, err
        }
        // 寫入區塊
        if err := WriteBlock(db, block); err != nil {
            return nil, err
        }
        // 寫入區塊收據
        if err := WriteBlockReceipts(db, block.Hash(), block.NumberU64(), nil); err != nil {
            return nil, err
        }
        // 寫入 headerPrefix + num (uint64 big endian) + numSuffix -> hash
        if err := WriteCanonicalHash(db, block.Hash(), block.NumberU64()); err != nil {
            return nil, err
        }
        // 寫入 "LastBlock" -> hash
        if err := WriteHeadBlockHash(db, block.Hash()); err != nil {
            return nil, err
        }
        // 寫入 "LastHeader" -> hash
        if err := WriteHeadHeaderHash(db, block.Hash()); err != nil {
            return nil, err
        }
        config := g.Config
        if config == nil {
            config = params.AllProtocolChanges
        }
        // 寫入 ethereum-config-hash -> config
        return block, WriteChainConfig(db, block.Hash(), config)
    }
    
    // MustCommit writes the genesis block and state to db, panicking on error.
    // The block is committed as the canonical head block.
    func (g *Genesis) MustCommit(db ethdb.Database) *types.Block {
        block, err := g.Commit(db)
        if err != nil {
            panic(err)
        }
        return block
    }

返回各種模式的預設Genesis
    
    // DefaultGenesisBlock returns the Ethereum main net genesis block.
    func DefaultGenesisBlock() *Genesis {
        return &Genesis{
            Config: params.MainnetChainConfig,
            Nonce: 66,
            ExtraData: hexutil.MustDecode("0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa"),
            GasLimit: 5000,
            Difficulty: big.NewInt(17179869184),
            Alloc: decodePrealloc(mainnetAllocData),
        }
    }
    
    // DefaultTestnetGenesisBlock returns the Ropsten network genesis block.
    func DefaultTestnetGenesisBlock() *Genesis {
        return &Genesis{
            Config: params.TestnetChainConfig,
            Nonce: 66,
            ExtraData: hexutil.MustDecode("0x3535353535353535353535353535353535353535353535353535353535353535"),
            GasLimit: 16777216,
            Difficulty: big.NewInt(1048576),
            Alloc: decodePrealloc(testnetAllocData),
        }
    }
    
    // DefaultRinkebyGenesisBlock returns the Rinkeby network genesis block.
    func DefaultRinkebyGenesisBlock() *Genesis {
        return &Genesis{
            Config: params.RinkebyChainConfig,
            Timestamp: 1492009146,
            ExtraData: hexutil.MustDecode("0x52657370656374206d7920617574686f7269746168207e452e436172746d616e42eb768f2244c8811c63729a21a3569731535f067ffc57839b00206d1ad20c69a1981b489f772031b279182d99e65703f0076e4812653aab85fca0f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"),
            GasLimit: 4700000,
            Difficulty: big.NewInt(1),
            Alloc: decodePrealloc(rinkebyAllocData),
        }
    }
    
    // DevGenesisBlock returns the 'geth --dev' genesis block.
    func DevGenesisBlock() *Genesis {
        return &Genesis{
            Config: params.AllProtocolChanges,
            Nonce: 42,
            GasLimit: 4712388,
            Difficulty: big.NewInt(131072),
            Alloc: decodePrealloc(devAllocData),
        }
    }







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